A Large Area Position-Sensitive Scintillation Neutron Detector For Upgrading Senju Diffractometer

A large area, position-sensitive scintillation neutron detector was developed for upgrading the SENJU, a time-off-light Laue single crystal neutron diffractometer, in J-PARC MLF. The detector has a neutron-sensitive area of 512 x 512 mm with a pixel size of 4 x 4 mm. The detector is to be installed below the new vacuum tank to enlarge its scattering angle coverage. A 6Li:ZnS (Ag) scintillator and wavelength-shifting fiber technology is employed to make the prototype detector. Each fiber channel is read out individually with a photon counting method. Detector electronics boards are implemented at the backside of the detector. This configuration enables the detector depth as short as 200 mm. The detector exhibits a detection efficiency of 45% for 1.8-A neutron. No degradation has been observed both in the fiber position and in the neutron sensitivity over one year after the detector assembly. The detector design and its performances are presented.