Detection of 14-MeV Neutrons by Optical System with Radioluminescence Material and Optical Fiber

Abstract

Detection of the 14-MeV neutrons in the D-T fusion reaction is an important topic in burning plasma diagnostics. Simple, compact, robust, and easy to maintain are strongly preferable features for the 14-MeV neutron detection system. An optical dosimetry system, composed of a radiation-resistant thin optical fiber, with a small radioluminescence material attached to one end, satisfies these requirements. Irradiation tests for two types of strontium-aluminates (SrAl2O :Eu2+,Dy3+ and Sr4Al14O25:Eu2+,Dy3+) were performed using a 14-MeV fusion neutron, 0.5-2 MeV protons, and 60Co γ-ray. Both types of strontium-aluminates emit strong radioluminescence under the 14-MeV neutron irradiation. SrAl2O4:Eu2+,Dy3+ emit strong radioluminescence under the 14-MeV neutron irradiation. However, SrAl2O4:Eu2+,Dy3+ continue to emit luminescence after the irradiation stops. The radioluminescent spectrum of Sr4Al14O25:Eu2+,Dy3+ have characteristic peaks at approximately 400, 480, and 570 nm though the peaks can not distinguish in case of SrAl2O4:Eu2+,Dy3+. The peak at 570 nm promptly disappeared when the neutron radiation stopped though the peaks at 400 and 480 nm indicate long lasting phosphorescence. Therefore, a rapid change of the 14-MeV neutron flux could be monitored by the radioluminescence peak intensity at 570 nm. The spectrum for the 14-MeV neutrons is different from those for the ions and γ−ray irradiation. Thus, the 14-MeV neutron flux can be distinguished from ion influxes as well as from background γ−ray by measuring a detailed spectrum of the radioluminescence. The present system, being compact, simple and robust, can detect the D-T 14-MeV neutrons, discriminating 14-MeV neutrons from the background ions and γ-ray. There is a possibility to discriminate neutron energy with the present optical system.