High precision branching ratio measurement for the superallowed beta decay of Rb-74: A prerequisite for exacting tests of the standard model

Journals published by the American Physical Society can be found at http://publish.aps.org/Nonanalog Fermi and Gamow-Teller branches in the superallowed beta decay of Rb-74 have been investigated using gamma-ray and conversion-electron spectroscopy. Nine observed transitions, in conjunction with a recent shell model calculation, determine the branching ratio of the analog transition to be 99.5(1)%. The experimental upper limits for the Fermi decay to the 0(2)(+) and (0(3)(+)) levels are in agreement with recent theoretical predictions. The Q(EC) value for the Rb-74 beta decay is predicted to be 10405(9) keV

Electric monopole transitions from low-energy excitations in nuclei.

Electric monopole (E0) properties are studied across the entire nuclear mass surface. Besides an introductory discussion of various model results (shell model, geometric vibrational and rotational models, algebraic models), we point out that many of the largest E0 transition strengths, p2(E0), are associated with shape mixing. We discuss in detail the manifestation of E0 transitions and present extensive data for single-closed shell nuclei, vibrational nuclei, well-deformed nuclei, nuclei that exhibit sudden ground-state changes, and nuclei that exhibit shape coexistence and intruder states. We also pay attention to light nuclei, odd-A nuclei, and illustrate a suggested relation between p2(E0) and isotopic shifts. © 1999 Elsevier Science B.V. All rights reserved

Discovery of a new 2.3 s isomer in neutron-rich ¹⁷⁴Tm

A new program of K-isomer research has been initiated with the 8π spectrometer sited at the ISAC facility of TRIUMF. We discuss in this paper the identification of a new 2.3 s isomer in 174Tm and its implications. © Società Italiana di Fisica / Springer-Verlag 2005

Half-Life Measurement for the r p-Process Waiting Point Nuclide 80Zr

X-ray bursts have been suggested as a possible site for the astrophysical rp-process. The time scale for the process is governed by β-decay half-lives of several even-even N = Z waiting point nuclei, in particular, N = Z = 40 80Zr. A 4.1(+0.8-0.6)-s β+/EC half-life for 80Zr was determined by observing delayed 84-keV γ rays depopulating a T1/2 = 4-μs isomer at 312 keV in the daughter 80Y. As this half-life is lower than many previously predicted values, the calculated excessive production of A = 80 nuclides in astrophysical x-ray burst scenarios is reduced, and less extreme conditions are necessary for the production of heavier nuclides

Beta decay of the proton-f5/2 ground state of 77Cu studied with 255 MeV and 0.2 MeV purified radioactive beams

Isobarically purified beams of 77Cu with energies of 225 and 0.2 MeV were used at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory to study beta decay into states in 77Zn. Data taken at 225 MeV allowed the determination of absolute branching ratios relative to the decay of 77Cu for this beta decay as well as its daughters. From these we obtained a refined beta-delayed neutron emission probability of 30.3(22)% and a probability that the decay proceeds through 77Zn(g) of 49.1(26)%. A total of 64 gamma rays were placed in a level scheme for 77Zn containing 35 excited states including one state above the neutron separation energy, whereas two gamma rays were observed for the βn branch to states in 76Zn. The growth and decay curves of some prominent gamma rays indicate a single beta-decaying state with a half-life of 480(9) ms. The decay pattern for 77Cu, with observed feeding of 8(3)% to 7/2+ 77Zn(g) and 6(3)% to 1/2− 77Zn(m), in contrast to the large feeding observed for decay of proton-p3/2 73Cu(g) to 1/2− 73Zn(g), strongly suggests a proton-f5/2 ground state for the studied 77Cu activity.status: publishe

β-decay studies of the transitional nucleus 75Cu and the structure of 75Zn

The β decay of 75Cu [t1/2 = 1.222(8) s] to levels in 75Zn was studied at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory. The γγ and βγ data were collected at the Low-energy Radioactive Ion Beam Spectroscopy Station using the high-resolution isobar separator to obtain a purified 75Cu beam with a rate of over 2000 ions per second. The excited states in 75Zn have been identified for the first time. A total of 120 γ-ray transitions were placed in a level scheme containing 59 levels including two states above the neutron separation energy and a previously unknown 1/2− isomeric state at 127 keV. Spins and parities of several states were deduced and interpreted based on the observed β feeding and γ-decay pattern.status: publishe