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NEW
YORK
UNIVERSITY
Institute of Environmental
550FIRST
AVENUE,
AREA
679-3200
212
ANTHONY
LONG
MAIL
J. LANZA
MEADOW
AND
NEW
TELEPHONE
CENTER
Medicine
YORK,
RESEARCH
“ROAD,
MEDICAL
N.Y.
LABORATORIES
STERLING
ADDRESS:
10016
AT
UNIVERSITY
FOREST,
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5S0 FIRST
AVENUE,
VALLEY
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NEW
YORK,
N.Y.
10016
June 19, 197S
.*
Dr. Robert A. Conard
Brookhaven National Laboratory
Upton, New York
11973
Dear Dr. Conard:
As I mentioned i.n our phone conversation this past
Tuesday, (June 17) , we have now completed the measurements
necessary to estimate our lower limit of detection for 241Am
(in the skull bones) in the presence of elevated levels of
137C.S. Briefly, the way in which this was calculated is as
follows: we started by making the assumption that cesium and
potassium have approximately the same distribution in the
body; if this is true then there is.approximately 6.6% of
the total 137CS body burden present in the head. A further
assumption was then made that the average elevated 137CS body
burden i.sabout 200 nCi whi,ch would mean a head burden of
approximately 13 nCi. A “phantom” head was then fabricated
to contain this amount of activity and was employed to derive
the background used in the calculation of a lower limit of
detection of 40 nCi 241Am. Employing a safety factor of 10
and assuming that that skull contains 10% of the skeletal
burden, 4000 pCi represents only 10% of one maximum permissible
body burden.
As we discussed, I think that the head would be the best
measurement site for determining possible internal contamination for several reasons:
it represents a high bone mass with
very little intervening soft tissue, 241~ is a bone-seeking
radi.onuclide, 137cs if present, will be in the brain which.
is not a concentrator of this nuclide and which is partially
Furthermore, as I mentioned a
shielded by the skull bones.
body burden of 12 nCi of 90Sr would not add any appreciable
Bremsstrahlung background to the 241Am energy region of
interest.
In general, then, this site would be much more
applicable to measurements of the systemic burden of this
nuclide than is the anterior thorax for lung counting.