A High Resolution Disk Chopper with Two-Stage Rotors for Neutron Time-of-Flight Spectroscopy

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The objectives are to establish the novel version of the four kinds of Bragg scattering set-ups installed at the supermirror neutron guide hall in Kyoto University Research Reactor (5 MW,light water moderated) : i.e.the three set-ups are time-of-flight diffractometers with point detectors using neutrons from a disk chopper (TOF), and the rest set-up is a crystal diffractometer with two one-dimensional position sensitive detectors with use of neutrons from a pyrolytic graphite monochromator (PSD).1.TOF System : A novel disk chopper with two-stage rotors was designed and constructed based on the calculation of neutron transmission probability. The spectrometer was optimized with the measurements of standard sample Fe-Cr-Ni, alpha/gamma two phase steel, and supplied for the common studies by researchers from universities in Japan after its establishment, Nov.1996.(1)Performance Tests :(1)-1.Neutron wavelength resolution and its intensity became 2.5 and 3.3 times highe, resulting about 8 t … More imes improvement of the diffractometer.(1)-2.The samples of alpha/gamma steels and SiCw/Al were examined to verify the strain measurements of the crystal lattice specings over 10^<-3> to 10^<-4>. The gauge volume defined by the slit system before and after the sample was 2x30 in mm.2.PSD System : The several Si single crystals (311), i) 3x30x200, ii) 4x30x200 and iii) 4x30x200, two layrs (in mm), were used for the optimization of the monochromator device. The beam profiles of the monochromatic neutrons were characterized by the Neutron Imaging Plate method. The absolute value of the neutrons was determined by the Au-foil Activation method. The performance tests of the ststerm were carried out with the standard samples of alpha Fe.(2) Performance Tests :(2)-1.The quasi-parallel diffraction pattern from alpha Fe (211) was obtained and its FWHM was 11.4' which was consistent with the prediction.(2)-2.The angular resolution and the diffraded intensity were improved to be 10-15 times higher with repect to the conventional mosaic crystal of pyrolytic graphite monochromator. Less