.. ,:. l= ., Eil 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, TUXEDO, 5S0 FIRST AVENUE, VALLEY N.Y. 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.