37
Thesesamples were placed on weighed, stainless steel] discs, one and
one-halfinches in diameter.
th
The discs containing the samples were then weighed again on a torsion analytical balance accurate to .01 gram.
Due to the motion of the ship, )
however, an accuracy of probably not more than .03 gram was obtainable,
The size of the sample used depended upon the amount of material available
but in most cases was approximately a gram,
The discs holding the samples were next placed on an asbestos tray and
heated to about 300° C, which dried and charred the tissues. Several drops of
concentrated nitric acid were then added to further oxidize the materi al and
to reduce the residue to a minimm.
Samples were then placed in the furnace.
The nitric acid treatment was usually repeated several times until the
residue was spread as evenly as possible over the bottom of the plate.
MWinally
the temperature of the muffle furnace was raised to about 800° C. to complete
the ashing.
After cooling, the plates were mounted on cards bearing an identification
number and were sent to the counting room.
All samples were counted in an
aluminum shelf sample holder, with a thin window, argon-alcohol Geiger tube,
and a Tracerlab autoscaler circuit.
22%.
The geometryof this arrangement was about
Total absorption, exclusive of self absorption which varied widely for
different samples, was about 6 mg on7,
Counter background averaged 18.5 ¢/min.
The tabulated data refer to the above arrangement, and if total counts uncorrec:
for absorption are desired, the tabulated values should be miltiplied by 4.5.
A total count of 128 was obtained on most samples.
In cases where greater
than average radioactive materials were present, howaver, total counts of 256,
512, or 1024 were made.
To determine the background the time to record ‘a count
Lo.
UNIVERS
GS
8
Wea
UNIV, OF
oh
of 1024 and occasionally »f 4096 waa obtained each day.