Search

New half-lives for exotic isotopes approaching the neutron drip-line in the vicinity of N∼28 for Z=12-15 were measured at the Facility for Rare Isotope Beams (FRIB) with the FRIB decay station initiator. The first experimental results are compared to the latest quasiparticle random phase approximation and shell-model calculations. Overall, the measured half-lives are consistent with the available theoretical descriptions and suggest a well-developed region of deformation below ^{48}Ca in the N=28 isotones. The erosion of the Z=14 subshell closure in Si is experimentally confirmed at N=28, and a reduction in the ^{38}Mg half-life is observed as compared with its isotopic neighbors, which does not seem to be predicted well based on the decay energy and deformation trends. This highlights the need for both additional data in this very exotic region, and for more advanced theoretical efforts.

The β-delayed one- and two-neutron emission probabilities (P_{1n} and P_{2n}) of 20 neutron-rich nuclei with N≥82 have been measured at the RIBF facility of the RIKEN Nishina Center. P_{1n} of ^{130,131}Ag, ^{133,134}Cd, ^{135,136}In, and ^{138,139}Sn were determined for the first time, and stringent upper limits were placed on P_{2n} for nearly all cases. β-delayed two-neutron emission (β2n) was unambiguously identified in ^{133}Cd and ^{135,136}In, and their P_{2n} were measured. Weak β2n was also detected from ^{137,138}Sn. Our results highlight the effect of the N=82 and Z=50 shell closures on β-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star merger scenario. Our P_{1n} and P_{2n} have a direct impact on the odd-even staggering of the final abundance, improving the agreement between calculated and observed Solar System abundances. The odd isotope fraction of Ba in r-process-enhanced (r-II) stars is also better reproduced using our new data.

Imperfections in analog-to-digital conversion (ADC) cannot be ignored when signal digitization requirements demand both wide dynamic range and high resolution, as is the case for the Majorana Demonstrator 76Ge neutrinoless double-beta decay search. Enabling the experiment’s high-resolution spectral analysis and efficient pulse shape discrimination required careful measurement and correction of ADC nonlinearities. A simple measurement protocol was developed that did not require sophisticated equipment or lengthy data-taking campaigns. A slope-dependent hysteresis was observed and characterized. A correction applied to digitized waveforms prior to signal processing reduced the differential and integral nonlinearities by an order of magnitude, eliminating these as dominant contributions to the systematic energy uncertainty at the double-beta decay $Q$ value.

The structure of nuclei around the neutron-rich nucleus 132Sn is of particular interest due to the vicinity of the Z = 50 and N = 82 shell closures and the r-process nucleosynthetic path. Four states in 131Sn with a strong single-particle-like component have previously been studied via the (d,p) reaction, with limited excitation energy resolution. The 130Sn(9Be,8Be)131Sn and 130Sn(13C,12C)131Sn single-neutron transfer reactions were performed in inverse kinematics at the Holifield Radioactive Ion Beam Facility using particle-gamma coincidence spectroscopy. The uncertainties in the energies of the single-particle-like states have been reduced by more than an order of magnitude using the energies of gamma rays. The previous tentative Jpi values have been confirmed. Decays from high-spin states in 131Sn have been observed following transfer on the isomeric component of the 130Sn beam. The improved energies and confirmed spin-parities of the p-wave states important to the r-process lead to direct-semidirect cross-sections for neutron capture on the ground state of 130Sn at 30 keV that are in agreement with previous analyses. A similar assessment of the impact of neutron-transfer on the isomer would require significant nuclear structure and reaction theory input. There are few measurements of transfer reaction on isomers, and this is the first on an isomer in the 132Sn region., Comment: 7 pages, 4 figures

At the RIKEN Nishina Center, exotic neutron-rich isotopes of Ba, La, Ce, Pr, and Nd were measured. This work reports their half-lives (T1/2) and β-delayed neutron-emission probabilities (Pxn). The setup consisted of the BigRIPS in-flight separator for particle identification, the Advanced Implantation Detector Array (AIDA) for ions and β detection, and the BRIKEN neutron counter for neutron detection. Using this arrangement, 4 new T1/2 and 14 new P1n were measured. Furthermore, 38 T1/2 and 2 P1n values were remeasured, decreasing the uncertainties for some of them. In addition to improving predictions of nucleosynthesis models that describe the production of the rare-earth peak at A ∼ 160 via the r-process, these additional experimental data should help to constrain theoretical models for calculations of T1/2 and Pxn in this region.

The β-delayed neutron-emission probabilities of 28 exotic neutron-rich isotopes of Pm, Sm, Eu, and Gd were measured for the first time at RIKEN Nishina Center using the Advanced Implantation Detector Array (AIDA) and the BRIKEN neutron detector array. The existing β-decay half-life (T 1/2) database was significantly increased toward more neutron-rich isotopes, and uncertainties for previously measured values were decreased. The new data not only constrain the theoretical predictions of half-lives and β-delayed neutron-emission probabilities, but also allow for probing the mechanisms of formation of the high-mass wing of the rare-earth peak located at A ≈ 160 in the r-process abundance distribution through astrophysical reaction network calculations. An uncertainty quantification of the calculated abundance patterns with the new data shows a reduction of the uncertainty in the rare-earth peak region. The newly introduced variance-based sensitivity analysis method offers valuable insight into the influence of important nuclear physics inputs on the calculated abundance patterns. The analysis has identified the half-lives of 168Sm and of several gadolinium isotopes as some of the key variables among the current experimental data to understand the remaining abundance uncertainty at A = 167–172.

This experiment was performed at RI Beam Factory operated by RIKEN Nishina Center and CNS, University of Tokyo. O.H, T.D, P.J.W, C.G.B, C.J.G and D.K would like to thank STFC, UK for support. This research was sponsored in part by the Office of Nuclear Physics, U.S. Department of Energy under Award No. DE-FG02-96ER40983 (UTK) and DEAC05-00OR22725 (ORNL), and by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Award No. DENA0002132. This work was supported by National Science Foundation under Grants No. PHY-1430152 (JINA Center for the Evolution of the Elements), No. PHY-1565546 (NSCL), and No. PHY-1714153 (Central Michigan University). This work was supported by the Polish National Science Center under Contracts No. UMO-2015/18/E/ST2/00217, No. 2017/01/X/ST2/01144, No. 2019/33/N/ST2/03023 and No. 2020/36/T/ST2/00547. This work was also supported by JSPS KAKENHI (Grants No. 14F04808, No. 17H06090, No. 25247045, and No. 19340074). This work was also supported by Spanish Ministerio de Economia y Competitividad grants (FPA2011-06419, FPA2011-28770-C03-03, FPA2014-52823-C2-1-P, FPA2014-52823-C2-2-P, SEV-2014-0398, IJCI-2014-19172), by European Commission FP7/EURATOM Contract No. 605203, by the UK Science and Technology Facilities Council Grant No. ST/N00244X/1, by the National Research Foundation (NRF) in South Korea (No. 2016K1A3A7A09005575, No. 2015H1A2A1030275) and by the Natural Sciences and Engineering Research Council of Canada (NSERC) via the Discovery Grants SAPIN-2014-00028 and RGPAS 462257-2014. TRIUMF receives federal funding via a contribution agreement with the National Research Council Canada. This work was also supported by NKFIH (NN128072), and by the UNKP-20-5-DE-2 New National Excellence Program of the Ministry of Human Capacities of Hungary. G.G.K. acknowledges support from the Janos Bolyai research fellowship of the Hungarian Academy of Sciences. M.W.-C. acknowledges support from the Polish NCN project Miniatura No. 2017/01/X/ST2/01144. Z.L was supported by the National Key Research and Development Program of China (Contract No. 2018YFA0404402), the National Natural Science Foundation of China (Grants No. 11961141004, No. 11735017, No. 11675225 and No. 11635003) and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB34000000). M.R.M. performed this work under the auspice of the U.S. Department of Energy at Los Alamos National Laboratory. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (Contract No. 89233218CNA000001).

The ground-state properties of neutron-rich $^{106}\mathrm{Nb}$ and its $\ensuremath{\beta}$ decay into $^{106}\mathrm{Mo}$ have been studied using the CARIBU radioactive-ion-beam facility at Argonne National Laboratory. Niobium-106 ions were extracted from a $^{252}\mathrm{Cf}$ fission source and mass separated before being delivered as low-energy beams to the Canadian Penning Trap, as well as the X-Array and SATURN $\ensuremath{\beta}$-decay-spectroscopy station. The measured $^{106}\mathrm{Nb}$ ground-state mass excess of $\ensuremath{-}66202.0(13)$ keV is consistent with a recent measurement but has three times better precision; this work also rules out the existence of a second long-lived, $\ensuremath{\beta}$-decaying state in $^{106}\mathrm{Nb}$ above 5 keV in excitation energy. The decay half-life of $^{106}\mathrm{Nb}$ was measured to be 1.097(21) s, which is $8%$ longer than the adopted value. The level scheme of the decay progeny, $^{106}\mathrm{Mo}$, has been expanded up to $\ensuremath{\approx}4\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. The distribution of decay strength and considerable population of excited states in $^{106}\mathrm{Mo}$ of $J\ensuremath{\ge}3$ emphasizes the need to revise the adopted ${J}^{\ensuremath{\pi}}={1}_{}^{\ensuremath{-}}$ ground-state spin-parity assignment of $^{106}\mathrm{Nb}$; it is more likely to be $J\ensuremath{\ge}3$.

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the Gd155(α,2n)Dy157 and Nd148(C12,5n)Dy155 reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a Kπ=2+γ vibrational band, built on the [505]11/2− neutron orbital, in both odd-ADy155,157 isotopes. The coupling of the first excited K=0+ states or the so-called β vibrational bands at 661 and 676 keV in Dy154 and Dy156 to the [505]11/2− orbital, to produce a Kπ=11/2− band, was not observed in both Dy155 and Dy157, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei Dy154 and Dy156 are also discussed.

Radioactive ^{129}Sb, which can be treated as a proton plus semimagic ^{128}Sn core within the particle-core coupling scheme, was studied by Coulomb excitation. Reduced electric quadrupole transition probabilities, B(E2), for the 2^{+}⊗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 wave functions 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.

International audience; The low-energy electromagnetic structure of 110Cd was studied using safe-energy Coulomb excitation at the Heavy Ion Laboratory, University of Warsaw. The preliminary results on the quadrupole deformation of lowlying 0+ states in 110Cd are presented and compared to the recent beyondmean-field and General Bohr Hamiltonian calculations.

Empirical moments of inertia, J 1 , J 2 , J 3 , of atomic nuclei with E ( 4 1 + ) / E ( 2 1 + ) > 2.7 are extracted from experimental 2 g , γ + energies and electric quadrupole matrix elements, determined from multi-step Coulomb excitation data, and the results are compared to expectations based on rigid and irrotational inertial flow. Only by having the signs of the E2 matrix elements, i.e., 〈 2 g + ‖ M ˆ ( E 2 ) ‖ 2 g + 〉 and 〈 0 g + ‖ M ˆ ( E 2 ) ‖ 2 g + 〉 〈 2 g + ‖ M ˆ ( E 2 ) ‖ 2 γ + 〉 〈 2 γ + ‖ M ˆ ( E 2 ) ‖ 0 g + 〉 , can a unique solution to all three components of the inertia tensor of an asymmetric top be obtained. While the absolute moments of inertia fall between the rigid and irrotational values as expected, the relative moments of inertia appear to be qualitatively consistent with the β 2 sin 2 ⁡ ( γ ) dependence of the Bohr Hamiltonian which originates from a SO(5) invariance. A better understanding of inertial flow is central to improving collective models, particularly hydrodynamic-based collective models. The results suggest that a better description of collective dynamics and inertial flow for atomic nuclei is needed. The inclusion of vorticity degrees of freedom may provide a path forward. This is the first report of empirical moments of inertia for all three axes and the results should challenge both collective and microscopic descriptions of inertial flow.

Aquesta es una copia de la versio author’s final draft d'un article publicat a la revista [Physical Review C ]. URL d'aquest document a UPCommons E-prints: http://hdl.handle.net/2117/174873

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., Comment: 5 pages, 3 figures, Submitted to Proceedings HIAS 2019, EPJ Web of Conferences

Half of the elements heavier than iron are believed to be produced through the rapid neutron-capture process ($r$ process). The astrophysical environment(s) where the $r$ process occurs remains an open question, even after recent observations of neutron-star mergers and the associated kilonova. Features in the abundance pattern of $r$-process ashes may provide critical insight for distinguishing contributions from different possible sites, including neutron-star mergers and core-collapse supernovae. In particular, the largely unknown neutron-capture reaction rates on neutron-rich unstable nuclei near $^{132}\mathrm{Sn}$ could have a significant impact on the final $r$-process abundances. To better determine these neutron-capture rates, the $(d,p)$ reaction has been measured in inverse kinematics using radioactive ion beams of $^{126}\mathrm{Sn}$ and $^{128}\mathrm{Sn}$ and a stable beam of $^{124}\mathrm{Sn}$ interacting with a ${({\mathrm{CD}}_{2})}_{n}$ target. An array of position-sensitive silicon strip detectors, including the Super Oak Ridge Rutgers University Barrel Array, was used to detect light reaction products. In addition to the present measurements, previous measurements of $^{130,132}\mathrm{Sn}(d,p)$ were reanalyzed using state-of-the-art reaction theory to extract a consistent set of spectroscopic factors for $(d,p)$ reactions on even tin nuclei between the heaviest stable isotope $^{124}\mathrm{Sn}$ and doubly magic $^{132}\mathrm{Sn}$. The spectroscopic information was used to calculate direct-semidirect $(n,\ensuremath{\gamma})$ cross sections, which will serve as important input for $r$-process abundance calculations.

The higher-spin structure of $^{38}$Cl ($N = 21$) was investigated following the $^{26}$Mg($^{14}$C, $pn$) reaction at 30 and 37 MeV beam energies. The outgoing protons were detected in an $E- \Delta E$ Si telescope placed at 0$^\circ$ close to the target with a Ta beam stopper between the target and telescope. Multiple $\gamma$ rays were detected in time coincidence with the protons using an enhanced version of the FSU $\gamma$ detection array. The level scheme was extended up to 8420 keV with a likely spin of 10 $\hbar$. A new multishell interaction was developed guided by the experimental information. This FSU interaction was built by fitting to the energies of 270 experimental states from $^{13}$C to $^{51}$Ti. Calculations using the FSU interaction reproduce observed properties of $^{38}$Cl rather well, including the spectroscopic factors. The interaction has been successfully used to interpret the $1p1h$ and $2p2h$ configurations in some nearby nuclei as well., Comment: Published in https://doi.org/10.1103/PhysRevC.100.034308

Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL’s CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

Shell-model calculations for 127,129In and 129,131Sb are presented, and interpreted in the context of the particle-core coupling scheme, wherein proton g9/2 holes or g7/2 particles are added to semimagic 128,130Sn cores. These results indicate that the particle-core coupling scheme is appropriate for the Sb isotopes, whilst less so for the In isotopes. B(E2) excitation strengths are also calculated, and show evidence of enhanced collectivity in both Sb isotopes, especially 131Sb. This observation suggests that 131Sb would be an excellent case for an experimental study seeking to investigate the early onset of collectivity near 132Sn.

Excited states in $^{137}\mathrm{Cs}$ have been studied by using the near-barrier, single-proton transfer reaction $^{10}\mathrm{B}(^{136}\mathrm{Xe},\phantom{\rule{4pt}{0ex}}^{9}\mathrm{Be}\ensuremath{\gamma})^{137}\mathrm{Cs}$ in inverse kinematics and performing particle-$\ensuremath{\gamma}$ and particle-$\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence measurements. The low-spin level scheme of $^{137}\mathrm{Cs}$ has been augmented: (i) The expected set of single-proton, seniority $\ensuremath{\upsilon}=1$ states has been delineated in its entirety; (ii) Another member of the $\ensuremath{\upsilon}=3$ proton $0{g}_{7/2}$ multiplet, a low-lying $9/{2}^{+}$ level, has been identified and this set of states now approaches completion; (iii) A second $9/{2}^{+}$ and a candidate $13/{2}^{+}$ level have been observed. The results are discussed in the framework of shell-model calculations in the proton $2s1d0g0h$ shell.

A new detection system has been installed at the RIKEN Nishina Center (Japan) to investigate decay properties of very neutron-rich nuclei. The setup consists of three main parts: a moderated neutron counter , a detection system sensitive to the implantation and decay of radioactive ions, and γ -ray detectors. We describe here the setup, the commissioning experiment and some selected results demonstrating its performance for the measurement of half-lives and β -delayed neutron emission probabilities. The methodology followed in the analysis of the data is described in detail. Particular emphasis is placed on the correction of the accidental neutron background.

© 2017 Elsevier B.V. We have characterized, for the first time, an n-type segmented inverted coaxial point-contact detector. This novel detector technology relies on a large variation in drift time of the majority charge carriers, as well as image and net charges observed on the segments, to achieve a potential γ-ray interaction position resolution of better than 1 mm. However, the intrinsic energy resolution in this detector is poor (more than 20 keV at 1332 keV) because of charge (electron) trapping effects. We propose an algorithm that enables restoration of the resolution to a value of 3.44 ± 0.03 keV at 1332 keV for events with a single interaction. The algorithm is based on a measurement of the azimuthal angle and the electron drift time of a given event; the energy of the event is corrected as a function of these two values.

Electromagnetic properties of atomic nuclei such as $E2$ transition rates and $M1$ magnetic moments (or $g$ factors) are crucial characteristics of structure. For unstable nuclei produced as reaccelerated radioactive beams, measurements of $g$ factors present numerous challenges. This paper develops the important recoil-in-vacuum technique to obtain a $g$ factor for the ${2}^{+}$ state in ${}^{136}$Te. The result fits existing systematics but also highlights anomalous values in other $N=84$ isotones, thus presenting an important challenge to theory in the region just above doubly magic ${}^{132}$Sn.

Radioactive ^{136}Te has two valence protons and two valence neutrons outside of the ^{132}Sn double shell closure, providing a simple laboratory for exploring the emergence of collectivity and nucleon-nucleon interactions. Coulomb excitation of ^{136}Te on a titanium target was utilized to determine an extensive set of electromagnetic moments for the three lowest-lying states, including B(E2;0_{1}^{+}→2_{1}^{+}), Q(2_{1}^{+}), and g(2_{1}^{+}). The results indicate that the first-excited state, 2_{1}^{+}, composed of the simple 2p⊕2n system, is prolate deformed, and its wave function is dominated by excited valence neutron configurations, but not to the extent previously suggested. It is demonstrated that extreme sensitivity of g(2_{1}^{+}) to the proton and neutron contributions to the wave function provides unique insight into the nature of emerging collectivity, and g(2_{1}^{+}) was used to differentiate among several state-of-the-art theoretical calculations. Our results are best described by the most recent shell model calculations.

International audience; A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich $^{110}$Ru (t$_{1/2}$= 12 s) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations.

New levels and $\ensuremath{\gamma}$-ray transitions were identified in $^{150,152}\mathrm{Sm}$ utilizing the $(p,t)$ reaction and particle-$\ensuremath{\gamma}$ coincidence data. A large, peak-like structure observed between 2.3--3.0 MeV in excitation energy in the triton energy spectra was also investigated. The orbital angular-momentum transfer was probed by comparing the experimental angular distributions of the outgoing tritons to calculated distorted wave Born approximation curves. The angular distributions of the outgoing tritons populating the peak-like structure are remarkably similar in the two reactions and are significantly different from the angular distributions associated with the nearby continuum region. Relative partial cross sections for the observed levels, angle averaged between 34 and 58 degrees, were measured. In $^{150}\mathrm{Sm}$, 39(4)% of the strength of the peak-like structure could be accounted for by the observed discrete states. This compares with a value of 93(15)% for $^{152}\mathrm{Sm}$.

Radioactive ^{136}Te has two valence protons and two valence neutrons outside of the ^{132}Sn double shell closure, providing a simple laboratory for exploring the emergence of collectivity and nucleon-nucleon interactions. Coulomb excitation of ^{136}Te on a titanium target was utilized to determine an extensive set of electromagnetic moments for the three lowest-lying states, including B(E2;0_{1}^{+}→2_{1}^{+}), Q(2_{1}^{+}), and g(2_{1}^{+}). The results indicate that the first-excited state, 2_{1}^{+}, composed of the simple 2p⊕2n system, is prolate deformed, and its wave function is dominated by excited valence neutron configurations, but not to the extent previously suggested. It is demonstrated that extreme sensitivity of g(2_{1}^{+}) to the proton and neutron contributions to the wave function provides unique insight into the nature of emerging collectivity, and g(2_{1}^{+}) was used to differentiate among several state-of-the-art theoretical calculations. Our results are best described by the most recent shell model calculations.

Excited states in 137Xe have been studied by using the near-barrier single-neutron transfer reactions 13C(136Xe,12C )137Xe and 9Be(136Xe,8Be )137Xe in inverse kinematics.Particle- and particle- coincidence measurements have been performed with the Phoswich Wall and Digital Gammasphere detector arrays. Evidence is found for a 13/2+2 level (E = 3137 keV) and for additional high-lying 3/2– and 5/2– states. The results are discussed in the framework of realistic shell-model calculations. These calculations are also extended to the 13/2+1 and 13/2+2 levels in the N = 83 isotonic chain. Furthermore, they indicate that there is a need for a value of the neutron 0i13/2 single-particle energy (ESPE = 2366 keV) lower than the one proposed in the literature. It is also demonstrated that the population patterns of the j = l ± 1/2 single-particle states in 137Xe are different for the two targets used in these measurements and the implications of this effect are addressed.

Background: The Cd isotopes are well studied, but experimental data for the rare isotopes are sparse. At energies above the Coulomb barrier, higher states become accessible.Purpose: Remeasure and supplement existing lifetimes and magnetic moments of low-lying states in $^{106}\mathrm{Cd}$.Methods: In an inverse kinematics reaction, a $^{106}\mathrm{Cd}$ beam impinging on a $^{12}\mathrm{C}$ target was used to Coulomb excite the projectiles. The high recoil velocities provide a unique opportunity to measure $g$ factors with the transient-field technique and to determine lifetimes from lineshapes by using the Doppler-shift-attenuation method. Large-scale shell-model calculations were carried out for $^{106}\mathrm{Cd}$.Results: The $g$ factors of the ${2}_{1}^{+}$ and ${4}_{1}^{+}$ states in $^{106}\mathrm{Cd}$ were measured to be $g({2}_{1}^{+})=+0.398(22)$ and $g({4}_{1}^{+})=+0.23(5)$. A lineshape analysis yielded lifetimes in disagreement with published values. The new results are $\ensuremath{\tau}(^{106}\mathrm{Cd};{2}_{1}^{+})=7.0(3)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ and $\ensuremath{\tau}(^{106}\mathrm{Cd};{4}_{1}^{+})=2.5(2)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$. The mean life $\ensuremath{\tau}(^{106}\mathrm{Cd};{2}_{2}^{+})=0.28(2)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ was determined from the fully-Doppler-shifted $\ensuremath{\gamma}$ line. Mean lives of $\ensuremath{\tau}(^{106}\mathrm{Cd};{4}_{3}^{+})=1.1(1)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ and $\ensuremath{\tau}(^{106}\mathrm{Cd};{3}_{1}^{\ensuremath{-}})=0.16(1)\phantom{\rule{4.pt}{0ex}}\mathrm{ps}$ were determined for the first time.Conclusions: The newly measured $g({4}_{1}^{+})$ of $^{106}\mathrm{Cd}$ is found to be only 59% of the $g({2}_{1}^{+})$. This difference cannot be explained by either shell-model or collective-model calculations.

In this study, the presence of neutron transfer channels with positive Q values can enhance sub-barrier fusion cross sections. Recent measurements of the fusion excitation functions for 58Ni+132,124Sn found that the fusion enhancement due to the influence of neutron transfer is smaller than that in 40Ca +132,124Sn although the Q values for multineutron transfer are comparable. The purpose of this study is to investigate the differences observed between the fusion of Sn + Ni and Sn + Ca. Methods: Fusion excitation functions for 46,50Ti +124Sn have been measured at energies near the Coulomb barrier. As a result, a comparison of the barrier distributions for 46Ti+124Sn and 40Ca+124Sn shows that the 40Ca+124Sn system has a barrier strength resulting from the coupling to the very collective octupole state in 40Ca at an energy significantly lower than the uncoupled barrier. In conclusion, the large sub-barrier fusion enhancement in 40Ca induced reactions is attributed to both couplings to neutron transfer and inelastic excitation, with the octupole vibration of 40Ca playing a major role.

In this study, the structure of the semimagic Sn50 isotopes were previously studied via measurements of B(E2;21+ → 01+) and g factors of 21+ states. The values of the B(E2;21+) in the isotopes below midshell at N = 66 show an enhancement in collectivity, contrary to predictions from shell-model calculations. This work presents the first measurement of the 21+ and 41+ states' magnetic moments in the unstable neutron-deficient 110Sn. The g factors provide complementary structure information to the interpretation of the observed B(E2) values.

The $\ensuremath{\gamma}$-ray strength function and level density in the quasi-continuum of $^{151,153}\mathrm{Sm}$ have been measured using bismuth germanate shielded Ge clover detectors of the STARLiTeR system. The Compton shields allow an extraction of the $\ensuremath{\gamma}$ strength down to unprecedentedly low $\ensuremath{\gamma}$ energies of $\ensuremath{\approx}500$ keV. For the first time an enhanced low-energy $\ensuremath{\gamma}$-ray strength has been observed in the rare-earth region. In addition, for the first time both the upbend and the well-known scissors resonance have been observed simultaneously for the same nucleus. Hauser-Feshbach calculations show that this strength enhancement at low $\ensuremath{\gamma}$ energies could have an impact of 2--3 orders of magnitude on the ($n,\ensuremath{\gamma}$) reaction rates for $r$-process nucleosynthesis.

The emission of γ rays from neutron-bound and neutron-unbound states in Mo95, populated in the Mo94(d,p) reaction, has been investigated. Charged particles and γ radiation were detected with arrays of annular silicon and Clover-type high-purity Germanium detectors, respectively. Utilizing p-γ and p-γ-γ coincidences, the Mo95 level scheme was greatly enhanced with 102 new transitions and 43 new states. It agrees well with shell model calculations for excitation energies below ≈2 MeV. From p-γ coincidence data, a new method for the determination of spins of discrete levels is proposed. The method exploits the suppression of high-angular momentum neutron emission from levels with high spins populated in the (d,p) reaction above the neutron separation energy. Spins for almost all Mo95 levels below 2 MeV (and for a few levels above) have been determined with this method.

The quadrupole collectivity of low-lying states and the anomalous behavior of the $0^+_2$ and $2^+_3$ levels in $^{72}$Ge are investigated via projectile multi-step Coulomb excitation with GRETINA and CHICO-2. A total of forty six $E2$ and $M1$ matrix elements connecting fourteen low-lying levels were determined using the least-squares search code, gosia. Evidence for triaxiality and shape coexistence, based on the model-independent shape invariants deduced from the Kumar-Cline sum rule, is presented. These are interpreted using a simple two-state mixing model as well as multistate mixing calculations carried out within the framework of the triaxial rotor model. The results represent a significant milestone towards the understanding of the unusual structure of this nucleus., Comment: 7 pages and 7 figures

The synthesis of Coulomb excitation and β decay offers very practical advantages in the study of nuclear shapes and collectivity. For instance, Coulomb excitation is unique in its ability to measure the electric quadrupole moments, i.e., 〈I 2π∥M(E2)∥I1π〉$\langle I_2^\pi \parallel M(E2)\parallel I_1^\pi \rangle $ matrix elements, of excited, non-isomeric states in atomic nuclei, providing information on the intrinsic shape. However, the Coulomb excitation analysis and structural interpretation can be strongly dependent upon weak transitions or decay branches, which are often obscured by the Compton background. Transitions of particular interest are those low in energy and weak in intensity due to the Eγ5 attenuation factor. These weak decay branches can often be determined with high precision from β-decay studies. Recently, 106Mo and 110Cd were studied by both Coulomb excitation and β decay. Preliminary results of new weak decay branches following β decay of 110mAg to 110Cd are presented; these results will challenge competing interpretations based on vibrations and configuration mixing.

A new and model-independent experimental method has been developed to determine the energy dependence of the photon strength function. It is designed to study statistical feeding from the quasi continuum to individual low-lying discrete levels. This new technique is presented and results for 95Mo are compared to data from the University of Oslo. In particular, questions regarding the existence of the low-energy enhancement in the photon strength function are addressed.

We report results from an experiment on the decay of the high-K isomers in 254No. We have been able to establish the decay from the known high-lying four-quasiparticle isomer, which we assign as a K π = 16 + state at an excitation energy of E x = 2.928 ( 3 ) MeV . The decay of this state passes through a rotational band based on a previously unobserved state at E x = 2.012 ( 2 ) MeV , which we suggest is based on a two-quasineutron configuration with K π = 10 + . This state in turn decays to a rotational band based on the known K π = 8 − isomer, which we infer must also have a two quasineutron configuration. We are able to assign many new gamma-rays associated with the decay of the K π = 8 − isomer, including the identification of a highly K-forbidden Δ K = 8 E1 transition to the ground-state band. These results provide valuable new information on the orbitals close to the Fermi surface, pairing correlations, deformation and rotational response, and K-conservation in nuclei of the deformed trans-fermium region.

An ambitious program to measure decay properties, primarily β-delayed neutron emission probabilities and half-lives, for a significant number of nuclei near or on the path of the rapid neutron capture process, has been launched at the RIKEN Nishina Center. We give here an overview of the status of the project.

To evaluate the effect of neutron damage on the performance of highly segmented germanium detectors the P3 prototype detector for the GRETINA array was subjected to a neutron flux of ∼3×109 n/cm2 over a period of 5 days. During the irradiation, the resolution (full-width half-maximum (FWHM)) of the 1332 keV 60Co photopeak increased from ∼1.8 to ∼6.0 keV while the full-width at tenth maximum (FWTM) increased from ∼4 keV to more than 12 keV. Following the irradiation the detector was successfully annealed and the energy resolution returned to pre-irradiation values. All detector segments were fully functional before and after the annealing and following multiple room-temperature cycles. A comparison of digitized pulse shapes in the damaged and annealed detector indicates that the effect of extreme neutron damage (FWHM=6 keV) on the position resolution is on the order of ∼1.7 mm while for 3 keV resolution the position resolution degrades by ∼0.5 mm.

A complete set of electromagnetic moments, B(E2;0+1 2+1), Q(2+1), and g(2+1), have been measured from Coulomb excitation of semi-magic 112,114,116,118,120,122,124Sn (Z = 50) on natural carbon and titanium targets. The magnitude of the B(E2) values, measured to a precision of ~4%, disagree with a recent lifetime study [Phys. Lett. B 695, 110 (2011)] that employed the Doppler- shift attenuation method. The B(E2) values show an overall enhancement compared with recent theoretical calculations and a clear asymmetry about midshell, contrary to naive expectations. A new static electric quadrupole moment, Q(2+1), has been measured for 114Sn. The static quadrupole moments are generally consistent with zero but reveal an enhancement near midshell; this had not been previously observed. The magnetic dipole moments are consistent with previous measurements and show a near monotonic decrease in value with neutron number. The current theory calculations fail to reproduce the electromagnetic moments of the tin isotopes. The role of 2p-2h and 4p-4h intruders, which are lowest in energy at mid shell and outside of current model spaces, needs to be investigated in the future.

The experimental signature in searches for the neutrinoless double-$\ensuremath{\beta}$ decay of $^{76}\mathrm{Ge}$ is a peak near 2039 keV in the spectrum. Given the low probability of the process, it is important that the background in this region be well understood. Inelastic scattering reactions with neutrons from muon-induced interactions and $(\ensuremath{\alpha},n)$ reactions in the surrounding materials or in the detector can provide contributions to the background. We have measured the production cross sections for $\ensuremath{\gamma}$ rays from the $^{76}\mathrm{Ge}(n,{n}^{\ensuremath{'}}\ensuremath{\gamma})$ reaction in the 2039-keV region at incident neutron energies up to 4.9 MeV. In addition to determining that the cross sections of a previously known 2040.7-keV $\ensuremath{\gamma}$ ray from the 3952-keV level in $^{76}\mathrm{Ge}$ are rather small, we find that a larger contribution arises from a 2037.5-keV $\ensuremath{\gamma}$ ray which is attributed to a newly identified level at 3147 keV in $^{76}\mathrm{Ge}$. A third contribution is also possible from another new level at 3577 keV. These results indicate that the 2039-keV region in $^{76}\mathrm{Ge}$ neutrinoless double-$\ensuremath{\beta}$ decay searches is more complex than was previously thought.

The nuclear structure of $^{124}\mathrm{Xe}$ has been investigated via measurements of the ${\ensuremath{\beta}}^{+}$/EC decay of $^{124}\mathrm{Cs}$ with the $8\ensuremath{\pi}\ensuremath{\gamma}$-ray spectrometer at the TRIUMF-ISAC facility. The data collected have enabled branching ratio measurements of weak, low-energy transitions from highly excited states, and the ${2}^{+}\ensuremath{\rightarrow}{0}^{+}$ in-band transitions have been observed. Combining these results with those from a previous Coulomb excitation study, $B(E2;{2}_{3}^{+}\ensuremath{\rightarrow}{0}_{2}^{+})=78(13)$ W.u. and $B(E2;{2}_{4}^{+}\ensuremath{\rightarrow}{0}_{3}^{+})=53(12)$ W.u. were determined. The ${0}_{3}^{+}$ state, in particular, is interpreted as the main fragment of the proton-pairing vibrational band identified in a previous $^{122}\mathrm{Te}$($^{3}\mathrm{He},n$)$^{124}\mathrm{Xe}$ measurement, and has quadrupole collectivity equal to, within uncertainty, that of the ground-state band.