11C and 15O induced in the mouse by 175 MeV protons

The total production of 11C, 13N and 15O in the mouse by protons with a mean energy of about 175 MeV was found to be 8 200, 1 500 and 14 000 nuclei per g-rad, respectively. About 40 per cent of the total induced 11C activity was eliminated through expiration and about 2.5 per cent with the urine during the first hour after irradiation. The expired gas contained 11CO and 11CO2 in the ratio 2/1. The urinary 11C activity was bound to several compounds, the chemical nature of which was not established. The 15O activity behaved as H2O and was found not to be eliminated from the body during the short observation time available. The additional, fractional, integral radiation dose due to decay of induced nuclides is less than 0.1 per cent, and can be neglected since no accumulation to any small organ was seen. Sensitive means for an estimate of integral dose based on the induced nuclides would be the detection of 11CO activity in expired gas or in blood.