This study explores the use of digital pulse processing techniques for n/y pulse shape discrimination (PSD) in liquid scintillators, and the application of these techniques to a capture-gated fast neutron monitor developed using an enriched '°B-loaded liquid scintillator (BC523A). The motivation for this study has been to develop a computationally-fast digital PSD algorithm, which can be used to detect a weak neutron flux in the presence of a strong gamma ray background and to assess its suitability for use as a portable neutron monitor for fast neutron dosimetry. BC523A can operate as a full-energy neutron spectrometer when used in the 'capturegated' mode, where a characteristic capture time is observed between the proton recoil and neutron capture pulses, thus producing a very clean signature for those fast neutrons which are completely moderated within the detector volume. The use of digital waveform capture of this double-pulse sequence is a powerful technique that allows acquiring both the timestamped pulse amplitudes and the capture lifetime in a single data set. The capture-gated performance of a 105 cm' BC523A detector was investigated using fast neutrons from an Am-Be source. The measured mean neutron capture time in BC523A was 470±80 ns, which is a factor of 5 shorter than that reported for liquid scintillators loaded with natural boron. Due to its limited neutron detection efficiency, an extension of this technique to a large volume (685 cm) BC523A was developed, and provided an efficiency increase by a factor of 7. The efficiency enhancement was modelled using MCNP-4C. Good n/y separation was obtained using digital PSD applied to BC523A. The PSD figure of- merit (FOM) was investigated for various organic scintillators, and compared between digital and analogue pulse processing techniques. The application of digital PSD to the capture-gate detection mode was investigated, as an additional method for suppression of gamma sensitivity.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:288673 |
| Date | January 2003 |
| Creators | Jastaniah, Saddig Darwish |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/2792/ |
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