Search

We have used the (d,He-2) reaction to obtain the GT(+) strength distribution for Sn-116 ->In-116 transitions. Here, In-116 is the intermediate nucleus in the second-order perturbative description of Cd-116 double beta (beta beta) decay. In this paper we will review what is known about the nuclear matrix elements for the Cd-116 2 nu beta beta decay, discuss the single-state dominance hypothesis and combine our new data with other existing data from charge-exchange reactions to obtain a 2 nu beta beta-decay half-life. The deduced value T-1/2=(4 +/- 1)x10(19)y compares well with the one known from direct counting experiments.

Cross sections for the charge-exchange reaction (d,He-2) on V-50, the only odd-odd stable nucleus in the pf shell, have been measured at an incident energy of 171 MeV. The two correlated protons of the unbound He-2 system were both momentum analyzed and detected by the same spectrometer and detector. Measurements have been carried out at forward center-of-mass angles up to 6degrees. The GT(+) strength distribution has been extracted up to about 12 MeV of excitation energy. Because charge-exchange reactions from V-50 provide a unique opportunity to probe Gamow-Teller response from an odd-odd nucleus of the pf shell, the present study serves as important test case for model calculations and astrophysical processes that proceed through GT-type transitions. Consequently, the experimental result is compared with a large-scale shell-model calculation, and the implications for electron-capture processes in presupernova environments are discussed.

The two-neutrino double-beta (2nubetabeta) decay represents a test case for our knowledge about the nuclear structure of the involved isobars. The decay of Ca-48 is an especially interesting case because it holds an anomaly of a uniquely high Q(betabeta) value and a comparatively long half-life, which points to a peculiar nuclear structure situation. The nuclear matrix element relevant for betabeta decay can be calculated, if the complete set of Gamow-Teller (GT) matrix elements for the two virtual transitions in the perturbative description are known. Using the high-resolution (d, He-2) probe, we have measured the GT(+) strength distribution in Sc-48, which is the intermediate nucleus in the Ca-48 betabeta decay. By combining our measured GT distribution with data from a Ca-48(p, n) experiment and taking into account relative phases between individual matrix elements, which can be gained from theoretical models, one can compute the double-GT matrix element and deduce the half-life of the Ca-48 2nubetabeta decay.

The V-51(d,He-2)Ti-51 charge-exchange reaction has been investigated at an incident energy of 171 MeV and scattering angles near 0degrees. The two protons in the S-1(0)(pp) state (denoted as He-2) were both momentum analyzed and detected by the same spectrometer and detector. Spectra with a resolution of about 125 keV (full width at half maximum) have been obtained allowing identification of many levels in Ti-51 with high precision. The GT(+) strength distribution for transitions to levels up to about 6 MeV of excitation energy has been extracted. The results are compared with a large-scale shell-model calculation in the full pf shell.