Background: Neutron-rich nuclei around neutron number N = 60 show a dramatic shape transition from spherical ground states to prolate deformation in Sr-98 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 Sr-93,Sr-94,Sr-95 were studied via the H-2(Sr-94,Sr-95,Sr-96, t) one-neutron stripping reactions at TRIUMF using a beam energy of 5.5 AMeV. gamma-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 gamma radiation. Results: Triton angular distributions for the reactions populating states in ejectile nuclei Sr-93,Sr-94,Sr-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 H-2(Sr-94, t) Sr-93 and H-2(Sr-95, t) Sr-94 reactions are in good agreement with shell-model calculations. A two-level mixing analysis for the 0(+) states in Sr-94 suggest strong mixing of two shapes. For the H-2(Sr-96, t) Sr-95 reaction the agreement with the shell-model is less good. The configuration of the ground state of Sr-96 is already more complex than predicted, and therefore indications for the shape transition can already be observed before N = 60.

The region around neutron number N = 60 in the neutron-rich Sr and Zr nuclei is one of the most dramatic examples of a ground state shape transition from (near) spherical below N = 60 to strongly deformed shapes in the heavier isotopes. The single-particle structure of 95-97Sr approaching the ground state shape transition at 98 Sr has been investigated via single-neutron transfer reactions using the (d, p) reaction in inverse kinematics. These reactions selectively populate states with a large overlap of the projectile ground state coupled to a neutron in a single-particle orbital. Radioactive 94,95,96Sr nuclei with energies of 5.5 AMeV were used to bombard a CD 2 target. Recoiling light charged particles and {\gamma} rays were detected using a quasi-4{\pi} silicon strip detector array and a 12 element Ge array. The excitation energy of states populated was reconstructed employing the missing mass method combined with {\gamma}-ray tagging and differential cross sections for final states were extracted. A reaction model analysis of the angular distributions allowed for firm spin assignments to be made for the low-lying 352, 556 and 681 keV excited states in 95Sr and a constraint has been placed on the spin of the higher-lying 1666 keV state. Angular distributions have been extracted for 10 states populated in the d(95Sr,p)96Sr reaction, and constraints have been provided for the spins and parities of several final states. Results are compared to shell model calculations in several model spaces and the structure of low-lying states in 94Sr and 95Sr is well-described. The spectroscopic strength of the 0+ and 2 states in 96Sr is significantly more fragmented than predicted.

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency γ-ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF’s Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) γ-ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

Background: The region around neutron number N = 60 in the neutron-rich Sr and Zr nuclei is one of the most dramatic examples of a ground-state shape transition from (near) spherical below N = 60 to strongly deformed shapes in the heavier isotopes. Purpose: The single-particle structure of Sr95-97 approaching the ground-state shape transition at Sr-98 has been investigated via single-neutron transfer reactions using the (d, p) reaction in inverse kinematics. These reactions selectively populate states with a large overlap of the projectile ground state coupled to a neutron in a single-particle orbital. Method: Radioactive Sr-94,Sr-95,Sr-96 nuclei with energies of 5.5 A MeV were used to bombard a CD2, where D denotes H-2, target. Recoiling light charged particles and gamma rays were detected using a quasi-4 pi silicon strip detector array and a 12-element Ge array. The excitation energy of states populated was reconstructed employing the missing mass method combined with gamma-ray tagging and differential cross sections for final states were extracted. Results: A reaction model analysis of the angular distributions allowed for firm spin assignments to be made for the low-lying 352, 556, and 681 keV excited states in Sr-95 and a constraint has been placed on the spin of the higher-lying 1666 keV state. Angular distributions have been extracted for ten states populated in the 2H(Sr-95, p)Sr-96 reaction, and constraints have been provided for the spins and parities of several final states. Additionally, the 0, 167, and 522 keV states in Sr-97 were populated through the 2H(Sr-96, p) reaction. Spectroscopic factors for all three reactions were extracted. Conclusions: Results are compared to shell-model calculations in several model spaces and the structure of low-lying states in Sr-94 and Sr-95 is well described. The spectroscopic strength of the 0(+) and 2(+) states in Sr-96 is significantly more fragmented than predicted. The spectroscopic factors for the H-2(Sr-96, p)Sr-97 reaction suggest that the two lowest-lying excited states have significant overlap with the weakly deformed ground state of Sr-96, but the ground state of Sr-97 has a different structure.

The low energy excited 02,3+ states in 96Sr are amongst the most prominent examples of shape coexistence across the nuclear landscape. In this work, the neutron [2s1/2]2 content of the 01,2,3+ states in 96Sr was determined by means of the d(95Sr, 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 96Sr ground and 1229 keV 0+ states, respectively, by fitting the experimental angular distributions to DWBA reaction model calculations. A detailed analysis of the γ-decay of the isomeric 03+ 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 96Sr. The strengths of the excited 02,3+ states were also analyzed within a two-level mixing model and are consistent with a mixing strength of a2=0.40(14) and a difference in intrinsic deformations of |Δβ|=0.31(3). These results suggest coexistence of three different configurations in 96Sr and strong shape mixing of the two excited 0+ states.

Several lifetimes in 23Mg have been determined for the first time using the Doppler-shift attenuation method. A Monte Carlo simulation code has been written to model the gamma-ray line shape. An upper limit of 12 fs at the 95% C.L. has been obtained for the astrophysically important 7787 keV state.

The GRIFFIN (Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei) project is a major upgrade of the decay spectroscopy capabilities at TRIUMF-ISAC. GRIFFIN will replace the 8π spectrometer with an array of up to 16 large-volume HPGe clover detectors and use a state-of-the-art digital data acquisition system. The existing ancillary detector systems that had been developed for 8π, such as the SCEPTAR array for β-tagging, PACES for high-resolution internal conversion electron spectroscopy, and the DANTE array of LaBr3/BaF2 scintillators for fast γ-ray timing, will be used with GRIFFIN. GRIFFIN can also accommodate the new neutron detector array DESCANT (Deuterated Scintillator Array for Neutron Tagging), enabling the study of β-delayed neutron emitters. DESCANT consists of up to 70 detectors, each filled with approximately 2 liters of deuterated benzene, a liquid scintillator that provides pulse-shape discrimination (PSD) capabilities to distinguish between neutrons and γ-rays interacting with the detector. In addition, the anisotropic nature of n-d scattering as compared to the isotropic n-p scattering allows for the determination of the neutron energy spectrum directly from the pulse-height spectrum, complementing the time-of-flight (TOF) information. The installation of GRIFFIN is under way and first experiments are planned for the fall of 2014. The array will be completed in 2015 with the full complement of 16 clovers. DESCANT will be tested coupled with GRIFFIN in spring of 2015.

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.