Improved alpha-background cancellation circuit for tritium gas monitor

A new cancellation circuit which eliminates component due to α-particles from Rn in the ionization current of a tritium gas monitor has been designed and constructed. In order to eliminate the α-particle component, a gated integrator circuit that form signals having the same pulse shape as initial α-particle signals was newly adopted in the cancellation circuit. The transfer function of the cancellation circuit was calculated for the α-particle signal by means of the Laplace transformation. The test for the system showed that the cancellation circuit eliminated successfully the component of α-particle signals. By use of the gated integrator, the cancellation circuit functioned very well even when the counting rate of α-particle signals is as high as 1 cps in the input. This circuit is essential to measure the tritium-gas concentration below the maximum permissible concentration. (author)