Precise determination of critical features in radiohalo-type coloration of biotite

Abstract

HIGH precision techniques of photomicrography and densitometry are here used to investigate the coloration of artificially α-irradiated biotite. A computer simulated spherical radiation pattern is found to produce coloration peaks, contrary to the negative results of earlier investigators. A clearer understanding of the relationship between the usually defined α ranges and ‘coloration ranges’ is obtained as well as the elucidation of several other features of radiohaloes. In spite of more than a half a century of investigation, the parameters of α-induced radiation damage in biotite are still only crudely known. The principal parameter, the ‘range’ of the α particle, has been studied primarily by means of the uranium radiohalo and its close relatives (ref. 1; see also, refs 2 and 5). The coloration rings of these haloes lend themselves to direct, though somewhat inexact, measurements of the ranges of α particles of various energies. Early investigators also made use of measured α ranges in air and then converted these to ranges in biotite. Recently, Gentry^2,3 has made a substantial number of direct ‘range’ measurements in biotite and other minerals by bombardment with accelerator-produced α particles.