Amplifier with time-invariant trapezoidal shaping and shape-sensitive pileup rejector for high-rate spectroscopy

An amplifier with trapezoidal pulse shaping was developed for high-rate high-energy gamma spectroscopy using NaI(Tl) scintillation detectors. It used a double-delay-line technique for producing a nearly triangular pulse shape combined with a linear circuit for producing a flat-topped pulse. Good energy resolution and short resolution time make this amplifier especially suitable for high-count-rate gamma-ray spectroscopy. To provide a versatile high-performance system, it includes a pileup rejector based on inspection of a pileup signal obtained by combining the slow output signal and fast-shaped input signal. The trapezoidal shape provides a short resolution time for minimal occurrence of pileup with a width suitable for presentation to a standard multichannel analyzer. The performance of the system was tested, and the results are presented.