Low-lying states of ^94Zr were investigated via low-energy multi-step Coulomb excitation. From the measured γ-ray yields, 16 reduced E2 transition probabilities between low-spin states were determined, together with the spectroscopic quadrupole moments of the 2_1,2^+ states. Based on this information, for the first time in the Zr isotopic chain, the shapes of the 0_1,2^+ states including their deformation softness were inferred in a model-independent way using the quadrupole sum rules approach. The ground state of ^94Zr possesses a rather diffuse shape associated with a spherical configuration, while the 0_2^+ state is triaxial tending towards oblate and more strongly deformed. The observed features of shape coexistence in ^94Zr are consistent with both Monte-Carlo shell-model predictions and IBM-CM calculations, and provide model-independent constraints on the shape character assigned in the IBM-CM to the intruder configuration in ^92–96Zr.

Lead-208 is the heaviest known doubly magic nucleus and its structure is therefore of special interest. Despite this magicity, which acts to provide a strong restorative force toward sphericity, it is known to exhibit both strong octupole correlations and some of the strongest quadrupole collectivity observed in doubly magic systems. In this Letter, we employ state-of-the-art experimental equipment to conclusively demonstrate, through four Coulomb-excitation measurements, the presence of a large, negative, spectroscopic quadrupole moment for both the vibrational octupole 31− and quadrupole 21+ state, indicative of a preference for prolate deformation of the states. The observed quadrupole moment is discussed in the context of the expected splitting of the 3−⊗3− two-phonon states, due to the coupling of the quadrupole and octupole motion. These results are compared with theoretical values from three different methods, which are unable to reproduce both the sign and magnitude of this deformation. Thus, in spite of its well-studied nature, Pb208 remains a puzzle for our understanding of nuclear structure. Published by the American Physical Society 2025

Background: gamma -ray spectroscopy studies of the Sn isotopes provide important information on nuclear structure and shell evolution across the long isotopic chain between the doubly-magic Sn-100 and Sn-132 nuclei. These studies also offer great value to test and tune nuclear models which can then be applied to other regions of the nuclear chart. Purpose: We aim to expand the level scheme of Sn-118 by populating low-spin states in the range of 3-5 MeV and determine their angular momentum for the possible connection of these states to pygmy quadrupole Resonances, a new phenomenon observed in the neighboring Sn-112,Sn-114,Sn-124 isotopes as a resonance-like structure in the 3-5 MeV range. Method: Excited states in Sn-118 were populated via the Sn-117(n, gamma)Sn-118 reaction at the Institut Laue-Langevin in Grenoble, France. The FIssion Product Prompt gamma-ray Spectrometer (FIPPS), an array of eight n -type high purity Germanium clover detectors augmented with eight additional clover detectors from IFIN "Horia Hulubei" were used to detect gamma rays from excited states in Sn-118. The array provides a superior efficiency for gamma -ray detection and nearly 4 pi coverage for the measurements of angular correlations for spin assignment of excited nuclear levels. Results: Through gamma -gamma coincidences, 112 excited states were identified with 57 being newly placed in the level scheme. From these states, 567 gamma -ray transitions were observed with 501 being newly identified. Many levels were identified in the 3-5 MeV region. Further, an indirect measurement of the E0 transition which decays from the 0(3)(+) state to the 2p -2h, 0(2)(+) state was performed and the q(K)(2)(E0/E 2) and X(E0/E2) for this transition were determined to be 12.7(11) and 6.3(5), respectively. The 10(3) x rho(2)(E0) was determined to be >38 based on a half-life limit of <200 ps of the 2057-keV, 0(3)(+) level. Conclusions: The abundant spectroscopic information on Sn-118 obtained in the present experiment is an important input to the theoretical description of nuclei in the region and highlights the capabilities of the FIPPS array at ILL in conjunction with neutron capture reactions. Many states identified in the 3-5 MeV region could very likely have J = 2(+) and contribute to the pygmy quadrupole resonances.

Excited states of 122Xe populated via 8+and electron capture (EC) decay of 122Cs have been studied with gamma -ray spectroscopy using the 8n spectrometer at the TRIUMF Isotope Separator and Accelerator facility. Two sets of data were collected to optimize the signal-to-background ratio for decays of the ground (t1/2 = 21.2 s) and isomeric (t1/2 = 3.7 min) states of 122Cs. The data collected have enabled the observation of 520 transitions and 191 levels, including eight new excited 0+ states in 122Xe. The gamma -gamma angular correlations have been analyzed that permitted the assignment or restriction of the spins for 66 levels. The E2/M1 multipolarity mixing ratios for 38 gamma -ray transitions were also extracted from these analyses. Low-spin members of the 0+2 , 0+3 , 0+4 , and Kn= 4+ bands are assigned, as well as suggested Kn= 2+2 and Kn= 2+3 bandheads. Combined with previous results for high-spin states, rotational bands built on a newly assigned Kn= 3-1 state and its 4-1 signature partner, the 5-2 and its 6-2 signature partner, are suggested. The results for the positive-parity bands are compared with a model using a general Bohr Hamiltonian derived from a mean-field theory based on the UNEDF0 energy-density functional that displays good overall agreement.

High-precision lifetime measurements in 28Mg were performed to study neutron shell evolution in Mg isotopes and the onset of the =20 island of inversion. Using both the recoil distance and Doppler shift attenuation methods, five lifetimes were measured in addition to six upper limits. The observation of two long-lived, negative-parity states demonstrate the importance of studying Mg isotopes for the contribution of intruder configurations to -shell nuclei. Lifetimes of the 2+1 and 4+1 states of 1.81(5) ps and 172(+11-10)stat.(4)stop.(8)feed.(4)targ.fs, respectively, demonstrate a loss of collectivity with increasing spin in the yrast band, permitting for distinguishing between current theoretical models. These measurements also highlight the progression of yrast structure across the Mg isotopic chain from rotational at =12 to large shape mixing at =16 and back to collective behavior at =20 but with dominating intruder configurations.

The utilization of large-scale neutron detector arrays in future experiments is of vital importance to increase our understanding of β-delayed neutron emitters. A new device, DAEMON (Detector Array for Energy Measurements Of Neutrons), is being designed for the GRIFFIN decay station at TRIUMF-ISAC. DAEMON will improve the precision on the measurement of the neutron kinetic energy through the use of thin plastic scintillators, SiPMs arrays, and the Time-of-Flight technique, to enhance the current capabilities to study neutron rich nuclei at TRIUMF. The performance and feasibility of the DAEMON array was investigated using the Geant4 package to simulate and optimize the experimental design. To test the optical parameters and models implemented in the Geant4 simulations, a comparison with experimental data from small plastic scintillators combined with SiPM detectors was performed. The simulations reproduce the experimental data very well, including features introduced by summing 2 × 2-SiPM arrays in software. This work lays the foundation for simulations of the full DAEMON array.

The excited states of N=44 ^{74}Zn were investigated via γ-ray spectroscopy following ^{74}Cu β decay. By exploiting γ-γ angular correlation analysis, the 2_{2}^{+}, 3_{1}^{+}, 0_{2}^{+}, and 2_{3}^{+} states in ^{74}Zn were firmly established. The γ-ray branching and E2/M1 mixing ratios for transitions deexciting the 2_{2}^{+}, 3_{1}^{+}, and 2_{3}^{+} states were measured, allowing for the extraction of relative B(E2) values. In particular, the 2_{3}^{+}→0_{2}^{+} and 2_{3}^{+}→4_{1}^{+} transitions were observed for the first time. The results show excellent agreement with new microscopic large-scale shell-model calculations, and are discussed in terms of underlying shapes, as well as the role of neutron excitations across the N=40 gap. Enhanced axial shape asymmetry (triaxiality) is suggested to characterize ^{74}Zn in its ground state. Furthermore, an excited K=0 band with a significantly larger softness in its shape is identified. A shore of the N=40 "island of inversion" appears to manifest above Z=26, previously thought as its northern limit in the chart of the nuclides.

Background: Detailed spectroscopy of neutron-rich, heavy, deformed nuclei is of broad interest for nuclear astrophysics and nuclear structure. Nuclei in the r-process path and following freeze-out region impact the resulting r-process abundance distribution, and the structure of nuclei midshell in both proton and neutron number helps to understand the evolution of subshell gaps and large deformation in these nuclei. Purpose: We aim to improve the understanding of the nuclear structure of 160Gd, specifically the K & pi; = 4+ bands, as well as study the & beta; decay of 160Eu into 160Gd. Methods: High-statistics decay spectroscopy of 160Gd resulting from the & beta;-decay of 160Eu was collected using the GRIFFIN spectrometer at the TRIUMF-ISAC facility. Results: Two new excited states and ten new transitions were observed in 160Gd. The & beta;-decaying half-lives of the low-and high-spin isomers in 160Eu were determined, and the low-spin state's half-life was measured to be t1/2 = 26.0(8) s, & AP;16% shorter than previous measurements. Lifetimes of the two K & pi; = 4+ bandheads in 160Gd were measured for the first time, as well as & gamma; -& gamma; angular correlations and mixing ratios of intense transitions out of those bandheads. Conclusions: Lifetimes and mixing ratios suggest that the hexadecapole phonon model of the K & pi; = 4+ bandheads in 160Gd is preferred over a simple two-state strong mixing scenario, although further theoretical calculations are needed to fully understand these states. Additionally, the 1999.0-keV state in 160Gd heavily populated in & beta; decay is shown to have positive parity, which raises questions regarding the structure of the high-spin & beta;-decaying state in 160Eu.

Background: Detailed spectroscopy of neutron-rich, heavy, deformed nuclei is of broad interest for nuclear astrophysics and nuclear structure. Nuclei in the $r$-process path and following freeze-out region impact the resulting $r$-process abundance distribution, and the structure of nuclei midshell in both proton and neutron number helps to understand the evolution of subshell gaps and large deformation in these nuclei.Purpose: We aim to improve the understanding of the nuclear structure of $^{160}\mathrm{Gd}$, specifically the ${K}^{\ensuremath{\pi}}={4}^{+}$ bands, as well as study the $\ensuremath{\beta}$ decay of $^{160}\mathrm{Eu}$ into $^{160}\mathrm{Gd}$.Methods: High-statistics decay spectroscopy of $^{160}\mathrm{Gd}$ resulting from the $\ensuremath{\beta}$-decay of $^{160}\mathrm{Eu}$ was collected using the GRIFFIN spectrometer at the TRIUMF-ISAC facility.Results: Two new excited states and ten new transitions were observed in $^{160}\mathrm{Gd}$. The $\ensuremath{\beta}$-decaying half-lives of the low- and high-spin isomers in $^{160}\mathrm{Eu}$ were determined, and the low-spin state's half-life was measured to be ${t}_{1/2}=26.0(8)$ s, $\ensuremath{\approx}16%$ shorter than previous measurements. Lifetimes of the two ${K}^{\ensuremath{\pi}}={4}^{+}$ bandheads in $^{160}\mathrm{Gd}$ were measured for the first time, as well as $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ angular correlations and mixing ratios of intense transitions out of those bandheads.Conclusions: Lifetimes and mixing ratios suggest that the hexadecapole phonon model of the ${K}^{\ensuremath{\pi}}={4}^{+}$ bandheads in $^{160}\mathrm{Gd}$ is preferred over a simple two-state strong mixing scenario, although further theoretical calculations are needed to fully understand these states. Additionally, the 1999.0-keV state in $^{160}\mathrm{Gd}$ heavily populated in $\ensuremath{\beta}$ decay is shown to have positive parity, which raises questions regarding the structure of the high-spin $\ensuremath{\beta}$-decaying state in $^{160}\mathrm{Eu}$.

We used the ^{138}Ba(d,α) reaction to carry out an in-depth study of states in ^{136}Cs, up to around 2.5 MeV. In this Letter, we place emphasis on hitherto unobserved states below the first 1^{+} level, which are important in the context of solar neutrino and fermionic dark matter (FDM) detection in large-scale xenon-based experiments. We identify for the first time candidate metastable states in ^{136}Cs, which would allow a real-time detection of solar neutrino and FDM events in xenon detectors, with high background suppression. Our results are also compared with shell-model calculations performed with three Hamiltonians that were previously used to evaluate the nuclear matrix element (NME) for ^{136}Xe neutrinoless double beta decay. We find that one of these Hamiltonians, which also systematically underestimates the NME compared with the others, dramatically fails to describe the observed low-energy ^{136}Cs spectrum, while the other two show reasonably good agreement.

A beta-decay experiment aiming at investigation of the low-spin structure of 100Zr was performed using the GRIFFIN spectrometer at TRIUMF-ISAC. Based on the obtained data, a new 2+ state is postulated which is degenerate in energy with the established (5+) level at 2209 keV.

As part of a systematic study of the nuclear structure of the Ru isotopes, 98Ru was investigated via the β-decay of 98Rh at iThemba LABS, and the 100Ru(p, t) reaction at the Maier-Leibnitz Laboratory. The combined data results in significant revision of the previous spin assignments and clarification of the nature of levels in 98Ru, as well as providing insights into the evolution of the structures across the Ru isotopic chain.

The use of large-scale neutron detector arrays with high energy resolution, especially those that can be coupled with highly efficient γ-ray spectrometers, is imperative in order to increase the understanding of the decay of β-delayed neutron emitters. The DAEMON array, currently being designed for the GRIFFIN decay station at TRIUMF, will improve the precision on the neutron kinetic energy measurement enhancing the current capabilities to study neutron rich nuclei at TRIUMF. The innovative design for DAEMON uses thin fast plastic scintillators placed directly on the front of the DESCANT liquid scintillator cans. To investigate the viability of this augmentation, Geant4 was used to simulate and optimize the experimental design. Two configurations were considered; a geometry using vertical bars spanning the inner arc of DESCANT, and individual tiles matching the geometry of the DESCANT scintillator cans. The latter was found to be the most optimum design, enabling the project to enter a prototype testing phase.

We used the $^{138}\mathrm{Ba}(d,\ensuremath{\alpha})$ reaction to carry out an in-depth study of states in $^{136}\mathrm{Cs}$, up to around 2.5 MeV. In this Letter, we place emphasis on hitherto unobserved states below the first ${1}^{+}$ level, which are important in the context of solar neutrino and fermionic dark matter (FDM) detection in large-scale xenon-based experiments. We identify for the first time candidate metastable states in $^{136}\mathrm{Cs}$, which would allow a real-time detection of solar neutrino and FDM events in xenon detectors, with high background suppression. Our results are also compared with shell-model calculations performed with three Hamiltonians that were previously used to evaluate the nuclear matrix element (NME) for $^{136}\mathrm{Xe}$ neutrinoless double beta decay. We find that one of these Hamiltonians, which also systematically underestimates the NME compared with the others, dramatically fails to describe the observed low-energy $^{136}\mathrm{Cs}$ spectrum, while the other two show reasonably good agreement.

The Coulomb excitation of $^{102}\mathrm{Ru}$ was performed with beams of $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ ions. The beam particles scattered at forward angles were momentum analyzed with a magnetic spectrograph. The resolution achieved enabled the populations of the ${2}_{1}^{+}$ state, the unresolved ${2}_{2}^{+}/{4}_{1}^{+}$, and ${2}_{4}^{+}/{3}_{1}^{\ensuremath{-}}$, doublets of states, and the ${3}_{2}^{\ensuremath{-}}$ state to be determined as a function of the scattering angle. These populations are compared with gosia calculations, yielding $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})=41.5\ifmmode\pm\else\textpm\fi{}2.3$ W.u., $B(E2;{2}_{2}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})=1.75\ifmmode\pm\else\textpm\fi{}0.11$ W.u., $B(E3;{3}_{1}^{\ensuremath{-}}\ensuremath{\rightarrow}{0}_{1}^{+})=31.5\ifmmode\pm\else\textpm\fi{}3.5$ W.u., and $B(E3;{3}_{2}^{\ensuremath{-}}\ensuremath{\rightarrow}{0}_{1}^{+})=6.8\ifmmode\pm\else\textpm\fi{}0.5$ W.u. The $B(E3;{3}_{1}^{\ensuremath{-}}\ensuremath{\rightarrow}{0}_{1}^{+})$ value is significantly larger than previously measured. The weakly populated ${2}_{3}^{+}$ state, presumed to be a member of the band built on the ${0}_{2}^{+}$ state, was observed clearly for a single angle only, and a fit to its population results in $B(E2;{2}_{3}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})=0.053\ifmmode\pm\else\textpm\fi{}0.011$ W.u. Using the known $\ensuremath{\gamma}$-ray branching ratios for the ${2}_{3}^{+}$ level, the $B(E2;{2}_{3}^{+}\ensuremath{\rightarrow}{0}_{2}^{+})$ value is calculated to be $18\ifmmode\pm\else\textpm\fi{}4$ W.u., substantially less than the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$. This suggests that the deformation of the ${0}_{2}^{+}$ state is lower than that of the ${0}_{1}^{+}$ state. The results are compared with beyond-mean-field calculations with the Gogny-D1S interaction using the symmetry-conserving configuration-mixing method.

We use a high-resolution S-32(d , t) measurement to investigate the claimed existence of a 6401(3) keV state in S-31 that may affect the P-30(p, gamma) nuclear reaction rate in oxygen-neon (ONe) novae. Our data are shown to exclude the null hypothesis-that the state does not exist-with high significance. Additionally, the data also suggest the existence of a hitherto unreported state at 6648(4) keV. This state corresponds to a P-30(p, gamma) resonance at 517(4) keV, located below the higher edge of the Gamow window for peak nova temperatures of about 0.4 GK.

The nature of quadrupole and octupole collectivity in 222 Rn was investigated by determining the electric-quadrupole ( E 2) and octupole ( E 3) matrix elements using subbarrier, multistep Coulomb excitation. The radioactive 222 Rn beam, accelerated to 4.23 MeV / u, was provided by the HIE-ISOLDE facility at CERN. Data were collected in the Miniball γ -ray spectrometer following the bombardment of two targets, 120 Sn and 60 Ni. Transition E 2 matrix elements within the ground-state and octupole bands were measured up to 10¯ h and the results were consistent with a constant intrinsic electric-quadrupole moment, 518(11) e fm 2 . The values of the intrinsic electric-octupole moment for the 0 + → 3 − and 2 + → 5 − transitions were found to be respectively 2360 + 300 − 210 e fm 3 and 2300 + 300 − 500 e fm 3 while a smaller value, 1200 + 500 − 900 e fm 3 , was found for the 2 + → 1 − transition. In addition, four excited non-yrast states were identified in this work via γ - γ coincidences. 10.1103/PhysRevC.105.024323

The Coulomb excitation of 102Ru was performed with beams of 12C and 16O ions. The beam particles scattered at forward angles were momentum analyzed with a magnetic spectrograph. The resolution achieved enabled the populations of the 2+1 state, the unresolved 2+ 2 /4+ 1 , and 2+ 4 /3- 1 , doublets of states, and the 3-2 state to be determined as a function of the scattering angle. These populations are compared with GOSIA calculations, yielding B(E2; 2+1 -> 0+1 ) = 41.5 +/- 2.3 W.u., B(E2; 2+ 2 -> 0+1 ) = 1.75 +/- 0.11 W.u., B(E3; 3-1 -> 0+1 ) = 31.5 +/- 3.5 W.u., and B(E3; 3-2 -> 0+1 ) = 6.8 +/- 0.5 W.u. The B(E3; 3-1 -> 0+1 ) value is significantly larger than previously measured. The weakly populated 2+3 state, presumed to be a member of the band built on the 0+2 state, was observed clearly for a single angle only, and a fit to its population results in B(E2; 2+3 -> 0+1 ) = 0.053 +/- 0.011 W.u. Using the known gamma-ray branching ratios for the 2+3 level, the B(E2; 2+3 -> 0+2 ) value is calculated to be 18 +/- 4 W.u., substantially less than the B(E2; 2+1 -> 0+1 ). This suggests that the deformation of the 0+2 state is lower than that of the 0+1 state. The results are compared with beyond-mean-field calculations with the Gogny-D1S interaction using the symmetry-conserving configuration-mixing method.

B. Olaizola, ∗ A. Babu, R. Umashankar, 2 A.B. Garnsworthy, G.C. Ball, V. Bildstein, M. Bowry, † C. Burbadge, R. Cabellero-Folch, I. Dillmann, 4 A. Diaz-Varela, R. Dunlop, A. Estradé, P.E. Garrett, G. Hackman, A.D. MacLean, J. Measures, 6 C.J. Pearson, B. Shaw, D. Southall, ‡ C.E. Svensson, J. Turko, K. Whitmore, and T. Zidar TRIUMF, 4004 Wesbrook Mall, Vancouver, BC, V6T 2A3, Canada Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Department of Physics, University of Guelph, Guelph, ON, N1G 2W1, Canada Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8P 5C2, Canada Department of Physics, Central Michigan University, Mount Pleasant, MI 48859, USA Department of Physics, University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom Department of Chemistry, Simon Fraser University, Burnaby, British Colombia V5A 1S6, Canada (Dated: September 13, 2021)