\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