XVII. The application of proportional ?-ray counters to the determination of the decay scheme of I 131

Abstract

A naphthalene-anthracene crystal has been used to separate the high energy γ-rays in I¹³¹ from the main low energy component. Coincidence absorption measurements with β-rays and the high energy γ-rays show that the latter are in cascade with β-rays of maximum energy 315 kev. Consideration of the bias curve of these coincidences however shows that the coincidence /3-spectrum is complex and may be analysed into components of maximum energy 328 and 246 kev in the ratio (2:1) expected if they are in cascade with the 638 and 720 kev γ-rays respectively, which are known to be emitted. This suggests that the latter are emitted in transitions to the ground state of Xe¹³¹.