Digital Pulse Pile-up Management in Organic Liquid Scintillators

M D Aspinall 1, B D’Mellow 1, R O Mackin 1, M J Joyce 1 and A J Peyton 2

1 Control and Instrumentation Group, Engineering Department, Lancaster University, Lancaster, UK Email: m.aspinall@lancs.ac.uk

2 School of Electrical and Electronic Engineering, University of Manchester, Manchester, UK

ABSTRACT

In this paper a recently reported digital pulse shape discrimination technique known as pulse gradient analysis (PGA) was used to discriminate digitally recorded neutron/gamma data. PGA typically involves comparison of the peak amplitude and the discrimination sample that follows a specific number of channels after the peak. A desirable advantage of this technique is that neutron/gamma pulse shape discrimination can be achieved relatively soon after the peak amplitude. This provides the technique with the ability to discriminate signals disrupted by pile-up, providing the second superimposed pulse occurs after the discrimination amplitude used for discrimination. The PGA technique shows promise of digitally discriminating as early as 4 ns after the peak amplitude.

We report on a hypothesis for the identification and disentanglement of pile-up events from scintillation detectors. The average neutron and gamma pulse can be produced from the distinguished data. The average pulse is scaled and time-shifted to fit the first pulse of a pile-up signal, the signal can be disentangled by simply subtracting the fitted pulse. The results of practical tests performed on generated pile-up events from experimental data are presented to support the proposed methodology.

Keywords organic liquid scintillator, digital pulse shape discrimination, pulse gradient analysis, pulse pile-up