Abstract
Micronucleus formation frequency of onion root tip cells induced by high LET radiations showed a characteristic dose-effect relationship; in the low dose region that averagely a few tenth of the charged particles traverse the cell nucleus, the frequency per dose is larger than that in higher dose region. It may be due to some specific phenomena such as by-stander effect in low dose rate low dose irradiations; we examined difference between high dose rate and low dose rate low dose irradiations intensively. But no significant difference could be found.
By examinations of the higher doses, we confirmed a bell-shaped dose-effect curve. The peak corresponds to dose that averagely from five to ten particles traverse the cell nucleus. A mathematical model was constructed using a: micronucleus formation frequency per particle traversal, n: number of the particles traversing the cell nucleus following a Poisson distribution of average m, μ: frequency of the micronucleus, and Sn: surviving probability of a cell of which nucleus is traversed by n particles escaping direct death or mitotic delay. Observed value could be explained with the model; the micronucleus formation was found to be strongly related to a character of radiations, which is assembly of particles.
We now investigate LET dependence of a and S for heavy ions, and dose-effect relationship of X-rays, to make comprehensive evaluation of the micronucleus formation.
