Abstract
Gamma-ray detection following the inelastic neutron scattering reaction on isotopically enriched material was used to study the nuclear structure of 74Ge. From these measurements, low-lying, low-spin excited states were characterized, new states and their decays were identified, level lifetimes were measured with the Doppler-shift attenuation method (DSAM), multipole mixing ratios were established, and transition probabilities were determined. New structural features in 74Ge were identified, and the reanalysis of older 76Ge data led to the placement of the 2+ member of the intruder band. In addition, a number of previously placed states in 74Ge were shown not to exist. A procedure for future work, which will lead to meaningful data for constraining calculations of the neutrinoless double-beta decay matrix element, is suggested.
Highlights
Double-beta decay with the emission of two β− particles and two antineutrinos (2νββ) has been observed in a handful of nuclei [1]; the neutrinoless double-beta decay process without the emission of antineutrinos (0νββ) remains unobserved, several large-scale international searches are in progress. 0νββ, a lepton-numberviolating nuclear process, will only occur if the neutrinos have mass, which has been established from several sources, and if they are Majorana particles, i.e., they are their own antiparticles
Figure 2. 74Ge (n, n γ) spectrum obtained with 3.0 MeV incident neutrons at a detection angle of 90◦. γ rays of interest are labeled
We determine γ-ray reduced transition probabilities, which can be compared with nuclear structure calculations
Summary
Double-beta decay with the emission of two β− particles and two antineutrinos (2νββ) has been observed in a handful of nuclei [1]; the neutrinoless double-beta decay process without the emission of antineutrinos (0νββ) remains unobserved, several large-scale international searches are in progress. 0νββ, a lepton-numberviolating nuclear process, will only occur if the neutrinos have mass, which has been established from several sources, and if they are Majorana particles, i.e., they are their own antiparticles. In addition to being the only practical way to establish if neutrinos are Majorana particles, the observation of 0νββ promises to provide perhaps the best method for obtaining the mass of the neutrino. The rate of 0νββ will be obtained with the first experimental observation of this process, and the mass of the neutrino will become available, if the NME is known. As meaningful nuclear structure calculations should be able to explain the structure of a region of nuclei rather than just an isolated nucleus, we have initiated studies of other nuclei in the A = 76 region (see Fig. 1) The structure of this region is not simple, as previous work has provided evidence of shape transitions, shape coexistence, and triaxiality [7,8,9,10,11,12]. In the case of 74Ge, the first additional nucleus in the region we have chosen to study, a great deal of information is available from other studies [13,14,15,16,17,18]; some of these works are very dated and there is need for improvement
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