\Na24 is a major source of radiation hazard in fallout ‘padiation one day past shot time, __ There are several possible mechanisms for the production of Na24 by neutron induction: A127 (n,a)Na’*, Mg(n,p) Na@4, and Na235(n,y )Na?4 with respective cross sections of about 100 mb for 14-Mev neutrons, 191 +35 mb for 14.5+Mev neutrons . eat about 0.5 b for thermal neutrons ,11 However, at the time of writing enough detailed information was not immediately available to permit intelligent speculation on which of these processes predominates. Another interesting result apparent on most of the series of recordings begun at early enough times is the build-up of the 1.59-Mev activity from Lal49, The fact that there is evidence of an increase in this activity at early times indicates that most of the original fission product of the mass number-140 series was Bal4°0 or a percursor. Assuming that all of the Ba!40-Lal40 rissi on-product complex was Bal40 originally, the build-up of the 1.59-Mev activity should reach its maximim time. Theoretically at there 136 hours should be after no shot build-up in