Constant Radiation Dose Research Articles

Relation between free radicals and ultraviolet absorption in poly(methyl methacrylate)

AbstractA correlation between the radiation‐induced nine‐line electron spin resonance signal and the unstable component of the optical absorption in the near ultraviolet in poly(methyl methacrylate) is made on the basis of the radiation dose relationship, the dependence of production on irradiation temperature at a constant radiation dose, and on the fading of both signals on oxygen diffusion into the poly(methyl methacrylate) after irradiation. It is concluded that this correlation is applicable only immediately after irradiation and the stability of the initial radical is discussed with respect to the fading results. A process of radical decay and conversion is suggested to account for differences found in the fading characteristics of the two signals.

Der Einfluss des Wassergehaltes auf Inaktivierung und Mutationsrate von r�ntgen- und gammabestrahltenNeurospora Crassa-Conidien

InNeurospora crassa X- and gamma-ray induced inactivation- and reversion-rates for conidia of HNO2 induced mutants were measured. With constant radiation dose inactivation rate is lowest for conidia of medium moisture content. It increases for higher and also for very low moisture content. The semilogarithmic plot of inactivation data for conidia irradiated in suspension or at medium moisture content results in a shouldered curve. A formal analysis using the number of nuclei of multinucleated conidia as numerical reference indicates that ca. 0.5 hits per nucleus are needed to inactivate such a conidium. The data for extremely dry conidia plotted from 0–210 kr likewise closely approximate a single hit curve with a steeper slope than that of the corresponding curve for conidia of medium moisture content.

Relative Biological Effectiveness of Tritium Beta-Particles and Co 60 Gamma-Rays Measured by Lethality in CF1 Mice

The relative biological effectiveness (RBE) of tritium ,-radiation is of interest in establishing tolerance criteria for tritium and for relating RBE to lineal energy transfer (LET). Tritium has considerable application as a tracer for ordinary hydrogen in biological studies (1, 2) and in studies of water-exchange barriers and body water measurements (3). The application of tritium in such studies has been reviewed by Pinson (4). The maximum permissible concentration of tritium in the body and in air and water depends ultimately on the RBE value accepted for its d-radiation. Thompson reported RBE values between 1 and 2 (5), most of which were obtained from studies involving static exposure conditions produced by a constant tritium water (HTO) level in the exposure medium and thus a constant radiation dose rate. Single acute exposures of mammals to tritium result in dose rates that decrease as the concentration of HTO in body water decreases with body water turnover. Some tritium is bound to organic constituents and contributes to the radiation dose (6). This phenomenon, however, is believed to add relatively little to the total dose delivered by the concentration of HTO in body fluids required to introduce the tritium into the more stable positions (7). Effective comparison of two radiations requires that they be delivered at about the same rate. The present study was undertaken to determine the RBE of tritium A-particles and Co60 y-rays for the production of acute lethality in mice when the Co60 e-radiation is delivered at the same exponentially decreasing dose-rate characteristic of a single injection of HTO.