Year

2016

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

A continuing problem in nuclear physics research and medicine is the accurate detection of neutrons for radiation protection purposes. The detector most commonly used for this purpose is the REM counter. This is a detector based on a proportional counter that is sensitive to thermal neutrons, embedded in a moderator. However, these detectors are prone to underestimation of the neutron fluence in highly intense neutron fields, specifically those in which a Pulsed Neutron Field (PNF) is present.

The LUPIN-II is the latest iteration of the LUPIN (Long-interval, Ultra-wide dynamic, PIle-up free Neutron REM counter) system. The improvements present in this iteration of the LUPIN are the capability to cope with higher intensity PNFs and a greater ability to distinguish neutrons from photons. Further improvements have been implemented, however, in both of these capabilities. Through the use of correction algorithms, detector performance has been improved without a major redesign. This is made possible though the use of an FPGA (Field Programmable Gate Array) in the read out electronics of the detector, allowing additional algorithms to be programmed in. This is important, as particle accelerators used in research provide increases in energy and beam intensity which in turn result in a more intense secondary neutron field during beam losses. The bulk of these accelerators are synchrotrons, which produce intense neutron bursts during losses due to their working principle. This means that a detector used for radiation protection in these fields must be capable of accurately measuring intense PNFs.

Another algorithm implemented in the LUPIN-II also allows the detector to distinguish between neutrons and photons with a high degree of accuracy. Experimental testing has shown that this algorithm is effective in separating the photon and neutron components.

Simulations were also performed to characterise the response of the LUPIN-II versus neutron energy, an important part of the REM counter system. Finally, simulations were also run to determine the time profile of the neutron burst interaction, which is important for future improvement of the algorithm introduced to expand the LUPIN-II capabilities to cope with intense PNFs.

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