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$l$-forbidden $\mathbf{M1}$ strengths near $^{100}$Sn from knockout reactions in Cd and Sn
Authors:
T. J. Gray,
K. L. Jones,
R. Grzywacz,
B. A. Brown,
A. Gade,
B. C. He,
T. Miyagi,
A. Peter,
M. J. Basson,
T. Beck,
C. M. Campbell,
G. Cerizza,
J. Chung-Jung,
I. Cox,
P. Farris,
R. Ghimire,
S. Gillespie,
M. Grinder,
A. Hill,
S. D. Pain,
A. Palmisano-Kyle,
K. P. Rykaczewski,
D. Weisshaar,
M. Williams
Abstract:
Neutron knockout reactions on beams of $^{104,102}$Cd, and $^{104}$Sn are presented. States in the residual $^{103,101}$Cd and $^{103}$Sn nuclei are populated, including low-lying $7/2^+$ states of $νg_{7/2}$ character. These states have half-lives $\approx 400$ ps due to their low energy and hindered $B(M1; 7/2^+ \rightarrow 5/2^+)$ strengths. The excited-state half-lives were measured using thei…
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Neutron knockout reactions on beams of $^{104,102}$Cd, and $^{104}$Sn are presented. States in the residual $^{103,101}$Cd and $^{103}$Sn nuclei are populated, including low-lying $7/2^+$ states of $νg_{7/2}$ character. These states have half-lives $\approx 400$ ps due to their low energy and hindered $B(M1; 7/2^+ \rightarrow 5/2^+)$ strengths. The excited-state half-lives were measured using their Doppler-shifted lineshapes, and the resulting $B(M1)$ strengths are compared to Valence Space In Medium Similarity Renormalization Group (VS-IMSRG) calculations. The VS-IMSRG calculations under-predict the $l$-forbidden $M1$ strengths in the $^{100}$Sn region, as well as in other regions of the nuclear chart near $^{40}$Ca and $^{208}$Pb.
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Submitted 2 July, 2026;
originally announced July 2026.
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Resolving anomalous collectivity in the $4_1^+$ to $2_1^+$ transition of $^{58}$Fe
Authors:
J. A. Woodside,
B. J. Coombes,
A. E. Stuchbery,
A. J. Mitchell,
M. Reece,
G. J. Lane,
T. J. Gray,
G. Pasqualato,
L. J. McKie,
N. J. Spinks
Abstract:
The low-excitation states of atomic nuclei in the region around the $N = Z = 28$ shell closure are generally well described by the shell model. Most experimental observables in the iron isotopes $^{56}$Fe, $^{58}$Fe, and $^{60}$Fe ($Z = 26$; $N=30$, $32$, $34$) support a shell-model description. However, the lifetimes of the $4_1^+$ state in $^{58}$Fe in the literature result in a reduced transiti…
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The low-excitation states of atomic nuclei in the region around the $N = Z = 28$ shell closure are generally well described by the shell model. Most experimental observables in the iron isotopes $^{56}$Fe, $^{58}$Fe, and $^{60}$Fe ($Z = 26$; $N=30$, $32$, $34$) support a shell-model description. However, the lifetimes of the $4_1^+$ state in $^{58}$Fe in the literature result in a reduced transition strength that deviates markedly from shell-model predictions. There are three independent measurements, all in agreement and all based on the Doppler Shift Attenuation Method (DSAM) or Doppler-Broadened Line Shape method (DBLS). In this work, Coulomb-excitation measurements were performed on $^{56}$Fe and $^{58}$Fe beams to determine the ratios $B(E2; 4_1^+ \to 2_1^+)/B(E2; 2_1^+ \to 0_1^+)$. Thus, $B(E2; 4_1^+ \to 2_1^+)$ is determined relative to the known $B(E2; 2_1^+ \to 0_1^+)$ values. For $^{56}$Fe, $B(E2; 4_1^+ \to 2_1^+) = 23(4)$ W.u., agreeing with the adopted value. However, for $^{58}$Fe, the $B(E2; 4_1^+ \to 2_1^+)$ values obtained (for the various combinations of matrix element signs that could not be firmly established) are all significantly lower than the value derived from the previous lifetime measurements, and are in accord with shell-model calculations. The 1978 DSAM measurement of Bolotin et al., Nucl. Phys. A 311, 75 (1978), has been re-examined. The discrepancy between that measurement and the Coulomb-excitation measurement can be ascribed to the Lindhard-Scharff-Schiøtt (LSS) electronic stopping powers adopted for the DSAM analysis, which considerably overestimate contemporary values. Evidently, lifetime measurements from that era that are based on LSS stopping powers should be used with caution. The revised lifetime data, incorporating current stopping powers, are compared with shell-model calculations.
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Submitted 18 March, 2026;
originally announced March 2026.
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Commissioning the Resonance Ionization Spectroscopy Experiment at FRIB
Authors:
A. J. Brinson,
B. J. Rickey,
J. M. Allmond,
A. Dockery,
A. Fernandez Chiu,
R. F. Garcia Ruiz,
T. J. Gray,
J. Karthein,
T. T. King,
K. Minamisono,
A. Ortiz-Cortes,
S. V. Pineda,
M. Reponen,
B. C. Rasco,
S. M. Udrescu,
A. R. Vernon,
S. G. Wilkins
Abstract:
This manuscript reports on the commissioning of the Resonance Ionization Spectroscopy Experiment (RISE) at the BECOLA facility at FRIB. The new instrument implements the collinear resonance ionization spectroscopy technique for sensitive measurements of isotope shifts and hyperfine structure of short-lived isotopes produced at FRIB. The existing BECOLA beamline was extended to integrate an electro…
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This manuscript reports on the commissioning of the Resonance Ionization Spectroscopy Experiment (RISE) at the BECOLA facility at FRIB. The new instrument implements the collinear resonance ionization spectroscopy technique for sensitive measurements of isotope shifts and hyperfine structure of short-lived isotopes produced at FRIB. The existing BECOLA beamline was extended to integrate an electrostatic ion-beam bender and an ion detector at ultra-high vacuum. An injection-seeded Ti:Sapphire laser and a multi-harmonic pulsed Nd:YAG laser were installed to perform resonant excitation and selective ionization. Commissioning tests were performed to demonstrate the capabilities of the new instrument by measuring the hyperfine structure of stable $^{27}$Al produced in an offline ion source. The RISE instrument is ready and operational for future studies of short-lived isotopes at FRIB.
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Submitted 17 February, 2026; v1 submitted 11 November, 2025;
originally announced November 2025.
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Triaxiality and shape dynamics in $^{70}$Ge
Authors:
T. M. Kowalewski,
A. D. Ayangeakaa,
N. Sensharma,
R. V. F. Janssens,
Y. M. Wang,
Q. B. Chen,
J. M. Allmond,
C. M. Campbell,
S. Carmichael,
M. P. Carpenter,
P. Copp,
C. Cousins,
M. Devlin,
U. Garg,
C. Müller-Gatermann,
T. J. Gray,
D. J. Hartley,
J. Heery,
J. Henderson,
H. Jayatissa,
S. R. Johnson,
S. P. Kisyov,
F. G. Kondev,
T. Lauritsen,
S. Nandi
, et al. (9 additional authors not shown)
Abstract:
The electromagnetic properties of low-lying states in $^{70}$Ge were investigated via multi-step Coulomb excitation of a $^{70}$Ge beam impinging on a $^{208}$Pb target at the ATLAS facility of the Argonne National Laboratory. A total of 27 transitional elements and six diagonal matrix elements coupling 11 low-lying states, were extracted from the measured cross sections. These were used to calcul…
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The electromagnetic properties of low-lying states in $^{70}$Ge were investigated via multi-step Coulomb excitation of a $^{70}$Ge beam impinging on a $^{208}$Pb target at the ATLAS facility of the Argonne National Laboratory. A total of 27 transitional elements and six diagonal matrix elements coupling 11 low-lying states, were extracted from the measured cross sections. These were used to calculate reduced transition probabilities, spectroscopic quadrupole moments, and rotational invariant shape parameters, providing enhanced precision and expanding on previous studies. The experimental data were compared within several theoretical frameworks, including the generalized triaxial rotor model, configuration interaction shell-model calculations, and computations within the combined frameworks of relativistic density functional theory and the five-dimensional collective Hamiltonian. The results demonstrate a good agreement with the experimental data and, in conjunction with calculations using a two-state mixing model, support significant triaxiality and strong mixing between the $0^+_1$ and $0^+_2$ states. This results in the magnitudes of their respective quadrupole deformations $[β_\text{rms}(0^+_1) = 0.228\,(3),\,β_\text{rms}(0^+_2) = 0.273\,(1)]$ being more similar than previously observed. The implications of these results for understanding the complex shape coexistence phenomena, the role of triaxiality, and shape evolution along the Ge isotopic chain are discussed.
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Submitted 13 October, 2025;
originally announced October 2025.
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Universal Effective Charges in the $sd$ and $fp$ Shells
Authors:
T. H. Ogunbeku,
J. M. Allmond,
T. J. Gray,
W. -J. Ong,
B. A. Brown,
A. Gargano,
R. Grzywacz,
J. D. Holt,
A. O. Macchiavelli,
T. Miyagi,
S. Neupane,
B. C. Rasco,
H. Schatz,
B. M. Sherrill,
O. B. Tarasov,
H. Arora,
A. D. Ayangeakaa,
H. C. Berg,
J. M. Berkman,
D. L. Bleuel,
K. Bosmpotinis,
M. P. Carpenter,
G. Cerizza,
A. Chester,
J. M. Christie
, et al. (57 additional authors not shown)
Abstract:
The 247-keV state in $^{54}$Sc, populated in the $β$ decay of $^{54}$Ca, is reported here as a nanosecond isomer with a half-life of 26.0(22) ns. The state is interpreted as the $1^+$ member of the $πf_{7/2}\otimesνf_{5/2}$ spin-coupled multiplet, which decays to the $3^+,πf_{7/2} \otimes νp_{1/2}$ ground state. The new half-life corresponds to a pure $E2$ transition with a strength of 1.93(16) W.…
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The 247-keV state in $^{54}$Sc, populated in the $β$ decay of $^{54}$Ca, is reported here as a nanosecond isomer with a half-life of 26.0(22) ns. The state is interpreted as the $1^+$ member of the $πf_{7/2}\otimesνf_{5/2}$ spin-coupled multiplet, which decays to the $3^+,πf_{7/2} \otimes νp_{1/2}$ ground state. The new half-life corresponds to a pure $E2$ transition with a strength of 1.93(16) W.u., providing the most precise, unambiguous $B(E2)$ value in the neutron-rich $fp$ region to date for a nucleus with valence protons above $Z=20$. Notably, it is roughly four times larger than the $B(E2; 1/2^{-} \rightarrow 5/2^{-})$ value in $^{55}$Ca. The results, as compared to semi-empirical and ab initio shell-model calculations, indicate (1) a weak $N=34$ sub-shell gap relative to $N = 32$, (2) a large $E2$ enhancement in Sc as compared to Ca due to $1p-1h$ proton excitations across $Z=28$, and (3) empirical effective proton and neutron charges, $e_π$ = 1.30(8)$e$ and $e_ν$ = 0.452(7)$e$, respectively, that are in contrast to reports of $e_π\approx 1.1-1.15e$ and $e_ν\approx 0.6-0.8e$ for $fp$-shell nuclei near $N = Z$. We demonstrate that these reports are erroneous and that, in fact, a universal set of effective charges can be used across the $sd$ and $fp$ shells.
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Submitted 26 June, 2025;
originally announced June 2025.
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Object Detection with Deep Learning for Rare Event Search in the GADGET II TPC
Authors:
Tyler Wheeler,
S. Ravishankar,
C. Wrede,
A. Andalib,
A. Anthony,
Y. Ayyad,
B. Jain,
A. Jaros,
R. Mahajan,
L. Schaedig,
A. Adams,
S. Ahn,
J. M. Allmond,
D. Bardayan,
D. Bazin,
K. Bosmpotinis,
T. Budner,
S. R. Carmichael,
S. M. Cha,
A. Chen,
K. A. Chipps,
J. M. Christie,
I. Cox,
J. Dopfer,
M. Friedman
, et al. (28 additional authors not shown)
Abstract:
In the pursuit of identifying rare two-particle events within the GADGET II Time Projection Chamber (TPC), this paper presents a comprehensive approach for leveraging Convolutional Neural Networks (CNNs) and various data processing methods. To address the inherent complexities of 3D TPC track reconstructions, the data is expressed in 2D projections and 1D quantities. This approach capitalizes on t…
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In the pursuit of identifying rare two-particle events within the GADGET II Time Projection Chamber (TPC), this paper presents a comprehensive approach for leveraging Convolutional Neural Networks (CNNs) and various data processing methods. To address the inherent complexities of 3D TPC track reconstructions, the data is expressed in 2D projections and 1D quantities. This approach capitalizes on the diverse data modalities of the TPC, allowing for the efficient representation of the distinct features of the 3D events, with no loss in topology uniqueness. Additionally, it leverages the computational efficiency of 2D CNNs and benefits from the extensive availability of pre-trained models. Given the scarcity of real training data for the rare events of interest, simulated events are used to train the models to detect real events. To account for potential distribution shifts when predominantly depending on simulations, significant perturbations are embedded within the simulations. This produces a broad parameter space that works to account for potential physics parameter and detector response variations and uncertainties. These parameter-varied simulations are used to train sensitive 2D CNN object detectors. When combined with 1D histogram peak detection algorithms, this multi-modal detection framework is highly adept at identifying rare, two-particle events in data taken during experiment 21072 at the Facility for Rare Isotope Beams (FRIB), demonstrating a 100% recall for events of interest. We present the methods and outcomes of our investigation and discuss the potential future applications of these techniques.
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Submitted 28 January, 2025;
originally announced January 2025.
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Suppressed Electric Quadrupole Collectivity in $^{49}$Ti
Authors:
T. J. Gray,
J. M. Allmond,
C. Benetti,
C. Wibisono,
L. Baby,
A. Gargano,
T. Miyagi,
A. O. Macchiavelli,
A. E. Stuchbery,
J. L. Wood,
S. Ajayi,
J. Aragon,
B. W. Asher,
P. Barber,
S. Bhattacharya,
R. Boisseau,
J. M. Christie,
A. L. Conley,
P. De Rosa,
D. T. Dowling,
C. Esparza,
J. Gibbons,
K. Hanselman,
J. D. Holt,
S. Lopez-Caceres
, et al. (12 additional authors not shown)
Abstract:
Single-step Coulomb excitation of $^{46,48,49,50}$Ti is presented. A complete set of $E2$ matrix elements for the quintuplet of states in $^{49}$Ti, centered on the $2^+$ core excitation, was measured for the first time. A total of nine $E2$ matrix elements are reported, four of which were previously unknown. $^{49}_{22}$Ti$_{27}$ shows a $20\%$ quenching in electric quadrupole transition strength…
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Single-step Coulomb excitation of $^{46,48,49,50}$Ti is presented. A complete set of $E2$ matrix elements for the quintuplet of states in $^{49}$Ti, centered on the $2^+$ core excitation, was measured for the first time. A total of nine $E2$ matrix elements are reported, four of which were previously unknown. $^{49}_{22}$Ti$_{27}$ shows a $20\%$ quenching in electric quadrupole transition strength as compared to its semi-magic $^{50}_{22}$Ti$_{28}$ neighbour. This $20\%$ quenching, while empirically unprecedented, can be explained with a remarkably simple two-state mixing model, which is also consistent with other ground-state properties such as the magnetic dipole moment and electric quadrupole moment. A connection to nucleon transfer data and the quenching of single-particle strength is also demonstrated. The simplicity of the $^{49}$Ti-$^{50}$Ti pair (i.e., approximate single-$j$ $0f_{7/2}$ valence space and isolation of yrast states from non-yrast states) provides a unique opportunity to disentangle otherwise competing effects in the ground-state properties of atomic nuclei, the emergence of collectivity, and the role of proton-neutron interactions.
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Submitted 3 July, 2024;
originally announced July 2024.
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Shape polarization in the tin isotopes near $N=60$ from precision $g$-factor measurements on short-lived $11/2^-$ isomers
Authors:
T. J. Gray,
A. E. Stuchbery,
J. Dobaczewski,
A. Blazhev,
H. A. Alshammari,
L. J. Bignell,
J. Bonnard,
B. J. Coombes,
J. T. H. Dowie,
M. S. M. Gerathy,
T. Kibédi,
G. J. Lane,
B. P. McCormick,
A. J. Mitchell,
C. Nicholls,
J. G. Pope,
P. -G. Reinhard,
N. J. Spinks,
Y. Zhong
Abstract:
The $g$ factors of $11/2^-$ isomers in semimagic $^{109}$Sn and $^{111}$Sn (isomeric lifetimes $τ= 2.9(3)$ ns and $τ= 14.4(7)$ ns, respectively) were measured by an extension of the Time Differential Perturbed Angular Distribution technique, which uses \LaBr detectors and the hyperfine fields of a gadolinium host to achieve precise measurements in a new regime of short-lived isomers. The results,…
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The $g$ factors of $11/2^-$ isomers in semimagic $^{109}$Sn and $^{111}$Sn (isomeric lifetimes $τ= 2.9(3)$ ns and $τ= 14.4(7)$ ns, respectively) were measured by an extension of the Time Differential Perturbed Angular Distribution technique, which uses \LaBr detectors and the hyperfine fields of a gadolinium host to achieve precise measurements in a new regime of short-lived isomers. The results, $g(11/2^-; {^{109}\textrm{Sn}}) = -0.186(8)$ and $g(11/2^-; {^{111}\textrm{Sn}}) = -0.214(4)$, are significantly lower in magnitude than those of the $11/2^-$ isomers in the heavier isotopes and depart from the value expected for a near pure neutron $h_{11/2}$ configuration. Broken-symmetry density functional theory calculations applied to the sequence of $11/2^-$ states reproduce the magnitude and location of this deviation. The $g(11/2^-)$ values are affected by shape core polarization; the odd $0h_{11/2}$ neutron couples to $J^π=2^+,4^+,6^+...$ configurations in the weakly-deformed effective core, causing a decrease in the $g$-factor magnitudes.
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Submitted 18 October, 2023;
originally announced October 2023.
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Microsecond Isomer at the N=20 Island of Shape Inversion Observed at FRIB
Authors:
T. J. Gray,
J. M. Allmond,
Z. Xu,
T. T. King,
R. S. Lubna,
H. L. Crawford,
V. Tripathi,
B. P. Crider,
R. Grzywacz,
S. N. Liddick,
A. O. Macchiavelli,
T. Miyagi,
A. Poves,
A. Andalib,
E. Argo,
C. Benetti,
S. Bhattacharya,
C. M. Campbell,
M. P. Carpenter,
J. Chan,
A. Chester,
J. Christie,
B. R. Clark,
I. Cox,
A. A. Doetsch
, et al. (41 additional authors not shown)
Abstract:
Excited-state spectroscopy from the first Facility for Rare Isotope Beams (FRIB) experiment is reported. A 24(2)-$μ$s isomer was observed with the FRIB Decay Station initiator (FDSi) through a cascade of 224- and 401-keV $γ$ rays in coincidence with $^{32}\textrm{Na}$ nuclei. This is the only known microsecond isomer ($1{\text{ }μ\text{s}}\leq T_{1/2} < 1\text{ ms}$) in the region. This nucleus is…
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Excited-state spectroscopy from the first Facility for Rare Isotope Beams (FRIB) experiment is reported. A 24(2)-$μ$s isomer was observed with the FRIB Decay Station initiator (FDSi) through a cascade of 224- and 401-keV $γ$ rays in coincidence with $^{32}\textrm{Na}$ nuclei. This is the only known microsecond isomer ($1{\text{ }μ\text{s}}\leq T_{1/2} < 1\text{ ms}$) in the region. This nucleus is at the heart of the $N=20$ island of shape inversion and is at the crossroads of spherical shell-model, deformed shell-model, and ab initio theories. It can be represented as the coupling of a proton hole and neutron particle to $^{32}\textrm{Mg}$, $^{32}\textrm{Mg}+π^{-1} + ν^{+1}$. This odd-odd coupling and isomer formation provides a sensitive measure of the underlying shape degrees of freedom of $^{32}\textrm{Mg}$, where the onset of spherical-to-deformed shape inversion begins with a low-lying deformed $2^+$ state at 885 keV and a low-lying shape-coexisting $0_2^+$ state at 1058 keV. We suggest two possible explanations for the 625-keV isomer in $^{32}$Na: a $6^-$ spherical shape isomer that decays by $E2$ or a $0^+$ deformed spin isomer that decays by $M2$. The present results and calculations are most consistent with the latter, indicating that the low-lying states are dominated by deformation.
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Submitted 26 April, 2023; v1 submitted 22 February, 2023;
originally announced February 2023.
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E2 Rotational Invariants of $0^+_1$ and $2^+_1$ states for $^{106}$Cd: the Emergence of Collective Rotation
Authors:
T. J. Gray,
J. M. Allmond,
R. V. F. Janssens,
W. Korten,
A. E. Stuchbery,
J. L. Wood,
A. D. Ayangeakaa,
S. Bottoni,
B. M. Bucher,
C. M. Campbell,
M. P. Carpenter,
H. L. Crawford,
H. David,
D. Doherty,
P. Fallon,
M. T. Febbraro,
A. Galindo-Uribarri,
C. J. Gross,
M. Komorowska,
F. G. Kondev,
T. Lauritsen,
A. O. Macchiavelli,
P. Napiorkowsi,
E. Padilla-Rodal,
S. D. Pain
, et al. (7 additional authors not shown)
Abstract:
The collective structure of $^{106}$Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/$A$ beam of $^{106}$Cd on a 1.1 mg/cm$^2$ $^{208}$Pb target using GRETINA-CHICO2 at ATLAS. Fourteen $E2$ matrix elements were obtained. The nucleus $^{106}$Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has…
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The collective structure of $^{106}$Cd is elucidated by multi-step Coulomb excitation of a 3.849 MeV/$A$ beam of $^{106}$Cd on a 1.1 mg/cm$^2$ $^{208}$Pb target using GRETINA-CHICO2 at ATLAS. Fourteen $E2$ matrix elements were obtained. The nucleus $^{106}$Cd is a prime example of emergent collectivity that possesses a simple structure: it is free of complexity caused by shape coexistence and has a small, but collectively active number of valence nucleons. This work follows in a long and currently active quest to answer the fundamental question of the origin of nuclear collectivity and deformation, notably in the cadmium isotopes. The results are discussed in terms of phenomenological models, the shell model, and Kumar-Cline sums of $E2$ matrix elements. The ${\langle 0_2^+ ||E2||2_1^+ \rangle}$ matrix element is determined for the first time, providing a total, converged measure of the electric quadrupole strength, $\langle Q^2 \rangle$, of the first-excited $2_1^+$ level relative to the $0_1^+$ ground state, which does not show an increase as expected of harmonic and anharmonic vibrations. Strong evidence for triaxial shapes in weakly collective nuclei is indicated; collective vibrations are excluded. This is contrary to the only other cadmium result of this kind in $^{114}$Cd by C. Fahlander et al., Nucl. Phys. A485, 327 (1988), which is complicated by low-lying shape coexistence near midshell.
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Submitted 13 September, 2022;
originally announced September 2022.
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CLARION2-TRINITY: a Compton-suppressed HPGe and GAGG:Ce-Si-Si array for absolute cross-section measurements with heavy ions
Authors:
T. J. Gray,
J. M. Allmond,
D. T. Dowling,
M. Febbraro,
T. T. King,
S. D. Pain,
D. W. Stracener,
S. Ajayi,
J. Aragon,
L. Baby,
P. Barber,
C. Benetti,
S. Bhattacharya,
R. Boisseau,
J. Gibbons,
S. L. Tabor,
V. Tripathi,
C. Wibisono,
I. Wiedenhoever,
L. Bignell,
M. S. M. Gerathy,
G. Lane,
L. J. McKie,
A. J. Mitchell,
J. Pope
, et al. (4 additional authors not shown)
Abstract:
The design and performance of a new Compton-suppressed HPGe and charged-particle array, CLARION2-TRINITY, are described. The TRINITY charged-particle array is comprised of 64 Cerium-doped Gadolinium Aluminium Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7-54 degrees, and two annular silicon detectors that can shadow or extend the angular coverage to backward angles with mi…
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The design and performance of a new Compton-suppressed HPGe and charged-particle array, CLARION2-TRINITY, are described. The TRINITY charged-particle array is comprised of 64 Cerium-doped Gadolinium Aluminium Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7-54 degrees, and two annular silicon detectors that can shadow or extend the angular coverage to backward angles with minimal $γ$-ray attenuation. GAGG:Ce is a non-hygroscopic, bright, and relatively fast scintillator with a light distribution well matched to SiPMs. Count rates up to 40 kHz per crystal are sustainable. Fundamental characteristics of GAGG:Ce are measured and presented, including light- and heavy-ion particle identification (PID) capability, pulse-height defects, radiation hardness, and emission spectra. The CLARION2 array consists of up to 16 Compton-suppressed HPGe Clover detectors ($\approx4\%$ efficiency at 1 MeV) configured into four rings (eight HPGe crystal rings) using a non-Archimedean geometry that suppresses back-to-back coincident 511-keV gamma rays. The entire array is instrumented with 100- and 500-MHz (14 bit) waveform digitizers which enable triggerless operation, pulse-shape discrimination, fast timing, and pileup correction. Finally, two examples of experimental data taken during the commissioning of the CLARION2-TRINITY system are given: a PID spectrum from $^{16}$O + $^{18}$O fusion-evaporation, and PID and Doppler-corrected $γ$-ray spectra from $^{48}$Ti + $^{12}$C Coulomb excitation.
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Submitted 10 August, 2022;
originally announced August 2022.
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Hyperfine fields at $^{66}$Ga, $^{67,69}$Ge implanted into iron and gadolinium hosts at 6 K, and applications to g-factor measurements
Authors:
T. J. Gray,
A. E. Stuchbery,
B. J. Coombes,
J. T. H. Dowie,
M. S. M. Gerathy,
T. Kibedi,
G. J. Lane,
B. P. McCormick,
A. J. Mitchell,
M. W. Reed
Abstract:
Isomers in $^{66}$Ga, $^{67}$Ge, and $^{69}$Ge were recoil-implanted into ferromagnetic hosts of iron and gadolinium at $\approx 6$~K, and the hyperfine magnetic fields were determined by Time Differential Perturbed Angular Distribution (TDPAD) measurements. The hyperfine field strengths at $\approx 6$~K are compared to the results of previous higher-temperature measurements and the amplitudes of…
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Isomers in $^{66}$Ga, $^{67}$Ge, and $^{69}$Ge were recoil-implanted into ferromagnetic hosts of iron and gadolinium at $\approx 6$~K, and the hyperfine magnetic fields were determined by Time Differential Perturbed Angular Distribution (TDPAD) measurements. The hyperfine field strengths at $\approx 6$~K are compared to the results of previous higher-temperature measurements and the amplitudes of the $R(t)$ functions are compared to empirical expectations. The results show that gadolinium can be a suitable host for high-precision in-beam $g$-factor measurements. The results of new $g$-factor measurements for isomers in $^{66}$Ga and $^{67}$Ge are $g(^{66}$Ga$,7^{-}) = +0.126(4)$, supporting a $[π_{f5/2} \otimes νg_{9/2}]_{7^-}$ configuration assignment, and $g(^{67}$Ge$,\frac{9}{2}^{+})=-0.1932(22)$, derived from a new measurement of the ratio $g(^{67}\mathrm{Ge})/g(^{69}\mathrm{Ge}) = 0.869(9)$. These values are in agreement with previous results. The $R(t)$ amplitudes indicate that the nuclear alignment produced in the isomeric states was significantly lower than the empirically expected $σ/I \approx 0.35$.
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Submitted 15 June, 2022;
originally announced June 2022.
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Electric monopole transition from the superdeformed band in $^{40}$Ca
Authors:
E. Ideguchi,
T. Kibédi,
J. T. H. Dowie,
T. H. Hoang,
M. Kumar Raju,
N. Aoi,
A. J. Mitchell,
A. E. Stuchbery,
N. Shimizu,
Y. Utsuno,
A. Akber,
L. J. Bignell,
B. J. Coombes,
T. K. Eriksen,
T. J. Gray,
G. J. Lane,
B. P. McCormick
Abstract:
The electric monopole ($E0$) transition strength $ρ^2$ for the transition connecting the third 0$^+$ level, a "superdeformed" band head, to the "spherical" 0$^+$ ground state in doubly magic $^{40}$Ca has been determined via $e^+e^-$ pair-conversion spectroscopy. The measured value, $ρ^2(E0; 0^+_3 \to 0^+_1)~=~2.3(5)\times10^{-3}$, is the smallest $ρ^2(E0; 0^+ \to 0^+)$ found in $A<50$ nuclei. In…
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The electric monopole ($E0$) transition strength $ρ^2$ for the transition connecting the third 0$^+$ level, a "superdeformed" band head, to the "spherical" 0$^+$ ground state in doubly magic $^{40}$Ca has been determined via $e^+e^-$ pair-conversion spectroscopy. The measured value, $ρ^2(E0; 0^+_3 \to 0^+_1)~=~2.3(5)\times10^{-3}$, is the smallest $ρ^2(E0; 0^+ \to 0^+)$ found in $A<50$ nuclei. In contrast, the $E0$ transition strength to the ground state observed from the second 0$^+$ state, a band head of "normal" deformation, is an order of magnitude larger, $ρ^2(E0; 0^+_2 \to 0^+_1)~=~25.9(16)\times~10^{-3}$, which shows significant mixing between these two states. Large-Scale Shell Model (LSSM) calculations were performed to understand the microscopic structure of the excited states, and the configuration mixing between them; experimental $ρ^2$ values in $^{40}$Ca and neighboring isotopes were well reproduced by the LSSM calculations. The unusually small $ρ^2(E0; 0^+_3 \to 0^+_1)$ value is due to destructive interference in the mixing of shape-coexisting structures, which are based on several different multiparticle-multihole excitations. This observation goes beyond the usual treatment of $E0$ strengths, where two-state shape mixing cannot result in destructive interference.
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Submitted 13 May, 2022;
originally announced May 2022.
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Improved precision on the experimental E0 decay branching ratio of the Hoyle state
Authors:
T. K. Eriksen,
T. Kibédi,
M. W. Reed,
A. E. Stuchbery,
K. J. Cook,
A. Akber,
B. Alshahrani,
A. A. Avaa,
K. Banerjee,
A. C. Berriman,
L. T. Bezzina,
L. Bignell,
J. Buete,
I. P. Carter,
B. J. Coombes,
J. T. H. Dowie,
M. Dasgupta,
L. J. Evitts,
A. B. Garnsworthy,
M. S. M. Gerathy,
T. J. Gray,
D. J. Hinde,
T. H. Hoang,
S. S. Hota,
E. Ideguchi
, et al. (13 additional authors not shown)
Abstract:
Stellar carbon synthesis occurs exclusively via the $3α$ process, in which three $α$ particles fuse to form $^{12}$C in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the $α$ threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be…
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Stellar carbon synthesis occurs exclusively via the $3α$ process, in which three $α$ particles fuse to form $^{12}$C in the excited Hoyle state, followed by electromagnetic decay to the ground state. The Hoyle state is above the $α$ threshold, and the rate of stellar carbon production depends on the radiative width of this state. The radiative width cannot be measured directly, and must instead be deduced by combining three separately measured quantities. One of these quantities is the $E0$ decay branching ratio of the Hoyle state, and the current $10$\% uncertainty on the radiative width stems mainly from the uncertainty on this ratio. The $E0$ branching ratio was deduced from a series of pair conversion measurements of the $E0$ and $E2$ transitions depopulating the $0^+_2$ Hoyle state and $2^+_1$ state in $^{12}$C, respectively. The excited states were populated by the $^{12}$C$(p,p^\prime)$ reaction at 10.5 MeV beam energy, and the pairs were detected with the electron-positron pair spectrometer, Super-e, at the Australian National University. The deduced branching ratio required knowledge of the proton population of the two states, as well as the alignment of the $2^+_1$ state in the reaction. For this purpose, proton scattering and $γ$-ray angular distribution experiments were also performed. An $E0$ branching ratio of $Γ^{E0}_π/Γ=8.2(5)\times10^{-6}$ was deduced in the current work, and an adopted value of $Γ^{E0}_π/Γ=7.6(4)\times10^{-6}$ is recommended based on a weighted average of previous literature values and the new result. The new recommended value for the $E0$ branching ratio is about 14% larger than the previous adopted value of $Γ^{E0}_π/Γ=6.7(6)\times10^{-6}$, while the uncertainty has been reduced from 9% to 5%.
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Submitted 30 July, 2020;
originally announced July 2020.
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Emerging nuclear collectivity in $^{124-130}$Te
Authors:
B. J. Coombes,
A. E. Stuchbery,
J. M. Allmond,
A. Gargano,
J. T. H. Dowie,
G. Georgiev,
M. S. M. Gerathy,
T. J. Gray,
T. Kibédi,
G. J. Lane,
B. P. McCormick,
A. J. Mitchell,
N. J. Spinks,
B. P. E. Tee
Abstract:
The emergence of nuclear collectivity near doubly-magic $^{132}$Sn was explored along the stable, even-even $^{124-130}$Te isotopes. Preliminary measurements of the $B(E2;4^{+}_{1}\rightarrow2^{+}_{1})$ transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the $g$ factors of the $4^{+}_{1}$ states. Isotopically enriched Te targets were excited by 198-20…
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The emergence of nuclear collectivity near doubly-magic $^{132}$Sn was explored along the stable, even-even $^{124-130}$Te isotopes. Preliminary measurements of the $B(E2;4^{+}_{1}\rightarrow2^{+}_{1})$ transition strengths are reported from Coulomb excitation experiments primarily aimed at measuring the $g$ factors of the $4^{+}_{1}$ states. Isotopically enriched Te targets were excited by 198-205 MeV $^{58}$Ni beams. A comparison of transition strengths obtained is made to large-scale shell-model calculations with successes and limitations discussed.
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Submitted 11 February, 2020;
originally announced February 2020.
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Early signal of emerging nuclear collectivity in neutron-rich $^{129}$Sb
Authors:
T. J. Gray,
J. M. Allmond,
A. E. Stuchbery,
C. -H. Yu,
C. Baktash,
A. Gargano,
A. Galindo-Uribarri,
D. C. Radford,
J. C. Batchelder,
J. R. Beene,
C. R. Bingham,
L. Coraggio,
A. Covello,
M. Danchev,
C. J. Gross,
P. A. Hausladen,
N. Itaco,
W. Krolas,
J. F. Liang,
E. Padilla-Rodal,
J. Pavan,
D. W. Stracener,
R. L. Varner
Abstract:
Radioactive $^{129}$Sb, which can be treated as a proton plus semi-magic $^{128}$Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, $B(E2)$, for the $2^+$ $\times$ $πg_{7/2}$ multiplet members and candidate $πd_{5/2}$ state were measured. The results indicate that the total electric quadrupole strength of…
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Radioactive $^{129}$Sb, which can be treated as a proton plus semi-magic $^{128}$Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, $B(E2)$, for the $2^+$ $\times$ $πg_{7/2}$ multiplet members and candidate $πd_{5/2}$ state were measured. The results indicate that the total electric quadrupole strength of $^{129}$Sb is a factor of 1.39(11) larger than the $^{128}$Sn core, which is in stark contrast to the expectations of the empirically successful particle-core coupling scheme. Shell-model calculations performed with two different sets of nucleon-nucleon interactions suggest that this enhanced collectivity is due to constructive quadrupole coherence in the wavefunctions stemming from the proton-neutron residual interactions, where adding one nucleon to a core near a double-shell closure can have a pronounced effect. The enhanced electric quadrupole strength is an early signal of the emerging nuclear collectivity that becomes dominant away from the shell closure.
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Submitted 19 December, 2019;
originally announced December 2019.
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First-excited state $g$ factors in the stable, even Ge and Se isotopes
Authors:
B. P. McCormick,
A. E. Stuchbery,
B. A. Brown,
G. Georgiev,
B. J. Coombes,
T. J. Gray,
M. S. M. Gerathy,
G. J. Lane,
T. Kibédi,
A. J. Mitchell,
M. W. Reed,
A. Akber,
L. J. Bignell,
J. T. H. Dowie,
T. K. Eriksen,
S. Hota,
N. Palalani,
T. Tornyi
Abstract:
Transient-field $g$-factor measurements in inverse kinematics were performed for the first-excited states of the stable, even isotopes of Ge and Se. The $g$ factors of $^{74}$Ge and $^{74}$Se were measured simultaneously using a cocktail beam, which eliminates most possible sources of systematic error in a relative $g$-factor measurement. The results are…
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Transient-field $g$-factor measurements in inverse kinematics were performed for the first-excited states of the stable, even isotopes of Ge and Se. The $g$ factors of $^{74}$Ge and $^{74}$Se were measured simultaneously using a cocktail beam, which eliminates most possible sources of systematic error in a relative $g$-factor measurement. The results are $g(^{74}{\rm Se})/g(^{74}{\rm Ge})=1.34(7)$, $g(^{70}{\rm Ge})/g(^{74}{\rm Ge}) = 1.16(15)$, $g(^{72}{\rm Ge})/g(^{74}{\rm Ge})=0.92(13)$, $g(^{76}{\rm Ge})/g(^{74}{\rm Ge})=0.88(5)$, $g(^{76}{\rm Se})/g(^{74}{\rm Se})=0.96(7)$, $g(^{78}{\rm Se})/g(^{74}{\rm Se})=0.82(5)$, $g(^{80}{\rm Se})/g(^{74}{\rm Se})=0.99(7)$ and $g(^{82}{\rm Se})/g(^{74}{\rm Se})=1.19(6)$. The measured $g$-factor ratios are in agreement with ratios from previous measurements, despite considerable variation in previous reported absolute values. The absolute values of the $g$ factors remain uncertain, however the Rutgers parametrization was used to set the transient-field strength and then compare the experimental $g$ factors with shell-model calculations based on the JUN45 and jj44b interactions. Modest agreement was found between experiment and theory for both interactions. The shell model calculations indicate that the $g(2^+_1)$ values and trends are determined largely by the balance of the spin carried by orbital motion of the protons.
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Submitted 23 October, 2019;
originally announced October 2019.
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Spectroscopy and excited-state $g$~factors in weakly collective ${^{111}}$Cd: confronting collective and microscopic models
Authors:
B. J. Coombes,
A. E. Stuchbery,
A. Blazhev,
H. Grawe,
M. W. Reed,
A. Akber,
J. T. H. Dowie,
M. S. M. Gerathy,
T. J. Gray,
T. Kibédi,
A. J. Mitchell,
T. Palazzo
Abstract:
The even cadmium isotopes near the neutron midshell have long been considered good examples of vibrational nuclei. However, the vibrational nature of these nuclei has been questioned based on E2 transition rates that are not consistent with vibrational excitations. In the neighbouring odd-mass nuclei, the g factors of the low-excitation collective states have been shown to be more consistent with…
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The even cadmium isotopes near the neutron midshell have long been considered good examples of vibrational nuclei. However, the vibrational nature of these nuclei has been questioned based on E2 transition rates that are not consistent with vibrational excitations. In the neighbouring odd-mass nuclei, the g factors of the low-excitation collective states have been shown to be more consistent with a deformed rotational core than a vibrational core. Beyond the comparison of vibrational versus rotational models, recent advances in computational power have made shell-model calculations feasible for Cd isotopes, which may give insights into the emergence and nature of collectivity in the Cd isotopes. Collective excitations in the A ~ 100 region were studied through magnetic moments and electromagnetic transitions in 111Cd. The spectroscopy of 111Cd has been studied following Coulomb excitation. Angular correlation measurements, transient-field g-factor measurements and lifetime measurements by the Doppler-broadened line shape method were performed. The structure of the nucleus was explored in relation to particle-vibration versus particle-rotor interpretations. Large-scale shell-model calculations were performed with the SR88MHJM Hamiltonian. Excited-state g factors have been measured, spin assignments examined and lifetimes determined. Attention was given to the reported $5/2^{+}$ 753-keV and $3/2^{+}$ 755-keV states. The $3/2^{+}$ 755-keV level was not observed; evidence is presented that the reported $3/2^+$ state was a misidentification of the $5/2^{+}$ 753-keV state. It is shown that the g factors and level structure of 111Cd are not readily explained by the particle-vibration model. A particle-rotor approach has both successes and limitations. The shell-model approach successfully reproduces much of the known low-excitation structure in 111Cd.
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Submitted 7 August, 2019;
originally announced August 2019.
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Pushing the limits of excited-state $g$-factor measurements
Authors:
Andrew E. Stuchbery,
Brendan P. McCormick,
Timothy J. Gray,
Ben J. Coombes
Abstract:
Current developments in excited-state $g$-factor measurements are discussed with an emphasis on cases where the experimental methodology is being extended into new regimes. The transient-field technique, the recoil in vacuum method, and moment measurements with LaBr$_3$ detectors are discussed.
Current developments in excited-state $g$-factor measurements are discussed with an emphasis on cases where the experimental methodology is being extended into new regimes. The transient-field technique, the recoil in vacuum method, and moment measurements with LaBr$_3$ detectors are discussed.
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Submitted 25 June, 2018;
originally announced June 2018.
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Perturbed angular distributions with LaBr$_3$ detectors: the $g$ factor of the first ${10^+}$ state in $^{110}$Cd revisited
Authors:
T. J. Gray,
A. E. Stuchbery,
M. W. Reed,
A. Akber,
B. J. Coombes,
J. T. H. Dowie,
T. K. Eriksen,
M. S. M. Gerathy,
T. Kibedi,
G. J. Lane,
A. J. Mitchell,
T. Palazzo,
T. Tornyi
Abstract:
The Time Differential Perturbed Angular Distribution technique with LaBr$_3$ detectors has been applied to the $I^π= \frac{11}{2}^-$ isomeric state ($E_x = 846$ keV, $τ=107$~ns) in $^{107}$Cd, which was populated and recoil-implanted into a gadolinium host following the $^{98}$Mo($^{12}$C, $3n$)$^{107}$Cd reaction. The static hyperfine field strength of Cd recoil implanted into gadolinium was thus…
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The Time Differential Perturbed Angular Distribution technique with LaBr$_3$ detectors has been applied to the $I^π= \frac{11}{2}^-$ isomeric state ($E_x = 846$ keV, $τ=107$~ns) in $^{107}$Cd, which was populated and recoil-implanted into a gadolinium host following the $^{98}$Mo($^{12}$C, $3n$)$^{107}$Cd reaction. The static hyperfine field strength of Cd recoil implanted into gadolinium was thus measured, together with the fraction of nuclei implanted into field-free sites, under similar conditions as pertained for a previous implantation perturbed angular distribution $g$-factor measurement on the $I^π= 10^+$ state in $^{110}$Cd. The $^{110}$Cd $g(10^+)$ value was thereby re-evaluated, bringing it into agreement with the value expected for a seniority-two $νh_{\frac{11}{2}}$ configuration.
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Submitted 28 September, 2017;
originally announced September 2017.