Optimization of the thickness of a ZnS/ 6 LiF scintillator for a high‐resolution detector installed on a focusing small‐angle neutron scattering spectrometer (SANS‐U)

This study involves the upgrade of a high‐resolution position‐sensitive detector (HR‐PSD) installed on the small‐angle neutron scattering spectrometer (SANS‐U) at the Japan Atomic Energy Agency. By using both neutron lenses and the HR‐PSD, the accessible low‐ Q limit can be extended to the order of 10 −4  Å −1 [ Q is the magnitude of the scattering vector defined by Q = (4π/λ)sinθ, where λ and 2θ are the wavelength and the scattering angle, respectively]. The HR‐PSD consists of a cross‐wired position‐sensitive photomultiplier tube (PSPMT) and a commercial ZnS/ 6 LiF scintillator. To improve the experimental efficiency of focusing small‐angle neutron scattering (FSANS) experiments, a high‐performance ZnS/ 6 LiF scintillator developed at the Japan Atomic Energy Agency has been utilized. For the PSPMT and data‐acquisition system installed on SANS‐U, the thickness of the ZnS/ 6 LiF scintillator was optimized by measuring the thickness dependence of the pulse‐height spectra. Under the experimental conditions of SANS‐U, the optimum thickness of the ZnS/ 6 LiF scintillator (ZnS: 6 LiF = 2:1) was determined to be 0.433 mm by measuring the total counts and peak positions of the pulse‐height spectra. Installation of the optimized ZnS/ 6 LiF scintillator improved detection efficiency by 1.39 times over that of a commercial scintillator at the same level of background counts and Q resolution in FSANS experiments.