Correlation RTOF diffractometry at long-pulse neutron source: I. Data acquisition in list-mode

Abstract

The Fourier diffractometer is a neutron time-of-flight spectrometer using a special correlation technique — a fast Fourier chopper for incident neutron beam intensity modulation and the reverse time-of-flight (RTOF) method for data acquisition. This makes it possible to obtain high-resolution neutron diffraction spectra in a wide range of interplanar spacing at relatively short flight paths both on steady state reactors and on pulsed neutron sources. The RTOF technique provides optimal balance between intensity and resolution in neutron diffraction experiment allowing the precise determination of structural parameters. Currently, all three existing Fourier diffractometers (HRFD, FSD and FSS) operate at the long-pulse neutron source – the IBR-2 reactor – in FLNP JINR (Dubna, Russia). Recently, a new high-performance DAQ system for recording RTOF data in list-mode was implemented on Fourier diffractometers in FLNP JINR. The developed algorithms provide fast off-line reconstruction of high-resolution RTOF spectra from the raw list-mode data with important additional features for spectra improvement: fine tuning of the TOF scale, phase error correction, detector signal filtering, precise electronic focusing for multi-element detectors, etc. In this paper main aspects of diffraction spectra reconstruction from raw list-mode data and capabilities of the new DAQ system are discussed.