The effect of dose rate on the induction of micronuclei (MN) in human peripheral blood lymphocytes was investigated over a range of dose rates from 0.125 Gy h(-1) to 178.2 Gy h(-1). The response of MN induction was fitted with a linear quadratic model and the alpha and beta coefficients were estimated. It was found that beta values decrease with decreasing dose rate as in the case of chromosomal aberration. At the dose rate of 0.125 Gy h(-1), pure linear response of MN induction was observed. An attempt was made to simulate the calibration curve for the purpose of biological dosimetry at different dose rates and exposure times. The yields when simulated with the exposure time or the dose rate are in agreement with experimental results.

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The effect of electrons and gamma irradiation on the induction of micronuclei in cytokinesis-blocked human peripheral blood lymphocytes was investigated to understand the relative biological effectiveness (RBE) of electrons compared with gamma rays. Blood samples were irradiated with an 8 MeV pulsed electron beam, at a mean instantaneous dose rate of 2.6 x 10(5) Gy s(-1). Gamma irradiation was carried out at a dose rate of 1.98 Gy min(-1) using (60)Co gamma source. A dose-dependent increase in micronuclei yield was observed. The dose-response relationships for induction of micronuclei fitted well to a linear-quadratic relationship and the coefficients alpha and beta of the dose-response curve were estimated by fitting the data using error-weighted minimum chi (2) method. The RBE of 8 MeV electrons were found to be near unity as compared with gamma rays.

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