Correlation RTOF diffractometry at long-pulse neutron source: II. Analysis of frequency windows and diffraction peak profiles

Abstract

Neutron RTOF diffractometry is a special correlation technique, combining the use of a fast Fourier chopper for modulation of the incident neutron beam intensity and the reverse time-of-flight (RTOF) method for data acquisition. This approach allows one to achieve a high-resolution level of the instrument over a wide range of interplanar spacing dhkl at a relatively short flight distance between the chopper and the sample position. Recently, a new high-performance DAQ system for recording RTOF data in a list mode was implemented on high-resolution Fourier diffractometers operating at the long-pulse neutron source – the IBR-2 reactor – in FLNP JINR (Dubna, Russia). One of the most important features of list-mode data acquisition is the possibility to analyze real frequency window of the Fourier chopper and compensate the chopper phase mismatch, which is crucial for obtaining diffraction peaks with a symmetric Gaussian profile. This paper discusses the experience of using list-mode DAQ for analysis of real frequency windows reconstructed from pickup signal events. In addition, a comparison of various frequency windows and their influence on the diffraction peak shape is performed.