Short-Lived Halogen Fission Products

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Abstract
Half‐life values have been determined for some short‐lived Br and I fission products. The chemical isolation of Br from irradiated uranyl nitrate led to a half‐life for Br85 of 3.00±0.05 min. The energy of the β‐radiation of Br85 was found to be 2.5 Mev by Feather analysis of the Al absorption curve. The half‐lives found for Br87 and Br88 by extraction of the Kr daughter activities from AgBr precipitates were 56.1±0.7 sec. and 15.5±0.3 sec., respectively, on the basis of a 3‐min. half‐life for Br85. Attempts to measure the half‐lives of Br89 and Br91 by extraction of the descendant Sr activity were unsuccessful because of the absence of activity. The identity in half‐lives of Br87 and the 55.6‐sec. Br delayed neutron emitter makes it probable that the mass assignment of the delayed neutron emitter is 87. The half‐life of I137 was found to be 19.3±0.5 sec. by extraction of Xe137 from AgI precipitates, on the assumption of constant chemical yield of the Xe extraction. Isolation of Cs138 both from the gas separated from AgI precipitates and from the precipitates directly led to a half‐life determination for I138 of 5.9±0.4 sec. Extractions of Ba149 yielded a value of 2.7±0.1 sec. for the half‐life of I139. The absence of Ba140 activity in AgI precipitates made it impossible to determine the half‐life of I140. Because of the agreement in half‐lives of I137 and the 22.0‐sec. I delayed neutron emitter it is probable that the two are identical. The low retention of the decay products of the short‐lived halogens by the silver halide precipitates led to an estimate of 20 sec. for the ``setting'' time of the precipitate.