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The effects of single pulses and multiple pulses of 7 MV electrons on micronuclei (MN) induction in cytokinesis-blocked human peripheral blood lymphocytes (PBLs) were investigated over a wide range of dose rates per pulse (instantaneous dose rate). PBLs were exposed to graded doses of 2, 3, 4, 6, and 8 Gy of single electron pulses of varying pulse widths at different dose rates per pulse, ranging from 1 × 10(6) Gy s(-1) to 3.2 × 10(8) Gy s(-1). Different dose rates per pulse were achieved by changing the dose per electron pulse by adjusting the beam current and pulse width. MN yields per unit absorbed dose after irradiation with single electron pulses were compared with those of multiple pulses of electrons. A significant decrease in the MN yield with increasing dose rates per pulse was observed, when dose was delivered by a single electron pulse. However, no reduction in the MN yield was observed when dose was delivered by multiple pulses of electrons. The decrease in the yield at high dose rates per pulse suggests possible radical recombination, which leads to decreased biological damage. Cellular response to the presence of very large numbers of chromosomal breaks may also alter the damage.

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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The variable energy microtron at Mangalore University has been used to study the effect of radiation on different materials and biological systems. While studying the effects of radiation, it is essential to have complete knowledge of absorbed dose. In the present study the dose due to 8 MeV electron beam from microtron accelerator has been calculated using chemical dosimeters. The uniformity of dose distribution at various points of the irradiation area also has been calibrated. From the dosimetry studies it is observed that there is a linear relation between dose and electron numbers over a wide range of absorbed doses. It is evaluated that the electron counts of about 1.15 9 10 14 corresponds to an absorbed dose of 100 Gy and a field size of about 4 9 4 cm is available at 30 cm distance from the beam exit window over which the dose distribution is uniform.