Some Physical Aspects of Relative Biological Efficiency

TLDR

The paper reviews existing methods for characterising ionising radiation quality, noting that prior approaches ignored δ‑track formation and highlighting the special issue of local energy transfer (L.E.T.) and its mean value. It aims to define the concept of local energy losses, derive new values for electrons below 2 keV from recent experiments, and calculate a mean L.E.T. while emphasizing its limitations. The study evaluates a range of radiations—including 1 MeV and 210Po α particles, tritium β particles, 1–2 MeV monochromatic electrons, 25 MVp, 220 and 100 kVp X‑rays, and 60Co γ rays—to quantify local energy deposition in water.

Abstract

After surveying the broad nature of the problem of relative biological efficiency, an account is given of methods which have been used to characterise the quality of ionizing radiations. These former methods have ignored the phenomenon of secondary or δ-track formation and reference is made to treatments which take this factor into account. The concept of “local” energy losses is defined, and tables are given for various radiations, showing the amounts of “local' energy dissipated in water with respect to particle kinetic energy range. The radiations considered are 1 MeV and 210Po α particles, tritium β particles, 1 and 2 MeV monochromatic electrons, 25 MVp, 220 and 100 kVp X rays and 60Co γ rays. The special problem of the L.E.T. of electrons of less than 2 keV is considered and new values are derived from recently published experimental results. A mean L.E.T. is defined and calculated; its limitations are emphasised.