with a background of approximately 30 counts per
have been written to relate urine assay data t
minute.
body content at a given time after contaminati
Simpson gas flow proportional counters,
acquired in May 1945, were operated originally with
or at the time of contamination.
an efficiency of 48 to 50 percent and a background
one resorts to the convenience of computerizeca
of about 1 count per minute.
Modifications of these
However, whe
reduction and analysis or to hand calculations
counters, chiefly lining the counting chamber it-
practiced in the early days, the procedures ar
self with electrolytic copper foil, reduced the
based, at least in part, upon the systemic mod
background to 0.15 + 0.1 count per minute.
urinary elimination developed by Langham and c
These
counters, in continuous use until 1957, were sup-
leagues.“
plemented in 1952 by four NMC gas flow proportional
tained from studies of human subjects of short
counters operating at 48 to 49 percent efficiency
expectancy.
with backgrounds of about 0.1 count per minute.
The
This model was derived from data ob
These persons were given plutoniu
citrate by intravenous injection in 1945.>
La
NTA procedure, adopted in January 1957, involved the
used these data to derive a simple power funct
counting of microscopic tracks instead of electronic
equation to relate urinary excretion rate to b
detection.
This gave a background of 0.005 count
per minute with an efficiency of 50 percent.
The
overall procedure had a sensitivity limit (50 per-
content.
The power function is often used to
approximate a set of exponential functions cha
acterized by both decreasing the amount and re
cent confidence level) of about 0.05 disintegra-
rate from various compartments.
tion per minute per sample.
yses of the data from the original patients an
From April 1966 to
More recent a
January 1967, zinc sulfide scintillation counters
from industrial exposures suggest that either
were used; these devices were about 45 percent effi-
power function or multiple exponential functio:
cient with a background of 0.01 + 0.006 count per
can be used to fit the observed excretion patt
Minute.
Although most of the human data were obtained
Acquisition of alpha spectrometric equip-—
ment in 1966 led to measurement of all samples by
ing the first 140 days after injection, some
alpha spectrometry after January 1967; the proce-
information is available for excretion periods
dure yields an efficiency of 27 percent and a back-
to 5 years.
ground of 0,004 + 0.003 count per minute.
latter data give the following specific expres:
In use
Use of power functions based on t:!
presently is an 8-detector system with electronic
for rates of urinary and urinary plus fecal ex
data processing capability, which allows one to
tion in man given plutonium citrate over a per
Measure simultaneously isotopes of
239-240), and 2420
of 5 years:
2
36p,, 2385, >
ER.
In addition to techniques such as alpha spec~
trometry and proportional counting, plutonium can
be measured also in the urine by a track’etch procedure following neutron irradiation.
ER
= 0.002 t
0.74
~’
= 0.008 t0°74,
(Eq.
(Eq.
[In the lat-
ter system, neutrons are used to produce fission
where ER, and ER|
fragments, usually in a thick plastic material
injected dose exereted per day and t the days f
supporting the plutonium-containing sample.
lowing exposure.
The
damaged areas of the plastic are then etched and
represent the fraction ot
Following a single exposure at a known tin
can be quantitated by use of optical means or spark
one can estimate the body burden (Q) at time of
counters .?
exposure from measurement of a 24-hour urine sr
Although not in wide use at present,
this system is said to offer a considerable improve-
men collected at a later time (t).
Ment over others in terms of sensitivity.
the relation
ESTIMATES OF BODY BURDEN FROM BIOASSAY TECHNIQUES
ER. = 0v/Q,
Using Eq. 1
(Eq.
Urine assay data are used as the basis for
determining the body burden of internally deposited
plutonium.
26
In more recent times, computer programs
where U is the amount of plutonium measured in
24-hour urine sample at time t, then