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SENJU, a TOF-Laue single crystal neutron diffractometer at the BL18 of MLF/J-PARC, was designed for precise crystal and magnetic structure analyses under multiple extreme environments such as low-temperature, high-pressure and high-magnetic field, and also capable of taking diffraction measurements of small single crystals, less than 1.0 mm3 in volume [1]. Just after the launch of SENJU in March 2012, we newly installed and/or upgraded some sample environment devices. SENJU has a vacuum sample chamber and 37 two-dimensional scintillation detectors. Wavelength of incident neutron is 0.3 - 4.4 Å for the 1st frame and 4.6 - 8.8 Å for the 2nd frame. Because the short wavelength neutron is available and the sample position is covered by large solid angle of the detectors, wide reciprocal space within 30 Å-1 can be measured simultaneously by one measurement. As sample environment devices, 4K cryostat with 2-axes goniometer, longitudinal magnet, high-pressure cell, high temperature furnace and other devices are available or in commissioning. The most popular sample environment device on SENJU is the 4 K cryostat with a fixed-chi type 2-axes goniometer. We adopted piezo-rotators to rotate the sample crystal under vacuumed and cryo conditions. The 2-axes goniometer works stably even at 4 K and the time for cooling was 4.5 hours. A longitudinal magnet was recently installed on SENJU. The lowest temperature was 1.42 K and the maximum magnetic field was 6.85 T. A test diffraction measurement of a CeCoGe3 single crystal (1.5 x 1.5 x 3.0 mm) under 1.5 K and 0.5 T showed that Bragg reflections from the sample was clearly observed and the Bragg peaks of the sample crystal were much higher than the peaks from the magnet itself as shown in the figure. In this presentation, we will show the current status of sample environment devices for SENJU such as cryostat, magnet and other devices.
abstracts
"SENJU" is a newly built pulsed neutron single crystal diffractometer at J-PARC/MLF for structural research of inorganic and organic materials with relatively small cell sizes under multiple extreme environments, such as low temperature and a high magnetic field. Since the launch of the instrument in 2012, SENJU has been commissioned and now tuned to be capable of crystal and magnetic structure analyses with a sample as tiny as 1mm cube or less. SENJU has the total of 37 two-dimensional scintillation detectors installed. Groups of 3 detectors are accommodated in detector banks and 12 detector banks are placed so as to cylindrically surround the sample chamber (Figure), and additional one detector is settled at the bottom. The instrumental parameters including the positions of the detectors and the neutron flight path length were determined in order to obtain accurate lattice parameters of samples. Since the instrumental parameters correlate with each other, series of different measurements were needed in order to obtain unique values for each parameter. As the first step of the procedure, a powder diffraction pattern of diamond was measured in order to determine the scattering angle of 90 [deg] utilizing the nature that a Bragg reflection vertically lines up at 90 [deg]. Simultaneously, we determined the neutron path length L1 from the neutron source to the sample position. As a next step, a Bragg reflection was repeatedly measured as the sample crystal was rotated with small steps. From this data, the equatorial plane on the detectors and the distance between the sample and the detectors L2 were determined. As a third step, many Bragg reflections from a sample with known lattice constants were measured and from the positions of the reflections the positions of each detector were determined. As a result, the lattice parameters can be obtained with the accuracy of about 0.05 % using the determined instrumental parameters.
