Moisture content of seeds affects relative biological effectiveness of alpha particles but not protons in thermal neutron exposure

Abstract

The influences of moisture content of barley (Hordeum vulgare L.) seeds which were presoaked for 13 h and re-dried before irradiation on boron addition effect (BAE) and relative biological effectiveness (RBE) of alpha particles and protons were evaluated. Seeds of normal (10.21% in embryo), low (2.55%) and high (28.0%) moisture content showed different regression of BAE values on the absorbed amount of 10 B. The regression coefficient was highest for normal moisture content, followed by low moisture content, and the lowest for high moisture content. RBE of alpha particles also significantly differed between the moisture contents. Seeds of normal, low and high moisture contents showed 46.4, 37.4 and 17.0 of RBE value, respectively. Contrarily, RBE values of protons did not significantly vary with moisture content. It was found that the ratio of RBE of alpha particles between different moisture contents could be expressed by the product of the three ratios, i.e. ratio of sensitivity to gamma-rays, ratio of BAE, and ratio of moisture content. It was concluded that adjustment of moisture of the seeds to normal content (about 10%) is important to get a high value of both BAE and RBE of alpha particles.

Relative biological effectiveness of alpha particles and protons varies with biological criteria, and values are mutually correlated in thermal neutron exposure

“…As shown previously (Ukai et al 2009a(Ukai et al , 2009b, the following relationship holds between the ratio of the D 50 of gamma-rays to that of thermal neutrons on the one hand and …”

“…Thermal neutron exposure and dosimetry of neutron flux and contaminating gamma-rays were performed at the Research Reactor of Kyoto University, as described previously (Ukai et al 2009a). Thermal neutron exposure was performed twice.…”

“…For each of the M 1 effects, the dose required to give 50% of the value of the non-irradiated control (half reduction dose, D 50 ) was estimated from dose-response curves as previously shown (Ukai et al 2009a). The dose required to give a mutation rate per cell of 8% (D 8 ) was similarly estimated.…”

“…Recently, we presented a method for the simultaneous estimation of the RBE of alpha particles and protons (Ukai et al 2009a(Ukai et al , 2009b. RBEs were as high as 55.0 and 48.7, respectively, in barley seeds immersed in various concentrations of 10 B-enriched boric acid and re-dried before thermal neutron exposure.…”