Elimination of ghosting artifacts from wavelength-shifting fiber neutron detectors

Abstract

Misassignment of neutron position (ghosting) produces artifacts which have been observed in wavelength-shifting (WLS) fiber detectors developed for time-of-flight (TOF) neutron powder diffraction. In position-sensitive detectors (PSDs) with WLS fiber encoding, thermal and cold neutrons interact with a monolithic (6)LiF/ZnS:Ag scintillator screen, and scintillation photons are generated and transported through the crossed fibers to photomultipliers (PMTs). The neutron position is determined by photon counts in the PMTs within a preset time window. Ghosting occurs when neutrons hit the group boundaries of two neighboring PMTs for x-position multiplexing, which is modeled as resulting from a long travel length (about 3-5 mm) of a small number of scintillation photons. This model is supported by the change observed in aperture images when the threshold number for photon-pulses was adjusted for neutron event determination. When the threshold number of photon-pulses was set above 10 for each PMT, the ghost peaks in the aperture images and TOF spectra of powder diffraction were strongly suppressed or completely eliminated, and the intrinsic background levels of the WLS detectors were significantly reduced. Our result indicates that WLS fiber detector is a promising alternative for (3)He PSDs for neutron scattering.

Bending Behavior of a Wrought Magnesium Alloy Investigated by the In Situ Pinhole Neutron Diffraction Method

“…At VULCAN, the diffraction patterns were recorded by the two detector banks (B1 and B2), positioned at diffraction angles of ±90 • with two convergent collimator options: 2 or 5 mm along the beam. Each bank includes three wavelength-shifting-fiber (WLSF) scintillator detectors [51], which have 154 by 7 pixels over a total area of 77 by 38 cm. The detector with a 5 mm horizontal pixel size ensured an average spatial resolution of~5.5 mm full width at half maximum (FWHM), with a rather large spread across the detector [52].…”

Enhanced position resolution for ZnS:Ag/$$^6$$LiF wavelength shifting fibre thermal neutron detectors

“…Scintillation detectors using ZnS:Ag/ 6 LiF are widely employed at SNS, J-PARC and ISIS. At SNS, a largearea linear position-sensitive detector for powder diffractometers [19] has been developed and improved [20,21], using a coincidence-coding method first implemented at ISIS [22]. Position-sensitive WLSF scintillator neutron detectors have been developed at J-PARC for neutron imaging [23], for the engineering material diffractometer [24] and for single-crystal diffractometers [25][26][27][28].…”

Development of a position-sensitive scintillation neutron detector for a new protein single-crystal diffractometer at J-PARC MLF

“…Crow et al developed a linear positionsensitive scintillation neutron detector for the POWGEN3 diffractometer [14]. The detectors have been improved and installed successfully in the spallation neutron source at the Oak Ridge National Laboratory [15,16]. In order to build a two-dimension detector the crossed WLS fibre arrays have been introduced and adopted in most cases [17,18].…”