| Radiation effects of fast and thermal neutrons on wheat
: I. Genetic effects of neutrons on Einkorn wheat S. MATSUMURA National lnstitute of Genetics, Misima, Japan Thermal neutron irradiations were conducted in the thermal column of the Japan Atomie Energy Research Institute's Nuclear Reactor, JRR-1. Dormant seeds of Triticum monococcum flavescens were treated at five different distances (I-V) for 2 weeks (actually 990.8 kWh). The thermal neutron integrated flux, therefore, ranged from 4.4 to 37.5 x 1012 nth/cm2. The data are shown in Table 1. The irradiated seeds were almost uniformly injured in each treatment. There was no germination in (V) and about 2/3 of seeds germinated but about one half of the seedlings soon died in (IV). The higher the dosage of thermal neutrons, the more delayed were germination and growth of seedlings and the more reduced were survival rate, height of mature plants and seed fertility. The frequency of chromosome aberrations and chlorophyll mutations increased with the increase of dosage, as expected. If we assume that gamma-contamination for 1012nth/cm2 is 430 r by Dr. KONDO's measurement with FRICKE's dosimeter, the 1r equivalent effects produced by thermal neutrons are calculated as follows, compared with the results conducted last year by X- and gamma-irradiations at 10 and 20 kr: for seedling growth, 1 r =2.0 x 109 nth/cm2 for seed fertility, 1 r=1.4 x 109 nth/cm2 for chromosome aberration, 1 r = 1.2 x 109 nth/cm2 for chlorophyll mutation, 1 r =2.3 x 108 nth/cm2. The exposure to 14 MeV neutrons obtained from (D, T) reaction was carried out in Oak Ridge National Laboratory. Dormant seeds of T. monococcum flavescens were fixed at the distance 6.3 cm from the tritium target and the exposure periods were varied at constant dose rate 65.4 rad/min. The dosage ranged from 0.5 to 20 krad. At the same time X- and gamma-radiations were used from comparison at 10 and 20 kr in ORNL. The effects of both radiations seemed to be rather stronger than those found in the same experiments last year in our institute. The data are given in Table 2. There was no germination or almost none at more than 2 krad of fast neutrons. At 0.5-2 krad survival rate, height of mature plants and seed fertility decreased and chromosome aberrations and chlorophyll mutations increased with the increase of dosage. Relative biological effectiveness (RBE) for fast neutrons, compared with X- and gamma-rays, is calculated as follows:
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