surrounded
each
methane-flow counting chamber
used in con-
junction with the Nucleometers to give a background of only about
45-50 counts per minute (c/m).
The same counting equipment was
used throughout the seven years covered by this report.
Counting time followed the schedule of WT-616:20 during the
earlier counting:
C/m, sample
plus background
Counting time,
minutes
< -500
500-1000
- 1000-2000
> -2000
20
10
5
2
For later counts, as more machine time became
available,
longer counts of from 30 minutes to several hours were frequently possible for the low-counting samples.
The absolute level of radioactivity as indicated in the column of
Table 1 headed "Plate count, 1000 days,'' serves as an index to the
reltability of the points.
Graphingand Reproduction
Values from the decay data-sheets were plotted as circles on
thin logarithmic graph paper.
Even where
all of the values were graphed.
circles overlapped, almost
Free, outstanding circles pertain to
the nearest curve, and lines connect
those points whose identity was