Some long-term effects of negative pions in mice exposed to partial body irradiation.

The long-term effects of partial body exposure of one-day-old mice given either 60Co gamma rays or negative pions have been studied. Both radiations produced considerable life-shortening; for pions 6.8 +/- 1.5% of life is lost per 100 rad and for gamma rays the value is 5.7 +/- 0.5% per 100 rad. The RBE of pions for ten weeks of life-shortening is about 1.3 compared with 60Co gamma rays, although at lower doses the RBE may be higher reaching about two for six weeks of life shortening. The incidence rate of tumours at any particular age was greater in mice irradiated with pions at the peak and in those given higher doses of gamma rays than in the controls.