Atsushi Kimura

The total and double differential scattering cross sections (DDSCS) of isotropic graphite have been measured in the J-PARC Materials and Life Science Experimental Facility using five samples with different porosities and grain sizes. The DDSCS measurements were performed in Beam Line No.14 (AMATERAS) with nine incident neutron energies ranging from 1.2 to 94 meV. In the derived cross sections, there are no clear sample dependence. The neutron total cross sections in the energy region from 1 to 100 meV were measured using Beam Line No. 04 (ANNRI). All samples in the epithermal range (over 40 meV) tended to have values close to the free atom cross-section of graphite. However, at the first Bragg edge, the deduced total cross sections by these measurements started to vary. The difference became more significant with decreasing the neutron energy.

To improve data accuracy of neutron-capture and total cross sections of minor actinides and long-lived fission products, the time-of-flight experimental instrument named ”Accurate Neutron-Nucleus Reaction measurement Instrument” was constructed, and neutron time-of-flight experiments have been performed with an intense pulsed-neutron beam at MLF in J-PARC. Detailed analysis methods and deduced uncertainties for capture and total cross-section measurements are presented using an example of the experiments of 243Am. The deduced uncertainties are categorized into five types.

Neutron capture and total cross sections of ¹⁵⁵Gd and ¹⁵⁷Gd were measured with the neutron time-of-flight method in Accurate Neutron-Nucleus Reaction measurement Instrument at Material and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex using the NaI (Tl) spectrometer and Li-glass detectors. Preliminary cross sections were obtained in the neutron energy region from 4 meV to 100 meV. The derived cross sections agree with evaluated values in JENDL 4.0 and the experimental results by Mastromarco but were not consistent with those by Leinweber.

Neutron total and capture cross sections of ²⁴¹Am have been measured with a new data acquisition system and a new neutron transmission measurement system installed in Accurate Neutron Nucleus Reaction measurement Instrument at Materials and Life Science Experimental Facility of Japan Proton Accelerator Research Complex. The neutron total cross sections of ²⁴¹Am were determined by using a neutron time-of-flight (TOF) method in the neutron energy region from 4 meV to 2 eV. The thermal total cross section of ²⁴¹Am was derived with an uncertainty of 2.9%. A pulse-height weighting technique was applied to determine neutron capture yields of ²⁴¹Am. The neutron capture cross sections were determined by the TOF method in the neutron energy region from the thermal to 100 eV, and the thermal capture cross section was obtained with an uncertainty of 4.1%. The evaluation data of JENDL-4.0 and JEFF-3.2 were compared with the present results.

The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.

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