Browsing by Author "Garrett, P.E."

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    High-Precision Branching Ratio Measurement for the Superallowed + Emitter 74Rb
    (American Physical Society, 2013) Dunlop, R.; Ball, G.C.; Leslie, J.R.; Svensson, C.E.; Towner, I.S.; Andreoiu, C.; Chagnon-Lessard, S.; Chester, A.; Cross, D.S.; Finlay, P.; Garnsworthy, A.B.; Garrett, P.E.; Glister, J.; Hackman, G.; Hadinia, B.; Leach, K. G.; Rand, E.T.; Starosta, K.; Tardiff, E.R.; Triambak, S.; Williams, S. J.; Wong, J.; Yates, S.W.; Zganjar, E.F.
    A high-precision branching-ratio measurement for the superallowed β + decay of 74Rb was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) radioactive ion-beam facility. The scintillating electronpositron tagging array (SCEPTAR), composed of 10 thin plastic scintillators, was used to detect the emitted β particles; the 8π spectrometer, an array of 20 Compton-suppressed HPGe detectors, was used for detecting γ rays that were emitted following Gamow-Teller and nonanalog Fermi β + decays of 74Rb; and the Pentagonal Array of Conversion Electron Spectrometers (PACES), an array of 5 Si(Li) detectors, was employed for measuring β-delayed conversion electrons. Twenty-three excited states were identified in 74Kr following 8.241(4) × 108 detected 74Rb β decays. A total of 58 γ -ray and electron transitions were placed in the decay scheme, allowing the superallowed branching ratio to be determined as B0 = 99.545(31)%. Combined with previous half-life and Q-value measurements, the superallowed branching ratio measured in this work leads to a superallowed f t value of 3082.8(65) s. Comparisons between this superallowed f t value and the world-average-corrected Ft value, as well as the nonanalog Fermi branching ratios determined in this work, provide guidance for theoretical models of the isospin-symmetry-breaking corrections in this mass region.
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    Spectroscopy of states in Ba 136 using the Ba 138 (p,t) reaction
    (American Physical Society, 2021) Rebeiro, B.M.; Triambak, S.; Garrett, P.E.; Lindsay, R.
    Background: The Ba136 isotope is the daughter nucleus in Xe136ββ decay. It also lies in a shape transitional region of the nuclear chart, making it a suitable candidate to test a variety of nuclear models. Purpose: To obtain spectroscopic information on states in Ba136, which will allow a better understanding of its low-lying structure. These data may prove useful to constrain future Xe136→Ba136 neutrinoless ββ decay matrix element calculations. Methods: A Ba138(p,t) reaction was used to populate states in Ba136 up to approximately 4.6 MeV in excitation energy. The tritons were detected using a high-resolution Q3D magnetic spectrograph. A distorted wave Born approximation analysis was performed for the measured triton angular distributions. Results: 102 excited states in Ba136 were observed, out of which 52 are reported for the first time. Definite spin-parity assignments are made for 26 newly observed states, while previously ambiguous assignments for ten other states are resolved. Together with other available data, the results are used to determine level densities in Ba136. These were compared with theory predictions, obtained using shell model calculations with Hamiltonians previously used for Xe136 neutrinoless ββ decay matrix element evaluations. Conclusions: The shell model predicted level densities agree reasonably well for the two Hamiltonians. However, the results for theory and experiment are found to agree only at lower energies, diverging from one another for the higher lying states, with the discrepancy increasing with energy. This is presumably because of lower production cross-sections for a majority of the higher-lying predicted states and the experimental limitations in resolving a large number of nearly degenerate states predicted by the theory. © 2021 American Physical Society.