Showing 1–50 of 76 results for author: Leung, K

The nEXO Radioassay Program

Authors: R. MacLellan, P. Acharya, B. Aharmim, S. Alcantar Anguiano, A. Anker, I. J. Arnquist, D. Auty, T. Bhatta, D. Chernyak, J. S. Choe, B. Cleveland, J. Daughhetee, A. Der Mesrobian-Kabakian, Y. Y. Ding, M. L. di Vacri, J. Farine, A. D. French, O. Gileva, R. Gornea, K. Harouaka, K. P. Hobbs, E. W. Hoppe, L. K. S. Horkley, M. Hughes, L. Kieser , et al. (126 additional authors not shown)

Abstract: Material radioactivity compilations, such as the one presented here, are important enablers of science. They are useful for the selection of radiopure materials used in the design and construction of low-energy rare-event search experiments. They allow researchers developing such experiments to save time on material studies and avoid costly duplication of effort. The data presented here were gener… ▽ More Material radioactivity compilations, such as the one presented here, are important enablers of science. They are useful for the selection of radiopure materials used in the design and construction of low-energy rare-event search experiments. They allow researchers developing such experiments to save time on material studies and avoid costly duplication of effort. The data presented here were generated in support of the planned nEXO double-beta decay search. This work contains among the most restrictive constraints on the natural radioactivity content of materials of general interest to the low-radioactivity community, found in any tabulation of this kind. In this study, various techniques were employed; they are described here. △ Less

Submitted 16 April, 2026; originally announced April 2026.

Design of a high voltage delivery system for noble liquid time projection chambers

Authors: R. Saldanha, L. Pagani, E. Angelico, E. P. Bernard, B. Chana, S. Delaquis, R. DeVoe, M. Elbeltagi, S. Ferrara, D. Goeldi, R. Gornea, A. Odian, G. S. Ortega, C. T. Overman, L. Placzek, P. C. Rowson, K. Skarpaas, F. Spadoni, P. Acharya, A. Amy, A. Anker, I. J. Arnquist, A. Atencio, J. Bane, V. Belov , et al. (107 additional authors not shown)

Abstract: Noble liquid time projection chambers (TPCs) are a leading technology in the detection of ionizing radiation, particularly in applications such as accelerator neutrino physics, dark matter detection, and neutrinoless double beta decay. This paper addresses the design considerations for implementing stable high voltage (HV) systems within large noble liquid TPCs, with a focus on the nEXO experiment… ▽ More Noble liquid time projection chambers (TPCs) are a leading technology in the detection of ionizing radiation, particularly in applications such as accelerator neutrino physics, dark matter detection, and neutrinoless double beta decay. This paper addresses the design considerations for implementing stable high voltage (HV) systems within large noble liquid TPCs, with a focus on the nEXO experiment. Utilizing insights from prior HV research and experimental investigations, we outline factors influencing HV stability and discuss design choices to improve stability and prevent electrical discharges. A novel HV delivery system concept is presented, tailored for the nEXO TPC, which incorporates these design considerations while also meeting the stringent radiopurity requirements of the nEXO neutrinoless double beta decay search. These design considerations and their specific implementation towards a HV delivery system offer guidance to future experiments applying high voltage in noble liquid environments. △ Less

Submitted 26 February, 2026; originally announced February 2026.

Comments: 18 pages, 10 figures, 1 table

Report number: PNNL-SA-220620

DC-to-GHz Modulation In Microring Modulators Using Ferroelectric Nematic Liquid Crystal-on-Silicon in a Foundry Photonic Process

Authors: Iman Taghavi, Alexander Tofini, Edward K. Leung, Cory Pecinovsky, Nicolas A. F. Jaeger, Lukas Chrostowski, Sudip Shekhar

Abstract: Silicon-organic hybrid (SOH) platforms exhibit exceptional electro-optic (EO) properties, including high-speed operation, low energy consumption, and compact footprints. However, the absence of a scalable poling method for EO polymers, combined with the slow switching speeds characteristic of liquid crystals, has impeded the integration and compatibility of these materials with commercial silicon… ▽ More Silicon-organic hybrid (SOH) platforms exhibit exceptional electro-optic (EO) properties, including high-speed operation, low energy consumption, and compact footprints. However, the absence of a scalable poling method for EO polymers, combined with the slow switching speeds characteristic of liquid crystals, has impeded the integration and compatibility of these materials with commercial silicon photonic foundries. On the other hand, the realization of very-large-scale photonic integrated circuits (PICs) in the native silicon photonics platform itself is impeded by the complexities associated with the wavelength and thermal stabilization for microring modulators (MRMs). This study establishes the foundation for a poling-free, CMOS-compatible SOH MRM platform by exploiting simultaneous AC phase shifts in ferroelectric nematic liquid crystals (FN-LCs). We present the first demonstration of an MRM coated with FN-LC, with both the RF signal and the DC bias applied to the same electrodes, taking advantage of the dual phase shift uniquely available in FN-LC. An EO bandwidth of f$_{-6dB}\approx$ 7.8 GHz is achieved \textendash~ the highest reported value for an SOH MRM to date. As a proof of concept, we demonstrate an approximately linear resonance shift across the full width at half maximum ($\approx$ 150 pm/V), with a static power efficiency of $\approx$ 4.5 nW/$π$ for an MRM occupying a total footprint of $\approx$ 0.084 mm$^2$ and exhibiting an on-chip optical insertion loss of $\approx$ 0.78 dB. Successful infiltration of FN-LC, selectively patterned on top of phase shifters, along with optical input/output channels established using free-form photonic wire bonds, is demonstrated in the proposed PIC. △ Less

Submitted 23 February, 2026; originally announced February 2026.

Comments: 16 pages, 6 figures

Characterization of CRYO ASIC for charge readout in the nEXO experiment

Authors: Z. Li, M. Yu, E. Angelico, A. Atencio, A. Gupta, P. Knauss, A. Pena-Perez, B. G. Lenardo, P. Acharya, A. Amy, A. Anker, I. J. Arnquist, J. Bane, V. Belov, T. Bhatta, A. Bolotnikov, J. Breslin, P. A. Breur, J. P. Brodsky, E. Brown, T. Brunner, B. Burnell, E. Caden, G. F. Cao, L. Q. Cao , et al. (119 additional authors not shown)

Abstract: nEXO is a proposed next-generation experiment searching for the neutrinoless double beta decay of $^{136}$Xe using a tonne-scale liquid xenon (LXe) time projection chamber (TPC). To image the ionization signals from events in the liquid xenon, the detector will employ metallized fused-silica charge collection tiles instrumented with cryogenic application-specific integrated circuits (ASICs), refer… ▽ More nEXO is a proposed next-generation experiment searching for the neutrinoless double beta decay of $^{136}$Xe using a tonne-scale liquid xenon (LXe) time projection chamber (TPC). To image the ionization signals from events in the liquid xenon, the detector will employ metallized fused-silica charge collection tiles instrumented with cryogenic application-specific integrated circuits (ASICs), referred to as CRYO ASIC, which are designed to operate directly in LXe to minimize input capacitance and pick-up noise. Here we present the performance of the CRYO ASIC mounted on an auxiliary printed circuit board and evaluated both in a cryogenic environmental chamber and in a dedicated LXe test stand. We demonstrate that the ASICs achieve the desired performance at liquid xenon temperatures, showing a gain stability better than 0.2% over 24-hour operation and reliable in-situ calibration using an on-chip pulser. In the LXe test stand, we show that boiling caused by the chip heat dissipation can be mitigated by operating the system above ~0.1 MPa. The in-LXe noise measured agrees with simulation, which indicates it the $150~e^-$ design requirement can be satisfied. These results establish CRYO ASIC as a viable low-noise in-LXe charge readout solution for nEXO. △ Less

Submitted 11 December, 2025; originally announced December 2025.

From Commissioning to Precision Data-Taking: Resolving Operational Challenges in the Nab Detector Systems

Authors: L. J. Broussard, H. Acharya, R. Alarcon, S. Baeßler, M. Benoit, K. Borah, C. L. Britton, E. Brown, J. Choi, S. Clymer, C. Crawford, N. Ericson, L. Fabris, N. Fomin, J. Fry, R. Godri, F. M. Gonzalez, A. Hagemeier, J. Hamblen, S. Hollander, A. Jezghani, K. Leung, N. Macsai, M. Makela, D. Mathews , et al. (14 additional authors not shown)

Abstract: Our understanding of the weak mixing of quarks, described by the Cabibbo Kobayashi Maskawa (CKM) matrix, currently presents an anomaly. Thanks to major strides in both theory and experiment, improved precision in determinations of the first row of matrix elements has revealed disagreement with the expectation of unitarity. The Nab experiment at the Spallation Neutron Source is designed to precisel… ▽ More Our understanding of the weak mixing of quarks, described by the Cabibbo Kobayashi Maskawa (CKM) matrix, currently presents an anomaly. Thanks to major strides in both theory and experiment, improved precision in determinations of the first row of matrix elements has revealed disagreement with the expectation of unitarity. The Nab experiment at the Spallation Neutron Source is designed to precisely extract the first matrix element $V_{ud}$ and shed light on experimental tensions within the neutron beta decay dataset. Nab's asymmetric spectrometer allows coincident reconstruction of the decay proton and electron energies, which will be used to determine the electron-neutrino correlation coefficient, and thus (with the neutron lifetime) determine $V_{ud}$. This unique approach has provided a more comprehensive view of neutron beta decay, including a first observation of the full momentum phase space of the decay above detector thresholds and limits on exotic neutron states. Recent upgrades to the Nab detector system have improved the robustness and stability of the detector performance in terms of proton detection efficiency, noise performance, and detector segment availability, setting the stage for high precision physics data-taking. △ Less

Submitted 10 November, 2025; originally announced November 2025.

Comments: Submitted to Proceedings of the 29th International Nuclear Physics Conference (INPC 2025), Daejeon, South Korea, 25 - 30 May 2025. 6 pages. 4 figures

Guidewire-driven deployment of high density ECoG arrays for large area brain-computer interface

Authors: Tao Zou, Na Xiao, Ruihong Weng, Yifan Guo, Danny Tat Ming Chan, Gilberto Ka Kit Leung, Paddy Kwok Leung Chan

Abstract: Electrocorticographic brain computer interfaces are powerful emergent technologies for advancing basic neuroscience research and targeted clinical interventions. However, existing devices require trade-offs between coverage area, electrode density, surgical invasiveness and complication risk: limitations that fail to meet the demands of next-generation BCI. Here, we report a guidewire-driven deplo… ▽ More Electrocorticographic brain computer interfaces are powerful emergent technologies for advancing basic neuroscience research and targeted clinical interventions. However, existing devices require trade-offs between coverage area, electrode density, surgical invasiveness and complication risk: limitations that fail to meet the demands of next-generation BCI. Here, we report a guidewire-driven deployable ECoG BCI device that can be epidurally implanted using minimally invasive procedures. Our ultra-flexible but strong thin-film electrode array, which packs 256 electrodes into 4 cm2, can be folded, pulled through millimetre-sized skull holes, and unfurled seamlessly onto the brain dura mater. When deployed on the canine brain, it captures abundant high-quality auditory neural signals with distinct features of hearing that can be used to classify sound types with over 80% accuracy using various standard machine learning models. Our device is biocompatible for chronic monitoring, easy and fast to deploy and importantly, resolves the key trade-offs limiting current BCI technologies. △ Less

Submitted 16 November, 2025; originally announced November 2025.

Sensitivity of nEXO to $^{136}$Xe Charged-Current Interactions: Background-free Searches for Solar Neutrinos and Fermionic Dark Matter

Authors: G. Richardson, B. G. Lenardo, D. Gallacher, R. Saldanha, P. Acharya, S. Al Kharusi, A. Amy, E. Angelico, A. Anker, I. J. Arnquist, A. Atencio, J. Bane, V. Belov, E. P. Bernard, T. Bhatta, A. Bolotnikov, J. Breslin, P. A. Breur, J. P. Brodsky, S. Bron, E. Brown, T. Brunner, B. Burnell, E. Caden, G. F. Cao , et al. (113 additional authors not shown)

Abstract: We study the sensitivity of nEXO to solar neutrino charged-current interactions, $ν_e + ^{136}$Xe$\rightarrow ^{136}$Cs$^* + e^-$, as well as analogous interactions predicted by models of fermionic dark matter. Due to the recently observed low-lying isomeric states of $^{136}$Cs, these interactions will create a time-delayed coincident signal observable in the scintillation channel. Here we develo… ▽ More We study the sensitivity of nEXO to solar neutrino charged-current interactions, $ν_e + ^{136}$Xe$\rightarrow ^{136}$Cs$^* + e^-$, as well as analogous interactions predicted by models of fermionic dark matter. Due to the recently observed low-lying isomeric states of $^{136}$Cs, these interactions will create a time-delayed coincident signal observable in the scintillation channel. Here we develop a detailed Monte Carlo of scintillation emission, propagation, and detection in the nEXO detector to model these signals under different assumptions about the timing resolution of the photosensor readout. We show this correlated signal can be used to achieve background discrimination on the order of $10^{-9}$, enabling nEXO to make background-free measurements of solar neutrinos above the reaction threshold of 0.668 MeV. We project that nEXO could measure the flux of CNO solar neutrinos with a statistical uncertainty of 25%, thus contributing a novel and competitive measurement towards addressing the solar metallicity problem. Additionally, nEXO could measure the mean energy of the $^7$Be neutrinos with a precision of $σ\leq 1.5$ keV and could determine the survival probability of $^{7}$Be and $pep$ solar $ν_e$ with precision comparable to state-of-the-art. These quantities are sensitive to the Sun's core temperature and to non-standard neutrino interactions, respectively. Furthermore, the strong background suppression would allow nEXO to search for for charged-current interactions of fermionic dark matter in the mass range $m_χ$ = $0.668$-$7$ MeV with a sensitivity up to three orders of magnitude better than current limits. △ Less

Submitted 27 June, 2025; originally announced June 2025.

Ultra-sensitive radon assay using an electrostatic chamber in a recirculating system

Authors: nEXO Collaboration, A. Anker, P. A. Breur, B. Mong, P. Acharya, A. Amy, E. Angelico, I. J. Arnquist, A. Atencio, J. Bane, V. Belov, E. P. Bernard, T. Bhatta, A. Bolotnikov, J. Breslin, J. P. Brodsky, S. Bron, E. Brown, T. Brunner, B. Burnell, E. Caden, L. Q. Cao, G. F. Cao, D. Cesmecioglu, D. Chernyak , et al. (116 additional authors not shown)

Abstract: Rare event searches such as neutrinoless double beta decay and Weakly Interacting Massive Particle detection require ultra-low background detectors. Radon contamination is a significant challenge for these experiments, which employ highly sensitive radon assay techniques to identify and select low-emission materials. This work presents the development of ultra-sensitive electrostatic chamber (ESC)… ▽ More Rare event searches such as neutrinoless double beta decay and Weakly Interacting Massive Particle detection require ultra-low background detectors. Radon contamination is a significant challenge for these experiments, which employ highly sensitive radon assay techniques to identify and select low-emission materials. This work presents the development of ultra-sensitive electrostatic chamber (ESC) instruments designed to measure radon emanation in a recirculating gas loop, for future lower background experiments. Unlike traditional methods that separate emanation and detection steps, this system allows continuous radon transport and detection. This is made possible with a custom-built recirculation pump. A Python-based analysis framework, PyDAn, was developed to process and fit time-dependent radon decay data. Radon emanation rates are given for various materials measured with this instrument. A radon source of known activity provides an absolute calibration, enabling statistically-limited minimal detectable activities of 20 $μ$Bq. These devices are powerful tools for screening materials in the development of low-background particle physics experiments. △ Less

Submitted 7 August, 2025; v1 submitted 21 April, 2025; originally announced April 2025.

Comments: 15 pages, 9 figures, 1 table

Journal ref: NIMA Volume 1081, January 2026, 170876

Superconducting properties of commercially available solders for low-field applications

Authors: C. Hickman, K. K. H. Leung, A. H. Al-Tawhid, B. W. Filippone, P. R. Huffman, E. Korobkina, D. P. Kumah, C. M. Swank

Abstract: Solders with superconducting properties around $4\,{\rm K}$ are useful in low magnetic field environments for AC current leads or in electrical and mechanical bonds. Accurate knowledge of these properties are needed in high precision experiments. We have measured the electrical resistance of five commercially-available solders: 50\%Sn-50\%Pb, 60\%Sn-40\%Pb, 60\%Sn-40\%Pb-0.3\%Sb, 52\%In-48\%Sn, an… ▽ More Solders with superconducting properties around $4\,{\rm K}$ are useful in low magnetic field environments for AC current leads or in electrical and mechanical bonds. Accurate knowledge of these properties are needed in high precision experiments. We have measured the electrical resistance of five commercially-available solders: 50\%Sn-50\%Pb, 60\%Sn-40\%Pb, 60\%Sn-40\%Pb-0.3\%Sb, 52\%In-48\%Sn, and 96.5\%Sn-3.5\%Ag, down to $2.3\,{\rm K}$ and in applied magnetic fields from 0 to 0.1$\,{\rm T}$. Their critical temperatures $T_c$ and critical fields $B_c$ were extracted in our analysis, taking into account the observed 90\%-to-10\% transition widths. Our best candidate for low-loss AC current leads in low fields is 50\%Sn-50\%Pb, which had zero-field $T_{c,0} = (7.1 \pm 0.3)\,{\rm K}$, and remained high to $T_c(B=0.1\,{\rm T}) = (6.9 \pm 0.3) \,{\rm K}$. We report $T_c$ and $B_c$ of 60\%Sn-40\%Pb-0.3\%Sb and $B_{c,0}$ of 96.5\%Sn-3.5\%Ag for the first time. Our $T_{c,0}= (3.31 \pm 0.04)\,{\rm K}$ for 96.5\%Sn-3.5\%Ag disagrees with a widely adopted value. △ Less

Submitted 21 March, 2025; originally announced March 2025.

The Systematics and Operational Studies (SOS) Apparatus as a testbed for nEDM@SNS experiment

Authors: V. Cianciolo, R. Golub, B. W. Filippone, P. R. Huffman, K. Leung, E. Korobkina, C. Swank

Abstract: The nEDM experiment at the SNS (nEDM@SNS) is the first measurement of the neutron EDM to directly measure the precession frequency of the neutron spin due to magnetic and electric fields. Previous measurements have inferred the precession frequency by measuring the residual polarization of neutrons after a long period of free precession. This difference provides independent information on potentia… ▽ More The nEDM experiment at the SNS (nEDM@SNS) is the first measurement of the neutron EDM to directly measure the precession frequency of the neutron spin due to magnetic and electric fields. Previous measurements have inferred the precession frequency by measuring the residual polarization of neutrons after a long period of free precession. This difference provides independent information on potential unknown systematic uncertainties compared to previous and on-going measurements. It is precisely because nEDM@SNS is using a number of novel techniques, that it is essential to perform detailed studies of these techniques in order to optimize the statistical sensitivity and minimize the systematic uncertainty. The Systematic and Operational Studies Apparatus (SOSA) was one of the main efforts of nEDM@SNS collaboration, concentrated on development of a cryogenic test-bed for learning precise manipulation of spins and studing systematic effects of the proposed new technique. The test bed does not need an electric field but designed to have full NMR capability to the same level as nEDM@SNS. △ Less

Submitted 6 January, 2025; v1 submitted 31 October, 2024; originally announced November 2024.

Comments: 21 pages, 11 figures. Scientific report written in 2017

Wideband Coherent Microwave Conversion via Magnon Nonlinearity in Hybrid Quantum System

Authors: Jiahao Wu, Jiacheng Liu, Zheyu Ren, Man Yin Leung, Wai Kuen Leung, Kin On Ho, Xiangrong Wang, Qiming Shao, Sen Yang

Abstract: Frequency conversion is a widely realized physical process in nonlinear systems of optics and electronics. As an emerging nonlinear platform, spintronic devices have the potential to achieve stronger frequency conversion. Here, we demonstrated a microwave frequency conversion method in a hybrid quantum system, integrating nitrogen-vacancy centers in diamond with magnetic thin film CoFeB. We achiev… ▽ More Frequency conversion is a widely realized physical process in nonlinear systems of optics and electronics. As an emerging nonlinear platform, spintronic devices have the potential to achieve stronger frequency conversion. Here, we demonstrated a microwave frequency conversion method in a hybrid quantum system, integrating nitrogen-vacancy centers in diamond with magnetic thin film CoFeB. We achieve a conversion bandwidth ranging from 0.1 to 12GHz, presenting an up to $\mathrm{25^{th}}$ order frequency conversion and further display the application of this method for frequency detection and qubits coherent control. Distinct from traditional frequency conversion techniques based on nonlinear electric response, our approach employs nonlinear magnetic response in spintronic devices. The nonlinearity, originating from the symmetry breaking such as domain walls in magnetic films, presents that our method can be adapted to hybrid systems of other spintronic devices and spin qubits, expanding the application scope of spintronic devices and providing a promising on-chip platform for coupling quantum systems. △ Less

Submitted 3 July, 2024; originally announced July 2024.

Comments: 11 pages, 5 figures

Journal ref: npj Spintronics volume 2, Article number: 30 (2024)

A tweezer array with 6100 highly coherent atomic qubits

Authors: Hannah J. Manetsch, Gyohei Nomura, Elie Bataille, Kon H. Leung, Xudong Lv, Manuel Endres

Abstract: Optical tweezer arrays have transformed atomic and molecular physics, now forming the backbone for a range of leading experiments in quantum computing, simulation, and metrology. Typical experiments trap tens to hundreds of atomic qubits, and recently systems with around one thousand atoms were realized without defining qubits or demonstrating coherent control. However, scaling to thousands of ato… ▽ More Optical tweezer arrays have transformed atomic and molecular physics, now forming the backbone for a range of leading experiments in quantum computing, simulation, and metrology. Typical experiments trap tens to hundreds of atomic qubits, and recently systems with around one thousand atoms were realized without defining qubits or demonstrating coherent control. However, scaling to thousands of atomic qubits with long coherence times, low-loss, and high-fidelity imaging is an outstanding challenge and critical for progress in quantum science, particularly towards quantum error correction. Here, we experimentally realize an array of optical tweezers trapping over 6,100 neutral atoms in around 12,000 sites, simultaneously surpassing state-of-the-art performance for several metrics that underpin the success of the platform. Specifically, while scaling to such a large number of atoms, we demonstrate a coherence time of 12.6(1) seconds, a record for hyperfine qubits in an optical tweezer array. We show room-temperature trapping lifetimes of 23 minutes, enabling record-high imaging survival of 99.98952(1)% with an imaging fidelity of over 99.99%. We present a plan for zone-based quantum computing and demonstrate necessary coherence-preserving qubit transport and pick-up/drop-off operations on large spatial scales, characterized through interleaved randomized benchmarking. Our results, along with recent developments, indicate that universal quantum computing and quantum error correction with thousands to tens of thousands of physical qubits could be a near-term prospect. △ Less

Submitted 29 July, 2025; v1 submitted 18 March, 2024; originally announced March 2024.

Comments: H.J.M., G.N., and E.B. contributed equally to this work. Added new Fig. 6 and new data on atom transfer between static and dynamic traps

Journal ref: Nature 647, 60-67 (2025)

Feasibility of PET-enabled dual-energy CT imaging: First physical phantom and initial patient results

Authors: Yansong Zhu, Siqi Li, Zhaoheng Xie, Edwin K. Leung, Reimund Bayerlein, Negar Omidvari, Yasser G. Abdelhafez, Simon R. Cherry, Jinyi Qi, Ramsey D. Badawi, Benjamin A. Spencer, Guobao Wang

Abstract: X-ray computed tomography (CT) in PET/CT is commonly operated with a single energy, resulting in a limitation of lacking tissue composition information. Dual-energy (DE) spectral CT enables material decomposition by using two different x-ray energies and may be combined with PET for improved multimodality imaging, but would either require hardware upgrade or increase radiation dose due to the adde… ▽ More X-ray computed tomography (CT) in PET/CT is commonly operated with a single energy, resulting in a limitation of lacking tissue composition information. Dual-energy (DE) spectral CT enables material decomposition by using two different x-ray energies and may be combined with PET for improved multimodality imaging, but would either require hardware upgrade or increase radiation dose due to the added second x-ray CT scan. Recently proposed PET-enabled DECT method allows dual-energy spectral imaging using a conventional PET/CT scanner without the need for a second x-ray CT scan. A gamma-ray CT (gCT) image at 511 keV can be generated from the existing time-of-flight PET data with the maximum-likelihood attenuation and activity (MLAA) approach and is then combined with the low-energy x-ray CT image to form dual-energy spectral imaging. To improve the image quality of gCT, a kernel MLAA method was further proposed by incorporating x-ray CT as a priori information. The concept of this PET-enabled DECT has been validated using simulation studies, but not yet with 3D real data. In this work, we developed a general open-source implementation for gCT reconstruction from PET data and use this implementation for the first real data validation with both a physical phantom study and a human subject study on a uEXPLORER total-body PET/CT system. These results have demonstrated the feasibility of this method for spectral imaging and material decomposition. △ Less

Submitted 19 November, 2024; v1 submitted 3 February, 2024; originally announced February 2024.

Comments: 20 pages, 7 figures

Electric Charging Effects on Insulating Surfaces in Cryogenic Liquids

Authors: Wolfgang Korsch, Mark Broering, Ashok Timsina, Kent K. H. Leung, Joshua Abney, Dmitry Budker, Bradley W. Filippone, Jiachen He, Suman Kandu, Mark McCrea, Murchhana Roy, Christopher Swank, Weijun Yao

Abstract: This paper presents a new technique to study the adsorption and desorption of ions and electrons on insulating surfaces in the presence of strong electric fields in cryoliquids. The experimental design consists of a compact cryostat coupled with a sensitive electro-optical Kerr device to monitor the stability of the electric fields. The behavior of nitrogen and helium ions on a poly(methyl methacr… ▽ More This paper presents a new technique to study the adsorption and desorption of ions and electrons on insulating surfaces in the presence of strong electric fields in cryoliquids. The experimental design consists of a compact cryostat coupled with a sensitive electro-optical Kerr device to monitor the stability of the electric fields. The behavior of nitrogen and helium ions on a poly(methyl methacrylate) (PMMA) surface was compared to a PMMA surface coated with a mixture of deuterated polystyrene and deuterated polybutadiene. Ion accumulation and removal on these surfaces were unambiguously observed. Within the precision of the data, both surfaces behave similarly for the physisorbed ions. The setup was also used to measure the (quasi-)static dielectric constant of PMMA at T = 70 K. The impact of the ion adsorption on the search for a neutron permanent electric dipole moment in a cryogenic environment, like the nEDM@SNS experiment, is discussed. △ Less

Submitted 31 December, 2023; originally announced January 2024.

The dotTHz Project: A Standard Data Format for Terahertz Time-Domain Data and Elementary Data Processing Tools

Authors: Jongmin Lee, Chi Ki Leung, Mingrui Ma, Jasper Ward-Berry, Supawan Santitewagun, J. Axel Zeitler

Abstract: From investigating molecular vibrations to observing galaxies, terahertz technology has found extensive applications in research and development over the past three decades. Terahertz time-domain spectroscopy and imaging have experienced significant growth and now dominate spectral observations ranging from 0.1 to 10 THz. However, the lack of standardised protocols for data processing, disseminati… ▽ More From investigating molecular vibrations to observing galaxies, terahertz technology has found extensive applications in research and development over the past three decades. Terahertz time-domain spectroscopy and imaging have experienced significant growth and now dominate spectral observations ranging from 0.1 to 10 THz. However, the lack of standardised protocols for data processing, dissemination, and archiving poses challenges in collaborating and sharing terahertz data between research groups. To tackle these challenges, we present the dotTHz project, which introduces a standardised terahertz data format and the associated open-source tools for processing and interpretation of dotTHz files. The dotTHz project aims to facilitate seamless data processing and analysis by providing a common framework. All software components are released under the MIT licence through GitHub repositories to encourage widespread adoption, modification, and collaboration. We invite the terahertz community to actively contribute to the dotTHz project, fostering the development of additional tools that encompass a greater breadth and depth of functionality. By working together, we can establish a comprehensive suite of resources that benefit the entire terahertz community. △ Less

Submitted 11 September, 2023; originally announced September 2023.

Adsorption at Nanoconfined Solid-Water Interfaces

Authors: Anastasia G. Ilgen, Kevin Leung, Louise J. Criscenti, Jeffery A. Greathouse

Abstract: Reactions at solid-water interfaces play a foundational role in water treatment systems, catalysis, chemical separations, and in predicting chemical fate and transport in the environment. Over the last century, experimental measurements and computational models have made tremendous progress in capturing reactions at solid surfaces. The interfacial reactivity of a solid surface, however, can change… ▽ More Reactions at solid-water interfaces play a foundational role in water treatment systems, catalysis, chemical separations, and in predicting chemical fate and transport in the environment. Over the last century, experimental measurements and computational models have made tremendous progress in capturing reactions at solid surfaces. The interfacial reactivity of a solid surface, however, can change dramatically and unexpectedly when it is confined to the nanoscale. Nanoconfinement can arise in different geometries such as pores/cages (3-D confinement), channels (2-D confinement) and slits (1-D confinement). Therefore, measurements on unconfined surfaces, and molecular models parameterized based on these measurements, fail to capture chemical behaviors under nanoconfinement. This review evaluates recent experimental and theoretical advances, with a focus on adsorption at solid-water interfaces. We review how nanoconfinement alters the physico-chemical properties of water, and how the structure and dynamics of nanoconfined water dictate energetics, pathways, and products of adsorption in nanopores. The implications of these findings and future research directions are discussed. △ Less

Submitted 13 December, 2022; originally announced December 2022.

Comments: Manuscript accepted for publication Annu. Rev. Phys. Chem (2023)

A terahertz vibrational molecular clock with systematic uncertainty at the $10^{-14}$ level

Authors: K. H. Leung, B. Iritani, E. Tiberi, I. Majewska, M. Borkowski, R. Moszynski, T. Zelevinsky

Abstract: Neutral quantum absorbers in optical lattices have emerged as a leading platform for achieving clocks with exquisite spectroscopic resolution. However, the studies of these clocks and their systematic shifts have so far been limited to atoms. Here, we extend this architecture to an ensemble of diatomic molecules and experimentally realize an accurate lattice clock based on pure molecular vibration… ▽ More Neutral quantum absorbers in optical lattices have emerged as a leading platform for achieving clocks with exquisite spectroscopic resolution. However, the studies of these clocks and their systematic shifts have so far been limited to atoms. Here, we extend this architecture to an ensemble of diatomic molecules and experimentally realize an accurate lattice clock based on pure molecular vibration. We evaluate the leading systematics, including the characterization of nonlinear trap-induced light shifts, achieving a total systematic uncertainty of $4.6\times10^{-14}$. The absolute frequency of the vibrational splitting is measured to be 31 825 183 207 592.8(5.1) Hz, enabling the dissociation energy of our molecule to be determined with record accuracy. Our results represent an important milestone in molecular spectroscopy and THz-frequency standards, and may be generalized to other neutral molecular species with applications for fundamental physics, including tests of molecular quantum electrodynamics and the search for new interactions. △ Less

Submitted 3 April, 2023; v1 submitted 22 September, 2022; originally announced September 2022.

Comments: 17 pages, 8 figures

Galvanic Corrosion and Electric Field in Lithium Anode Passivation Films: Effects on Self-Discharge

Authors: Kevin Leung, Laura C. Merrill, Katharine L. Harrison

Abstract: Battery interfaces help govern rate capability, safety/stability, cycle life, and self-discharge, but significant gaps remain in our understanding at atomic length scales that can be exploited to improve interfacial properties. In particular, Li partially plated on copper current collectors, relevant to the anodeless, lithium metal cell which is a holy grail of high density energy battery research… ▽ More Battery interfaces help govern rate capability, safety/stability, cycle life, and self-discharge, but significant gaps remain in our understanding at atomic length scales that can be exploited to improve interfacial properties. In particular, Li partially plated on copper current collectors, relevant to the anodeless, lithium metal cell which is a holy grail of high density energy battery research, has recently been reported to undergo galvanic corrosion and exhibit short shelf lives. We apply large scale Density Functional Theory (DFT) calculations and X-ray photoelectron spectroscopy to examine the reaction between the electrolyte and Li|Cu junctions coated with thin, uniform electrolyte interphase (SEI) passivating films at two applied voltages. These novel DFT galvanic corrosion simulations show that electrolyte degradation preferentially occurs on Li-plated regions and should lead to thicker SEI films. Our simulations reveal similarities but also fundamental differences between traditional metal localized pitting and Li-corrosion mechanisms. Furthermore, using the recently proposed, highly reactive lithium hydride (LiH) component SEI as example, we distinguish between electrochemical and chemical degradation pathways which are partially responsible for self-discharge, with the chemical pathway found to exhibit slow kinetics. We also predict that electric fields should in general exist across natural SEI components like LiH, and across artificial SEI films like LiI and LiAlO(2) often applied to improve battery cycling. Underlying and unifying these predictions is a framework of DFT voltage/overpotential definitions which we have derived from electrochemistry disciplines like structural metal corrosion studies; our analysis can only be made using the correct electronic voltage definitions. △ Less

Submitted 23 May, 2022; originally announced May 2022.

Comments: 41 pages. 8 figures

Journal ref: Journal of Physical Chemistry C (2022)

Quantum control of molecules for fundamental physics

Authors: D. Mitra, K. H. Leung, T. Zelevinsky

Abstract: The extraordinary success in laser cooling, trapping, and coherent manipulation of atoms has energized the efforts in extending this exquisite control to molecules. Not only are molecules ubiquitous in nature, but the control of their quantum states offers unparalleled access to fundamental constants and possible physics beyond the Standard Model. Quantum state manipulation of molecules can enable… ▽ More The extraordinary success in laser cooling, trapping, and coherent manipulation of atoms has energized the efforts in extending this exquisite control to molecules. Not only are molecules ubiquitous in nature, but the control of their quantum states offers unparalleled access to fundamental constants and possible physics beyond the Standard Model. Quantum state manipulation of molecules can enable high-precision measurements including tests of fundamental symmetries and searches for new particles and fields. At the same time, their complex internal structure presents experimental challenges to overcome in order to gain sensitivity to new physics. In this Perspective, we review recent developments in this thriving new field. Moreover, throughout the text we discuss many current and future research directions that have the potential to place molecules at the forefront of fundamental science. △ Less

Submitted 26 April, 2022; originally announced April 2022.

Comments: Perspective article

Journal ref: Phys. Rev. A 105, 040101 (2022)

Two-center basis generator method calculations for Li$^{3+}$, C$^{3+}$ and O$^{3+}$ ion impact on ground state hydrogen

Authors: Anthony C. K. Leung, Tom Kirchner

Abstract: The two-center basis generator method is used to obtain cross sections for excitation, capture, and ionization in Li$^{3+}$, C$^{3+}$, and O$^{3+}$ collisions with ground-state hydrogen at projectile energies from 1 to 100 keV/u. The interaction of the C$^{3+}$ and O$^{3+}$ projectiles with the active electron is represented by a model potential. Comparisons of cross sections with previously repor… ▽ More The two-center basis generator method is used to obtain cross sections for excitation, capture, and ionization in Li$^{3+}$, C$^{3+}$, and O$^{3+}$ collisions with ground-state hydrogen at projectile energies from 1 to 100 keV/u. The interaction of the C$^{3+}$ and O$^{3+}$ projectiles with the active electron is represented by a model potential. Comparisons of cross sections with previously reported data show overall good agreement while discrepancies in capture for C$^{3+}$ collisions at low energies are noted. The present results show that excitation and ionization are similar across the three collision systems, which indicates that these cross sections are mostly dependent on the net charge of the projectile only. The situation is different for the capture channel. △ Less

Submitted 21 January, 2022; v1 submitted 23 December, 2021; originally announced December 2021.

Ultracold $^{88}\rm{Sr}_2$ molecules in the absolute ground state

Authors: K. H. Leung, E. Tiberi, B. Iritani, I. Majewska, R. Moszynski, T. Zelevinsky

Abstract: We report efficient all-optical creation of an ultracold gas of alkaline-earth-metal dimers, $^{88}\rm{Sr}_2$, in their absolute ground state. Starting with weakly bound singlet molecules formed by narrow-line photoassociation in an optical lattice, followed by stimulated Raman adiabatic passage (STIRAP) via a singlet-dominant channel in the $(1)0_u^+$ excited potential, we prepare pure samples of… ▽ More We report efficient all-optical creation of an ultracold gas of alkaline-earth-metal dimers, $^{88}\rm{Sr}_2$, in their absolute ground state. Starting with weakly bound singlet molecules formed by narrow-line photoassociation in an optical lattice, followed by stimulated Raman adiabatic passage (STIRAP) via a singlet-dominant channel in the $(1)0_u^+$ excited potential, we prepare pure samples of more than 5500 molecules in $X^1Σ_g^+(v=0,J=0)$. We observe two-body collisional loss rates close to the universal limit for both the least bound and most bound vibrational states in $X^1Σ_g^+$. We demonstrate the enhancement of STIRAP efficiency in a magic-wavelength optical lattice where thermal decoherence is eliminated. Our results pave the way for the use of alkaline-earth-metal dimers for high-precision spectroscopy, and indicate favorable prospects for robust quantum state preparation of ultracold molecules involving closed-shell atoms, as well as molecule assembly in deep optical traps tuned to a magic wavelength. △ Less

Submitted 12 August, 2021; originally announced August 2021.

Edge-Propagation Discharge Mechanism in CFx Batteries -- a First Principles and Experimental Study

Authors: Kevin Leung, Noah B. Schorr, Matthew Mayer, Timothy N. Lambert, Y. Shirley Meng, K. L. Harrison

Abstract: Graphite fluoride (CFx) cathodes coupled with lithium anodes yield one of the highest theoretical energy densities (>860 Wh/g) among primary batteries. In practice, the observed discharge voltage (~2.5 V) is significantly lower than thermodynamic limits (>4.5 V), the discharge rate is low, and so far Li/CFx has only been used in primary batteries. Understanding the discharge mechanism at atomic le… ▽ More Graphite fluoride (CFx) cathodes coupled with lithium anodes yield one of the highest theoretical energy densities (>860 Wh/g) among primary batteries. In practice, the observed discharge voltage (~2.5 V) is significantly lower than thermodynamic limits (>4.5 V), the discharge rate is low, and so far Li/CFx has only been used in primary batteries. Understanding the discharge mechanism at atomic length scales will improve practical CFx energy density, rate capability, and rechargeability. So far, purely experimental techniques have not identified the correct discharge mechanism or explained the discharge voltage. We apply Density Functional Theory calculations to demonstrate that a CFx-edge propagation discharge mechanism based on lithium insertion at the CF/C boundary in partially discharged CFx exhibits a voltage range of 2.5 to 2.9 V -- depending on whether solvent molecules are involved. The voltages and solvent dependence agrees with our discharge and galvanostatic intermittent titration technique measurements. The predicted discharge kinetics are consistent with CFx operations. Finally, we predict Li/CFx rechargeability under the application of high potentials, along a charging pathway different from that of discharge. Our work represents a general, quasi-kinetic framework to understand the discharge of conversion cathodes, circumventing the widely used phase diagram approach which most likely does not apply to Li/CFx because equilibrium conditions are not attained in this system. △ Less

Submitted 2 July, 2021; originally announced July 2021.

Comments: 31 pages, 7 figures

Journal ref: Chemistry of Materials vol. 33, pp. 1760-1770 (2021)

Interplay of Physically Different Properties Leading to Challenges in Separating Lanthanide Cations -- an Ab Initio Molecular Dynamics and Experimental Study

Authors: Kevin Leung, Anastasia G. Ilgen, Louise J. Criscenti

Abstract: The lanthanide elements have well-documented similarities in their chemical behavior, which makes the valuable trivalent lanthanide cations (Ln(III)) particularly difficult to separate from each other in water. In this work, we apply ab initio molecular dynamics simulations to compare the free energies (Delta G(ads)) associated with the adsorption of lanthanide cations to silica surfaces at a pH c… ▽ More The lanthanide elements have well-documented similarities in their chemical behavior, which makes the valuable trivalent lanthanide cations (Ln(III)) particularly difficult to separate from each other in water. In this work, we apply ab initio molecular dynamics simulations to compare the free energies (Delta G(ads)) associated with the adsorption of lanthanide cations to silica surfaces at a pH condition where SiO- groups are present. The predicted Delta G(ads) for lutetium (Lu(III)) and europium (Eu(III)) are similar within statistical uncertainties; this is in qualitative agreement with our batch adsorption measurements on silica. This finding is remarkable because the two cations exhibit hydration free energies (Delta G(hyd}) that differ by >2 eV, different hydration numbers, and different hydrolysis behavior far from silica surfaces. We observe that the similarity in Lu(III) and Eu(III) Delta G(ads) is the result of a delicate cancellation between the difference in Eu(III) and Lu(III) hydration (Delta G(hyd})), and their difference in binding energies to silica. We propose that disrupting this cancellation at the two end points, either for adsorbed or completely desorbed lanthanides (e.g., via nanoconfinment or mixed solvents), will lead to effective Ln separation. △ Less

Submitted 2 July, 2021; originally announced July 2021.

Comments: 21 pages, 6 figures

Journal ref: Physical Chemistry Chemical Physics vol 23, pp. 5750-5759 (2021)

Measuring the repertoire of age-related behavioral changes in Drosophila melanogaster

Authors: Katherine E. Overman, Daniel M. Choi, Kawai Leung, Joshua W. Shaevitz, Gordon J. Berman

Abstract: Aging affects almost all aspects of an organism -- its morphology, its physiology, its behavior. Isolating which biological mechanisms are regulating these changes, however, has proven difficult, potentially due to our inability to characterize the full repertoire of an animal's behavior across the lifespan. Using data from fruit flies (D. melanogaster) we measure the full repertoire of behaviors… ▽ More Aging affects almost all aspects of an organism -- its morphology, its physiology, its behavior. Isolating which biological mechanisms are regulating these changes, however, has proven difficult, potentially due to our inability to characterize the full repertoire of an animal's behavior across the lifespan. Using data from fruit flies (D. melanogaster) we measure the full repertoire of behaviors as a function of age. We observe a sexually dimorphic pattern of changes in the behavioral repertoire during aging. Although the stereotypy of the behaviors and the complexity of the repertoire overall remains relatively unchanged, we find evidence that the observed alterations in behavior can be explained by changing the fly's overall energy budget, suggesting potential connections between metabolism, aging, and behavior. △ Less

Submitted 15 June, 2021; v1 submitted 14 June, 2021; originally announced June 2021.

Search For Electron-Antineutrinos Associated With Gravitational-Wave Events GW150914, GW151012, GW151226, GW170104, GW170608, GW170814, and GW170817 at Daya Bay

Authors: F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, G. F. Cao, J. Cao, J. F. Chang, Y. Chang, H. S. Chen, S. M. Chen, Y. Chen, Y. X. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, J. P. Cummings, O. Dalager, F. S. Deng, Y. Y. Ding, M. V. Diwan, T. Dohnal, J. Dove, M. Dvorak , et al. (161 additional authors not shown)

Abstract: Providing a possible connection between neutrino emission and gravitational-wave (GW) bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge. In the Daya Bay experiment, using data collected from December 2011 to August 2017, a search has been performed for electron-antineutrino signals coinciding with detected GW events, including GW1… ▽ More Providing a possible connection between neutrino emission and gravitational-wave (GW) bursts is important to our understanding of the physical processes that occur when black holes or neutron stars merge. In the Daya Bay experiment, using data collected from December 2011 to August 2017, a search has been performed for electron-antineutrino signals coinciding with detected GW events, including GW150914, GW151012, GW151226, GW170104, GW170608, GW170814, and GW170817. We used three time windows of $\mathrm{\pm 10~s}$, $\mathrm{\pm 500~s}$, and $\mathrm{\pm 1000~s}$ relative to the occurrence of the GW events, and a neutrino energy range of 1.8 to 100 MeV to search for correlated neutrino candidates. The detected electron-antineutrino candidates are consistent with the expected background rates for all the three time windows. Assuming monochromatic spectra, we found upper limits (90% confidence level) on electron-antineutrino fluence of $(1.13~-~2.44) \times 10^{11}~\rm{cm^{-2}}$ at 5 MeV to $8.0 \times 10^{7}~\rm{cm^{-2}}$ at 100 MeV for the three time windows. Under the assumption of a Fermi-Dirac spectrum, the upper limits were found to be $(5.4~-~7.0)\times 10^{9}~\rm{cm^{-2}}$ for the three time windows. △ Less

Submitted 14 September, 2020; v1 submitted 27 June, 2020; originally announced June 2020.

Comments: 16 pages, 12 figures, 9 tables

Transition strength measurements to guide magic wavelength selection in optically trapped molecules

Authors: K. H. Leung, I. Majewska, H. Bekker, C. -H. Lee, E. Tiberi, S. S. Kondov, R. Moszynski, T. Zelevinsky

Abstract: Optical trapping of molecules with long coherence times is crucial for many protocols in quantum information and metrology. However, the factors that limit the lifetimes of the trapped molecules remain elusive and require improved understanding of the underlying molecular structure. Here we show that measurements of vibronic line strengths in weakly and deeply bound $^{88}$Sr$_2$ molecules, combin… ▽ More Optical trapping of molecules with long coherence times is crucial for many protocols in quantum information and metrology. However, the factors that limit the lifetimes of the trapped molecules remain elusive and require improved understanding of the underlying molecular structure. Here we show that measurements of vibronic line strengths in weakly and deeply bound $^{88}$Sr$_2$ molecules, combined with \textit{ab initio} calculations, allow for unambiguous identification of vibrational quantum numbers. This, in turn, enables the construction of refined excited potential energy curves that inform the selection of magic wavelengths which facilitate long vibrational coherence. We demonstrate Rabi oscillations between far-separated vibrational states that persist for nearly 100 ms. △ Less

Submitted 25 May, 2020; originally announced May 2020.

Journal ref: Phys. Rev. Lett. 125, 153001 (2020)

Anodic Decomposition of Surface Films on High Voltage Spinel Surfaces -- Density Function Theory and Experimental Study

Authors: Kevin Leung, Rosy, Malachi Noked

Abstract: Oxidative decomposition of organic-solvent-based liquid electrolytes at cathode material interfaces has been identified as a main reason for rapid capacity fade in high-voltage lithium ion batteries. The evolution of "cathode electrolyte interphase: (CEI) films, partly or completely consisting of electrolyte decomposition products, has also recently been demonstrated to be correlated with battery… ▽ More Oxidative decomposition of organic-solvent-based liquid electrolytes at cathode material interfaces has been identified as a main reason for rapid capacity fade in high-voltage lithium ion batteries. The evolution of "cathode electrolyte interphase: (CEI) films, partly or completely consisting of electrolyte decomposition products, has also recently been demonstrated to be correlated with battery cycling behavior at high potentials. Using Density Functional Theory (DFT) calculations, the hybrid PBE0 functional, and the (001) surfaces of spinel oxides as models, we examine these two interrelated processes. Consistent with previous calculations, ethylene carbonate (EC) solvent molecules are predicted to be readily oxidized on the Li(x)Mn(2)O(4) (001) surface at modest operational voltages, forming adsorbed organic fragments. Further oxidative decompostion of such CEI fragments to release CO2 gas is however predicted to require higher voltages consistent with Li(x)Ni(0.5)Mn(1.5)O(4) (LNMO) at smaller x values. We argue that multi-step reactions, involving first formation of CEI films and then further oxidization of CEI at higher potentials, are most relevant to capacity fade. Mechanisms associated with dissolution or oxidation of native Li2CO3 films, which is removed before the electrolyte is in contact with oxide surfaces, are also explored. △ Less

Submitted 6 March, 2020; originally announced March 2020.

Comments: 8 figures

Journal ref: Journal of Chemical Physics volume 151, article 234713 (2019)

A Physics-Guided Modular Deep-Learning Based Automated Framework for Tumor Segmentation in PET Images

Authors: Kevin H. Leung, Wael Marashdeh, Rick Wray, Saeed Ashrafinia, Martin G. Pomper, Arman Rahmim, Abhinav K. Jha

Abstract: The objective of this study was to develop a PET tumor-segmentation framework that addresses the challenges of limited spatial resolution, high image noise, and lack of clinical training data with ground-truth tumor boundaries in PET imaging. We propose a three-module PET-segmentation framework in the context of segmenting primary tumors in 3D FDG-PET images of patients with lung cancer on a per-s… ▽ More The objective of this study was to develop a PET tumor-segmentation framework that addresses the challenges of limited spatial resolution, high image noise, and lack of clinical training data with ground-truth tumor boundaries in PET imaging. We propose a three-module PET-segmentation framework in the context of segmenting primary tumors in 3D FDG-PET images of patients with lung cancer on a per-slice basis. The first module generates PET images containing highly realistic tumors with known ground-truth using a new stochastic and physics-based approach, addressing lack of training data. The second module trains a modified U-net using these images, helping it learn the tumor-segmentation task. The third module fine-tunes this network using a small-sized clinical dataset with radiologist-defined delineations as surrogate ground-truth, helping the framework learn features potentially missed in simulated tumors. The framework's accuracy, generalizability to different scanners, sensitivity to partial volume effects (PVEs) and efficacy in reducing the number of training images were quantitatively evaluated using Dice similarity coefficient (DSC) and several other metrics. The framework yielded reliable performance in both simulated (DSC: 0.87 (95% CI: 0.86, 0.88)) and patient images (DSC: 0.73 (95% CI: 0.71, 0.76)), outperformed several widely used semi-automated approaches, accurately segmented relatively small tumors (smallest segmented cross-section was 1.83 cm2), generalized across five PET scanners (DSC: 0.74), was relatively unaffected by PVEs, and required low training data (training with data from even 30 patients yielded DSC of 0.70). In conclusion, the proposed framework demonstrated the ability for reliable automated tumor delineation in FDG-PET images of patients with lung cancer. △ Less

Submitted 18 February, 2020; originally announced February 2020.

A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

Authors: M. W. Ahmed, R. Alarcon, A. Aleksandrova, S. Baessler, L. Barron-Palos, L. M. Bartoszek, D. H. Beck, M. Behzadipour, I. Berkutov, J. Bessuille, M. Blatnik, M. Broering, L. J. Broussard, M. Busch, R. Carr, V. Cianciolo, S. M. Clayton, M. D. Cooper, C. Crawford, S. A. Currie, C. Daurer, R. Dipert, K. Dow, D. Dutta, Y. Efremenko , et al. (69 additional authors not shown)

Abstract: A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallati… ▽ More A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized $^3$He from an Atomic Beam Source injected into the superfluid $^4$He and transported to the measurement cells as a co-magnetometer. The superfluid $^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level. △ Less

Submitted 20 November, 2019; v1 submitted 26 August, 2019; originally announced August 2019.

Journal ref: Journal of Instrumentation, Vol 14, P11017, 2019

Proton impact on ground and excited states of atomic hydrogen

Authors: Anthony C. K. Leung, Tom Kirchner

Abstract: The processes of electron excitation, capture, and ionization were investigated in proton collisions with atomic hydrogen in the initial $n=1$ and $n=2$ states at impact energies from 1 to 300 keV. The theoretical analysis is based on the close-coupling two-center basis generator method in the semiclassical approximation. Calculated cross sections are compared with previous results which include d… ▽ More The processes of electron excitation, capture, and ionization were investigated in proton collisions with atomic hydrogen in the initial $n=1$ and $n=2$ states at impact energies from 1 to 300 keV. The theoretical analysis is based on the close-coupling two-center basis generator method in the semiclassical approximation. Calculated cross sections are compared with previous results which include data obtained from classical-trajectory Monte Carlo, convergent close-coupling, and other two-center atomic orbital expansion approaches. There is an overall good agreement in the capture and excitation cross sections while there are some discrepancies in the ionization results at certain impact energies. These discrepancies in the present results can be partially understood through the use of a $1/n^{3}$ scaling model. △ Less

Submitted 6 December, 2019; v1 submitted 18 July, 2019; originally announced July 2019.

Comments: 7 pages, 4 figures, Eur. Phys. J. D. Final Accepted Version

Journal ref: Eur. Phys. J. D (2019) 73: 246

A next-generation inverse-geometry spallation-driven ultracold neutron source

Authors: K. K. H. Leung, G. Muhrer, T. Hügle, T. M. Ito, E. M. Lutz, M. Makela, C. L. Morris, R. W. Pattie, Jr., A. Saunders, A. R. Young

Abstract: The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an-order-of-magnitude higher than the strongest proposed sources, and around three-orders-of-magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that ar… ▽ More The physics model of a next-generation spallation-driven high-current ultracold neutron (UCN) source capable of delivering an extracted UCN rate of around an-order-of-magnitude higher than the strongest proposed sources, and around three-orders-of-magnitude higher than existing sources, is presented. This UCN-current-optimized source would dramatically improve cutting-edge UCN measurements that are currently statistically limited. A novel "Inverse Geometry" design is used with 40 L of superfluid $^4$He (He-II), which acts as a converter of cold neutrons (CNs) to UCNs, cooled with state-of-the-art sub-cooled cryogenic technology to $\sim$1.6 K. Our design is optimized for a 100 W maximum heat load constraint on the He-II and its vessel. In our geometry, the spallation target is wrapped symmetrically around the UCN converter to permit raster scanning the proton beam over a relatively large volume of tungsten spallation target to reduce the demand on the cooling requirements, which makes it reasonable to assume that water edge-cooling only is sufficient. Our design is refined in several steps to reach $P_{UCN}=2.1\times10^9\,/$s under our other restriction of 1 MW maximum available proton beam power. We then study effects of the He-II scattering kernel as well as reductions in $P_{UCN}$ due to pressurization to reach $P_{UCN}=1.8\times10^9\,/$s. Finally, we provide a design for the UCN extraction system that takes into account the required He-II heat transport properties and implementation of a He-II containment foil that allows UCN transmission. We estimate a total useful UCN current from our source of $R_{use}=5\times10^8\,/$s from a 18 cm diameter guide 5 m from the source. Under a conservative "no return" approximation, this rate can produce an extracted density of $>1\times10^4\,/$cm$^3$ in $<$1000~L external experimental volumes with a $^{58}$Ni (335 neV) cut-off potential. △ Less

Submitted 24 October, 2019; v1 submitted 23 May, 2019; originally announced May 2019.

Comments: Submitted to Journal of Applied Physics

Extraction of the $^{235}$U and $^{239}$Pu Antineutrino Spectra at Daya Bay

Authors: Daya Bay collaboration, D. Adey, F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, J. F. Chang, Y. Chang, H. S. Chen, S. M. Chen, Y. Chen, Y. X. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, A. Chukanov, J. P. Cummings, N. Dash, F. S. Deng, Y. Y. Ding , et al. (171 additional authors not shown)

Abstract: This Letter reports the first extraction of individual antineutrino spectra from $^{235}$U and $^{239}$Pu fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses $3.5\times 10^6$ inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, $^{235}$U… ▽ More This Letter reports the first extraction of individual antineutrino spectra from $^{235}$U and $^{239}$Pu fission and an improved measurement of the prompt energy spectrum of reactor antineutrinos at Daya Bay. The analysis uses $3.5\times 10^6$ inverse beta-decay candidates in four near antineutrino detectors in 1958 days. The individual antineutrino spectra of the two dominant isotopes, $^{235}$U and $^{239}$Pu, are extracted using the evolution of the prompt spectrum as a function of the isotope fission fractions. In the energy window of 4--6~MeV, a 7\% (9\%) excess of events is observed for the $^{235}$U ($^{239}$Pu) spectrum compared with the normalized Huber-Mueller model prediction. The significance of discrepancy is $4.0σ$ for $^{235}$U spectral shape compared with the Huber-Mueller model prediction. The shape of the measured inverse beta-decay prompt energy spectrum disagrees with the prediction of the Huber-Mueller model at $5.3σ$. In the energy range of 4--6~MeV, a maximal local discrepancy of $6.3σ$ is observed. △ Less

Submitted 16 September, 2019; v1 submitted 16 April, 2019; originally announced April 2019.

Comments: Updated title

Journal ref: Phys. Rev. Lett. 123, 111801 (2019)

Molecular lattice clock with long vibrational coherence

Authors: S. S. Kondov, C. -H. Lee, K. H. Leung, C. Liedl, I. Majewska, R. Moszynski, T. Zelevinsky

Abstract: Atomic lattice clocks have spurred numerous ideas for tests of fundamental physics, detection of general relativistic effects, and studies of interacting many-body systems. On the other hand, molecular structure and dynamics offer rich energy scales that are at the heart of new protocols in precision measurement and quantum information science. Here we demonstrate a fundamentally distinct type of… ▽ More Atomic lattice clocks have spurred numerous ideas for tests of fundamental physics, detection of general relativistic effects, and studies of interacting many-body systems. On the other hand, molecular structure and dynamics offer rich energy scales that are at the heart of new protocols in precision measurement and quantum information science. Here we demonstrate a fundamentally distinct type of lattice clock that is based on vibrations in diatomic molecules, and present coherent Rabi oscillations between weakly and deeply bound molecules that persist for 10's of milliseconds. This control is made possible by a state-insensitive magic lattice trap that weakly couples to molecular vibronic resonances and enhances the coherence time between molecules and light by several orders of magnitude. The achieved quality factor $Q=8\times10^{11}$ results from 30-Hz narrow resonances for a 25-THz clock transition in Sr$_2$. Our technique of extended coherent manipulation is applicable to long-term storage of quantum information in qubits based on ultracold polar molecules, while the vibrational clock enables precise probes of interatomic forces, tests of Newtonian gravitation at ultrashort range, and model-independent searches for electron-to-proton mass ratio variations. △ Less

Submitted 9 April, 2019; originally announced April 2019.

Journal ref: Nat. Phys. 15, 1118 (2019)

The neutron electric dipole moment experiment at the Spallation Neutron Source

Authors: K. K. H. Leung, M. Ahmed, R. Alarcon, A. Aleksandrova, S. Baeßler, L. Barrón-Palos, L. Bartoszek, D. H. Beck, M. Behzadipour, J. Bessuille, M. A. Blatnik, M. Broering, L. J. Broussard, M. Busch, R. Carr, P. -H. Chu, V. Cianciolo, S. M. Clayton, M. D. Cooper, C. Crawford, S. A. Currie, C. Daurer, R. Dipert, K. Dow, D. Dutta , et al. (68 additional authors not shown)

Abstract: Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarize… ▽ More Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized $^3$He, and superfluid $^4$He will be exploited to provide a sensitivity to $\sim 10^{-28}\,e{\rm \,\cdot\, cm}$. Our cryogenic apparatus will deploy two small ($3\,{\rm L}$) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our $^3$He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of "critical component demonstration," our collaboration transitioned to a "large scale integration" phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings. △ Less

Submitted 4 October, 2019; v1 submitted 6 March, 2019; originally announced March 2019.

Comments: Submitted to proceedings of PPNS 2018 - International Workshop on Particle physics at Neutron Sources (https://www.webofconferences.org/epj-web-of-conferences-forthcoming-conferences/1148-ppns-2018)

A high precision calibration of the nonlinear energy response at Daya Bay

Authors: Daya Bay collaboration, D. Adey, F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, J. F. Chang, Y. Chang, H. S. Chen, S. M. Chen, Y. Chen, Y. X. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, A. Chukanov, J. P. Cummings, N. Dash, F. S. Deng, Y. Y. Ding , et al. (173 additional authors not shown)

Abstract: A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment's antineutrino detectors is presented in detail. The energy nonlinearity originates from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by $γ$ calibration points from deployed and naturally occur… ▽ More A high precision calibration of the nonlinearity in the energy response of the Daya Bay Reactor Neutrino Experiment's antineutrino detectors is presented in detail. The energy nonlinearity originates from the particle-dependent light yield of the scintillator and charge-dependent electronics response. The nonlinearity model is constrained by $γ$ calibration points from deployed and naturally occurring radioactive sources, the $β$ spectrum from $^{12}$B decays, and a direct measurement of the electronics nonlinearity with a new flash analog-to-digital converter readout system. Less than 0.5% uncertainty in the energy nonlinearity calibration is achieved for positrons of kinetic energies greater than 1 MeV. △ Less

Submitted 27 June, 2019; v1 submitted 21 February, 2019; originally announced February 2019.

Comments: 17 pages, 22 figures, 4 tables. Final version to be published in NIM-A

Concerted Metal Cation Desorption and Proton Transfer on Deprotonated Silica Surfaces

Authors: Kevin Leung, Louise J. Criscenti, Andrew W. Knight, Anastasia G. Ilgen, Tuan A. Ho, Jeffery A. Greathouse

Abstract: The adsorption equilibrium constants of monovalent and divalent cations to material surfaces in aqueous media are central to many technological, natural, and geochemical processes. Cation adsorption/desorption is often proposed to occur in concert with proton-transfer on hydroxyl-covered mineral surfaces, but so far this cooperative effect has been inferred indirectly. This work applies Density Fu… ▽ More The adsorption equilibrium constants of monovalent and divalent cations to material surfaces in aqueous media are central to many technological, natural, and geochemical processes. Cation adsorption/desorption is often proposed to occur in concert with proton-transfer on hydroxyl-covered mineral surfaces, but so far this cooperative effect has been inferred indirectly. This work applies Density Functional Theory (DFT)-based molecular dynamics simulations of explicit liquid water/mineral interfaces to calculate metal ion desorption free energies. Monodentate adsorption of Na(+), Mg(2+), and Cu(2+) on partially deprotonated silica surfaces are considered. Na(+) is predicted to be unbound, while Cu(2+) exhibits larger binding free energies to surface SiO(-) groups than Mg(2+). The predicted trends agree with competitive adsorption measurements on fumed silica surfaces. As desorption proceeds, Cu(2+) dissociates one of the H2O molecules in its first solvation shell, turning into Cu(2+)O(-)(H2O)(3), while Mg remains Mg(2+)(H2O)(6). The protonation state of the SiO(-) group at the initial binding site does not vary monotonically with cation desorption. △ Less

Submitted 6 October, 2018; originally announced November 2018.

Comments: 4 figures

Journal ref: Journal of Physical Chemistry Letters 9(18), 5379-5385 (2018)

Measurement of electron antineutrino oscillation with 1958 days of operation at Daya Bay

Authors: Daya Bay Collaboration, D. Adey, F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, Y. L. Chan, J. F. Chang, Y. Chang, H. S. Chen, S. M. Chen, Y. Chen, Y. X. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, A. Chukanov, J. P. Cummings, F. S. Deng, Y. Y. Ding , et al. (180 additional authors not shown)

Abstract: We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor $\overlineν_{e}$ inverse beta decay candidates observed over 1958 days of data collection. The installation of a Flash-ADC readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration… ▽ More We report a measurement of electron antineutrino oscillation from the Daya Bay Reactor Neutrino Experiment with nearly 4 million reactor $\overlineν_{e}$ inverse beta decay candidates observed over 1958 days of data collection. The installation of a Flash-ADC readout system and a special calibration campaign using different source enclosures reduce uncertainties in the absolute energy calibration to less than 0.5% for visible energies larger than 2 MeV. The uncertainty in the cosmogenic $^9$Li and $^8$He background is reduced from 45% to 30% in the near detectors. A detailed investigation of the spent nuclear fuel history improves its uncertainty from 100% to 30%. Analysis of the relative $\overlineν_{e}$ rates and energy spectra among detectors yields $\sin^{2}2θ_{13} = 0.0856\pm 0.0029$ and $Δm^2_{32}=(2.471^{+0.068}_{-0.070})\times 10^{-3}~\mathrm{eV}^2$ assuming the normal hierarchy, and $Δm^2_{32}=-(2.575^{+0.068}_{-0.070})\times 10^{-3}~\mathrm{eV}^2$ assuming the inverted hierarchy. △ Less

Submitted 19 December, 2018; v1 submitted 6 September, 2018; originally announced September 2018.

Comments: 6 pages, 4 figures, and 1 table. v4: the published version

Journal ref: Phys. Rev. Lett. 121, 241805 (2018)

Improved Measurement of the Reactor Antineutrino Flux at Daya Bay

Authors: Daya Bay Collaboration, D. Adey, F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, Y. L. Chan, J. F. Chang, Y. Chang, H. S. Chen, S. M. Chen, Y. Chen, Y. X. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, A. Chukanov, J. P. Cummings, F. S. Deng, Y. Y. Ding , et al. (178 additional authors not shown)

Abstract: This work reports a precise measurement of the reactor antineutrino flux using 2.2 million inverse beta decay (IBD) events collected with the Daya Bay near detectors in 1230 days. The dominant uncertainty on the neutron detection efficiency is reduced by 56% with respect to the previous measurement through a comprehensive neutron calibration and detailed data and simulation analysis. The new avera… ▽ More This work reports a precise measurement of the reactor antineutrino flux using 2.2 million inverse beta decay (IBD) events collected with the Daya Bay near detectors in 1230 days. The dominant uncertainty on the neutron detection efficiency is reduced by 56% with respect to the previous measurement through a comprehensive neutron calibration and detailed data and simulation analysis. The new average IBD yield is determined to be $(5.91\pm0.09)\times10^{-43}~\rm{cm}^2/\rm{fission}$ with total uncertainty improved by 29%. The corresponding mean fission fractions from the four main fission isotopes $^{235}$U, $^{238}$U, $^{239}$Pu, and $^{241}$Pu are 0.564, 0.076, 0.304, and 0.056, respectively. The ratio of measured to predicted antineutrino yield is found to be $0.952\pm0.014\pm0.023$ ($1.001\pm0.015\pm0.027$) for the Huber-Mueller (ILL-Vogel) model, where the first and second uncertainty are experimental and theoretical model uncertainty, respectively. This measurement confirms the discrepancy between the world average of reactor antineutrino flux and the Huber-Mueller model. △ Less

Submitted 31 August, 2018; originally announced August 2018.

Comments: 10 pages, 9 figures, and 2 tables

Journal ref: Phys. Rev. D 100, 052004 (2019)

Solid deuterium surface degradation at ultracold neutron sources

Authors: A. Anghel, T. L. Bailey, G. Bison, B. Blau, L. J. Broussard, S. M. Clayton, C. Cude-Woods, M. Daum, A. Hawari, N. Hild, P. Huffman, T. M. Ito, K. Kirch, E. Korobkina, B. Lauss, K. Leung, E. M. Lutz, M. Makela, G. Medlin, C. L. Morris, R. W. Pattie, D. Ries, A. Saunders, P. Schmidt-Wellenburg, V. Talanov , et al. (5 additional authors not shown)

Abstract: Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the m… ▽ More Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease. △ Less

Submitted 28 August, 2018; v1 submitted 23 April, 2018; originally announced April 2018.

Comments: 15 pages, 22 figures, accepted by EPJ-A

Design, construction, and characterization of a compact DD neutron generator designed for 40Ar/39Ar geochronology

Authors: Mauricio Ayllon, Parker A. Adams, Joseph D. Bauer, Jon C. Batchelder, Tim A. Becker, Lee A. Bernstein, Su-Ann Chong, Jay James, Leo E. Kirsch, Ka-Ngo Leung, Eric F. Matthews, Jonathan T. Morrell, Paul R. Renne, Andrew M. Rogers, Daniel Rutte, Andrew S. Voyles, Karl Van Bibber, Cory S. Waltz

Abstract: A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near futu… ▽ More A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58e7 n/cm2/s +/- 5% (approximately 3e8 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG. △ Less

Submitted 9 April, 2018; v1 submitted 9 March, 2018; originally announced March 2018.

Comments: 31 pages, 20 figures

Cosmogenic neutron production at Daya Bay

Authors: Daya Bay Collaboration, F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, Y. L. Chan, J. F. Chang, Y. Chang, H. S. Chen, S. M. Chen, Y. Chen, Y. X. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, A. Chukanov, J. P. Cummings, Y. Y. Ding, M. V. Diwan, M. Dolgareva , et al. (177 additional authors not shown)

Abstract: Neutrons produced by cosmic ray muons are an important background for underground experiments studying neutrino oscillations, neutrinoless double beta decay, dark matter, and other rare-event signals. A measurement of the neutron yield in the three different experimental halls of the Daya Bay Reactor Neutrino Experiment at varying depth is reported. The neutron yield in Daya Bay's liquid scintilla… ▽ More Neutrons produced by cosmic ray muons are an important background for underground experiments studying neutrino oscillations, neutrinoless double beta decay, dark matter, and other rare-event signals. A measurement of the neutron yield in the three different experimental halls of the Daya Bay Reactor Neutrino Experiment at varying depth is reported. The neutron yield in Daya Bay's liquid scintillator is measured to be $Y_n=(10.26\pm 0.86)\times 10^{-5}$, $(10.22\pm 0.87)\times 10^{-5}$, and $(17.03\pm 1.22)\times 10^{-5}~μ^{-1}~$g$^{-1}~$cm$^2$ at depths of 250, 265, and 860 meters-water-equivalent. These results are compared to other measurements and the simulated neutron yield in Fluka and Geant4. A global fit including the Daya Bay measurements yields a power law coefficient of $0.77 \pm 0.03$ for the dependence of the neutron yield on muon energy. △ Less

Submitted 23 March, 2018; v1 submitted 1 November, 2017; originally announced November 2017.

Comments: 13 pages, 13 figures

Journal ref: Phys. Rev. D 97, 052009 (2018)

Generation of High-Purity Millimeter-Wave Orbital Angular Momentum Modes Using Horn Antenna: Theory and Implementation

Authors: Jian Ren, Kwok Wa Leung

Abstract: Twisted electromagnetic waves, of which the helical phase front is called orbital angular momentum (OAM), have been recently explored for quantum information, high speed communication and radar detections. In this context, generation of high purity waves carrying OAM is of great significance and challenge from low frequency band to optical area. Here, a novel strategy of mode combination method is… ▽ More Twisted electromagnetic waves, of which the helical phase front is called orbital angular momentum (OAM), have been recently explored for quantum information, high speed communication and radar detections. In this context, generation of high purity waves carrying OAM is of great significance and challenge from low frequency band to optical area. Here, a novel strategy of mode combination method is proposed to generate twisted waves with arbitrary order of OAM index. The higher order mode of a circular horn antenna is used to generate the twisted waves with quite high purity. The proposed strategy is verified with theoretical analysis, numerical simulation and experiments. A circular horn antenna operating at millimeter wave band is designed, fabricated, and measured. Two twisted waves with OAM index of l=+1 and l=-1 with a mode purity as high as 87% are obtained. Compared with the other OAM antennas, the antenna proposed here owns a high antenna gain (over 12 dBi) and wide operating bandwidth (over 15%). The high mode purity, high antenna gain and wide operating band make the antenna suitable for the twisted-wave applications, not only in the microwave and millimeter wave band, but also in the terahertz band. △ Less

Submitted 7 September, 2017; originally announced October 2017.

Comments: 18 pages, 9 figures

Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay

Authors: F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, Y. L. Chan, J. F. Chang, Y. Chang, H. S. Chen, Q. Y. Chen, S. M. Chen, Y. X. Chen, Y. Chen, J. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu, A. Chukanov, J. P. Cummings, Y. Y. Ding, M. V. Diwan, M. Dolgareva , et al. (180 additional authors not shown)

Abstract: The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW$_{\textrm{th}}$ reactor cores at the Daya Bay and Ling Ao nuclear… ▽ More The Daya Bay experiment has observed correlations between reactor core fuel evolution and changes in the reactor antineutrino flux and energy spectrum. Four antineutrino detectors in two experimental halls were used to identify 2.2 million inverse beta decays (IBDs) over 1230 days spanning multiple fuel cycles for each of six 2.9 GW$_{\textrm{th}}$ reactor cores at the Daya Bay and Ling Ao nuclear power plants. Using detector data spanning effective $^{239}$Pu fission fractions, $F_{239}$, from 0.25 to 0.35, Daya Bay measures an average IBD yield, $\barσ_f$, of $(5.90 \pm 0.13) \times 10^{-43}$ cm$^2$/fission and a fuel-dependent variation in the IBD yield, $dσ_f/dF_{239}$, of $(-1.86 \pm 0.18) \times 10^{-43}$ cm$^2$/fission. This observation rejects the hypothesis of a constant antineutrino flux as a function of the $^{239}$Pu fission fraction at 10 standard deviations. The variation in IBD yield was found to be energy-dependent, rejecting the hypothesis of a constant antineutrino energy spectrum at 5.1 standard deviations. While measurements of the evolution in the IBD spectrum show general agreement with predictions from recent reactor models, the measured evolution in total IBD yield disagrees with recent predictions at 3.1$σ$. This discrepancy indicates that an overall deficit in measured flux with respect to predictions does not result from equal fractional deficits from the primary fission isotopes $^{235}$U, $^{239}$Pu, $^{238}$U, and $^{241}$Pu. Based on measured IBD yield variations, yields of $(6.17 \pm 0.17)$ and $(4.27 \pm 0.26) \times 10^{-43}$ cm$^2$/fission have been determined for the two dominant fission parent isotopes $^{235}$U and $^{239}$Pu. A 7.8% discrepancy between the observed and predicted $^{235}$U yield suggests that this isotope may be the primary contributor to the reactor antineutrino anomaly. △ Less

Submitted 20 June, 2017; v1 submitted 4 April, 2017; originally announced April 2017.

Comments: 7 pages, 5 figures

Journal ref: Phys. Rev. Lett. 118, 251801 (2017)

Confocal micro-Raman Spectra of untreated and lethally treated Escherichia coli exposed to UV-B and violet light

Authors: Werden Keeler, Kam Leung

Abstract: We report on changes in the Raman spectrum of live Escherichi coli (E.coli) that result from exposure to lethal fluences of 300 nm (UV-B) and 405 nm (violet) photons. In the first instance, the energy per photon of 4.13 eV is sufficient to break most of the inter-atomic bonds in the bacterium and major change in the Raman spectrum, particularly in the RNA/DNA regions is observed. This energy is in… ▽ More We report on changes in the Raman spectrum of live Escherichi coli (E.coli) that result from exposure to lethal fluences of 300 nm (UV-B) and 405 nm (violet) photons. In the first instance, the energy per photon of 4.13 eV is sufficient to break most of the inter-atomic bonds in the bacterium and major change in the Raman spectrum, particularly in the RNA/DNA regions is observed. This energy is in near resonance with the C-H, N-H, and P-O bond binding energies that interconnect phosphate backbone sections and may initiate the Raman modifications. By contrast, the 3.06 eV violet photon energy is insufficient to cleave the stronger system bonds. The much larger lethal fluence required in this case produces a significant change in the resonant C-N and C-P bond connected amino acid/protein groups and lipid peak signal but much less so in the nucleotide-DNA/RNA signature. △ Less

Submitted 6 January, 2017; originally announced January 2017.

Beam-induced Back-streaming Electron Suppression Analysis for Accelerator Type Neutron Generators

Authors: Cory Waltz, Mauricio Ayllon, Tim Becker, Lee Bernstein, Ka-Ngo Leung, Leo Kirsch, Paul Renne, Karl Van Bibber

Abstract: A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator design produces near monoenergetic 2.45 MeV neutrons at outputs of 10^8 n/s. Calculations provided show that future conditioning at higher currents and voltages will allow for a production rate over 10^10 n/s. A sign… ▽ More A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator design produces near monoenergetic 2.45 MeV neutrons at outputs of 10^8 n/s. Calculations provided show that future conditioning at higher currents and voltages will allow for a production rate over 10^10 n/s. A significant problem encountered was beam-induced electron backstreaming, that needed to be resolved to achieve meaningful beam currents. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics. Experimental tests verified these simulation results. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of -800 V relative to the target. △ Less

Submitted 1 January, 2017; originally announced January 2017.

Spin flip loss in magnetic confinement of ultracold neutrons for neutron lifetime experiments

Authors: A. Steyerl, K. K. H. Leung, C. Kaufman, G. Müller, S. S. Malik

Abstract: We analyze the spin flip loss for ultracold neutrons in magnetic bottles of the type used in experiments aiming at a precise measurement of the neutron lifetime, extending the one-dimensional field model used previously by Steyerl $\textit{et al.}$ [Phys.Rev.C $\mathbf{86}$, 065501 (2012)] to two dimensions for cylindrical multipole fields. We also develop a general analysis applicable to three di… ▽ More We analyze the spin flip loss for ultracold neutrons in magnetic bottles of the type used in experiments aiming at a precise measurement of the neutron lifetime, extending the one-dimensional field model used previously by Steyerl $\textit{et al.}$ [Phys.Rev.C $\mathbf{86}$, 065501 (2012)] to two dimensions for cylindrical multipole fields. We also develop a general analysis applicable to three dimensions. Here we apply it to multipole fields and to the bowl-type field configuration used for the Los Alamos UCN$τ$ experiment. In all cases considered the spin flip loss calculated exceeds the Majorana estimate by many orders of magnitude but can be suppressed sufficiently by applying a holding field of appropriate magnitude to allow high-precision neutron lifetime measurements, provided other possible sources of systematic error are under control. △ Less

Submitted 15 November, 2016; originally announced November 2016.

Journal ref: Phys. Rev. C 95, 035502 (2017)

Development of a Bonner Sphere Neutron Spectrometer from a Commercial Neutron Dosimeter

Authors: M. C. Chu, K. Y. Fung, T. Kwok, J. K. C. Leung, Y. C. Lin, H. Liu, K. B. Luk, H. Y. Ngai, C. S. J. Pun, H. L. H. Wong

Abstract: Bonner Spheres have been used widely for the measurement of neutron spectra with neutron energies ranged from thermal up to at least 20 MeV. A Bonner Sphere neutron spectrometer (BSS) was developed by extending a Berthold LB 6411 neutron-dose-rate meter. The BSS consists of a $^{3}$He thermal-neutron detector with integrated electronics, a set of eight polyethylene spherical shells and two optiona… ▽ More Bonner Spheres have been used widely for the measurement of neutron spectra with neutron energies ranged from thermal up to at least 20 MeV. A Bonner Sphere neutron spectrometer (BSS) was developed by extending a Berthold LB 6411 neutron-dose-rate meter. The BSS consists of a $^{3}$He thermal-neutron detector with integrated electronics, a set of eight polyethylene spherical shells and two optional lead shells of various sizes. The response matrix of the BSS was calculated with GEANT4 Monte Carlo simulation. The BSS had a calibration uncertainty of $\pm 8.6\%$ and a detector background rate of $(1.57 \pm 0.04) \times 10^{-3}$ s$^{-1}$. A spectral unfolding code NSUGA was developed. The NSUGA code utilizes genetic algorithms and has been shown to perform well in the absence of a priori information. △ Less

Submitted 12 November, 2016; originally announced November 2016.

Comments: 25 pages, 14 figures, 5 tables

Journal ref: J. Instrum. 11 (2016) P11005

Measurement of electron antineutrino oscillation based on 1230 days of operation of the Daya Bay experiment

Authors: Daya Bay Collaboration, F. P. An, A. B. Balantekin, H. R. Band, M. Bishai, S. Blyth, D. Cao, G. F. Cao, J. Cao, W. R. Cen, Y. L. Chan, J. F. Chang, L. C. Chang, Y. Chang, H. S. Chen, Q. Y. Chen, S. M. Chen, Y. X. Chen, Y. Chen, J. -H. Cheng, J. Cheng, Y. P. Cheng, Z. K. Cheng, J. J. Cherwinka, M. C. Chu , et al. (198 additional authors not shown)

Abstract: A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GW$_{\rm th}$ nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of $\overlineν_{e}$'s. Comparison of the $\overlineν_{e}$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors (… ▽ More A measurement of electron antineutrino oscillation by the Daya Bay Reactor Neutrino Experiment is described in detail. Six 2.9-GW$_{\rm th}$ nuclear power reactors of the Daya Bay and Ling Ao nuclear power facilities served as intense sources of $\overlineν_{e}$'s. Comparison of the $\overlineν_{e}$ rate and energy spectrum measured by antineutrino detectors far from the nuclear reactors ($\sim$1500-1950 m) relative to detectors near the reactors ($\sim$350-600 m) allowed a precise measurement of $\overlineν_{e}$ disappearance. More than 2.5 million $\overlineν_{e}$ inverse beta decay interactions were observed, based on the combination of 217 days of operation of six antineutrino detectors (Dec. 2011--Jul. 2012) with a subsequent 1013 days using the complete configuration of eight detectors (Oct. 2012--Jul. 2015). The $\overlineν_{e}$ rate observed at the far detectors relative to the near detectors showed a significant deficit, $R=0.949 \pm 0.002(\mathrm{stat.}) \pm 0.002(\mathrm{syst.})$. The energy dependence of $\overlineν_{e}$ disappearance showed the distinct variation predicted by neutrino oscillation. Analysis using an approximation for the three-flavor oscillation probability yielded the flavor-mixing angle $\sin^22θ_{13}=0.0841 \pm 0.0027(\mathrm{stat.}) \pm 0.0019(\mathrm{syst.})$ and the effective neutrino mass-squared difference of $\left|Δm^2_{\mathrm{ee}}\right|=(2.50 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$. Analysis using the exact three-flavor probability found $Δm^2_{32}=(2.45 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ assuming the normal neutrino mass hierarchy and $Δm^2_{32}=(-2.56 \pm 0.06(\mathrm{stat.}) \pm 0.06(\mathrm{syst.})) \times 10^{-3}\ {\rm eV}^2$ for the inverted hierarchy. △ Less

Submitted 15 October, 2016; originally announced October 2016.

Comments: 44 pages, 44 figures

Journal ref: Phys. Rev. D 95, 072006 (2017)

Neutron lifetime measurements and effective spectral cleaning with an ultracold neutron trap using a vertical Halbach octupole permanent magnet array

Authors: K. K. H. Leung, P. Geltenbort, S. Ivanov, F. Rosenau, O. Zimmer

Abstract: Ultracold neutron (UCN) storage measurements were made in a trap constructed from a 1.3 T Halbach Octupole PErmanent (HOPE) magnet array aligned vertically, using the TES-port of the PF2 source at the Institut Laue-Langevin. A mechanical UCN valve at the bottom of the trap was used for filling and emptying. This valve was covered with Fomblin grease to induce non-specular reflections and was used… ▽ More Ultracold neutron (UCN) storage measurements were made in a trap constructed from a 1.3 T Halbach Octupole PErmanent (HOPE) magnet array aligned vertically, using the TES-port of the PF2 source at the Institut Laue-Langevin. A mechanical UCN valve at the bottom of the trap was used for filling and emptying. This valve was covered with Fomblin grease to induce non-specular reflections and was used in combination with a movable polyethylene UCN remover inserted from the top for cleaning of above-threshold UCNs. Loss due to UCN depolarization was suppressed with a minimum 2 mT bias field. Without using the UCN remover, a total storage time constant of $(712 \pm 19)$ s was observed; with the remover inserted for 80 s and used at either 80 cm or 65 cm from the bottom of the trap, time constants of $(824 \pm 32)$ s and $(835 \pm 36)$ s were observed. Combining the latter two values, a neutron lifetime of $τ_{\rm n} = (887 \pm 39)$ s is extracted after primarily correcting for losses at the UCN valve. The time constants of the UCN population during cleaning were observed and compared to calculations based on UCN kinetic theory as well as Monte-Carlo studies. These calculations are used to predict above-threshold populations of $\sim 5\%$, $\sim 0.5\%$ and $\sim 10^{-12}\%$ remaining after cleaning in the no remover, 80~cm remover and 65~cm remover measurements. Thus, by using a non-specular reflector covering the entire bottom of the trap and a remover at the top of the trap, we have established an effective cleaning procedure for removing a major systematic effect in high-precision $τ_{\rm n}$ experiments with magnetically stored UCNs. △ Less

Submitted 2 June, 2016; originally announced June 2016.

Comments: To be submitted to Physical Review C

Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy

Authors: Wanchun Wei, L. J. Broussard, M. A. Hoffbauer, M. Makela, C. L. Morris, Z. Tang, E. R. Adamek, N. B. Callahan, S. M. Clayton, C. Cude-Woods, S. Currie, E. B. Dees, X. Ding, P. Geltenbort, K. P. Hickerson, A. T. Holley, T. M. Ito, K. K. Leung, C. -Y. Liu, D. J. Morley, Jose D. Ortiz, R. W. Pattie, Jr., J. C. Ramsey, A. Saunders, S. J. Seestrom , et al. (7 additional authors not shown)

Abstract: Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15 $μ$m has been achieved, which is equivalent to an UCN energy resolution below 2 pico-electron-volts through the relation $δE = m_0g δx$. Here, the symbols $δE$, $δx$, $m_0$ and $g$ are the energy resolution, the spatial resolution, the neu… ▽ More Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15 $μ$m has been achieved, which is equivalent to an UCN energy resolution below 2 pico-electron-volts through the relation $δE = m_0g δx$. Here, the symbols $δE$, $δx$, $m_0$ and $g$ are the energy resolution, the spatial resolution, the neutron rest mass and the gravitational acceleration, respectively. A multilayer surface convertor described previously is used to capture UCNs and then emits visible light for CCD imaging. Particle identification and noise rejection are discussed through the use of light intensity profile analysis. This method allows different types of UCN spectroscopy and other applications. △ Less

Submitted 12 May, 2016; v1 submitted 27 April, 2016; originally announced April 2016.

Comments: 12 figures, 28 pages, accepted for publication in NIMA

Report number: Los Alamos National Lab Report LA-UR-16-22875

Journal ref: Nuclear Instruments and Methods in Physics Research Section A, vol. 830, 36-43 (2016)