Profile functions to reproduce Bragg reflection shapes observed by a time-of-flight single-crystal diffractometer installed at a coupled moderator pulsed neutron source in J-PARC

We performed a time-of-flight (TOF) single-crystal neutron diffraction experiment with a diffractometer (the IBARAKI Biological Crystal Diffractometer (iBIX)) using single-crystal silicon, and we determined several candidates for fundamental fitting functions to faithfully reproduce the Bragg reflection profile with asymmetries in the TOF direction. The Vavilov and Landau distributions used to describe the energy loss of charged particles traversing a thin absorber were found to be in excellent agreement with the observed TOF profile. We have evaluated the obtained functions and the convolution of back-to-back exponentials with a Gaussian to determine which function provides the best fit to the data. Further, we have applied the obtained functions to the practical Bragg reflection profiles of proteins after subtraction of the background using the Statistics-sensitive Nonlinear Iterative Peak-clipping (SNIP) algorithm.