Abstract
Dry seeds of di-, tetra-, and hexaploid species of Triticum and Avena and of a diploid species of Aegilops, were exposed to thermal neutrons from the beam hole No. 16 of JRRl, and their biological effects were investigated. The seed germination was not affected by the dose of 9.2 x 1011nth/cm2 or 1.8x 1012n res /cm2 (obtained by using 0.5mm Cd-filter to exclude thermal neutrons), but was clearly disturbed by 9.2x1012n th/cm2, excepting hexaploid species. Seedling heights of diploid species decreased distinctly by 1.8x1012n es/cm and extremely by 9.2x1012nth/cm2, but tetra- and hexaploid species were more tolerant than diploids. Moreover, the experiments indicated that Avena is generally more resistant than Triticum. Both length and width of the first, second, and third leaf-blades were reduced by certain dosages, the first leaf being most tolerant and the third most sensitive. This fact may sugggest that leaves in different developmentai stages show different responses to radiations. LD-50 for thermal neutrons, X-rays and gamma-rays were determined for every species. Comparing the survival rate 100 days after sowing, the dose of about 2.1 x 108nth/cm2 of thermal neutrons (plus other contaminating radiations) in JRR-1 was calculated 40
