~
+i
used to supplement quanutative radiochenncal
analytical procedures, and has made posstble very
rapid and positive identibc avon of gamma-enuiing
radionuctides. The principles of ia ive gamma
spectcomnetrs as applied to human berngs have
been previously described.”
‘Phe steel room constructed at BNL. in 1957 tor
the Marshallese surveys has been described previously.” Phe “portable” 2t-ton steel room, 5x5
xb-ft with ¢-in.-chick steei walls, was used to
supply the required sielding (see Figure 49). This
stecl roum was mounted on a large trailer alung
with a 7x8 x 10-ft air-conditioned wooden :oom,
designed to house the electronic components of the
counter (see Figure 50). Uhe trailer was mounted
on the tank deck of the Navy LST, and the sub-
100, Quarts Line Storaye Pulse- Height Analyzer),
‘Pwo complete detectors aad analyzers with the
necessary adssodated clectromie circulars were
taken along, since considerable dithiculty had been
expernenced during the previous year if) alalatammunag the whole-bods counting svstem operaUonal under the conditions of tropical heat and
hamidity Housing of the elew tronic equipment 1
an air-conditioned, dehtunnditted togm during
operation was of considerable assistance tn iain:
Laing tts stability.
Since the pnneipal photopeaks un these persons
were known trom the prevtous studs to be due to
Csi
oand Zn". and since the levels were sutticently high, it was only necessary to count the
subyects for For LO min with the particular yeo-
jects to be counted were brought aboard up the
ship’s ramp from the beach on each island visited.
Atso available on the tank deck were shower
inetrical arrangement described abuse Cle data
were printed out on a paper tape of a Victor add-
avoid the possible risk of measuring any external
Analysis of Gamma-Ray Spectra
facHines where cach subject washed and then
changed into an uncontaminated paper stut to
contamination that might be present.
A S-in. Nal (V1) crystal (Harshaw) was placed
over the subject at a distanceol 19in, above the
apex of the chair (see Figure 5t}. Uhe pulses from
the photomuluplier were fed into a linear amplifier (Cosmic Radiation Lab Inc.. Mode! 101), and
thence into a 1OO-channel analyzer (TMC-PA
Ing machine, and the tapes were returned to BNE
for analysts.
The quantitative interpretation of the garmiarav pulse-height data lor che discrete garmima
energies involved the graphical reduction ot the
data. A typical spectrumof a Marshallese is shown
in Figure 52. The ordinate cepresents counts per
20-kev pulse-herght increment, and the abscissa
represents gamma energy. fo the graphical strip-
ping method employed, othe activity of the
highest energy gainiua-ray in the mixtuce, Kt
(1. t0-Mevi, ts determined dicectly from the
ordinate Value ofits total absorption peak Then a
COURTS 65 MINUTES ¢ 20 Kev CHANNE®
us 370 66 Mev)
za 112 Mew)
channet-by-channel subtraction of the distribution
corresponding to the abundance of this particuiar
gallna-ray or radionuclide is made trom the spec-
trum. When this subtraction is completed, the
concentration of the gamma-ray of the next
highest energy, Zn” (1. 14-Mews can be estimated
from the ordinate value of its peak. Uhe distribution corresponding to the cuncentration ol the
second gamma-rayis then subtracted from: the re-
WO :
Maining distribution, and the process is continued
with Cs’ (0.b0- Mev) uodl all che three niajor
uQo
+
G24
:
Y4O
see
960 080
100
ENERGY (Mev)
120
140)
1.60
Fietie 02 Gattina spectra ot Marshiadiese miaie (subject
Sdoaee owt 7 ke solid tines aad noroalized plastic
phantom (contain (bbe An O22 ee Gs. andl
Pie Ro
dashed tied, PG4
2alnina-ray-enutaog components fave been determined.
This stripping process is dlustrated on a spectrum of the plasac phantom containing known
amounts OF RY) Cs! and Zo (Fizure 3.5). bes
to be noted that at the concentrations used here
Cupprosumately che mean concentrations tound in
the Marshallese), the Compton comtirtbutanof