Showing 1–26 of 26 results for author: Coupland, D

Detector Response Matrices, Effective Areas, and Flash-Effective Areas for Radiation Detectors

Authors: Gregory Bowers, Eve Chase, William Ford, Daniel Coupland, Brian Larsen, Caleb Roecker, Karl Smith, Kurtis Bartlett, Katherine Gattiker Katherine Mesick

Abstract: A Detector Response Matrix (DRM) is a discrete representation of an instrument's Detector Response Function (DRF), which quantifies how many discrete energy depositions occur in a detector volume for a given distribution of particles incident on the detector. For simple radiation detectors that can count such energy depositions (such as scintillators, Proportional Counter Tubes (PCTs), etc), we co… ▽ More A Detector Response Matrix (DRM) is a discrete representation of an instrument's Detector Response Function (DRF), which quantifies how many discrete energy depositions occur in a detector volume for a given distribution of particles incident on the detector. For simple radiation detectors that can count such energy depositions (such as scintillators, Proportional Counter Tubes (PCTs), etc), we consider the ideal counting DRF, $\mathbf{G}_\varphi (E_\mathrm{in}, E_\mathrm{dep})$, which relates the detector's counting histogram (number of energy depositions within a given channel) to an incident particles characterization, $\varphi$ (e.g. incident flux, fluence, intensity). From the counting DRF we can derive the counting DRM, the effective area, and the flash effective area (which measures the total energy deposited in the detector from a large, instantaneous fluence). △ Less

Submitted 31 December, 2025; originally announced December 2025.

Systematic Uncertainties in the Measurement of Neutron lifetime Using Lunar Prospector Neutron Spectrometer

Authors: Akshatha K. Vydula, Daniel Coupland, Katherine Mesick, Craig Hardgrove

Abstract: The lifetime of free neutrons measured in the lab has a long standing disparity of $\sim$9~s. A space-based technique has recently been proposed to independently measure the neutron lifetime using interactions between the galactic cosmic rays and a low atmosphere planetary body. This technique has not produced competitive results yet due to constraints of non-optimized data that contain large syst… ▽ More The lifetime of free neutrons measured in the lab has a long standing disparity of $\sim$9~s. A space-based technique has recently been proposed to independently measure the neutron lifetime using interactions between the galactic cosmic rays and a low atmosphere planetary body. This technique has not produced competitive results yet due to constraints of non-optimized data that contain large systematic errors. We use data from the neutron spectrometer on-board NASA's Lunar Prospector, and study two large systematics in the measurement of neutron lifetime: the lunar sub-surface temperature and the lunar surface composition. We use the HeCd and HeSn neutron spectrometer data when the spacecraft was in a highly elliptical orbit during the orbit insertion period. We report the neutron lifetime using four different models that each have different choices of surface temperature and composition. 5$^{\circ}$ \cite{prettyman2006elemental} and 2$^{\circ}$ re-binned \cite{wilson2021measurement} maps result in 777.6$\pm$11.7~s and 739.6$\pm$10.8~s respectively. For the 20$^{\circ}$ map, constant equatorial and a latitude-dependent temperature model result in 738.6$\pm$10.8~s and 767.3$\pm$11.2~s respectively. Increasing the complexities of the models accounting for the systematic effects increase the measured lifetime. However, the reported measurements are not competitive with the laboratory results due to large unaccounted systematics resulting from non-optimized measurements and modeling assumptions. This work serves as a study of systematic uncertainties for future neutron lifetime measurements using the space-based technique. We estimate the effect on the lifetime from the choice of temperature model to be to be 28.7 $\pm$ 15.5~s, and choice of compositional map (for 20$^\circ$ and 5$^\circ$ maps) to be 10.3 $\pm$ 12.2~s. △ Less

Submitted 8 May, 2025; v1 submitted 30 January, 2025; originally announced January 2025.

Comments: 16 pages, 9 figures, accepted to PRC

Thermal Characterization of Tl$_2$LiYCl$_6$:Ce (TLYC)

Authors: M. M. Watts, K. E. Mesick, K. D. Bartlett, D. D. S. Coupland

Abstract: Tl$_2$LiYCl$_6$:Ce (TLYC) is a new dual-detection elpasolite scintillator that can detect and distinguish between gamma rays and neutrons using pulse-shape discrimination (PSD). It has a higher density and Z-number than the more mature and well-known elpasolite Cs$_2$LiYCl$_6$:Ce (CLYC), causing it to have a significantly better gamma-ray stopping power. These properties make TLYC an attractive al… ▽ More Tl$_2$LiYCl$_6$:Ce (TLYC) is a new dual-detection elpasolite scintillator that can detect and distinguish between gamma rays and neutrons using pulse-shape discrimination (PSD). It has a higher density and Z-number than the more mature and well-known elpasolite Cs$_2$LiYCl$_6$:Ce (CLYC), causing it to have a significantly better gamma-ray stopping power. These properties make TLYC an attractive alternative to CLYC for resource-constrained applications where size and weight are important, such as space or national security applications. Such applications may be subjected to a wide range of temperatures, and therefore TLYC's performance was characterized for the first time over a temperature range of -20$^{\circ}$C to +50$^{\circ}$C in 10$^{\circ}$C increments. TLYC's thermal response effects on light-output linearity with energy, gamma-ray photopeak energy resolution, detected neutron energy, pulse shapes, and figure of merit is analyzed and reported. The light output of TLYC was found to be linear with energy over the tested temperature range and was observed to decrease with increasing temperature. The decay time of the scintillation light output was observed to decrease with decreasing temperature at short times, leading to a decreasing PSD figure of merit. The gamma-ray photopeak energy resolution was also observed to degrade with decreasing temperature, due to an asymmetric broadening of the photopeak at low temperatures. △ Less

Submitted 24 December, 2019; originally announced December 2019.

Proton Irradiation Damage and Annealing Effects in ON Semiconductor J-Series Silicon Photomultipliers

Authors: K. D. Bartlett, D. D. S. Coupland, D. Beckman, K. E. Mesick

Abstract: Silicon photomultipliers (SiPMs) have become popular light conversion devices in recent years due to their low bias voltage and sensitivity to wavelengths emitted from common scintillating materials. These properties make them particularly attractive for resource-constrained missions such as space-based detector applications. However the space radiation environment is known to be particularly hars… ▽ More Silicon photomultipliers (SiPMs) have become popular light conversion devices in recent years due to their low bias voltage and sensitivity to wavelengths emitted from common scintillating materials. These properties make them particularly attractive for resource-constrained missions such as space-based detector applications. However the space radiation environment is known to be particularly harsh on semiconductor devices, where high particle fluences can degrade performance over time. The radiation hardness of a particular SiPM, manufactured by ON Semiconductor (formally SensL), has yet to be studied with high energy protons, which are native to the space radiation environment. To study these effects we have irradiated groups of two SiPMs to four different fluences of 800 MeV protons delivered by the accelerator at the Los Alamos Neutron Science Center. Fluences of $1.68\times10^{9}$, $1.73\times10^{10}$, $6.91\times10^{10}$, and $1.73\times10^{11}$ protons cm$^{-2}$, and their corresponding estimated doses of $0.15$, $1.55$, $6.19$, and $15.5$ kRad, were chosen based on estimates of the potential exposure a SiPM might receive during an interplanetary space mission lasting 10 years. We report the effects these doses have on dark current and the self-annealing time. △ Less

Submitted 19 November, 2019; originally announced November 2019.

Comments: 17 pages, 4 figures, 3 tables

Report number: LA-UR-19-31419

Effects of Proton-Induced Radiation Damage on CLYC and CLLBC Performance

Authors: K. E. Mesick, K. D. Bartlett, D. D. S. Coupland, L. C. Stonehill

Abstract: Cerium-doped Cs$_2$LiYCl$_6$ (CLYC) and Cs$_2$LiLaBr$_x$Cl$_{6-x}$ (CLLBC) are scintillators in the elpasolite family that are attractive options for resource-constrained applications due to their ability to detect both gamma rays and neutrons within a single volume. Space-based detectors are one such application, however, the radiation environment in space can over time damage the crystal structu… ▽ More Cerium-doped Cs$_2$LiYCl$_6$ (CLYC) and Cs$_2$LiLaBr$_x$Cl$_{6-x}$ (CLLBC) are scintillators in the elpasolite family that are attractive options for resource-constrained applications due to their ability to detect both gamma rays and neutrons within a single volume. Space-based detectors are one such application, however, the radiation environment in space can over time damage the crystal structure of the elpasolites, leading to degraded performance. We have exposed 4 samples each of CLYC and CLLBC to 800 MeV protons at the Los Alamos Neutron Science Center. The samples were irradiated with a total number of protons of 1.3$\times$10$^{9}$, 1.3$\times$10$^{10}$, 5.2$\times$10$^{10}$, and 1.3$\times$10$^{11}$, corresponding to estimated doses of 0.14, 1.46, 5.82, and 14.6 kRad, respectively on the CLYC samples and 0.14, 1.38, 5.52, and 13.8 kRad, respectively on the CLLBC samples. We report the impact these radiation doses have on the light output, activation, gamma-ray energy resolution, pulse shapes, and pulse-shape discrimination figure of merit for CLYC and CLLBC. △ Less

Submitted 17 July, 2019; originally announced July 2019.

Constraining the symmetry energy with heavy-ion collisions and Bayesian analyses

Authors: P. Morfouace, C. Y. Tsang, Y. Zhang, W. G. Lynch, M. B. Tsang, D. D. S Coupland, M. Youngs, Z. Chajecki, M. A. Famiano, T. K. Ghosh, G. Jhang, Jenny Lee, H. Liu, A. Sanetullaev, R. Showalter, J. Winkelbauer

Abstract: Efficiency corrected single ratios of neutron and proton spectra in central $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at 120 MeV/u are combined with double ratios to provide constraints on the density and momentum dependencies of the isovector mean-field potential. Bayesian analyses of these data reveal that the isoscalar and isovector nucleon effective masses, $m_s^* - m_v^*$ are… ▽ More Efficiency corrected single ratios of neutron and proton spectra in central $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at 120 MeV/u are combined with double ratios to provide constraints on the density and momentum dependencies of the isovector mean-field potential. Bayesian analyses of these data reveal that the isoscalar and isovector nucleon effective masses, $m_s^* - m_v^*$ are strongly correlated. The linear correlation observed in $m_s^* - m_v^*$ yields a nearly independent constraint on the effective mass splitting $Δm_{np}^*= (m_n^*-m_p^*)/m_N = -0.05_{-0.09}^{+0.09}δ$. The correlated constraint on the standard symmetry energy, $S_0$ and the slope, $L$ at saturation density yields the values of symmetry energy $S(ρ_s)=16.8_{-1.2}^{+1.2}$ MeV at a sensitive density of $ρ_s/ρ_0 = 0.43_{-0.05}^{+0.05}$. △ Less

Submitted 3 May, 2019; v1 submitted 29 April, 2019; originally announced April 2019.

Elpasolite Planetary Ice and Composition Spectrometer (EPICS): A Low-Resource Combined Gamma-Ray and Neutron Spectrometer for Planetary Science

Authors: K. E. Mesick, L. C. Stonehill, D. D. S Coupland, D. T. Beckman, S. T. West, S. F. Nowicki, N. A. Dallmann, S. A. Storms, W. C. Feldman

Abstract: Neutron and gamma-ray spectroscopy (NGRS) is a well established technique for studying the geochemical composition and volatile abundance relevant to planetary structure and evolution of planetary bodies. Previous NGRS instruments have used separate gamma-ray and neutron spectrometers. The Elpasolite Planetary Ice and Composition Spectrometer (EPICS) instrument is an innovative and fully integrate… ▽ More Neutron and gamma-ray spectroscopy (NGRS) is a well established technique for studying the geochemical composition and volatile abundance relevant to planetary structure and evolution of planetary bodies. Previous NGRS instruments have used separate gamma-ray and neutron spectrometers. The Elpasolite Planetary Ice and Composition Spectrometer (EPICS) instrument is an innovative and fully integrated NGRS with low resource requirements. EPICS utilizes elpasolite scintillator read out by silicon photomultipliers to combine the gamma-ray and neutron spectrometer into a single instrument, leading to a significant reduction in instrument size, weight, and power. An overview and motivation for the EPICS instrument, current status of the EPICS development, and a discussion of the expected sensitivity and performance are presented. △ Less

Submitted 9 January, 2019; originally announced January 2019.

Comments: Submitted to 2019 IEEE Nuclear Science Symposium Conference Proceedings

Benchmarking Geant4 for Simulating Galactic Cosmic Ray Interactions Within Planetary Bodies

Authors: K. E. Mesick, W. C. Feldman, D. D. S. Coupland, L. C. Stonehill

Abstract: Galactic cosmic rays undergo complex nuclear interactions with nuclei within planetary bodies that have little to no atmosphere. Radiation transport simulations are a key tool used in understanding the neutron and gamma-ray albedo coming from these interactions and tracing these signals back to geochemical composition of the target. We study the validity of the code Geant4 for simulating such inte… ▽ More Galactic cosmic rays undergo complex nuclear interactions with nuclei within planetary bodies that have little to no atmosphere. Radiation transport simulations are a key tool used in understanding the neutron and gamma-ray albedo coming from these interactions and tracing these signals back to geochemical composition of the target. We study the validity of the code Geant4 for simulating such interactions by comparing simulation results to data from the Apollo 17 Lunar Neutron Probe Experiment. Different assumptions regarding the physics are explored to demonstrate how these impact the Geant4 simulation results. In general, all of the Geant4 results over-predict the data, however, certain physics lists perform better than others. In addition, we show that results from the radiation transport code MCNP6 are similar to those obtained using Geant4. △ Less

Submitted 15 October, 2018; originally announced October 2018.

Journal ref: Earth and Space Science, 5, 324-338. (2018)

The Effects of Radiation Damage on CLYC Performance

Authors: K. E. Mesick, D. D. S. Coupland, S. F. Nowicki, L. C. Stonehill

Abstract: Cs$_2$LiYCl$_6$:Ce$^{3+}$ (CLYC) is a new scintillator that is an attractive option for applications requiring the ability to detect both gamma rays and neutrons within a single volume. It is therefore of interest in applications that require low size, weight, or power, such as space applications. The radiation environment in space can over time damage the crystal structure of CLYC, leading to red… ▽ More Cs$_2$LiYCl$_6$:Ce$^{3+}$ (CLYC) is a new scintillator that is an attractive option for applications requiring the ability to detect both gamma rays and neutrons within a single volume. It is therefore of interest in applications that require low size, weight, or power, such as space applications. The radiation environment in space can over time damage the crystal structure of CLYC, leading to reduced performance. We have exposed 2 CLYC samples to 800 MeV protons at the Los Alamos Neutron Science Center, one to approximately 10 kRad and one to approximately 100 kRad. We measured the pulse shapes and amplitudes, energy resolution, and figure of merit for pulse-shape discrimination before and after irradiation. We have also measured the activation products and monitored for room-temperature annealing of the irradiated samples. The results of these measurements and the impact of radiation damage on CLYC performance is presented. △ Less

Submitted 15 October, 2018; v1 submitted 29 November, 2017; originally announced November 2017.

Comments: Submitted to 2017 IEEE Nuclear Science Symposium Conference Proceedings

Pulse-shape discrimination and energy quenching of alpha particles in Cs$_2$LiLaBr$_6$:Ce$^{3+}$

Authors: Katherine E. Mesick, Daniel D. S. Coupland, Laura C. Stonehill

Abstract: Cs$_2$LiLaBr$_6$:Ce$^{3+}$ (CLLB) is an elpasolite scintillator that offers excellent linearity and gamma-ray energy resolution and sensitivity to thermal neutrons with the ability to perform pulse-shape discrimination (PSD) to distinguish gammas and neutrons. Our investigation of CLLB has indicated the presence of intrinsic radioactive alpha background that we have determined to be from actinium… ▽ More Cs$_2$LiLaBr$_6$:Ce$^{3+}$ (CLLB) is an elpasolite scintillator that offers excellent linearity and gamma-ray energy resolution and sensitivity to thermal neutrons with the ability to perform pulse-shape discrimination (PSD) to distinguish gammas and neutrons. Our investigation of CLLB has indicated the presence of intrinsic radioactive alpha background that we have determined to be from actinium contamination of the lanthanum component. We measured the pulse shapes for gamma, thermal neutron, and alpha events and determined that PSD can be performed to separate the alpha background with a moderate figure of merit of 0.98. We also measured the electron-equivalent-energy of the alpha particles in CLLB and simulated the intrinsic alpha background from $^{227}$Ac to determine the quenching factor of the alphas. A linear quenching relationship $L_α = E_α \times q + L_0$ was found at alpha particle energies above 5 MeV, with a quenching factor $q = 0.71$ MeVee/MeV and an offset $L_0 = - 1.19$ MeVee. △ Less

Submitted 27 September, 2016; originally announced September 2016.

Comments: Preprint submitted to NIMA

Performance of Several Solid State Photomultipliers with CLYC Scintillator

Authors: Katherine E. Mesick, Laura C. Stonehill, Jonathan T. Morrell, Daniel D. S. Coupland

Abstract: $Cs_2LiYCl_6:Ce^{3+}… ▽ More $Cs_2LiYCl_6:Ce^{3+}$ (CLYC) is an inorganic scintillator that has recently garnered attention for its ability to detect and discriminate between gammas and thermal neutrons. We investigate several important performance parameters of three different solid state photomultipliers (SSPMs) when reading out CLYC crystals: linearity, energy resolution, and pulse shape and discrimination ability. These performance parameters are assessed at a variety of temperatures between -20$^{\circ}$C and +50$^{\circ}$C. △ Less

Submitted 3 December, 2015; originally announced December 2015.

Comments: Submitted as conference record to IEEE Nucl. Sci. Symposium, San Diego, CA

Elastic breakup cross sections of well-bound nucleons

Authors: K. Wimmer, D. Bazin, A. Gade, J. A. Tostevin, T. Baugher, Z. Chajecki, D. Coupland, M. A. Famiano, T. K. Ghosh, G. F. Grinyer M. E. Howard, M. Kilburn, W. G. Lynch, B. Manning, K. Meierbachtol, P. Quarterman, A. Ratkiewicz, A. Sanetullaev, R. H. Showalter, S. R. Stroberg, M. B. Tsang, D. Weisshaar, J. Winkelbauer, R. Winkler, M. Youngs

Abstract: The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleon removal mec… ▽ More The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleon removal mechanisms. These deduced contributions are compared with the eikonal reaction model predictions and with the previously measured data for reactions involving the re- moval of more weakly-bound protons from lighter nuclei. The role of transitions of the proton between different bound single-particle configurations upon the elastic breakup cross section is also quantified in this well-bound case. The measured and calculated elastic breakup fractions are found to be in good agreement. △ Less

Submitted 6 December, 2014; originally announced December 2014.

Comments: Phys. Rev. C 2014 (accepted)

Effective Nucleon Masses from Heavy Ion Collisions

Authors: D. D. S. Coupland, M. Youngs, W. G. Lynch, M. B. Tsang, Z. Chajecki, Y. X. Zhang, M. A. Famiano, T. K. Ghosh, B. Giacherio, M. A. Kilburn, Jenny Lee, F. Lu, P. Russotto, A. Sanetullaev, R. H. Showalter, G. Verde, J. Winkelbauer

Abstract: We probe the momentum dependence of the isovector mean-field potential by comparing the energy spectra of neutrons and protons emitted in $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at incident energies of E/A=50 and 120 MeV. We achieve experimental precision that discriminates between different momentum dependencies for the symmetry mean-field potential. Comparisons of the experime… ▽ More We probe the momentum dependence of the isovector mean-field potential by comparing the energy spectra of neutrons and protons emitted in $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at incident energies of E/A=50 and 120 MeV. We achieve experimental precision that discriminates between different momentum dependencies for the symmetry mean-field potential. Comparisons of the experimental results to Improved Quantum Molecular Dynamics model calculations with Skyrme Interactions indicate small differences between the neutron and proton effective masses. △ Less

Submitted 17 June, 2014; originally announced June 2014.

Comments: 6 pages, 2 figures

Journal ref: Phys. Rev. C 94, 011601 (2016)

Scaling properties of light-cluster production

Authors: Z. Chajecki, M. Youngs, D. D. S. Coupland, W. G. Lynch, M. B. Tsang, D. Brown, A. Chbihi, P. Danielewicz, R. T. deSouza, M. A. Famiano, T. K. Ghosh, B. Giacherio, V. Henzl, D. Henzlova, C. Herlitzius, S. Hudan, M. A. Kilburn, Jenny Lee, F. Lu, S. Lukyanov, A. M. Rogers, P. Russotto, A. Sanetullaev, R. H. Showalter, L. G. Sobotka , et al. (5 additional authors not shown)

Abstract: We show that ratios of light-particle energy spectra display scaling properties that can be accu- rately described by effective local chemical potentials. This demonstrates the equivalence of t/3He and n/p spectral ratios and provides an essential test of theoretical predictions of isotopically resolved light-particle spectra. In addition, this approach allows direct comparisons of many theoretica… ▽ More We show that ratios of light-particle energy spectra display scaling properties that can be accu- rately described by effective local chemical potentials. This demonstrates the equivalence of t/3He and n/p spectral ratios and provides an essential test of theoretical predictions of isotopically resolved light-particle spectra. In addition, this approach allows direct comparisons of many theoretical n/p spectral ratios to experiments where charged-particle spectra but not neutron spectra are accurately measured. Such experiments may provide much more quantitative constraints on the density and momentum dependence of the symmetry energy. △ Less

Submitted 21 February, 2014; originally announced February 2014.

Neutron spectroscopic factors of $^{55}$Ni hole-states from (p,d) transfer reactions

Authors: A. Sanetullaev, M. B. Tsang, W. G. Lynch, Jenny Lee, D. Bazin, K. P. Chan, D. Coupland, V. Henzl, D. Henzlova, M. Kilburn, A. M. Rogers, Z. Y. Sun, M. Youngs, R. J. Charity, L. G. Sobotka, M. Famiano, S. Hudan, D. Shapira, W. A. Peters, C. Barbieri, M. Hjorth-Jensen, M. Horoi, T. Otsuka, T. Suzuki, Y. Utsuno

Abstract: Spectroscopic information has been extracted on the hole-states of $^{55}$Ni, the least known of the quartet of nuclei ($^{55}$Ni, $^{57}$Ni, $^{55}$Co and $^{57}$Co), one neutron away from $^{56}$Ni, the N=Z=28 double magic nucleus. Using the $^{1}$H($^{56}$Ni,d)$^{55}$Ni transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f… ▽ More Spectroscopic information has been extracted on the hole-states of $^{55}$Ni, the least known of the quartet of nuclei ($^{55}$Ni, $^{57}$Ni, $^{55}$Co and $^{57}$Co), one neutron away from $^{56}$Ni, the N=Z=28 double magic nucleus. Using the $^{1}$H($^{56}$Ni,d)$^{55}$Ni transfer reaction in inverse kinematics, neutron spectroscopic factors, spins and parities have been extracted for the f$_{7/2}$, p$_{3/2}$ and the s$_{1/2}$ hole-states of $^{55}$Ni. This new data provides a benchmark for large basis calculations that include nucleonic orbits in both the sd and pf shells. State of the art calculations have been performed to describe the excitation energies and spectroscopic factors of the s$_{1/2}$ hole-state below Fermi energy. △ Less

Submitted 30 January, 2014; originally announced January 2014.

Comments: Submitted to PLB

Tracking rare-isotope beams with microchannel plates

Authors: A. M. Rogers, A. Sanetullaev, W. G. Lynch, M. B. Tsang, J. Lee, D. Bazin, D. Coupland, V. Henzl, D. Henzlova, M. Kilburn, M. S. Wallace, M. Youngs, F. Delaunay, M. Famiano, D. Shapira, K. L. Jones, K. T. Schmitt, Z. Y. Sun

Abstract: A system of two microchannel-plate detectors has been successfully implemented for tracking projectile-fragmentation beams. The detectors provide interaction positions, angles, and arrival times of ions at the reaction target. The current design is an adaptation of an assembly used for low-energy beams ($\sim$1.4 MeV/nucleon). In order to improve resolution in tracking high-energy heavy-ion beams,… ▽ More A system of two microchannel-plate detectors has been successfully implemented for tracking projectile-fragmentation beams. The detectors provide interaction positions, angles, and arrival times of ions at the reaction target. The current design is an adaptation of an assembly used for low-energy beams ($\sim$1.4 MeV/nucleon). In order to improve resolution in tracking high-energy heavy-ion beams, the magnetic field strength between the secondary-electron accelerating foil and the microchannel plate had to be increased substantially. Results from an experiment using a 37-MeV/nucleon ${}^{56}$Ni beam show that the tracking system can achieve sub-nanosecond timing resolution and a position resolution of $\sim$1 mm for beam intensities up to $5\times10^{5}$ pps. △ Less

Submitted 11 September, 2013; originally announced September 2013.

Neutron-hole states in 45Ar from p(46Ar,d)45Ar reactions

Authors: F. Lu, Jenny Lee, M. B. Tsang, D. Bazin, D. Coupland, V. Henzl, D. Henzlova, M. Kilburn, W. G. Lynch, A. M. Rogers, A. Sanetullaev, Z. Y. Sun, M. Youngs, R. J. Charity, L. G. Sobotka, M. Famiano, S. Hudan, M. Horoi, Y. L. Ye

Abstract: To improve the effective interactions in the pf shell, it is important to measure the single particle- and hole- states near the N=28 shell gap. In this paper, the neutron spectroscopic factors of hole-states from the unstable neutron-rich 45Ar (Z=18, N=27) nucleus have been studied using 1H(46Ar, 2H)45Ar transfer reaction in inverse kinematics. Comparison of our results with the particle-states o… ▽ More To improve the effective interactions in the pf shell, it is important to measure the single particle- and hole- states near the N=28 shell gap. In this paper, the neutron spectroscopic factors of hole-states from the unstable neutron-rich 45Ar (Z=18, N=27) nucleus have been studied using 1H(46Ar, 2H)45Ar transfer reaction in inverse kinematics. Comparison of our results with the particle-states of 45Ar produced in 2H(44Ar, H)45Ar reaction shows that the two reactions populate states with different angular momentum. Using the angular distributions, we are able to confirm the spin assignments of four low-lying states of 45Ar. These are the ground state (f7/2), the first-excited (p3/2), the s1/2 and the d3/2 states. While large basis shell model predictions describe spectroscopic properties of the ground and p3/2 states very well, they fail to describe the s1/2 and d3/2 hole-states. △ Less

Submitted 16 August, 2013; originally announced August 2013.

Comments: Accepted for publication in PRC

Correlations in intermediate-energy two-proton removal reactions

Authors: K. Wimmer, D. Bazin, A. Gade, J. A. Tostevin, T. Baugher, Z. Chajecki, D. Coupland, M. A. Famiano, T. K. Ghosh, G. F. Grinyer, R. Hodges, M. E. Howard, M. Kilburn, W. G. Lynch, B. Manning, K. Meierbachtol, P. Quarterman, A. Ratkiewicz, A. Sanetullaev, E. C. Simpson, S. R. Stroberg, M. B. Tsang, D. Weisshaar, J. Winkelbauer, R. Winkler , et al. (1 additional authors not shown)

Abstract: We report final-state-exclusive measurements of the light charged fragments in coincidence with 26Ne residual nuclei following the direct two-proton removal from a neutron-rich 28Mg secondary beam. A Dalitz-plot analysis and comparisons with simulations show that a majority of the triple- coincidence events with two protons display phase-space correlations consistent with the (two-body) kinematics… ▽ More We report final-state-exclusive measurements of the light charged fragments in coincidence with 26Ne residual nuclei following the direct two-proton removal from a neutron-rich 28Mg secondary beam. A Dalitz-plot analysis and comparisons with simulations show that a majority of the triple- coincidence events with two protons display phase-space correlations consistent with the (two-body) kinematics of a spatially-correlated pair-removal mechanism. The fraction of such correlated events, 56(12) %, is consistent with the fraction of the calculated cross section, 64 %, arising from spin S = 0 two-proton configurations in the entrance-channel (shell-model) 28Mg ground state wave function. This result promises access to an additional and more specific probe of the spin and spatial correlations of valence nucleon pairs in exotic nuclei produced as fast secondary beams. △ Less

Submitted 13 October, 2012; originally announced October 2012.

Comments: accepted for publication in Physical Review Letters

Democratic decay of 6Be exposed by correlations

Authors: I. A. Egorova, R. J. Charity, L. V. Grigorenko, Z. Chajecki, D. Coupland, J. M. Elson, T. K. Ghosh, M. E. Howard, H. Iwasaki, M. Kilburn, Jenny Lee, W. G. Lynch, J. Manfredi, S. T. Marley, A. Sanetullaev, R. Shane, D. V. Shetty, L. G. Sobotka, M. B. Tsang, J. Winkelbauer, A. H. Wuosmaa, M. Youngs, M. V. Zhukov

Abstract: The interaction of an E/A=70 - MeV 7Be beam with a Be target was used to populate levels in 6Be following neutron knockout reactions. The three-body decay of the ground and first excited states into the alpha+p+p exit channel were detected in the High Resolution Array. Precise three-body correlations extracted from the experimental data allowed us to obtain insight into the mechanism of the three-… ▽ More The interaction of an E/A=70 - MeV 7Be beam with a Be target was used to populate levels in 6Be following neutron knockout reactions. The three-body decay of the ground and first excited states into the alpha+p+p exit channel were detected in the High Resolution Array. Precise three-body correlations extracted from the experimental data allowed us to obtain insight into the mechanism of the three-body democratic decay. The correlation data are in a good agreement with a three-cluster-model calculation and thus validate this theoretical approach over a broad energy range. △ Less

Submitted 1 November, 2012; v1 submitted 13 August, 2012; originally announced August 2012.

Comments: 5 pages, 7 figures; Corrected typos

Probing elastic and inelastic breakup contributions to intermediate-energy two-proton removal reactions

Authors: K. Wimmer, D. Bazin, A. Gade, J. A. Tostevin, T. Baugher, Z. Chajecki, D. Coupland, M. A. Famiano, T. K. Ghosh, G. F. Grinyer, R. Hodges, M. E. Howard, M. Kilburn, W. G. Lynch, B. Manning, K. Meierbachtol, P. Quarterman, A. Ratkiewicz, A. Sanetullaev, S. R. Stroberg, M. B. Tsang, D. Weisshaar, J. Winkelbauer, R. Winkler M. Youngs

Abstract: The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements… ▽ More The two-proton removal reaction from 28Mg projectiles has been studied at 93 MeV/u at the NSCL. First coincidence measurements of the heavy 26Ne projectile residues, the removed protons and other light charged particles enabled the relative cross sections from each of the three possible elastic and inelastic proton removal mechanisms to be determined. These more final-state-exclusive measurements are key for further interrogation of these reaction mechanisms and use of the reaction channel for quantitative spectroscopy of very neutron-rich nuclei. The relative and absolute yields of the three contributing mechanisms are compared to reaction model expectations - based on the use of eikonal dynamics and sd-shell-model structure amplitudes. △ Less

Submitted 9 May, 2012; originally announced May 2012.

Comments: Accepted for publication in Physical Review C (Rapid Communication)

Angular Dependence in Proton-Proton Correlation Functions in Central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ Reactions

Authors: V. Henzl, M. A. Kilburn, Z. Chajecki, D. Henzlova, W. G. Lynch, D. Brown, A. Chbihi, D. Coupland, P. Danielewicz, R. deSouza, M. Famiano, C. Herlitzius, S. Hudan, Jenny Lee, S. Lukyanov, A. M. Rogers, A. Sanetullaev, L. Sobotka, Z. Y. Sun, M. B. Tsang, A. Vander Molen, G. Verde, M. Wallace, M. Youngs

Abstract: The angular dependence of proton-proton correlation functions is studied in central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ nuclear reactions at E=80 MeV/A. Measurements were performed with the HiRA detector complemented by the 4$π$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation functions for both systems that greatly exceeds the measured and e… ▽ More The angular dependence of proton-proton correlation functions is studied in central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ nuclear reactions at E=80 MeV/A. Measurements were performed with the HiRA detector complemented by the 4$π$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation functions for both systems that greatly exceeds the measured and expected isospin dependent difference between the neutron-rich and neutron-deficient systems. Sources measured at backward angles reflect the participant zone of the reaction, while much larger sources observed at forward angles reflect the expanding, fragmenting and evaporating projectile remnants. The decrease of the size of the source with increasing momentum is observed at backward angles while a weaker trend in the opposite direction is observed at forward angles. The results are compared to the theoretical calculations using the BUU transport model. △ Less

Submitted 11 August, 2011; originally announced August 2011.

Comments: 8 pages, 3 figures, submitted to PRC

Journal ref: Phys.Rev. C85 (2012) 014606

Influence of Transport Variables on Isospin Transport Ratios

Authors: D. D. S. Coupland, W. G. Lynch, M. B. Tsang, P. Danielewicz, Yingxun Zhang

Abstract: The symmetry energy in the nuclear equation of state affects many aspects of nuclear astrophysics, nuclear structure, and nuclear reactions. Recent constraints from heavy ion collisions, including isospin diffusion observables, have started to put constraints on the symmetry energy below nuclear saturation density, but these constraints depend on the employed transport model and input physics othe… ▽ More The symmetry energy in the nuclear equation of state affects many aspects of nuclear astrophysics, nuclear structure, and nuclear reactions. Recent constraints from heavy ion collisions, including isospin diffusion observables, have started to put constraints on the symmetry energy below nuclear saturation density, but these constraints depend on the employed transport model and input physics other than the symmetry energy. To understand these dependencies, we study the influence of the symmetry energy, isoscaler mean field compressibility and momentum dependence, in-medium nucleon-nucleon cross sections, and light cluster production on isospin diffusion within the pBUU transport code. In addition to the symmetry energy, several uncertain issues strongly affect isospin diffusion, most notably the cross sections and cluster production. In addition, there is a difference in the calculated isospin transport ratios, depending upon whether they are computed using the isospin asymmetry of either the residue or of all forward moving fragments. Measurements that compare the isospin transport ratios of these two quantities would help place constraints on the input physics, such as the density dependence of the symmetry energy. △ Less

Submitted 19 July, 2011; originally announced July 2011.

Comments: 31 pages, 15 figures, submitted to PRC

Investigations of three, four, and five-particle exit channels of levels in light nuclei created using a 9C beam

Authors: R. J. Charity, J. M. Elson, J. Manfredi, R. Shane, L. G. Sobotka, B. A. Brown, Z. Chajecki, D. Coupland, H. Iwasaki, M. Kilburn, Jenny Lee, W. G. Lynch, A. Sanetullaev, M. B. Tsang, J. Winkelbauer, M. Youngs, S. T. Marley, D. V. Shetty, A. H. Wuosmaa, T. K. Ghosh, M. E. Howard

Abstract: The interactions of a E/A=70-MeV 9C beam with a Be target was used to populate levels in Be, B, and C isotopes which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent… ▽ More The interactions of a E/A=70-MeV 9C beam with a Be target was used to populate levels in Be, B, and C isotopes which undergo decay into many-particle exit channels. The decay products were detected in the HiRA array and the level energies were identified from their invariant mass. Correlations between the decay products were examined to deduce the nature of the decays, specifically to what extent all the fragments were created in one prompt step or whether the disintegration proceeded in a sequential fashion through long-lived intermediate states. In the latter case, information on the spin of the level was also obtained. Of particular interest is the 5-body decay of the 8C ground state which was found to disintegrate in two steps of two-proton decay passing through the 6Beg.s. intermediate state. The isobaric analog of 8Cg.s. in 8B was also found to undergo two-proton decay to the isobaric analog of 6Beg.s. in 6Li. A 9.69-MeV state in 10C was found to undergo prompt 4-body decay to the 2p+2alpha exit channel. The two protons were found to have a strong enhancementin the diproton region and the relative energies of all four p-alpha pairs were consistent with the 5Lig.s. resonance. △ Less

Submitted 5 May, 2011; originally announced May 2011.

Journal ref: Phys.Rev.C84:014320,2011

Constraints on the density dependence of the symmetry energy from heavy ion collisions

Authors: M. B. Tsang, Z. Chajecki, D. Coupland, P. Danielewicz, F. Famiano, R. Hodges, M. Kilburn, F. Lu, W. G. Lynch, J. Winkelbauer, M. Youngs, YingXun Zhang

Abstract: Constraints on the Equation of State for symmetric matter (equal neutron and proton numbers) have been extracted from energetic collisions of heavy ions over a range of energies. Collisions of neutron-deficient and neutron-rich heavy ions now provide initial constraints on the EoS of neutron-rich matter at sub-saturation densities from isospin diffusions and neutron proton ratios. This article rev… ▽ More Constraints on the Equation of State for symmetric matter (equal neutron and proton numbers) have been extracted from energetic collisions of heavy ions over a range of energies. Collisions of neutron-deficient and neutron-rich heavy ions now provide initial constraints on the EoS of neutron-rich matter at sub-saturation densities from isospin diffusions and neutron proton ratios. This article reviews the experimental constraints on the density dependence of Symmetry Energy at sub-saturation density. △ Less

Submitted 19 January, 2011; originally announced January 2011.

Comments: 7 pages, 3 figures, to be published in: Progress in Particle and Nuclear Physics

Journal ref: Prog.Part.Nucl.Phys.66:400-404,2011

The Influence of in-medium NN cross-sections, symmetry potential and impact parameter on the isospin observables

Authors: Yingxun Zhang, D. D. S. Coupland, P. Danielewicz, Zhuxia Li, Hang Liu, Fei Lu, W. G. Lynch, M. B. Tsang

Abstract: We explore the influence of in-medium nucleon-nucleon cross section, symmetry potential and impact parameter on isospin sensitive observables in intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified version of Quantum Molecular Dynamics model. At incident velocities above the Fermi velocity, we find that the density dependence of symmetry potential plays a more important role… ▽ More We explore the influence of in-medium nucleon-nucleon cross section, symmetry potential and impact parameter on isospin sensitive observables in intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified version of Quantum Molecular Dynamics model. At incident velocities above the Fermi velocity, we find that the density dependence of symmetry potential plays a more important role on the double neutron to proton ratio $DR(n/p)$ and the isospin transport ratio $R_i$ than the in-medium nucleon-nucleon cross sections, provided that the latter are constrained to a fixed total NN collision rate. We also explore both $DR(n/p)$ and $R_i$ as a function of the impact parameter. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediate-energy heavy-ion collisions, we examine the isospin transport ratios constructed from different groups of fragments. We find that the values of the isospin transport ratios for projectile rapidity fragments with $Z\ge20$ are greater than those constructed from the entire projectile rapidity source. We believe experimental investigations of this phenomenon can be performed. These may provide significant tests of fragmentation time scales predicted by ImQMD calculations. △ Less

Submitted 20 January, 2012; v1 submitted 10 September, 2010; originally announced September 2010.

Comments: 24 pages, 9 figures, to be published in Phys. Rev. C

Neutron-proton asymmetry dependence of spectroscopic factors in Ar isotopes

Authors: Jenny Lee, M. B. Tsang, D. Bazin, D. Coupland, V. Henzl, D. Henzlova, M. Kilburn, W. G. Lynch, A. Rogers, A. Sanetullaev, A. Signoracci, Z. Y. Sun, M. Youngs, K. Y. Chae, R. J. Charity, H. K. Cheung, M. Famiano, S. Hudan, P. OMalley, W. A. Peters, K. Schmitt, D. Shapira, L. G. Sobotka

Abstract: Spectroscopic factors have been extracted for proton rich 34Ar and neutron rich 46Ar using the (p,d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on… ▽ More Spectroscopic factors have been extracted for proton rich 34Ar and neutron rich 46Ar using the (p,d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements. △ Less

Submitted 24 February, 2010; v1 submitted 25 November, 2009; originally announced November 2009.

Comments: 11 pages, 2 figures. submitted to PRL