RBE OF 440-MEV PROTON RADIATION COMPARED TO 125 KVP X-RAYS FOR LD-50(30) OF MICE.

The relative biological effects of 440-Mev protons were compared with the eifects of 125-kvp x rays using the included for mice exposed to 730-Mev protons at a dose rate ranging from 500 to 1000 rad/min and 200-kvp x rays at 30 rad/min, and for mice exposed to 440-Mev protons at a dose rate of 80 rad/min and 250-kvp x rays at 43 rad/ min. The values for relative biological effectiveness were calculated as 0.7 plus or minus 0.2; 0.8 plus or minus 0.1; and 0.7 plus or minus 0.3, respectively. (C.H.)