48
F
ri
to
Zn (1 12 Mev)
a
tet
=
>
cr
3
L
r
{
b
F
Nw
=
|
1000
s
°
5
Z
=
presence and concentration of other components
or
cs37 (0 66 Mev)
100E
Cc
F
E
5
3
b
b
L
1
i
:
1
\
zn*hs cs”
\
NET UN IVO-—"7'
CONTRIBUTION
|
40
ts"? SPECTRUM |
Kv) 46Mev)
\
i
‘
NET TOTAL
BODY
+
SPECTRUM
L
t
.
24
in
i
48
1
‘2
i
“a
36 120
L
ENERGY (Mev)
laa
4
ab
i
.
i6a—~=C«*' 2
Figure 53. Gamma spectrum of phantom illustrating
graphical stripping of K*°, Zn**, and Cs'*’ from total
spectrum.
one isotope to the photopeakof the otherisotopes
of lower energy is very small.
In orderto carry outthis stripping method,itis
necessary to have calibrated pulse-height distribution spectra for each gamma emitter encountered.
Further, these spectra must ideally be obtained
from a subject of the same size and bodybuild. To
obtain these spectral data, known amounts of
Cs'** and Zn® were administered to subjects at
BNL, and their spectra were obtained. Laterin
the study, a plastic phantom (REMAB-Alderson)
wasobtained andusedfor calibration (Figure 54).
of the spectrum.
This procedure was further complicated in this
study by severalfactors. In thefield study the subjects were measured with a 5-in. Nal (T1) crystal.
The calibration was originally carried out in the
field with a Presdwood phantom, but when the
Alderson plastic phantom later becameavailable
it was foundto give a better approximation of the
spectrum for each isotope, and therefore most of
the calibration was repeated with it at BNL.
However, the geometry in the field situation was
rather difficult to duplicate exactly. Also, counting
the subjects for 5 to 10 min was sufficient toestimate accurately the levels of Cs**’ and Zn® but
not the K*° body concentration and trace amounts
of otherfission products in the presenceofthe relatively large amounts of Cs'*’ and Zn**, Thelack
of a statistically significant number of counts to
measure K*° accurately is evident from the poorly
defined K*° photopeakof the subject as compared
oo
10,000 patton
Spectra were also obtained from the phantom
with known amounts of KCl, Cs'*’, and Zn®.
From these spectra, an average spectrum for each
isotope was obtained. The pulse-height distribution spectrum of one of the Marshallese subjects is
compared with the spectrum obtained with the
plastic phantom containing the same concentrations of K, Cs'*", and Zn® in nearly identical
counting geometry in Figure 52. In this way it was
possible to simulate the multicomponentspectra
of the Marshallese by use of the phantom.
Since it is not possible to measure a photopeak
until the contributions of other peaks of higher
energy and their Compton continua have been
subtracted out, and since the presence of small
amounts of unknown radionuclidesis not always
ence of very small amounts ofother fission products. However, when all the major components
have been stripped out, the presence of any remaining photopeak should serve to identify the
Figure 54. Calibration phantom in standard counting
position in BNL whole-body counter.
os
obvious in the presenceof large concentrations of
other radionuclides, it is possible to miss the pres-