A general purpose pulse shape discriminating circuit

Abstract

A new general purpose pulse shape discriminating circuit and its applications are described. The circuit is based on a risetime to pulse height converter which can measure, independently of its input pulse height, an arbitrary fraction of the risetime of the input pulses. The feature of this circuit is that this can define the risetime of the input signals in the range of 0.2 to 10μsec with an accuracy of ±2% for a pulse height range of 0.3 to 10 V. In applications, this circuit can perform n-γ discrimination with a liquid scintillator, a usual photomultiplier and a linear amplifier, and the gamma rejection ratio obtained for neutrons less than 500 keV is better than 1/500. Also a gamma rejection ratio nearly 1/50 can be obtained for neutrons less than 60 keV by using an H-filled proportional counter. When neutron capture gamma rays are measured with a 20 cm 3 coaxial type Ge(Li) detector in the reactor, the background reduction by 50% and the improvement of a photopeak width by 20% are obtained by using this circuit. Furthermore, when it is applied to (n-γ)T reaction measurement with a Si(SB) detector in the reactor, an improvement of the tritium peak width by 50% and a background reduction by a factor of ten are obtained. It is also investigated that pileup rejection and characteristics measurement of semiconductor detectors can be easily performed by using this circuit.