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Modelling instrumental response for neutron scattering experiments at CSNS

Ni Yang, Zi-Yi Pan, Ming Tang, Wen Yin, Xiao-Xiao Cai

Abstract

Thermal neutron total scattering experiments of light and heavy water were reproduced using the CSNS in-house Monte Carlo thermal neutron transport code, Prompt, with a focus on the instrumental detector response and the accurate derivation of thermal neutron scattering cross-sections. In this work, a data reduction method is developed to process both the measured and simulated detector events for estimating angular, wavelength distributions, as well as angular differential cross sections. The reduction results of simulations and experiments show a high degree of consistency. The prominent inelasticity signatures observed in the experiments can be accurately reproduced in simulations. We discuss the cause of the inelasticity effects, and demonstrate the elimination of such effects when the inelastic scattering process is taken into account in simulations. In addition, multiple scattering in samples is analysed and discussed.

Modelling instrumental response for neutron scattering experiments at CSNS

Abstract

Thermal neutron total scattering experiments of light and heavy water were reproduced using the CSNS in-house Monte Carlo thermal neutron transport code, Prompt, with a focus on the instrumental detector response and the accurate derivation of thermal neutron scattering cross-sections. In this work, a data reduction method is developed to process both the measured and simulated detector events for estimating angular, wavelength distributions, as well as angular differential cross sections. The reduction results of simulations and experiments show a high degree of consistency. The prominent inelasticity signatures observed in the experiments can be accurately reproduced in simulations. We discuss the cause of the inelasticity effects, and demonstrate the elimination of such effects when the inelastic scattering process is taken into account in simulations. In addition, multiple scattering in samples is analysed and discussed.
Paper Structure (11 sections, 23 equations, 16 figures, 5 tables)

This paper contains 11 sections, 23 equations, 16 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Method
  3. Data normalisation
  4. Data analysis
  5. Measurement
  6. Prompt-based simulation
  7. Results
  8. Discussion
  9. Multiple scattering
  10. Inelasticity signature
  11. Conclusion

Figures (16)

  • Figure 1: Basic experimental setup of the time-of-flight neutron total scattering technique, showing the incident flight path distance $L_{0}$, the scattered flight path distance $L_{1}$, the moderator-to-monitor distance $L_{m}$ and the scattering angle $\theta$.
  • Figure 2: (a) Geometry visualisation of the simulated MPI in Prompt. (b) Zoom-in of the the simulated MPI.
  • Figure 3: TOF count rate for monitors in the measurement (dots) and simulation (solid line). Since the distance from the moderator to the monitor is 29.543, the corresponding wavelengths of the four sharp dips observed in both results are respectively $2.34\angstrom$, $2.44\angstrom$, $2.86\angstrom$ and $4.05\angstrom$.
  • Figure 4: TOF count rate of all 800 pixels in detector module A for the measurement of $\rm{D}_{2}\rm{O}$ sample with container.
  • Figure 5: Differential count (Eq. (\ref{['ecountDensity']})) in wavelength and scattering angle for $\rm{D}_{2}\rm{O}$ sample with container. (a) Measured data and (b) the corresponding simulated data.
  • ...and 11 more figures