Investigation of parity mixing in 203Tl by measurement of the forward-backward asymmetry of γ-rays after β-decay

Abstract

A multiple detector arrangement of fixed geometry and high inherent accuracy has been used to measure the forward-backward asymmetry coefficient A 1 in the β-γ transition of 203Hg → 203Tl. Moreover, a control value has been determined which should exhibit no asymmetry. A non-zero coefficient A 1 is indicative of small admixtures of opposite parity in nuclear states. The properties of a multiple detector arrangement and systematic asymmetries are discussed in detail. Sources of 203Hg of high quality have been prepared with a mass separator. To avoid a systematic bias due to non-negligible quadratic terms in the statistical errors a new technique of data analysis has been applied. The measurements of several sources yielded for the asymmetry coefficient A 1 = −(2.6±0.7) × 10 −4 and for the control value (1.3±0.7) × 10 −4, where the quoted errors represent one standard deviation.