ASH OF BIKINI AND ITS EFFEJ'@ O_N_'JlflJMAN
- . .
I' :_ _...'
H. Kakehi .-'.
1. Introduction (omitted).
2. Physical Properties of the Ashesr
According to the report of the'fisherinen
began to come down about 3 hours after the hydrogen bomb explosion.
It continued to fall about 5 hours at varying rates and covered the
boat like the light snow that footprints were left on the deck as they
The ash consists of light and white grains of various size less
than 1 mm in diameter. Microscopic examination shows that they are
amorphous and porous. It might be the fragment of the coralline sub-
1) Its radioactivity
strong and even a
few grains of ash showed ten-thousands
counts per minute on March 16.
The thickness of the absorber to reduce the intensity of radiation to
a half (or the inverse of the absorption coefficient)
for the-e- ray and 5.5mmPb for the1 - ray (March 17). The radioaut<graph
of theFray from the ash is shown in Pig. 2. The half-life-was about 8 dqs
at first, but it is in these days (about April 5) of the order of 18 dqs.
the damping curve of radioactivity
observed after March 17,
the intensity of thee- ray on the next day of the explosion (March 2)
is estimated to be about 50 times larger than that of March 17. Similar
result q be obtained for theI- ray too.
The chemical analysis of the ash has been performed at Kimura lab-
of Chemistry, Tokyo University). The result pub-
lished so far is shown in Table 1. There are several definitions of the
half-life according to the purpose as is shown below. The half-life given
in Table 1 is the pwsical half-life defined as the period of time during
which the munt of