Physical parameters of radiations determined from the inactivation of ribonuclease.

Abstract

SummaryIn a previous paper the target theory of Lea was examined and the data required by the theory were modified. Several assumptions were made about the stopping power for low-energy electrons and the molecular cross-section for primary ionization. An experiment with the enzyme, ribonuclease, has been performed to determine which assumptions give consistent results.The effects of several radiations on the enzymic activity of the ribonuclease have been found. The exponential decrease in activity with dose in all cases indicates that a single-hit process is involved. Cross-sections have been calculated by the modified Lea theory. Consistent values of the cross-section of ribonuclease have been obtained for a specific value of the parameter used to calculate the primary ionization (M = 0·3), and for a certain model of the stopping power of low-energy electrons (dE/dx follows the Bethe-Bloch theory for E⩾400 eV and dE/dx∝ E−0.5 for E < 400 eV). The average cross-section of (8·4 ± 0·2) × 10−14 cm2 is close ...