Level Structure of ¹²⁹Cs

Abstract

The level structure of ¹²⁹Cs was investigated by measuring gamma-rays and internal conversion electrons following the decay of ¹²⁹Ba with a Ge(Li) detector and a \sqrt2π air core beta-ray spectrometer. About one hundred fifty gamma-rays were observed. The L-subshell ratios of the 6.5, 53.2, 129.1, 182.3 and 202.4 keV transitions were measured, and the multipolarities and the mixing ratios of these transitions were determined. For the 6.5 keV transition, zero energy loss peaks were observed. The low-lying level energies, spins and parities are as follows: 0(1/2+), 6.545(5/2+), 135.6(3/2+), 188.87(7/2+), 208.9(5/2+) and 220.8 keV(3/2+). The experimental results of l-forbidden M1 transitions are compared with the theoretical predictions.