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In this study, the germanium detector assembly, installed at the Accurate Neutron-Nuclear Reaction measurement Instruments (ANNRI) in the Material and Life Science Facility (MLF) operated by the Japan Proton Accelerator Research Complex (J-PARC), has been characterized for extension to the measurement of the angular distribution of individual gamma-ray transitions from neutron-induced compound states. We have developed a Monte Carlo simulation code using the GEANT4 toolkit, which can reproduce the pulse-height spectra of gamma-rays from radioactive sources and (n,gamma) reactions. The simulation is applicable to the measurement of gamma-rays in the energy region of 0.5-11.0 MeV.

We measured invariant mass spectra of e+e− pairs produced in 12 GeV p + A interaction to investigate in-medium mass modification of vector mesons. We observed an enhancement over the known hadronic sources on the low-mass side of the ω meson mass peak. The obtained ρ/ω ratio indicates that this enhancement mainly results from ρ mesons whose mass was modified in nuclear matter. We performed a toy model calculation based on the prediction using the QCD sum rule. It reproduced well the tendency of our data.

The neutron electric dipole moment (nEDM) is sensitive to new physics beyond the standard model and could prove to be a new source of CP violation. Several experiments are being planned worldwide for its high-precision measurement. The nEDM is measured as the ultracold neutron (UCN) spin precession in a storage bottle under homogeneous electric and magnetic fields. In nEDM measurement, the systematic uncertainties are due to the motion of the UCNs, the geometry of the measurement system, and inhomogeneous electric and magnetic fields. Therefore, it is essential to quantitatively understand these effects in order to reduce them. Geant4UCN is an ideal simulation framework because it can compute the UCN trajectory, evaluate the time evolution of the spin precession due to arbitrary electric and magnetic fields, and define the storage geometry flexibly. We checked how accurately Geant4UCN can calculate the spin precession. We found that because of rounding errors, it cannot simulate it accurately enough for nEDM experiments, assuming homogeneous electric and magnetic fields with strengths of 10 kV/cm and 1 μT, respectively, and 100 s of storage. In this paper, we report on its discrepancies and describe a solution.

Ultracold neutrons (UCNs) are neutrons whose kinetic energy is around a few hundred nanoelectronvolts. Neutrons with such small kinetic energy can be trapped in a material vessel or magnetic fields. Because of these unique characteristics, UCNs are used for some important experiments of fundamental physics. The Doppler shifter is a device to produce UCN by slowing them down by the reflection on a mirror moving with half of the velocity of incoming neutrons. A Doppler shifter using a quadruple-stack of monochromatic supermirrors that reflects neutrons with a velocity around 68m/s [1, Hino et al.(2010)] was fabricated, and operated with a pulsed neutron source of J-PARC. An important feature of the Doppler shifter is the use of a pulsed neutron beam. Unlike in continuous neutron beams, the neutron velocity can be selected by choosing a time slice in a pulsed neutron bunch. Thus the UCN production improves by ~80 times in the case of J-PARC. We successfully produced the UCNs by the Doppler shifter: the measured UCN production rate is consistent with the simulations.

We developed a new neutron mirror made of Diamond-like carbon (DLC). DLC is a film of amorphous carbon that has characteristics of both diamond and graphite. We produced DLC mirrors by ionization deposition method which is one of the chemical vapor deposition (CVD). Generally, DLC made by CVD contents a few tens of percentages of hydrogen. It decreases the Fermi potential of the DLC coating because hydrogen has negative Fermi potential. In order to increase the Fermi potential of the coating, we deuterated the DLC by using deuterated benzene for the source gas. The characteristics of the deuterated DLC(DDLC) coating was evaluated by RBS, ERDA, x-ray reflectivity, AFM. As a result, DDLC coating has 243neV due to deuteration, which is the same level as Ni. The RMS of height of the DDLC was 0.6nm so that the DDLC coating can be applied for a focusing mirror or specular transportation of pulsed neutron. Besides, we also develop Hydrogen/Deuterium DLC multiple layer mirror. So far, 4 layers mirror has been succeeded.

We have measured the optical thickness of a phase object for the first time using multilayer cold neutron interferometer. The measured phase shift of 15.1 ± 1.9 wavelength agreed with the expected value of 17.4 ± 0.7 wavelength due to an about 600-μm-thick silicon plate. This demonstration reconfirmed that two paths in our new interferometer were completely separate, and showed its applicability into various precise measurements.

The neutron interference imaging experiment with two absorption gratings has been done. We develop new way to fabricate absorption gratings for neutron with the pitch of 150 μ m, 180 μ m, and 200 μ m. Compact imaging detector system is developed, whose weight is 2kg. Small break in an acrylic plate, the welded place of Nb plate were observed, it reveals that the neutron interference imaging method can become new method of a nondestructive inspection for reinforced plastics and composite material such as CFRP and so on.

A correction for the beam divergence effect in a neutron resonance spin echo (NRSE) spectrometer will be discussed. The new type of device called 'coupling coils' is proposed to change the spin quantization axis for the correction. The feasibility of correction for the vertical divergence has been demonstrated by numerical calculations and Monte Carlo simulations.

We have installed a MIEZE (modulated intensity by zero effort) spectrometer in the C3-1-2-2(MINE1) port at JRR-3M. In the MIEZE spectrometer, a sample is placed after the analyzer. Thus the contrast of the MIEZE signal can be observed without reduction even in the case of magnetic scattering where the signal for NSE (neutron spin echo) and NRSE (neutron resonance spin echo) instruments is less than half. The MIEZE signal is sensitive to the dispersion of neutron trajectories from the sample to the detector. In other words, the MIEZE signal is reduced only due to the dispersion even without in- and quasi-elastic scattering. We studied the correlation between experimental configuration and its resolution function using the Monte Carlo simulation. We prepared a magnetite ferrofluid sample with a typical particle diameter of 84 Å, and examined the simulation model by experiments.