Chromosome aberrations induced in human lymphocytes by radiation from ²⁵²cf

In vitro dose-response curves of unstable chromosome aberrations in human lymphocytes have been obtained for ²⁵²Cf neutron radiation. The aberration yields fitted best to the linear function Y = aD, which is consistent with the single-track model of aberration formation for high LET radiation. The curves have been compared with others previously produced in this laboratory for several energies of neutrons and for ⁶⁰Co gamma radiation. The r.b.e. for ²⁵²Cf with respect to ⁶⁰Co is 27 at very low doses, decreasing to 6 at an aberration yield equivalent to 400 rad of 18 rad/hour gamma radiation. A profile of chromosome-aberration induction with depth in a perspex phantom was obtained by placing blood samples at several distances over the range 0·65-2·0 cm from the californium source. This profile was compared with depth-damage calculations for a radium needle. The r.b.e. of ²⁵²Cf radiation relative to ²²⁶Ra gamma radiation increased with the distance from the source, implying that californium is more effective at greater distances in destroying the ability of cells to divide, which may be an advantage in the treatment of large tumours.