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12 pags., 16 figs., 2 tabs., Background: Neutron-rich nuclei around neutron number N=60 show a dramatic shape transition from spherical ground states to prolate deformation in Sr98 and heavier nuclei. Purpose: The purpose of this study is to investigate the single-particle structure approaching the shape transitional region. Method: The level structures of neutron-rich Sr93,94,95 were studied via the H2(Sr94,95,96,t) one-neutron stripping reactions at TRIUMF using a beam energy of 5.5 AMeV. γ-rays emitted from excited states and recoiling charged particles were detected by using the TIGRESS and SHARC arrays, respectively. States were identified by gating on the excitation energy and, if possible, the coincident γ radiation.Results: Triton angular distributions for the reactions populating states in ejectile nuclei Sr93,94,95 were compared with distorted wave Born approximation calculations to assign and revise spin and parity quantum numbers and extract spectroscopic factors. The results were compared with shell-model calculations and the reverse (d,p) reactions and good agreement was obtained. Conclusions: The results for the H2(Sr94,t)Sr93 and H2(Sr95,t)Sr94 reactions are in good agreement with shell-model calculations. A two-level mixing analysis for the 0+ states in Sr94 suggest strong mixing of two shapes. For the H2(Sr96,t)Sr95 reaction the agreement with the shell-model is less good. The configuration of the ground state of Sr96 is already more complex than predicted, and therefore indications for the shape transition can already be observed before N=60., We acknowledge support from the Science and Technologies Facility Council (UK, Grants No. EP/D060575/1 and No. ST/L005727/1), the National Science Foundation (US, Grant No. PHY-1306297), the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation and the British Columbia Knowledge and Development Fund. TRIUMF receives federal funding via a contribution through the National Research Council Canada. K.W. acknowledges the support from the Spanish Ministerio de Economía, Industria y Competitividad, Gobierno de España RYC-2017-22007.

From detailed spectroscopy of ^{110}Cd and ^{112}Cd following the β^{+}/electron-capture decay of ^{110,112}In and the β^{-} decay of ^{112}Ag, very weak decay branches from nonyrast states are observed. The transition rates determined from the measured branching ratios and level lifetimes obtained with the Doppler-shift attenuation method following inelastic neutron scattering reveal collective enhancements that are suggestive of a series of rotational bands. In ^{110}Cd, a γ band built on the shape-coexisting intruder configuration is suggested. For ^{112}Cd, the 2^{+} and 3^{+} intruder γ-band members are suggested, the 0_{3}^{+} band is extended to spin 4^{+}, and the 0_{4}^{+} band is identified. The results are interpreted using beyond-mean-field calculations employing the symmetry conserving configuration mixing method with the Gogny D1S energy density functional and with the suggestion that the Cd isotopes exhibit multiple shape coexistence.

From detailed spectroscopy of ^{110}Cd and ^{112}Cd following the β^{+}/electron-capture decay of ^{110,112}In and the β^{-} decay of ^{112}Ag, very weak decay branches from nonyrast states are observed. The transition rates determined from the measured branching ratios and level lifetimes obtained with the Doppler-shift attenuation method following inelastic neutron scattering reveal collective enhancements that are suggestive of a series of rotational bands. In ^{110}Cd, a γ band built on the shape-coexisting intruder configuration is suggested. For ^{112}Cd, the 2^{+} and 3^{+} intruder γ-band members are suggested, the 0_{3}^{+} band is extended to spin 4^{+}, and the 0_{4}^{+} band is identified. The results are interpreted using beyond-mean-field calculations employing the symmetry conserving configuration mixing method with the Gogny D1S energy density functional and with the suggestion that the Cd isotopes exhibit multiple shape coexistence.

The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult---if not impossible---to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. In this Letter we demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the $(d,p)$ transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the $^{95}\mathrm{Mo}(d,p)$ reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators.

The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult-if not impossible-to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. In this Letter we demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the (d,p) transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the ^{95}Mo(d,p) reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators.

The low energy excited $0_{2,3}^+$ states in $^{96}$Sr are amongst the most prominent examples of shape coexistence across the nuclear landscape. In this work, the neutron $[2s_{1/2}]^2$ content of the $0_{1,2,3}^+$ states in $^{96}$Sr was determined by means of the d($^{95}$Sr,p) transfer reaction at the TRIUMF-ISAC2 facility using the SHARC and TIGRESS arrays. Spectroscopic factors of 0.19(3) and 0.22(3) were extracted for the $^{96}$Sr ground and 1229~keV $0^+$ states, respectively, by fitting the experimental angular distributions to DWBA reaction model calculations. A detailed analysis of the $\gamma$-decay of the isomeric $0_3^+$ state was used to determine a spectroscopic factor of 0.33(13). The experimental results are compared to shell model calculations, which predict negligible spectroscopic strength for the excited $0^+$ states in $^{96}$Sr. The strengths of the excited $0_{2,3}^+$ states were also analyzed within a two-level mixing model and are consistent with a mixing strength of $a^2$=0.40(14) and a difference in intrinsic deformations of $|\Delta \beta|=0.31(3)$. These results suggest coexistence of three different configurations in $^{96}$Sr and strong shape mixing of the two excited $0^+$ states., Comment: Phys Lett B accepted

Author(s): Munson, JM; Norman, EB; Burke, JT; Casperson, RJ; Phair, LW; McCleskey, E; McCleskey, M; Lee, D; Hughes, RO; Ota, S; Czeszumska, A; Chodash, PA; Saastamoinen, AJ; Austin, RAE; Spiridon, AE; Dag, M; Chyzh, R; Basunia, MS; Ressler, JJ; Ross, TJ | Abstract: The nuclear reactions C12(C12,α)Ne20, C12(C12,p)Na23, and C12(C12,n)Mg23 are the primary reactions in carbon burning, which occurs as part of several stellar processes. The Gamow window, which describes the energy range where most of these reactions take place, is typically around 1.5 MeV in the center-of-mass frame. Direct measurements of the cross sections at this energy are difficult due to the large Coulomb barrier present between the carbon nuclei; however, a successful surrogate measurement can provide the branching ratios between these reactions while avoiding the C12+C12 Coulomb barrier. An experiment was performed using inelastic scattering of 40 MeV α particles on Mg24 as a possible surrogate for the C12+C12 compound nucleus.

The TIGRESS Integrated Plunger device is a new experimental tool for nuclear structure investigations via gamma-ray spectroscopy with post-accelerated beams from the ISAC-II facility at TRIUMF. Several ancillary detection systems integral to the device׳s capabilities for charged-particle tagging and light-ion identification following a variety of nuclear reaction mechanisms have been constructed and characterized. In particular, a silicon PIN diode wall, an annular silicon segmented detector, and a CsI(Tl) scintillator wall have together enabled particle-gamma correlations for reaction channel selectivity and precision kinematic reconstruction in recent measurements. We highlight the construction, characteristics, and implementation of the device׳s ancillary detectors as they enable a rich set of electromagnetic transition rate measurements via Doppler-shift lifetime techniques and low-energy Coulomb excitation.

The low-energy identification station at SPIRAL (Systeme de Production d'Ions Radioactifs Acceleres en Ligne) has been upgraded for studying the β decays of short-lived radioactive isotopes and to perform high-precision half-life and branching-ratio measurements for superallowed Fermi and isospin T= 1 / 2 mirror β decays. These new capabilities, combined with an existing Paul trap setup for measurements of β–ν angular-correlation coefficients, provide a powerful facility for investigating fundamental properties of the electroweak interaction through nuclear β decays. A detailed description of the design study, construction, and first results obtained from an in-beam commissioning experiment on the β+ decays 14 O and 17F are presented.

High precision measurements of the $ft$ values for superallowed Fermi $\beta$ transitions between $J^\pi~=~0^+$ isobaric analogue states allow for stringent tests of the electroweak interaction described by the Standard Model. These transitions provide an experimental probe of the Conserved-Vector-Current hypothesis, enable the most precise determination of the up-down ($V_{ud}$) element of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix, and allow one to set stringent limits on the existence of scalar currents in the weak interaction. An extensive program of superallowed branching-ratio and half-life measurements at TRIUMF's Isotope Separator and Accelerator (ISAC) facility has covered the full range of superallowed emitters, from the lightest case, $^{10}$C, to the heaviest case for which precision data are currently available, $^{74}$Rb. These experiments have been performed using a 4$\pi$ continuous-flow gas proportional $\beta$ counter, the 8$\pi$ $\gamma$-ray spectrometer, and, most recently, the new high-efficiency GRIFFIN $\gamma$-ray spectrometer. In this paper, recent highlights from the superallowed Fermi $\beta$ decay program at TRIUMF will be summarized, including high-precision half-life measurements for all three of the lightest superallowed emitters, $^{10}$C, $^{14}$O, and $^{18}$Ne, with the greatest sensitivity to a potential weak scalar current contribution, as well as high-precision branching-ratio measurements for the heavy superallowed emitters $^{62}$Ga and $^{74}$Rb.

Precision measurements of superallowed Fermi β-decay transitions, particularly for the lightest superallowed emitters ^{10}C and ^{14}O, set stringent limits on possible scalar current contributions to the weak interaction. In the present work, a discrepancy between recent measurements of the ^{10}C half-life is addressed through two high-precision half-life measurements, via γ-ray photopeak and β counting, that yield consistent results for the ^{10}C half-life of T_{1/2}=19.2969±0.0074 s and T_{1/2}=19.3009±0.0017 s, respectively. The latter is the most precise superallowed β-decay half-life measurement reported to date and the first to achieve a relative precision below 10^{-4}. A fit to the world superallowed β-decay data including the ^{10}C half-life measurements reported here yields b_{F}=-0.0018±0.0021 (68% C.L.) for the Fierz interference term and C_{S}/C_{V}=+0.0009±0.0011 for the ratio of the weak scalar to vector couplings assuming left-handed neutrinos.

Precision measurements of superallowed Fermi β-decay transitions, particularly for the lightest superallowed emitters ^{10}C and ^{14}O, set stringent limits on possible scalar current contributions to the weak interaction. In the present work, a discrepancy between recent measurements of the ^{10}C half-life is addressed through two high-precision half-life measurements, via γ-ray photopeak and β counting, that yield consistent results for the ^{10}C half-life of T_{1/2}=19.2969±0.0074 s and T_{1/2}=19.3009±0.0017 s, respectively. The latter is the most precise superallowed β-decay half-life measurement reported to date and the first to achieve a relative precision below 10^{-4}. A fit to the world superallowed β-decay data including the ^{10}C half-life measurements reported here yields b_{F}=-0.0018±0.0021 (68% C.L.) for the Fierz interference term and C_{S}/C_{V}=+0.0009±0.0011 for the ratio of the weak scalar to vector couplings assuming left-handed neutrinos.

We studied the low-spin structure of odd-odd 88Y via (p,dγ) reactions on an 89Y target. The K150 Cyclotron at the Texas A&M University Cyclotron Institute was employed to provide a 28.5-MeV proton beam, and particle-γ and particle-γ-γ coincidence data were collected with the STARLiTeR array. Moreover, a number of new levels and γ rays have been observed below 2.5 MeV, while level and γ-ray energies as well as spin-parity assignments have been re-evaluated.

The effect of the production mechanism on the decay of a compound nucleus is investigated. The nucleus $^{90}\mathrm{Zr}$ was produced by three different reactions, namely $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}})^{90}\mathrm{Zr}$, $^{91}\mathrm{Zr}(p,d)^{90}\mathrm{Zr}$, and $^{92}\mathrm{Zr}(p,t)^{90}\mathrm{Zr}$, which served as surrogate reactions for $^{89}\mathrm{Zr}(n,\ensuremath{\gamma})$. The spin-parity $({J}^{\ensuremath{\pi}})$ distributions of the states populated by these reactions were studied to investigate the surrogate reaction approach, which aims at indirectly determining cross sections for compound-nuclear reactions involving unstable targets such as $^{89}\mathrm{Zr}$. Discrete $\ensuremath{\gamma}$ rays, associated with transitions in $^{90}\mathrm{Zr}$ and $^{89}\mathrm{Zr}$, were measured in coincidence with light ions for scattering angles of ${25}^{\ensuremath{\circ}}--{60}^{\ensuremath{\circ}}$ and $^{90}\mathrm{Zr}$ excitation energies extending above the neutron separation energy. The measured transition systematics were used to gain insights into the ${J}^{\ensuremath{\pi}}$ distributions of $^{90}\mathrm{Zr}$. The $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}})$ reaction was found to produce fewer $\ensuremath{\gamma}$ rays associated with transitions involving high spin states $(J=6--8\phantom{\rule{4.pt}{0ex}}\ensuremath{\hbar})$ than the other two reactions, suggesting that inelastic scattering preferentially populates states in $^{90}\mathrm{Zr}$ that have lower spins than those populated in the transfer reactions investigated. The $\ensuremath{\gamma}$-ray production was also observed to vary by factors of 2--3 with the angle at which the outgoing particle was detected. These findings are relevant to the application of the surrogate reaction approach.

The wave-function composition for the low-lying states in 29 Na was explored by measuring their electromagnetic properties using the Coulomb-excitation technique. A beam of 29 Na ions, postaccelerated to 70 MeV, bombarded a 110 Pd target with a rate of up to 600 particles per second at the recently commissioned ISAC-II facility at TRIUMF. Six segmented HPGe clover detectors of the TIGRESS γ -ray spectrometer were used to detect deexcitation γ rays in coincidence with scattered or recoiling charged particles in the segmented silicon detector, BAMBINO. The reduced transition matrix element | 〈 5 2 1 + | | E 2 | | 3 2 gs + 〉 | in 29 Na was derived to be 0.237(21) e b from the measured γ -ray yields for both projectile and target. This first-time measured value is consistent with the most recent Monte Carlo shell-model calculation, indicating a significant admixture of both sd and pf components in the wave function, and also providing evidence for the narrowing of the neutron s d – p f shell gap from ∼ 6 MeV for stable nuclei to ∼ 3 MeV for 29 Na.

A general technique that corrects γ -ray gated β decay-curve data for detector pulse pile-up is presented. The method includes corrections for non-zero time-resolution and energy-threshold effects in addition to a special treatment of saturating events due to cosmic rays. This technique is verified through a Monte Carlo simulation and experimental data using radioactive beams of Na 26 implanted at the center of the 8 π γ -ray spectrometer at the ISAC facility at TRIUMF in Vancouver, Canada. The β -decay half-life of Na 26 obtained from counting 1809-keV γ -ray photopeaks emitted by the daughter Mg 26 was determined to be T 1 / 2 = 1.07167 ± 0.00055 s following a 27 σ correction for detector pulse pile-up. This result is in excellent agreement with the result of a previous measurement that employed direct β counting and demonstrates the feasibility of high-precision β -decay half-life measurements through the use of high-purity germanium γ -ray detectors. The technique presented here, while motivated by superallowed-Fermi β decay studies, is general and can be used for all half-life determinations (e.g. α -, β -, X-ray, fission) in which a γ -ray photopeak is used to select the decays of a particular isotope.

The isotope separator and accelerator (ISAC) facility located at the TRIUMF laboratory in Vancouver, Canada, is one of the world’s most advanced isotope separator on-line-type radioactive ion beam facilities. An extensive γ-ray spectroscopy programme at ISAC is centred around two major research facilities: (i) the 8π γ-ray spectrometer for β-delayed γ-ray spectroscopy experiments with the low-energy beams from ISAC-I, and (ii) the next generation TRIUMF-ISAC gamma-ray escape suppressed spectrometer (TIGRESS) for in-beam experiments with the accelerated radioactive-ion beams. An overview of these facilities and recent results from the diverse programme of nuclear structure and fundamental interaction studies they support is presented.

Methods of optimizing the performance of an array of Compton-suppressed, segmented HPGe clover detectors have been developed which rely on the physical position sensitivity of both the HPGe crystals and the Compton-suppression shields. These relatively simple analysis procedures promise to improve the precision of experiments with the TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). Suppression schemes will improve the efficiency and peak-to-total ratio of TIGRESS for high γ-ray multiplicity events by taking advantage of the 20-fold segmentation of the Compton-suppression shields, while the use of different summing schemes will improve results for a wide range of experimental conditions. The benefits of these methods are compared for many γ-ray energies and multiplicities using a GEANT4 simulation, and the optimal physical configuration of the TIGRESS array under each set of conditions is determined.

Tests of the performance of a 32-fold segmented HPGe clover detector coupled to a 20-fold segmented Compton-suppression shield, which form a prototype element of the TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS), have been made. Peak-to-total ratios and relative efficiencies have been measured for a variety of γ -ray energies. These measurements were used to validate a GEANT4 simulation of the TIGRESS detectors, which was then used to create a simulation of the full 12-detector array. Predictions of the expected performance of TIGRESS are presented. These predictions indicate that TIGRESS will be capable, for single 1 MeV γ rays, of absolute detection efficiencies of 17% and 9.4%, and peak-to-total ratios of 54% and 61% for the “high-efficiency” and “optimized peak-to-total” configurations of the array, respectively.

The TRIUMF-ISAC gamma-ray escape-suppressed spectrometer (TIGRESS) is a new γ-ray detector array being developed for use at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. TIGRESS will comprise 12 32-fold segmented clover-type HPGe detectors coupled with 20-fold segmented modular Compton suppression shields and custom digital signal processing electronics. This paper provides an overview of the TIGRESS project and progress in its development to date.

High-resolution γ-ray spectroscopy is essential to fully exploit the unique, high-quality beams available at the next generation of radioactive ion beam facilities such as the TRIUMF isotope separator and accelerator (ISAC). The 8π spectrometer, which consists of 20 Compton-suppressed HPGe detectors, has recently been reconfigured for a vigorous research programme in weak interaction and nuclear structure physics. With the addition of a variety of ancillary detectors it has become the world's most powerful device dedicated to β-decay studies. This paper provides a brief overview of the apparatus and highlights from recent experiments.

Sensitivity to the locations of γ -ray interactions within a 32-fold segmented clover-type HPGe detector has been investigated through 90 ∘ Compton scattering of 661.6 keV γ -rays from a collimated Cs 137 source. A mean position sensitivity of 0.44 mm at an energy of 373 keV is deduced by comparing the average pulse shapes for net charge collecting signals, as well as transient induced signals in neighbouring contacts, from 1007 pairs of three-dimensionally localized interaction points. The reconstruction of individual event locations based on a χ 2 comparison with the measured set of basis waveforms is presented.

A superdeformed rotational band has been identified in ${}^{36}\mathrm{Ar}$, linked to known low-spin states, and observed to its high-spin termination at ${I}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}16}^{+}$. Cranked Nilsson-Strutinsky and spherical shell model calculations assign the band to a configuration in which four $\mathrm{pf}$-shell orbitals are occupied, leading to a low-spin deformation ${\ensuremath{\beta}}_{2}\ensuremath{\approx}0.45$. Two major shells are active for both protons and neutrons, yet the valence space remains small enough to be confronted with the shell model. This band thus provides an ideal case to study the microscopic structure of collective rotational motion.

Results are presented of a systematic survey of {Delta}I=4 bifurcation in 19 superdeformed bands in A{approximately}150 Eu and Gd nuclei. The majority of bands show no sign of this regular oscillation in energy levels. The statistical significance of the few examples that exhibit the effect is examined. {copyright} {ital 1998} {ital The American Physical Society}

Eight superdeformed bands have been observed in the nuclei {sup 147,148}Eu. Some of these are identical to bands in the Z+1 nuclei {sup 148,149}Gd, and are interpreted as having the same single-particle configurations with the exception of a hole in one of the [301]1/2 proton orbitals. Some of the bands in {sup 147}Eu exhibit either upbends or downbends in their moments of inertia which are related to the crossing of {pi}6{sup 1} and {pi}6{sup 3} proton intruder configurations. These results constitute the first evidence of this crossing. {copyright} {ital 1998} {ital The American Physical Society}

The half-life of 14 O, a superallowed Fermi β + emitter, has been determined via simultaneous γ and β counting experiments at TRIUMF’s Isotope Separator and Accelerator facility. Following the implantation of 14 O samples at the center of the 8 π spectrometer, a γ counting measurement was performed by detecting the 2313 keV γ -rays emitted from the first excited state of the daughter 14 N using 20 high-purity germanium (HPGe) detectors. A simultaneous β counting experiment was performed using a fast plastic scintillator positioned directly behind the implantation site. The results, T ½ ( γ ) = 70:632 ± 0:094 s and T ½ ( β ) = 70:610 ± 0:030 s, are consistent with one another and, together with eight previous measurements, establish a new average for the 14 O half-life of T ½ = 70:619 ± 0:011 s with a reduced χ 2 of 0.99.

International audience; A program of high-precision half-life and branching-ratio measurements for superallowed Fermi emitters is being carried out at TRIUMF's Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14O, 18Ne, and 26Alm, as well as branching-ratio measurements for 26Alm and 74Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi decays.

In response to new opportunities presented by re-accelerated beams from the ISAC-II facility at TRIUMF, a plunger-type Recoil Distance Method device, the TIGRESS Integrated Plunger, is under construction to be used with the TIGRESS segmented germanium array. An experimental program aimed in nuclear structure measurements along the N=Z line is planned. Lifetime measurements in the shape-coexistence region near N∼Z∼36 are anticipated to provide information of significance to Vud matrix element evaluation from superallowed beta-decay measurements.

A program of high-precision superallowed Fermi β decay studies is being carried out at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. Recent high-precision branching ratio measurements for the superallowed decays of 74Rb and 26Alm, as well as a half-life measurement for 26Alm that is the most precise half-life measurement for any superallowed emitter to date, are reported. These results provide demanding tests of the theoretical isospin symmetry breaking corrections in superallowed Fermi β decays.

We report a precise determination of the $^{19}\mathrm{Ne}$ half-life to be ${T}_{1/2}=17.262\ifmmode\pm\else\textpm\fi{}0.007\text{ }\text{ }\mathrm{s}$. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current standard model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods.

A high-precision half-life measurement for the superallowed ${\ensuremath{\beta}}^{+}$ emitter $^{26}\mathrm{Al}^{m}$ was performed at the TRIUMF-ISAC radioactive ion beam facility yielding ${T}_{1/2}=6346.54\ifmmode\pm\else\textpm\fi{}{0.46}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.60}_{\mathrm{syst}}\text{ }\text{ }\mathrm{ms}$, consistent with, but 2.5 times more precise than, the previous world average. The $^{26}\mathrm{Al}^{m}$ half-life and $ft$ value, 3037.53(61) s, are now the most precisely determined for any superallowed $\ensuremath{\beta}$ decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected $\mathcal{F}t$ value for $^{26}\mathrm{Al}^{m}$, 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi $\ensuremath{\beta}$-decay studies used to test the conserved vector current hypothesis and determine the ${V}_{ud}$ element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

Nucleon transfer experiments have in recent years begun to be exploited in the study of nuclei far from stability, using radioactive beams in inverse kinematics. New techniques are still being developed in order to perform these experiments. The present experiment is designed to study the odd-odd nucleus Na which has a high density of states and therefore requires gamma-ray detection to distinguish between them. The experiment employed an intense beam of up to 3×10 pps of Na at 5.0 MeV/nucleon from the ISAC-II facility at triumf. The new silicon array SHARC was used for the first time and was coupled to the segmented clover gamma-ray array TIGRESS. A novel thin plastic scintillator detector was employed at zero degrees to identify and reject reactions occurring on the carbon component of the (CD) target. The efficiency of the background rejection using this detector is described with respect to the proton and gamma-ray spectra from the (d,p) reaction. © Published under licence by IOP Publishing Ltd.

The stable Cd isotopes have long been used as paradigms for spherical vibrational motion. Extensive investigations with in‐beam γ spectroscopy have resulted in very‐well‐established level schemes, including many lifetimes or lifetime limits. A programme has been initiated to complement these studies with very‐high‐statistics β decay using the 8π spectrometer at the TRIUMF radioactive beam facility. The decays of 112In and 112Ag have been studied with an emphasis on the observation of, or the placement of stringent limits on, low‐energy branches between potential multi‐phonon levels. A lack of suitable 0+ or 2+ three‐phonon candidates has been revealed. Further, the sum of the B(E2) strength from spin 0+ and 2+ states up to 3 MeV in excitation energy to the assigned two‐phonon levels falls far short of the harmonic‐vibrational expectations. This lack of strength points to the failing of collective models based on vibrational phonon structures.

A high-precision half-life measurement for the superallowed β+ emitter 26Al(m) was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1/2 6346.54 ± 0.46(stat) ± 0.60 (syst) ms, consistent with, but 2.5 times more precise than, the previous world average. The 26Al(m) half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed β decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for (26)Al(m), 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi β-decay studies used to test the conserved vector current hypothesis and determine the V(ud) element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

The low-energy structure of the proton dripline nucleus {sup 20}Na has been studied using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. A 1.7-MeV/nucleon {sup 20}Na beam of {approx}5x10{sup 6} ions/s was Coulomb excited by a 0.5-mg/cm{sup 2nat}Ti target. Scattered beam and target particles were detected by the BAMBINO segmented Si detector while {gamma} rays were detected by two TIGRESS HPGe clover detectors set perpendicular to the beam axis. Coulomb excitation from the 2{sup +} ground state to the first excited 3{sup +} and 4{sup +} states was observed, and B({lambda}L) values were determined using the 2{sup +}{yields}0{sup +} de-excitation in {sup 48}Ti as a reference. The resulting B({lambda}L){down_arrow} values are B(E2;3{sup +}{yields}2{sup +})=55{+-}6 e{sup 2} fm{sup 4} (17.0{+-}1.9 W.u.), B(E2;4{sup +}{yields}2{sup +})=35.7{+-}5.7 e{sup 2} fm{sup 4} (11.1{+-}1.8 W.u.), and B(M1;4{sup +}{yields}3{sup +})=0.154{+-}0.030 {mu}{sub N}{sup 2} (0.086{+-}0.017 W.u.). These measurements provide the first experimental determination of B({lambda}L) values for this proton dripline nucleus of astrophysical interest.

The $\ensuremath{\beta}$ decay of $^{11}\mathrm{Li}$ is studied at the TRIUMF Isotope Separation and Acceleration (ISAC) facility using the $8\ensuremath{\pi} \ensuremath{\gamma}$-ray spectrometer coupled with an inner array of $20$ plastic scintillators for $\ensuremath{\beta}$ detection. Doppler-broadened line shapes resulting from the decay of the excited states in $^{10}\mathrm{Be}$ populated by $\ensuremath{\beta}$-delayed one-neutron emission are analyzed using Monte Carlo simulations. New $\ensuremath{\beta}$-delayed neutron decay branches are shown to contribute to the complex decay of $^{11}\mathrm{Li}$. The half-lives of all but one bound excited state in $^{10}\mathrm{Be}$ are also deduced from this work. Among them, the half-life of the ${2}^{\ensuremath{-}}$ state in $^{10}\mathrm{Be}$ is shown to be much shorter than previously thought, yielding a new experimental $B(E1)$ now well within the range of theoretical predictions and providing further evidence that the ${2}^{\ensuremath{-}}$ state in $^{10}\mathrm{Be}$ is an excited halo state. The nature of the $8.82$-MeV state in $^{11}\mathrm{Be}$ and its decay paths to excited states in $^{10}\mathrm{Be}$ are found to be consistent with the $\ensuremath{\beta}$ decay of the core proceeding through this particular state.

High-statistics $\ensuremath{\beta}$-decay measurements of $^{112}\mathrm{Ag}$ and $^{112}\mathrm{In}$ were performed to study the structure of the $^{112}\mathrm{Cd}$ nucleus. The precise energies of the doublet of levels at 1871 keV, for which the ${0}^{+}$ member has been suggested as a possible daughter state following neutrinoless double electron capture of $^{112}\mathrm{Sn}$, were determined to be 1871.137(72) keV (${0}_{4}^{+}$ level) and 1870.743(54) keV (${4}_{2}^{+}$ level). The nature of the ${0}_{4}^{+}$ level, required for the calculation of the nuclear matrix element that would be needed to extract a neutrino mass from neutrinoless double electron capture to this state, is suggested to be of intruder origin.

The low-energy structures of the radioactive nuclei 20, 21Na have been examined using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of ∼ 5×106 ions/s were accelerated to 1.7MeV/A and Coulomb excited in a 0.5mg/cm^2 natTi target. Two TIGRESS HPGe clover detectors perpendicular to the beam axis were used for $ \gamma$ -ray detection, while scattered nuclei were observed by the Si detector BAMBINO. For 21Na , Coulomb excitation from the 3/2+ ground state to the first excited 5/2+ state was observed, while for 20Na , Coulomb excitation was observed from the 2+ ground state to the first excited 3+ and 4+ states. For both beams, B ( $ \lambda$ L) values were determined using the 2+ $ \rightarrow$ 0+ de-excitation in 48Ti as a reference. The resulting B(E2) ↓ value for 21Na is 137±9 e^2fm^4, while the resulting B( $ \lambda$ L) ↓ values for 20Na are 55±6 e^2fm^4 for the 3+ $ \rightarrow$ 2+ , 35.7±5.7 e^2 fm^4 for the 4+ $ \rightarrow$ 2+ , and 0.154±0.030 μ_N^2 for the 4+ $ \rightarrow$ 3+ transitions. This analysis significantly improves the measurement of the 21Na B(E2) value, and provides the first experimental determination of B( $ \lambda$ L) values for the proton dripline nucleus 20Na .-1

The TRIUMF‐ISAC Gamma‐Ray Escape Suppressed Spectrometer (TIGRESS) is a state‐of‐the‐art γ‐ray spectrometer being constructed at the ISAC‐II radioactive ion beam facility at TRIUMF. TIGRESS will be comprised of twelve 32‐fold segmented high‐purity germanium (HPGe) clover‐type γ‐ray detectors, with BGO∕CsI(Tl) Compton‐suppression shields, and is currently operational at ISAC‐II in an early‐implementation configuration of six detectors. Results have been obtained for the first experiments performed using TIGRESS, which examined the A = 20, 21, and 29 isotopes of Na by Coulomb excitation.

The low-energy structures of the mirror nuclei {sup 21}Ne and radioactive {sup 21}Na have been examined by using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of {approx}5x10{sup 6} ions/s were accelerated to 1.7 MeV/A and Coulomb excited in a 0.5 mg/cm{sup 2} {sup nat}Ti target. Scattered beam and target particles were detected by the segmented Si detector BAMBINO, while {gamma} rays were observed by using two TIGRESS HPGe clover detectors perpendicular to the beam axis. For each isobar, Coulomb excitation from the (3/2){sup +} ground state to the first excited (5/2){sup +} state was observed and B(E2) values were determined by using the 2{sup +}{yields}0{sup +} de-excitation in {sup 48}Ti as a reference. The {phi} segmentation of BAMBINO was used to deduce tentative assignments for the signs of the mixing ratios between the E2 and M1 components of the transitions. The resulting B(E2){up_arrow} values are 131{+-}9 e{sup 2} fm{sup 4} (25.4{+-}1.7 W.u.) for {sup 21}Ne and 205{+-}14 e{sup 2} fm{sup 4} (39.7{+-}2.7 W.u.) for {sup 21}Na. The fit to the present data and the known lifetimes determined E2/M1 mixing ratios and B(M1){down_arrow} values of {delta}=(-)0.0767{+-}0.0027 and 0.1274{+-}0.0025 {mu}{sub N}{sup 2} and {delta}=(+)0.0832{+-}0.0028 and 0.1513{+-}0.0017 {mu}{sub N}{sup 2} more » for {sup 21}Ne and {sup 21}Na, respectively (with Krane and Steffen sign convention). By using the effective charges e{sub p}=1.5e and e{sub n}=0.5e, the B(E2) values produced by the p-sd shell model are 30.7 and 36.4 W.u. for {sup 21}Ne and {sup 21}Na, respectively. This analysis resolves a significant discrepancy between a previous experimental result for {sup 21}Na and shell-model calculations. « less

A high-precision branching ratio measurement for the superallowed ${\ensuremath{\beta}}^{+}$ decay of $^{62}\mathrm{Ga}$ was performed at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. The 8\ensuremath{\pi} spectrometer, an array of 20 high-purity germanium detectors, was employed to detect the \ensuremath{\gamma} rays emitted following Gamow-Teller and nonanalog Fermi ${\ensuremath{\beta}}^{+}$ decays of $^{62}\mathrm{Ga}$, and the SCEPTAR plastic scintillator array was used to detect the emitted \ensuremath{\beta} particles. Thirty \ensuremath{\gamma} rays were identified following $^{62}\mathrm{Ga}$ decay, establishing the superallowed branching ratio to be $99.858(8)%$. Combined with the world-average half-life and a recent high-precision $Q$-value measurement for $^{62}\mathrm{Ga}$, this branching ratio yields an $\mathit{ft}$ value of $3074.3\ifmmode\pm\else\textpm\fi{}1.1$ s, making $^{62}\mathrm{Ga}$ among the most precisely determined superallowed $\mathit{ft}$ values. Comparison between the superallowed $\mathit{ft}$ value determined in this work and the world-average corrected $\overline{\mathcal{F}t}$ value allows the large nuclear-structure-dependent correction for $^{62}\mathrm{Ga}$ decay to be experimentally determined from the CVC hypothesis to better than 7$%$ of its own value, the most precise experimental determination for any superallowed emitter. These results provide a benchmark for the refinement of the theoretical description of isospin-symmetry breaking in $A\ensuremath{\geqslant}62$ superallowed decays.

The branching ratio for the superallowed ${\ensuremath{\beta}}^{+}$ decay of $^{38}\mathrm{K}^{m}$ was measured at TRIUMF's ISAC radioactive ion beam facility. The $M3$ internal transition between the isomer and the ground state of $^{38}\mathrm{K}^{m}$ was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue $\ensuremath{\beta}$-decay branch to the first excited ${0}^{+}$ state in $^{38}\mathrm{Ar}$ was also performed and yielded an upper limit of $\ensuremath{\le}12\text{ }\text{ }\mathrm{ppm}$ at 90% C.L. These measurements lead to a revised superallowed branching ratio for $^{38}\mathrm{K}^{m}$ of 99.967(4)%, and increase the $^{38}\mathrm{K}^{m}$ $ft$ value by its entire quoted uncertainty to $ft=3052.1(10)\text{ }\text{ }\mathrm{s}$. Implications for tests of the nuclear-structure dependent corrections in superallowed $\ensuremath{\beta}$ decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element ${V}_{\mathrm{ud}}$ are discussed.

The half-life of the superallowed {beta}{sup +} emitter {sup 62}Ga has been measured at TRIUMF's Isotope Separator and Accelerator facility using a fast-tape-transport system and 4{pi} continuous-flow gas proportional counter to detect the positrons from the decay of {sup 62}Ga to the daughter {sup 62}Zn. The result, T{sub 1/2}=116.100{+-}0.025 ms, represents the most precise measurement to date (0.022%) for any superallowed {beta}-decay half-life. When combined with six previous measurements of the {sup 62}Ga half-life, a new world average of T{sub 1/2}=116.121{+-}0.021 ms is obtained. This new half-life measurement results in a 20% improvement in the precision of the {sup 62}Ga superallowed ft value while reducing its mean by 0.9{sigma} to ft=3074.3(12) s. The impact of this half-life measurement on precision tests of the CVC hypothesis and isospin symmetry breaking corrections for A{>=}62 superallowed decays is discussed.