47
spectrometry as applied to human beings have
been previously described.*’
Thesteel room constructed at BNL in 1957 for
the Mafshallese surveys has been described previously.* The “portable” 21-ton steel room, 55
x 6-ft with 4-in.-thick steel walls, was used to
supply the required shielding (see Figure 49). This
steel room was mounted on largetrailer along
with a 78 10-ft air-conditioned wooden room,
designed to house the electronic components of the
counter (see Figure 50). The trailer was mounted
on the tank deck of the Navy LST, and the subjects to be counted were brought aboard up the
ship’s ramp from the beach on each island visited.
Also available on the tank deck were shower
facilities where each subject washed and then
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 fom
the photomultiplier were fed into a linear amplifier (Cosmic Radiation Lab. Inc., Model 101), and
thence into a 100-channel analyzer (TMC-PA
COUNTS /5 MINUTES / 20 Key CHANNEL
10,000 ¢
AR
,
1
taken along,since considerable difficulty had been
experienced during the previous year in main-
taining the whole-body counting system opera-
tional under the conditions of tropical heat and
humidity. Housing of the electronic equipmentin
an air-conditioned, dehumidified room during
operation was of considerable assistance in main-
taining its stability.
Since the principal photopeaksin these persons
were known from the previous study to be due to
Cs'*7 and Zn**, and since the levels were sufficiently high, it was only necessary to countthe
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, and the tapes were returned to BNL
for analysis.
Analysis of Gamma-Ray Spectra
The quantitative interpretation of the gamma-
ray 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 gammaenergy. In the graphical stripping method employed,**** the activity of the
highest energy gamma-ray in the mixture, K*°
(t.46-Mev), is determined directly from the
cs!37 (0.66 Mev
ordinate value ofits total absorption peak. Then a
channel-by-channel subtraction of the distribution
7
857), 12 Mev)
1000 F
corresponding to the abundance ofthis particular
gamma-rayor 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 ofits peak. The distribu-
tion corresponding to the concentration of the
100 F
(1.46Mevy)
second gamma-ray 1s then subtracted from the re-
maining distribution, and the process is continued
with Cs'?? (0.66-Mev) until all the three major
gamma-ray-emitting components have been deter0
Q
|
1
i
020
040
060
1
080
1.
100
oh
1.20
1.40
1.60
ENERGY (Mey)
Figure 52. Gamma spectra of Marshallese male (subject
#4, age 40, wt 70 kg - solid line) and normalized plastic
phantom (containing 0.64 nC Zn*, 1.22 uC Cs'*’, and
140 g K - dashed line}, 1959.
‘
1
+
‘
‘
mined.”
This stripping processis illustrated on a spectrum 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
a od
Mp»
rapid and positive identification of gamma-emutting
radionuclides. The principles of mn vivo gamma
100, Quartz Line Storage Pulse-Height Analyzer).
Two complete detectors and analyzers with the
necessary associated electronic circuitry were
a.
used to supplemeng.quantitative radiochemical
analytical procedures,and has made possible very