Deciphering the measured ratios of Iodine-131 to Cesium-137 at the   Fukushima reactors
  We calculate the relative abundance of the radioactive isotopes Iodine-131 and Cesium-137 produced by nuclear fission in reactors and compare it with data taken at the troubled Fukushima Dai-ichi nuclear power plant. The ratio of radioactivities of these two isotopes can be used to obtain information about when the nuclear reactions terminated. 
T. Matsui
nucl-th nucl-ex physics.soc-ph