Angular correlation studies of the 358 keV→81 keV cascade in Cs 133

Abstract

With the main aim of studying the nuclear structure effect on the internal conversion process of the l-forbidden 81 keV M1 transition, angular correlation measurements with the 358 and 81 keV gamma-rays, and with the 358 keV gamma-ray and the K-conversion electrons of the 81 keV transition have been performed. The results, after necessary corrections, are W( yy;θ) = 1+(0.046±0.011) P a(cosθ)−(0.008±0.014) P 4(cosθ), W( ye k −;θ) = 1+(0.014±0.008) P a(cosθ)+(0.007±0.011) P 4(cosθ). While gamma-gamma angular correlation alone could not choose between 1/2 or 3/2 spin assignment to the 439 keV state, the gamma-K-conversion electron angular correlation requires it to be only 3/2. These angular correlation results lead to a 0.7 M1 + 0.3 E2 multipolarity for the 358 keV transition and δ II 2(γe κ −) = 0.0066 for the 81 keV transition. These different mixing ratios for this transition indicate the possibility of the nuclear structure effect on the internal conversion process being operative. With the help of all these results, the nuclear structure effect parameter is deduced from the K-conversion coefficient of the 81 keV transition to be λ = −1.28or+253. The various factors leading to uncertainties in λ are presented. Nuclear structure effect on particle parameters is considered.