A quantitative study of pleochroic haloes. —I

Abstract

The beautiful phenomenon of pleochroic haloes is recognized as one of the most striking manifestations of radioactivity. The nature of these haloes was first explained by Joly in 1907 and much research has confirmed and expanded his theory. These haloes consist of minute discolorations occurring in certain minerals, notably mica (biotite). They are spherical in shape and bear at the centre a very small inclusion or nucleus. A thin section of one of these spheres shows under the microscope a series of concentric dark rings, whose radii may be identified with the ranges of α-particles ejected from radioactive substances in the nucleus. The individual haloes present varied appearances, but may be classified according to their blackening in a regular order of development.