~ 25 -
yi85 accounted for 67 to 70 per cent of the total radioactivity in samples of Scaevola leaves taken at Belle Island
on June 20,
1958 (Table 3).
On August 20 the same isotope
contributed 73 per cent of the total activity in a similar
sample.
The disintegration rates of the August 20 samples
corrected to the June 20 date,
however,
indicate that wis
would have contributed 66 per cent of the total radioactivity
at that time,
the percentage difference being due to the
presence of more radioisotopes with a short half life in the
earlier sample.
June 23,
In Scaevola leaves taken from Henry Island on
wi85 contributed 17 per cent of the total activity.
On August 20 the same isotope accounted for 11 per cent of
the disintegration rate.
When the August 20 disintegration
rates were corrected to the June 23 date,
12 per cent of the
total radioactivity.
wi85 contributed
Thus the rate of
removal of this isotope from the Scaevola leaves by rain and
wind is not significantly different from the average of the
other radioisotopes.
The disintegration rate of wi85 on Scaevola leaves at
Belle Island on June 20 was 7,900,000 d/m/g and on August 20
180,000 d/m/g, a reduction in activity by a factor of 44.
The
disintegration rate of wi85 on Scaevola leaves at Henry Island
on June 23 was 2,500 d/m/g and on August 20, 510 d/m/g, a