UNCLASBIFIED
-1175-A5C
$2-30-53
| O7 -
counting period greater error is allowed.
The calculation of disintegrations per minute from the measu fed counts per
minute is made in the following way.
The counts per minate (cpm) are multiplied
by the appropriate geometry factor, by a factor to correct for ab porption by
the counter wall and absorbers (ex. (wall thickness mes/cm~)/(mean thickness
of radiation being measured))}, and by the sample weight ip mgs.
The resulting
le area,
number is divided by the mean thickness of the radiation, by the
and by ea correction factor for samples less than
tt
finitely” thi#k Q-1/exp.
(surface density of sample) /(mean thickness for the measured radigtion)).
For example, a sample of x7 counted or a miniature counter gives}5.7 + O.1
net cpm.
2
Its weight is 0.416 gms and its area is 5.75 cm.
An
sorber of
112 mgs om was used.
dpm
5.7 cpm x 3.0 x 416 mgs x eins
188 ngs/em” x 5.75 em> x (1-e
cell
37.6 dpm Y
Backscattering corrections have not been made in these calculations.
The
plastic sample mounts “reflect” only about & of the radiation st: riking them
' and this backscattered radiation has only about half the energy .o rP the original
radiation.
Since the samples are of finite thickness, ca. 60 to
most of the backscattered radiation is absorbed.
about 1% of the observed activity.
mgs/cn*,
The backscatter
contributes
This is at least partically c
cted for by
the geometry determinations where backscattering corrections were not made.
To calculate SUNSHINE UNITS from tris ipa figure,
{t is mult plied by the
decay correction factor (exp.(hours since milking from Sx") /(nest life of ys)
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