Improvement of Bremsstrahlung Counting Method for Measurements of Gaseous Tritium

A thin beryllium disk coated with a gold evaporated film of about 80 nm thickness was fabricated as an effective radiation window of bremsstrahlung X-rays. Its characteristics were examined in detail. The bremsstrahlung counting rate was proportional to the partial pressure of tritium above 0.1 Pa. The specific counting rate was evaluated as 70.8 cps/Pa. On the other hand, it decreased gradually with the total pressure above 2 kPa. This behavior was interpreted in terms of the self-absorption of β-particles in gas phase. It was revealed that the counting rate could be reproduced very well by a simple exponential function. From these results, it was concluded that the beryllium window coated with a thin gold evaporated film is a powerful device for in-situ measurements of tritium concentration in a wide range.