Because the fission representation goes to infinity at zero time,
the ratio of fission activity to uranium capture activity must be
found at some other time. In general, the time chosen was that at
which the uranium capture activity was measured. A variation in this
value could be used as a method of indication of fractionation of
uranium capture products with respect to fission products.
3.3 el Shot 1
Since little experimental decay data were obtained prior to
250 hours, a composite neutron capt
decay
curve was
ructed
for times shortly after the shoto e387, 239» Np 39 ’ eBis Np240
were found to be significant contributors to the decay curve. From
the parent-daughter relationship
wy
Ao = Ao. 1-01
(e*1bgM2*)
(3.6)
Ag)= activity of 0239 at initial time
where
Ao = activity of daughter Np239
239
wy, = decay constant of U
ug = decay constant of Np239
t+
= time after shot
In the case of the U239 and Np23? decay scheme, u, is much greater
than U, and e1® 4s mch less than e"Y2* at any time after initial
timee
hence
Ags = Age
(367)
Aon s we
(3-8)
thus, setting t = 0
Aon
“A
a
The initial activity of Np239_can be found from Eq. 38, ass
it
Np240,
of
case
the
in
rly,
Simila
1235,
for
1
ty
or
ve
activi
relati
can @shown that its activity equals up/(up - uw.) times the activity
of
after equilibrium is reac
The relative activities of ve to 0239 and 0240 to 0239 are
r
determined by the ratio of their decay constants miltiplied by
U*"';
of
The relative activity and decay constants
lds,
ure
oo55, wee88, 240, and Np240 are summarized in Table 3.1.
38