Induced Pollen Lethals from Seeds of Datura Stramonium Exposed to Radiation from a Nuclear Detonation.

Biological effects of ionizing radiations produced by an explosion of a nuclear device may be complicated by the heterogeneity and extreme intensity of the emissions. Changes in biological systems may be induced that are not attributable to blast, heat, or single-type radiation effects. Many data and discussions have resulted from laboratory studies of radiations, but until recently scant information was available on the effects induced by the unparalleled intensity of radiation from an explosion of a nuclear device. This study presents some of the results of the combined biological tests on the effectiveness of a nuclear detonation, reported in part by Conger' and Kirby-Smith and Swanson.2 The present investigations were particularly concerned with the biological efficiency of fast neutrons from a nuclear device, as compared to other types of radiation, especially X-radiation. Neutrons and X-rays produce the same kinds, or qualitative types, of rearrangements for chromatid as well as for chromosome effects, but the two radiations differ markedly in their quantitative effects.34' 5 The sensitivity ratio, about 3 or 4 for fast neutrons as compared to X-rays, is different for different kinds of aberrations. Fast neutrons have been observed to be about three times as efficient as X-rays in inducing single gene mutations in Drosophila.6 Thermal neutrons have been reported to have a cytogenetic effect of about eleven times that of X-rays per unit dose.' The difference in effectiveness between thermal neutrons and Xrays is believed to be due largely to the internal origin of the protons and alpha rays which result from capture reactions. However, the discrepancy that apparently exists between the two types of neutrons is thought to be a manifestation of the relative ease with which thermal neutrons are captured. Pollen lethals in Datura, as employed in studies of aged seeds8 and thermalneutron effects,9 furnish a method for determining with considerable accuracy the biological efficiency of fast neutrons as well as the dose estimates in roentgen equivalents. Additional advantages afforded by rates of pollen abortion in Datura include (1) the rapidity and ease by which large numbers of plants can be handled; (2) an indication of the type of aberration present, viz., chromosomal or gene, with an accuracy of over 80 per cent; and (3) a convenient method for detecting and delimiting the aberrant sectors. The source of neutrons furnished by a nuclear detonation made it possible to determine the relative effect of fast neutrons on mutation rates in comparison with plants from gamma-irradiated and X-irradiated control seeds. Experimental Procedures and Results.-Seeds of Datura stramonium, Line 1, dried to a constant moisture content of 4.9 per cent and sealed in aluminum vials, were exposed to fast-neutron radiation from a nuclear detonation. These seeds were shielded from blast, heat, and much of the gamma radiation, as noted by Conger,' by being inclosed in a temperature-controlled chamber capped with a lead hemis-