Neutron Sensitive Scintillating Glass Fiber
Technology and Its Application to Neutron Measurements

Richard Seymour
Nuclear Safeguards and Security Systems LLC (dba Nucsafe)
September 12, 2001

Abstract:
Most neutron detection systems employ 3He gas-filled detectors. Despite their excellent performance and widespread use, there are limitations to every technology. An alternative neutron sensor utilizing a 6Li doped glass scintillator offers novel commercial sensors not possible or practical with gas tube technology.

The scintillating optical fiber permits sensors with a multitude of sizes ranging from devices of a single fiber of 150mm to sensors with tens of thousands of fibers with areas as large as 5m2 depending on the neutron flux to be measured. A second advantage of the fiber technology is the fast scintillation and electronic processing that allow processing times of 150 nanoseconds, 20 times faster than 3He tubes, providing benefits to throughput for high count rate applications and to more precise time of flight measurements.

These sensors are flexible and conformable allowing optimization of the source-to-detector geometry. The solid-state glass fiber sensors are also less sensitive to vibration providing robust performance for in-situ and harsh environment measurements. As there is no pressurized gas, the fiber sensors are not classified as hazardous cargo allowing their transport on commercial aircraft. Although the glass-fibers are sensitive to both gamma rays and neutrons, the coincidence electronics are capable of significantly reducing the gamma ray to neutron spillover even for measurements with a much higher gamma ray field.

Applications include freight, pedestrian, vehicle monitoring, illicit trafficking, inspection for undeclared materials, counter-terrorism, emergency response, continuous monitoring of containers and spent fuel, position-sensitive measurements, detection of land mines, neutron spectroscopy, health physics, industrial and medical measurements. While no single technology can address every measurement requirement, the fiber technology offers the first commercially viable alternative to pressurized gas tubes and provides significant benefits for many applications.