A small high sensitivity neutron detector using a wavelength shifting fiber

A small neutron detector using an optical fiber was previously developed for reaction rate measurements at research reactors and accelerator facilities. This detector can be inserted into narrow spaces and its spatial resolution is less than 1 mm; however, its neutron sensitivity is low because of the small size of its detector. The purpose of this study is to develop a new optical fiber detector with high neutron sensitivity by using a wavelength shifting fiber. Through the measurement of the reaction rate distribution in a reactor core, we found that it is possible to increase the effective length of the detector, resulting in increased neutron sensitivity compared with a conventional optical fiber detector. Additionally, using a longer wavelength shifting fiber, the sensitivity can be increased until it is as large as that of a typical small BF3 proportional counter, which means that this detector can be used for even low neutron flux fields.