RBE OF MONOENERGETIC FAST NEUTRONS: CYTOGENETIC EFFECTS IN MAIZE

Abstract

>The relative biological effectiveness (RBE) of neutrons of 5 energies and x radiation at 3 exposure levels were compared in maize seeds. The maize material used in these experiments had the advantsge for RBE studies of yielding a basically first order dose-response curve (Y = alpha plus or minus BETA D) with low (x rays) as well as with high (fast neutron) LET radiations. The frequency of yellow-green (yg/sub 2/ sectors in leaves, 3, 4, and 5 of young plants grown from irradiated Yg/sub 2//Yg/syb 2/ seeds served as a quantitative measure of response. The mutant sectors are believed to be due mostly to simple chromosome breakage and deletion. An exposure apparatus was used which produced essentially equal dose rates in five rings of seeds placed so as to intercept neutrons of 0.43, 0.65, 1.00, 1.50, and 1.80 Mev. Dose average LET values for these energies are 72, ments were performed at dosages that gave responses which were linear, below saturation levels, and overlapping in range for x rays andd neutrons. These ranges in dosages were 32.8 to 126.4 rads of neutrons and 1500 to 15,600 rads of 250 kvp x rays. RBE values, calculated from relative slopes of linearmore » regression lines for N and X, randged from 42 to 135. Monoenergetic fast neutrons of 0.43 Mev were the most efficient in producing yg/sub 2/sectors as shown by the yield of sectors per krad andd highest RBE values. The RBE values obtained in these experiments are higher than commonly reported. With regard to minimum permissible levels of radiation, these results suggest the alternatives that either chromosome breaks in plants have a much higher RBE than comparable reactions in mand and need not be considered; or that the problem of chromosome damage per se in human tissues be reexamined after exposure to high LET radiations andd/or low LET radiations at low doses or dose rates. (auth)« less