High-counting-rate and high-position-resolution neutron imaging detectors using short-lifetime phosphors with crossed-fiber readout

In order to obtain high-counting-rate and high-position-resolution neutron imaging, two-dimensional neutron position sensitive detectors using short-lifetime phosphors with crossed-fiber readout were developed. In these detectors, 7Li210B4O7 (7L10BO) was used as the neutron converter, the phosphor Y2SiO5 (lifetime ∼40 ns) and other organic phosphors with lifetimes of less than 10 ns were also used. Crossed-wavelength-shifting fibers were arranged on and under the phosphor/neutron converter sheet. Light generated in the phosphor sheet was detected by the few fibers surrounding the neutron interaction point. The X and Y position of the neutron interaction were determined by a double coincidence photon counting method. By carrying out a series of fundamental experiments for the imaging detector, it was determined that a position resolution of less than 0.5 mm could be obtained with a 0.25 mm thick Y2SiO5/7L10BO sheet and wavelength shifting fibers 0.5 mm×0.5 mm in cross-sectional area. Experiments carried out at a cold neutron radiography facility, with maximum neutron flux of 1×108 n/s/cm2, confirmed that the detector could work at a counting rate of more than 3 Mcps/line.