Measurement of radiation and radioactivity

Studies in our laboratory on the detection and measurement of radiation and radioactivity which have been continued for the last more than twenty years are reviewed. As fundamental works, the mean free path length, energy loss and penetration ranges of electrons with a few keV in aluminum and stearic-acid monomolecular layers were measured. Gas multiplication factors in proportional counters with cylindrical- and rectangular-cathodes which have been extensively used in our works were examined experimentally and theoretically. Position-sensitive proportional counters of a charge division type were examined and found some new applications. The absolute radioactivity of β- and γ-ray emitting nuclide sources can be determined by applying 4πβ-γ coincidence absorption method. The sources for 4πβ counting using an aluminum compound which brought less self-absorption of β-rays were prepared successfully. Electrical condctivity of the thin film for source backing was evaluated. A new method with a position-sensitive proportional counter was developed for absolute activity measurement of gaseous samples. There are now intensive needs for tritium surface contamination monitor and gas monitor. Recently, we succeeded in developing a proportional counter with air as counting gas, named air proportional counter, for β-ray detection and applied it to tritium surface contamination monitor and gas monitor. A hybrid spark chamber was developed to obtain the image of geometrical distribution of β-ray emitting nuclides. (author) 157 refs