Unified mercury radioactivity monitoring system at J-PARC and its operation experiences

Harada, Masahide; Sekijima, Mitsuaki*; Morikawa, Noriyuki*; Masuda, Shiho; Kinoshita, Hidetaka; Sakai, Kenji; Kai, Tetsuya; Kasugai, Yoshimi; Muto, Giichi*; Suzuki, Akio*; et al.

JPS Conference Proceedings (Internet), 33, p.011099_1 - 011099_6, 2021/03

https://doi.org/10.7566/JPSCP.33.011099

In MLF at J-PARC, a unified mercury radioactivity monitor (UHAM) is installed to find an indication of failure of the mercury target and loop system by detecting radioactive materials leaked from the system with a -ray energy analysis with Germanium semi-conductor detectors (Ge detectors). It is composed of three units of sampling port and radiation monitors: (1) HAM for interstitial helium gas layer between the mercury vessel and surrounding water shroud of the mercury target, (2) CAM for atmosphere in the hot cell where the target loop is operated and (3) VAM for helium gas in the helium vessel where the target vessel is installed. Once any leakages of radioactive materials are detected, an alarm signal is issued immediately to the accelerator control system to stop beam operation. Software and hardware have been upgraded yearly. For example, two Ge detectors are used for HAM for redundancy, NaI Scintillation detectors are also used as supplemental for the Ge detector to keep availability of the system for high counting rate event. In April 2015, the UHAM activated when a small water coolant leakage from the water shroud of the mercury target occurred. VAM detected an abnormal increase of the counting rate in the helium vessel. It was also indicated that the measured radioactive nuclides were generated from the activation of the coolant (water) in the water shroud and not from the mercury.

Crystal structure and physical properties of trigonal NpGa and NpGa

Haga, Yoshinori; Aoki, Dai*; Homma, Yoshiya*; Matsuda, Tatsuma; Ikeda, Shugo*; Sakai, Hironori; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Onuki, Yoshichika

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA109_1 - SA109_3, 2011/07

https://doi.org/10.1143/JPSJS.80SA.SA109

Hyperfine interactions in the itinerant system UFeGa

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Chudo, Hiroyuki; Yasuoka, Hiroshi; Matsuda, Tatsuma; Haga, Yoshinori; Ikeda, Shugo; Nakamura, Akio; Yamamoto, Etsuji; et al.

Journal of Nuclear Materials, 385(1), p.1 - 3, 2009/03

https://doi.org/10.1016/j.jnucmat.2008.10.030

In 5f-electron systems, exotic magnetism and unconventional superconductivity appear at low temperatures owing to strong electron correlations and orbital degeneracy. For example, we have investigated the unconventional superconducting states of recently synthesized NpPdAl (=5K) and PuRhGa (=9K) in terms of both macroscopic (staticsusceptibility, specific heat, resistivity) and microscopic (NMR) probes. The relation between magnetic fluctuations and unconventional superconductivity in f-electron systems is also discussed. Another exciting topic concerns the series AnO (An; U, Np, Pu, Am). Besides the importance of AnO as a nuclear fuel, the magnetic properties of these compounds at low temperatures are particularly interesting. On the basis of O-NMR studies, multipolar ordered states have been identified in UO (dipolar + quadrupolar ordering) and NpO (quadrupolar + octupolar ordering), in contrast with the non-magnetic ground state of PuO.

Crystal structure and magnetic properties of the new ternary actinide compounds AnPdAl (An = U, Np)

Haga, Yoshinori; Aoki, Dai*; Homma, Yoshiya*; Ikeda, Shugo; Matsuda, Tatsuma; Yamamoto, Etsuji; Sakai, Hironori; Tateiwa, Naoyuki; Dung, N. D.*; Nakamura, Akio; et al.

Journal of Alloys and Compounds, 464(1-2), p.47 - 50, 2008/09

https://doi.org/10.1016/j.jallcom.2007.10.037

Pressure effect on paramagnet -US

Ikeda, Shugo; Sakai, Hironori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Nakamura, Akio; Yamamoto, Etsuji; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Hedo, Masato*; et al.

Physica B; Condensed Matter, 403(5-9), p.893 - 894, 2008/04

https://doi.org/10.1016/j.physb.2007.10.059

Single crystals of paramagnetic semiconductor -US with the orthorhombic () crystal structure were grown by chemical transport method. We measured the electrical resistivity under high pressure, and magnetization. With increasing pressure, the temperature dependence of approaches to semimetallic behavior and a kink anomaly appears at . shifts to higher temperature with increasing pressure. From the comparison with ferromagnetic semimetal UTeS having the same crystal structure, it seems that is a ferromagnetic transition.

P-NMR study of the neptunium-based filled-skutterudite NpFeP

Tokunaga, Yo; Aoki, Dai*; Homma, Yoshiya*; Sakai, Hironori; Chudo, Hiroyuki; Kambe, Shinsaku; Matsuda, Tatsuma; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 77(Suppl.A), p.211 - 213, 2008/00

https://doi.org/10.1143/JPSJS.77SA.211

P-NMR measurements have been performed on a single crystal of NpFeP which is the first crystallized transuranium filled-skutterudite compound. The field-orientation dependence of the hyperfine interaction has been measured using the single crystal, and the results compared with those obtained previously in isostructural compounds UFeP and PrFeP. We have also measured the field and temperature dependence of the nuclear spin-lattice relaxation rate in several fields between 1.8 and 8 T at temperatures between 4.2 and 300 K. The results are discussed on the basis of a localized picture for the 5f electrons.

Heavy fermion superconductivity with the strong Pauli paramagnetic effect on NpPdAl

Aoki, Dai*; Haga, Yoshinori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Ikeda, Shugo*; Homma, Yoshiya*; Sakai, Hironori; Shiokawa, Yoshinobu*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 77(Suppl.A), p.159 - 164, 2008/00

https://doi.org/10.1143/JPSJS.77SA.159

Superconducting properties are investigated on the new neptunium-based superconductor NpPdAl. The large electronic specific heat, anisotropy of magnetic as well as superconducting properties and strong paramagnetic effect implies spin-singlet pairing with anisotropic superconducting gap.

O NMR spin-lattice relaxation in NpO; Field-dependent cross-relaxation process driven by Np spins

Tokunaga, Yo; Walstedt, R. E.*; Homma, Yoshiya*; Aoki, Dai*; Kambe, Shinsaku; Sakai, Hironori; Fujimoto, Tatsuya; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of Physics and Chemistry of Solids, 68(11), p.2016 - 2019, 2007/11

https://doi.org/10.1016/j.jpcs.2007.08.018

In this paper, we report a comprehensive study of O nuclear spin-lattice relaxation in NpO for a wide range of fields and temperatures. In both the paramagnetic and ordered-state regions, a strong, field-dependent Np -O nuclei cross-relaxation process is observed in addition to the expected background rate. The cross relaxation process, driven by the Np spins, is conveyed to the O via a greatly enhanced indirect nuclear spin-spin coupling which is described and reported here for the first time. The magnitude and temperature dependence of the indirect coupling are in reasonable accord with a simple theoretical model. The magnitude and temperature dependence of the Np process are also deduced from the data obtained.

Anisotropic superconductivity in NpPdAl in the vicinity of the heavy fermion formation

Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Haga, Yoshinori; Matsuda, Tatsuma; Tateiwa, Naoyuki; Ikeda, Shugo; Sakai, Hironori; Yamamoto, Etsuji; Nakamura, Akio; et al.

Kotai Butsuri, 42(9), p.569 - 580, 2007/09

http://ci.nii.ac.jp/naid/40015634361

The first neptunium superconductor was discovered in NpPdAl. Unconventional superconductivity of NpPdAl is realized before onset of the heavy fermion state, which is compared with superconducting properties of CeCoIn and PuRhGa (PuCoGa).

Anisotropic spin fluctuations and anomalies of nuclear quadrupole interactions in the itinerant antiferromagnet NpCoGa; Co NMR and Ga NMR/NQR studies

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya*; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Physical Review B, 76(2), p.024410_1 - 024410_14, 2007/07

https://doi.org/10.1103/PhysRevB.76.024410

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)experiments have been performed on a single crystal of NpCoGa with a Nel temperature =47 K. Knight shift, electric field gradient (EFG), frequency, and asymmetry parameter of the EFG are deduced for each site. These parameters are confirmed by NQR measurements in zero field. Hyperfine tensors for each site are deduced. Antiferromagnetic NMR spectra in zero field were also observed. A sharp anisotropy for spin fluctuations in NpCoGa has also been demonstrated.