-
16
-
to one sixth the values for samples of tuna landed before or
after August.
The greatest difference was between the May and
August values.
8.
A strict relationship between the radioactivity in the
tuna and the distance from Christmas Island was not evident from
inspection of the analytical data.
The results of analyses by Kawabata et al.
(1963) to measure
radioactivity in duplicate samples also indicated little activity.
There were only seven samples with gross-beta activity greater
than background and no samples with gross-gamma activity greater
than background.
The beta detector at the Tokyo laboratory was
a 1.4 mg/om? end-window type G-M counter with an efficiency of
20.2 per cent for a uranium (U30,)
standard.
The
gamma detec-
tor was a l-inch x l-inch NaI crystal with type ND-10 probe for
which the efficiency was 7.0 per cent for a U30g standard.
The distribution of the seven radionuclides in the tissues
of whole tuna was determined by gamma-spectrum analysis of 13
kinds of tissues from 11 tuna landed in Tokyo between June and
September.
1.
The following results were observed:
The average values for Kt0 in pce/g (wet), ranged from
1.6 (gonad) to 7.7 (spleen), except for heart samples, for which
there were no values significantly greater than the background
count.
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