608
KURODA, KAURANEN, PALMER, MENON, AND FRY
Similarly, in the case of the mass chain 140, the most probable frag-
ment charge lies near Z= 54; hence the gaseous nuclide 40Xe plays
an important role.
15
According to Edvarson et al.,’ particle formation occurs about
to
20
sec after the explosion of a thermonuclear device of the
order of magnitude of 1 Mt. The half-life of "Xe is shorter than that
of Kr, whereas the half-life of °*Kr is much longer. Thusthe fission
products belonging to the mass chain 140 will have a much better
probability of being incorporated into particles that start growing
immediately after a nuclear explosion than those belonging to the mass
chain 89. This would tend to enrich ‘Ba in larger particles and ®Sr in
smaller particles.
Figure 4 comparesthe '4!Ce/!44Ce ratio data with the **Sr/"Sr and
the 9Ba/®*Sr ratio data. Here again, an impression is obtained that the
NUCLIDE RATIO
USSR TESTS
END
y ce Me
10°
107!
107?
NOV
DEC
1962
JAN
FEB
MAR
APR
MAY JUNE] JULY
1963
Fig, 4—'!4lCe/'4Ce, 'Sr/9Sr, andBa/*Sr ratios in rain after the
cessation of nuclear tests in December 1962,