LRAD, semiconductor, and other radiation detectors applied to environmental monitoring for alpha and beta contamination

摘要

The very short range of alpha particles in air (typically 2 to 3 cm) has severely limited the utility of traditional alpha monitors for detecting and identifying small amounts of alpha-producing contamination in soil, water, and other materials. Monitors based on the traditional alpha detector technology are often hard-pressed to meet continually increasing sensitivity requirements. The long-range alpha detector (LRAD) avoids the distance restriction by detecting the ions produced by the interaction of alpha particles with air, rather than the alpha particles directly. The ions are swept into an ion detector either by a moving air current (generated by a fan) or a weak electric field. The LRAD is limited by the distance the ions can travel in the (approximately)5-s ion lifetime (1 to 100 m), rather than by the several-centimeter range of the alpha particles. The LRAD can be used to perform sensitive (less than 10 disintegrations per minute per 100 cm(sup 2)) field scans of large surface areas (ranging from hundreds of square meters of concrete floor to thousands of square meters of soil). Since the ''active'' element in a LRAD is a solid-metal ion collection plate, the detector is relatively inexpensive, easy to service, and quite rugged. However, the LRAD cannot supply any spectroscopic information to help identify the contaminant. Semiconductor, ionization chamber, and other types of particle detector can generate clean spectra from small samples of material and identify trace amounts of surface contamination. These detectors are rugged enough to use routinely in a mobile laboratory for isotope identification of ''hot spots'' located by the LRAD system. This detector combination has applications to field beta-particle monitoring (such as would result from tritium contamination) as well as alpha particle detection.