Calibration and Unfolding of the Pulse Height Spectra of Liquid Scintillator-Based Neutron Detectors using Photon Sources

The accurate energy calibration of a 5×2" BC501A liquid scintillator-based neutron detector by means of photon sources and the unfolding of pulse height spectra is described. The photon responses were measured with 22Na, 137Cs and 54Mn photon sources and simulated using the GRESP code, which was developed at the Physikalisch Technische Bundesanstalt in Germany. Pulse height spectra produced by three different photon sources were employed to investigate the effects of the unfolding techniques. It was found that the four unfolding codes of the HEPRO and UMG3.3 packages, including GRAVEL, UNFANA, MIEKE and MAXED, performed well with the test spectra and produced generally consistent results. They could therefore be used to obtain neutron energy spectra in Tokamak experiments.