Alpha-particle spectroscopy with TASTRAK (CR-39 type) plastic, and its application to the measurement of hot particles

Two applications of TASTRAK plastic to measurement of alpha activity are described. (1) Alpha particle spectroscopy is possible by automated analysis of etched alpha particle tracks in TASTRAK (CR-39) type plastic. The method is based on the measurement of two geometric parameters of etched tracks, the minor axis, and the diameter of the etched out track end. Accurate measurement of these two parameters allows reliable separation of tracks according to alpha particle energy, with a FWHM of 80–110 keV (1.33–2%) over an energy band of 1.1 MeV. Within this band the intrinsic measurement efficiency is as high as 0.75, a critical factor for possible low level measurement applications. The results indicate that a basis exists for a robust working method for alpha particle spectroscopy in TASTRAK plastic. (2) A method is being developed for simultaneous measurement of size and activity of alpha emitting hot particles. A hot particle is defined here as a volume of alpha active material, which may be attached to an inert particle. Hot alpha emitting particles produce characteristic radial clusters of tracks in etched TASTRAK. Automated image analysis of each track yields the following values: track co-ordinate, azimuth angle, dip angle, and track range. With these values, track paths can be projected above the plastic surface. A multi-step procedure is described which calculates three parameters for a hot particle: the alpha activity, the physical size and distance of the particle above the plastic. The method is demonstrated as applied to anthropogenic hot particles in the Chernobyl region, Ukraine, and to natural uranium hot particles in soil from Bristol, UK.