Beta decay matrix elements in As 76

Abstract

Dynamic nuclear orientation has been used to study the 2 − ↔ 2 + 2.41 MeV β-ray in the decay of As 76. The As 76 was a substantial donot atom in a silicon crystal and it was oriented by saturating each of the four Δ ( m J + m I = 0 forbidden transitions. The angular distribution of the gamma rays following the 2.41 MeV β-ray was measured with two scintillation counters. The electron and nuclear relaxation times were determined by observing the rate of growth and decay of the anisotropy of the gamma rays. The electron ( Δm J = ± 1, Δm I = 0) relaxation time was (3.6 ± 0.7) min. The nuclear relaxation can be attributed to a modulation of the isotropic hyperfine interaction; the relaxation time for the nuclear polarization is (3.1 ± 1) × 10 3 min. An analogue computer was used to correct the initial orientation parameters for the effects of nuclear relaxation. From this orientation experiment restrictions can be placed on the angular momentum carried off by the 2.41 MeV β-ray. This result was analyzed in conjunction with β-γ angular correlation and β-γ circular polarization correlation experiments to determine the beta-decay matrix elements. The set which fits the data best is V = − (0.9 ± 0.2), Y = −(0.9 ± 0.2). It is not impossible to rule out the set V = −(18±5), Y = 0±4.