Exposure to External and Internal Radiation — in Vivo Measurement of Radionuclides in Man; Body Burden and Project Title: Kinetic Factors, Computer Applications 16, Technical Progress in FY 1973: (Cont'd. ) i RX-01-01-(b) The Pu-238, Be neutron trradiation facility currently employed for totalbody neutron activation analysis has shown itself to be superior in many respects to the previously employed 14 MeV neutron generator, In the first year of its operation, over 300 activation analyses have been performed on patients. The precision of the technique for measurement of calcium, sodium, and chlorine has been +1, 2, and 2% respectively. The precision for the measurement of phosphorus however, has not been satisfactory (+ 4%). Efforts are being made to improve the precision of this latter measurement primarily by means of an improved computer program for analysis of the gamma spectral data, Efforts are also in progress to improve the operation of the activation technique and to apply it to the analysis of other elements in the human body. (Cohn) oN In the efforts to define the radiation dose response curve between zero and the natural dose rate, screening studies directed to the selection of the most suibable organism and end point were continued. Most of the organisms considered were found to have such small responses at low doses as to not be useable for obtaining statistically significant results with feasible population numbers. The best organism now appears to be a strain of Eschericia coli identified as ATCC strain #10798 C,E, Clifton K-12 (A). In "Etude Radiobiologigue Du Systems Lysogene D'E.Coli K12. II Induction Par Les Rayons X., Etude Des Faibles Doses. "Annales de L'Institute Pasteur 90, 458-81 (1956), Marcovich reported on the effects of x rays on the induction of K-12(A) to produce A phage, using radiation doses as low as 0,3R. This is apparently the lowest dose for which an effect has been recorded in bacteria, In the current studies the K12 (A) is grown under various conditions, the free \} phage is harvested and the phage is plated with the indicator strain, ATCC # 12435, J. Lederberg W 1485, The end point measured is the number of plaques formed perplate, When grown under : - normal background conditions in a medium with reduced potassium content there is one plaque per 104 cells. The results under reduced background conditions are not available yet. Another aspect of the study is underway using 250 KVP x rays at various doses up to 1200 R to verify the dose- effect curve reported by Marcovich. Among the new computing programs developed is one that generates theoretical x-ray spectra associated with a given KVP and with specified filters. This is part of a combination of theoretical and experimental mehes to the development of special filters that utilize the K-edge fnuity in the mass absorption coefficients of various elements to .Yadiographs and to reduce patient radiation doses by cutting out x rays ‘of energies above and below those desired. This method may also become useful in enhancing the contrast associated with certain labeling elements, particularly iodine, in problems such as gall bladder visuali- zation and in thyroid studies. Combinations of silver, tin, rhodium, gadolinium, and cadmium filters used with 30, 35, 40, 70, 80, and 90 KVP (See Continuation Sheet) 1419174 . RX- 19