HIGH EFFICIENCY FAST NEUTRON DETECTION SYSTEM

Open Access
Author:
Mcgahee, Christopher Oliver
Graduate Program:
Nuclear Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 10, 2017
Committee Members:
  • Marek Flaska, Thesis Advisor
  • Justin Kyle Watson, Committee Member
Keywords:
  • Neutron
  • Radiation Detection
  • Safeguards
  • Nonproliferation
Abstract:
There has been a call over the past decade to create a replacement neutron detection technology for He gas proportional systems1. Following a drastic increase in demand for neutron detection systems for safeguards purposes, the cost of 3He gas has skyrocketed, to the point where it has become prohibitively expensive to use it for safeguards applications. As such, efforts to develop a replacement system has become a major focus for nonproliferation research groups. Any replacement system must be effective, economically viable, and relatively small. This project examines a potential replacement neutron detection system that utilizes a lithium doped zinc sulfide scintillation medium with a moderating material included in the detector geometry. The proposed design uses alternating concentric layers of scintillation material and moderating material, coupled to a photo multiplier and light sensor. The moderating material thermalizes incident neutrons to increase the capture probability in the lithium dopant. MCNP was used to design and optimize a full-scale detection system utilizing the EJ-426 scintillation layers and acrylic moderating material. These simulations were then coupled with experimental data obtained from EJ-426 sheets attached directly to a 1-inch Photomultiplier Tube to design a prototype detection system that could be constructed in the lab. The Mark 1 prototype system was constructed and characterized to obtain a .1% detection efficiency when exposed to a 252Cf neutron source. GEANT4 was used to model optical photon transport inside the detector geometry to compare the theoretical detection efficiency of the prototype system to the measured detection efficiency. These data will be used to improve future designs of this neutron detection system.