4;
rapid and positive identification of gamma-emitting
radionuclides. The principles of in vivo gamma
spectrometry as applied to human beings have
been previously described.”*
The stee! room constructed at BNL in 1957 for
the Mafshallese surveys has been described ore-
viously.* The “portable” 21-con steel room,
3
100, Quartz Line Storage Pulse-Height Analyzer).
Two complete detectors and analyzers with the
necessary associated electronic circuitry were
taken along, since considerable difficulty had been
experienced during the previous vear in main-
taining the whole-body counting svstem opera-
tional under the conditions of tropical heat and
humidity. Housing of the electronic equipment in
an air-conditioned, dehumidified room during
6-ft with 4-in.-chick steel walls, was used to
operation was of considerable assistance in maintaining its stability.
with a7 x8 10-ft air-conditioned wooden room,
were known from the previous study to be due to
counter (see Figure 50). The tratier was mounted
on the tank deck of the Navy LST, and the sub-
ciently high, it was only necessary to count the
facilities where each subject washed and then
for analysis.
supply the required shielding (see Figure 49). This
steel room was mounted on large trailer alang
designed to house the electronic components ofthe
jects to be counted were brought aboard up the
ship’s ramp from the beach on each istandvisited.
Also available on the tank deck were shower
changed into an uncontaminated paper suit to
avoid the possible risk of measuring any external
contamination that might be present.
A 5-in. NaI (Tl) crystal (Harshaw) was placed
over the subject at a distance of 19 in. above the
apex of the chair (see Figure 51). The pulses from
the photomultiplier were fed into a linear ampli-
fier (Cosmic Radiation Lab. Inc., Model 101), and
thence into a 100-channel analyzer (TMC-PA
10,000
T
i
T
COUNTS #5 MINUTES / 20 Key CHANNEL
cs'3" (9.66 Mev)
Since the principal photopeaks in these persons
Cs'3* and Zn**, and since the levels were suffi-
subjects for 5 or 10 min with the particular geometrical arrangement described above. The data
were printed outon a paper tape of a Victor adding machine, andthe tapes were returned to BNL
Analysis of Gamma-Ray Spectra
The quantitative interpretation of the gammaray pulse-height data for the discrete gamma
energies involved the graphical reduction of the
data. A typical spectrum of a Marshallese is shown
in Figure 52. The ordinate represents counts per
20-kev pulse-height increment, and the abscissa
represents gamma energy. In the graphical stripping method emploved,**? the activity of the
highest energy gamma-ray in the mixture, K*?
(1.46-Mev), is determined directly from the
ordinate value ofits total absorption peak. Then a
A
analytical procedures,and has made possible verv
~oet « ¥
used to supplemeng.quantitative radiochemical
channel-by-channel subtraction of the distribution
1000 +
L212 Mev) |
Ko
100
(1.46Mev)
corresponding to the abundanceofthis particular
gamma-ray or radionuclide is made from the spectrum. When this subtraction is completed, the
concentration of the gamma-ray of the next
highest energy, Zn®* (1.14-Mev) can be estimated
from the ordinate value of its peak. The distributlon corresponding to the concentration of the
second gamma-rayis then subtracted from the remainingdistribution, and the process is continued
with Cs'37 (0.66-Mev) until all the three major
0
L.
Oo
020
040
1
i
1
060 O80
100
ENERGY (Mev)
gamma-ray-emitting components have been determined.
i
1.20
1.
Figure 52. Gamma spectra of Marshallese male (subject
3¢4, age 40, wt 70 kg - solid line) and normalized plastic
phantom (containing 0.64 uC Zn**, 1.22 uC Cs'9’, and
140 g K - dashed line), 1959.
This stripping processis illustrated on a spec-
trum of the plastic phantom containing known
amounts of K*°, Cs'**, and Zn® (Figure 53). It is
to be noted that at the concentrations used here
(approximately the mean concentrations found in
the Marshallese), the Compton contribution of
1185591
Bt