Project Title: 16. Effects of Radiation on Living Organisms Early and Late Effects of Radiation of Different Quality and at Different Dose Rate Technical Progress in FY 19/3: RX-03-O1- (a) The Radiological Research Accelerator Facility (RARAF) has been fully developed to provide six target positions for various radiobiology and radiological physics experiments, including a low scatter irradiation environment and a special charged particle physics laboratory. Only minor additions to the instrumentation of some of the new beam lines are required. The transfer of all essential accelerator controls to the new console has been completed. Reliable semi-automatic operation of the Van de Graaff generator has been achieved to simplify routine operation of the accelerator after initial adjustments have been made by an experienced operator. Irradiations are terminated by an ionization monitor after the required dose has been delivered. Neutron-producing targets continue to be replaced periodically as they become exhausted or contaminated. A wide range of neutron energies from a low energy spectrum less than, 100 kev to monoenergetic neutrons in excess of 15 MeV have been used to irtadiate various systems including Drosophila, Tradescantia inflorescences, Vicia faba seedlings, Osmunda regalis spores, Chinese hamster lung cells, rats and mice. In all of these studies the relation between various effects and the absorbed dose was determined together with the dependence of RBE (relative to 200 kVp x rays) on dose. In the case of Vicia OER as well as RBE was determined as a function of neutron energy. Radiological physics support including design of irradiation techniques and construction of the required fixtures, dosimetry and spectrometry, was provided for all of these studies. Instrumentation has been acquired and is being developed to extend neutron spectrometry down to 2 keV. . A major radiological physics effort was the establishment of a special low-scatter environment essential for a new project involving an international intercomparison of neutron dosimetry sponsored by the ICRU. Special equipment developed for these measurements included precision radiation monitoring instruments, accurate optical alignment fixtures, and a pneumatically-handled 2.5 mg californium-252 source. Microdosimetry measurements using wall-less tissue equivalent proportional counters to determine event size distributions were completed for simulated tissue sphere diameters of 1, 2, and 4 um and for 13 neutron energies ranging from a spectrum less than 100 keV cto monoenergetic neutrons up to 15 MeV. A comparison of walled and wall-less proportional counter data was also completed using 0.5, also 1 and 2 um sphere diameters tron energies of 0.2, 0.5, 2.2, and 15 MeV. The accelerator is used by the BNL Applied Science Department for analysis of trace «in the environment by charged particle proton x-ray fluorescence. : (Bond, Rossi) Three reports show that fission neutrons have a high RBE for inducing mammary neoplasia in the rat with the suggestion that the RBE for neutrons is higher at low trons at various RARAF, and x-ray nical error, the doses than at high doses. To quantitate the RBE for neudoses, neutron doses of either 1, 4, or 16 rad, produced at doses of either 80 or 240 R were used. Because of a techexpected neutron energy ranged from approximately (See Continuation Sheet) t1V92b1 RX-168