Penetration matrix elements and nuclear structure effects in Tl 203

Abstract

Gamma-gamma, electron-gamma and gamma-electron directional correlation experiments on the d 3 2 (400 keV) d 3 2 (279 keV) s 1 2 cascade in Tl 203 are reported. The following results were obtained: A 2(γγ) = −0.130±0.006, A 2( eγ) = −0.011±0.004, A 2(γ e) = −0.030±0.003 . In addition the K-conversion coefficient of the 400 keV transition was determined from the coincidence experiments. The value obtained is β 1 K (400 keV) = 0.145±0.007 . The experiments were performed in order to search for nuclear structure effects in the M1 internal conversion process. These effects are expected to be negligible in the l-allowed (400 keV) transition. This is confirmed by the experiments which are in perfect agreement with the theory assuming no nuclear structure effects. Large nuclear structure effects are to be expected for the strongly retarded l-forbidden (279 keV) transition. This is also confirmed by the angular correlation experiments. It is shown that all experimental data are consistent with a λ-value of +76±1, where λ is defined as the ratio of the penetration matrix element and the normal gamma ray matrix element. The value for the weighting factor C(Z, k) was taken to be 0.0260. The errors for λ given here do not include the uncertainty in the weighting factor which is supposed to be known to within ±10%. The agreement between the theory and the experimental results is further improved if the particle parameters are corrected for the finite size of the nucleus in the E2 conversion process.