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Physical quantification of the biological effectiveness of ionizing radiations
Author(s) -
Watt D. E.,
Kadiri L. A.
Publication year - 1990
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560380402
Subject(s) - linear energy transfer , ionizing radiation , ionization , absorbed dose , radiation , atomic physics , neon , relative biological effectiveness , secondary electrons , dosimetry , electron , spectral line , gamma ray , irradiation , physics , neutron , chemistry , radiochemistry , nuclear physics , ion , nuclear medicine , medicine , quantum mechanics , astronomy , argon
Abstract The role, and limitations, of the fundamental physical quantities used in our current system of dosimetry for the protection of individuals against the hazardous effects of ionizing radiation is discussed briefly. A major limitation is the inability to correlate biological data, in a unified way, as a function of linear energy transfer with the consequent necessity for quality factors. From consideration of the various interaction processes undergone by charged particles in the equilibrium slowing down spectra generated by the incident radiation field, it is shown that good correlation of biological effects, for all radiation types, can be achieved in terms of linear primary ionization. The implication is that delta‐ray effects play at most a very minor role, at moderate fluences, and that, consequently, the absorbed dose is an unsuitable parameter for describing radiation effects. Structure in the radiosensitive targets is observed to have a critical dimension of about 2 nm. It occurs only when double‐stranded DNA is present and the magnitude of the inactivation probability is consistent with double‐stranded breaks being the significant lesion. Calculation is made of the yield of lesions as a function of the mean free path for primary ionization. Differential spectra of radiation quality are obtained for monoenergetic electrons (0.2 keV to 30 MeV); for characteristic X‐rays from carbon, aluminium, neon, potassium, copper, silver, and tungsten; for 50 kV X‐rays, 250 kV X‐rays, 241 Am, 137 Cs, and 60 Co gamma rays; and for neutrons with energies between 0.1 and 50 MeV. Damage by electrons is shown to be predominant at the ends of their tracks between 50 and 200 eV, whereas this is not so for the proton recoil spectrum generated by neutrons above 1 MeV. Proposals are made for a unified system of dosimetry that is independent of radiation type and that obviates the need for quality factors. The method is thought to be of general applicability to irradiations by nuclides incorporated into mammalian cells, by ingested emitters, and by external sources.