Kazuhiko Ninomiya

Evidence for Appearance of an Internal Field in the Ordered State of CeRu2Al10 by µ+SR

We report zero-field µ + SR measurements made at J-PARC on CeRu 2 Al 10 . Below the phase transition temperature T 0 ∼27 K, a clear modulation of µ + polarization due to an internal field is observed, indicating that magnetic ordering takes place. Compared with the internal field expected from the effective magnetic moment in the disordered state, the observed internal field at the µ + site is quite small. This indicates that the ordered Ce magnetic moment is small (∼10 -2 µ B ) and/or the nearest pair of Ce magnetic moments are mutually anti-parallel. The T -dependence of the internal field is somewhat peculiar, suggesting that another ordering is taking place as well.

A new X-ray fluorescence spectroscopy for extraterrestrial materials using a muon beam

The recent development of the intense pulsed muon source at J-PARC MUSE, Japan Proton Accelerator Research Complex/MUon Science Establishment (106 s−1 for a momentum of 60 MeV/c), enabled us to pioneer a new frontier in analytical sciences. Here, we report a non-destructive elemental analysis using µ− capture. Controlling muon momentum from 32.5 to 57.5 MeV/c, we successfully demonstrate a depth-profile analysis of light elements (B, C, N, and O) from several mm-thick layered materials and non-destructive bulk analyses of meteorites containing organic materials. Muon beam analysis, enabling a bulk analysis of light to heavy elements without severe radioactivation, is a unique analytical method complementary to other non-destructive analyses. Furthermore, this technology can be used as a powerful tool to identify the content and distribution of organic components in future asteroidal return samples.

µSR Evidence of Nonmagnetic Order and 141Pr Hyperfine-Enhanced Nuclear Magnetism in the Cubic Γ3 Ground Doublet System PrTi2Al20

A muon spin relaxation (µSR) study of the cubic Γ 3 ground doublet system PrTi 2 Al 20 is presented. The zero-field µSR rate shows no significant change while passing through the phase transition t...

Nondestructive Elemental Depth-Profiling Analysis by Muonic X-ray Measurement

Elemental analysis of materials is fundamentally important to science and technology. Many elemental analysis methods have been developed, but three-dimensional nondestructive elemental analysis of bulk materials has remained elusive. Recently, our project team, dreamX (damageless and regioselective elemental analysis with muonic X-rays), developed a nondestructive depth-profiling elemental analysis method after a decade of research. This new method utilizes a new type of probe; a negative muon particle and high-energy muonic X-rays emitted after the muon stops in a material. We performed elemental depth profiling on an old Japanese gold coin (Tempo-Koban) using a low-momentum negative muon beam and successfully determined that the Au concentration in the coin gradually decreased with depth over a micrometer length scale. We believe that this method will be a promising tool for the elemental analysis of valuable samples, such as archeological artifacts.

Nuclear γ Rays from Stopped Muon Capture Reactions for Nuclear Isotope Detection

Muon capture isotope detection (MuCID) is a non-destructive detection (assay) of composite and impurity nuclear isotopes by measuring γ rays following muon capture reaction products. Several nuclear isotopes are produced by muon capture reactions such as (μ, xn γ) with \(x = 0\), 1, 2, 3, and so on, and some of them are radioactive isotopes. The isotopes of the interest are identified by measuring γ rays characteristic of the reaction products by means of high-sensitivity Ge detectors. Composite and impurity nuclear isotopes of the orders of microgram–nanogram and ppm–ppb are investigated. The feasibility and the sensitivity of MuCID were shown experimentally by using μ capture reactions on Mo isotopes at MuSIC in RCNP. MuCID is used to study nuclear isotopes of astro-nuclear and particle physics interests and those of geological and historical interests.

Use of a size-resolved 1-D resuspension scheme to evaluate resuspended radioactive material associated with mineral dust particles from the ground surface.

A size-resolved, one-dimensional resuspension scheme for soil particles from the ground surface is proposed to evaluate the concentration of radioactivity in the atmosphere due to the secondary emission of radioactive material. The particle size distributions of radioactive particles at a sampling point were measured and compared with the results evaluated by the scheme using four different soil textures: sand, loamy sand, sandy loam, and silty loam. For sandy loam and silty loam, the results were in good agreement with the size-resolved atmospheric radioactivity concentrations observed at a school ground in Tsushima District, Namie Town, Fukushima, which was heavily contaminated after the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. Though various assumptions were incorporated into both the scheme and evaluation conditions, this study shows that the proposed scheme can be applied to evaluate secondary emissions caused by aeolian resuspension of radioactive materials associated with mineral dust particles from the ground surface. The results underscore the importance of taking soil texture into account when evaluating the concentrations of resuspended, size-resolved atmospheric radioactivity.

Muon capture probability of carbon and oxygen for CO, CO2, and COS under low-pressure gas conditions

When a negatively charged muon is stopped in a substance, it is captured by an atom of the substance, and the muonic atom is formed. The muon capture process is significantly affected by the chemical environment of the atom and factors such as molecular structure (chemical effect). In this study, we performed muon irradiation for low-pressure CO, CO2, and COS molecules and measured the muonic X-rays emitted immediately after muon capture by an atom. In this paper, we quantitatively discuss the muon capture probability of each type of atom using the LMM model.

Incommensurate-to-Commensurate Magnetic Phase Transition in SmIn3 Observed by Muon Spin Relaxation

Magnetic susceptibility and muon spin relaxation (µSR) measurements in the intermetallic cubic compound SmIn 3 with a Γ 8 crystalline-electric-field ground state are reported. Anomalies corresponding to successive phase transitions were observed in the magnetic susceptibility at T I ∼16.5 K, T II ∼15.1 K, and T III ∼14.7 K. A spontaneous local magnetic field was detected below T I using the µSR technique in zero applied field in contrast to the pure quadrupolar ordering scenario proposed in the phase between T I and T II . This result clearly indicates that the primary order parameters in all the ordered phases are magnetic. The local field distribution changes at around T II from a continuous broad one to a sharp one with decreasing temperature, suggesting that an incommensurate-to-commensurate magnetic phase transition takes place at this temperature. A possible magnetic structure in the ground state and the importance of multipolar interactions in the Γ 8 subspace are discussed.

Measurements of the neutron activation cross sections for Bi and Co at 386 MeV.

Neutron activation cross sections for Bi and Co at 386 MeV were measured by activation method. A quasi-monoenergetic neutron beam was produced using the (7)Li(p,n) reaction. The energy spectrum of these neutrons has a high-energy peak (386 MeV) and a low-energy tail. Two neutron beams, 0° and 25° from the proton beam axis, were used for sample irradiation, enabling a correction for the contribution of the low-energy neutrons. The neutron-induced activation cross sections were estimated by subtracting the reaction rates of irradiated samples for 25° irradiation from those of 0° irradiation. The measured cross sections were compared with the findings of other studies, evaluated in relation to nuclear data files and the calculated data by Particle and Heavy Ion Transport code System code.

Energy shift of electronic X-rays emitted from pionic atoms

Summary The electronic K X-ray energies of pionic atoms were precisely measured on elements ranging from zinc to lead with a low-energy photon detection system. Some differences between pionic and muonic atoms were found in the atomic-number (Z) dependence of the energy shift. In the pionic atoms, the energy shift gradually decreases with an increase in atomic number, which is opposite to the trend for muonic atoms. In the low-Z region investigated elements, the energy shifts of Kβ X-rays were obviously larger than those of Kα X-rays.