Remote detection of radioactive hotspot using a Compton camera mounted on a moving multi-copter drone above a contaminated area in Fukushima

Sato, Yuki; Ozawa, Shingo*; Terasaka, Yuta; Minemoto, Kojiro*; Tamura, Satoshi*; Shingu, Kazutoshi*; Nemoto, Makoto*; Torii, Tatsuo

Journal of Nuclear Science and Technology, 57(6), p.734 - 744, 2020/06

https://doi.org/10.1080/00223131.2020.1720845

Application of multiple -ray detection to long-lived radioactive nuclide determination in environmental samples

Oshima, Masumi*; Goto, Jun*; Haraga, Tomoko; Kin, Tadahiro*; Ikebe, Yurie*; Seto, Hirofumi*; Bamba, Shigeru*; Shinohara, Hirofumi*; Morimoto, Takao*; Isogai, Keisuke*

Journal of Nuclear Science and Technology, 57(6), p.663 - 670, 2020/06

https://doi.org/10.1080/00223131.2019.1710614

Gamma-gamma coincidence measurement utilized in -ray spectroscopy experiments is well known to be effective for the improvement of signal-to-noise ratio in a -ray spectrum. We study its applicability to determination of long-lived radioactive nuclides in environmental samples. The -ray simulation code Geant 4.10.2 was used. We took up 35 nuclides which need to be determined for the evaluation of fission product leakage at the nuclear accident in the Fukushima nuclear power plants. Among them five nuclides of Co, Nb, Cs, Eu and Eu can be the objectives of the multiple -ray detection method. The simulation results indicate that the signal-to-noise ratio can be improved by a factor between 9.8 and 283, and the detection limit by a factor between 2.7 and 8.5 relative to the singles measurement, implying that the method can be well applied to the determination of the long-lived radioactive nuclides.

Water leakage due to the welding defect and improvement to reach 1-MW beam operation in the mercury target of J-PARC

Kogawa, Hiroyuki; Wakui, Takashi; Naoe, Takashi; Haga, Katsuhiro; Takada, Hiroshi; Futakawa, Masatoshi

Journal of Nuclear Science and Technology, 57(5), p.487 - 494, 2020/05

https://doi.org/10.1080/00223131.2020.1715899

Neutron flux per pulse reached world record at neutron source in the J-PARC. In the J-PARC, mercury target system is used as a spallation neutron source. A target vessel has the multi-walled protection system that comprises a mercury vessel enclosed with a double-walled water shroud. This is to prevent the leakage of the mercury outside the mercury vessel. The multi-walled structure needed to be complicated with a lot of welding lines. However, during the operation, we faced an unscheduled shutdown due to water leakage to the intermediate layer between the mercury vessel and water shroud. An investigation on the cause of the leakage was carried out. It is deduced that the leakage path was formed due to the crack propagation from welding defects that is caused by the complicated multi-walled structure. The crack propagation is attributed to the repeated stress by pressure waves generated in the mercury target. Based on the investigation results, the design was improved to remove the welding line on the complicated structure and to realize the stable operation with 1 MW proton beam.

Determination of humic substances in deep groundwater from sedimentary formations by the carbon concentration-based DAX-8 resin isolation technique

Terashima, Motoki; Endo, Takashi*; Miyakawa, Kazuya

Journal of Nuclear Science and Technology, 57(4), p.380 - 387, 2020/04

https://doi.org/10.1080/00223131.2019.1688730

Measurements of thermal-neutron capture cross-section of cesium-135 by applying mass spectrometry

Nakamura, Shoji; Shibahara, Yuji*; Kimura, Atsushi; Iwamoto, Osamu; Uehara, Akihiro*; Fujii, Toshiyuki*

Journal of Nuclear Science and Technology, 57(4), p.388 - 400, 2020/04

https://doi.org/10.1080/00223131.2019.1691077

The thermal-neutron capture cross-section () and resonance integral(I) were measured for the Cs(n,)Cs reaction by an activation method and mass spectrometry. We used Cs contained as an impurity in a normally available Cs standard solution. An isotope ratio of Cs and Cs in a standard Cs solution was measured by mass spectrometry to quantify Cs. The analyzed Cs samples were irradiated at the hydraulic conveyer of the research reactor in Institute for Integral Radiation and Nuclear Science, Kyoto University. Wires of Co/Al and Au/Al alloys were used as neutron monitors to measure thermal-neutron fluxes and epi-thermal Westcott's indices at an irradiation position. A gadolinium filter was used to measure the , and a value of 0.133 eV was taken as the cut-off energy. Gamma-ray spectroscopy was used to measure induced activities of Cs, Cs and monitor wires. On the basis of Westcott's convention, the and I values were derived as 8.570.25 barn, and 45.33.2 barn, respectively. The obtained in the present study agreed within the limits of uncertainties with the past reported value of 8.30.3 barn.

Neutron emission spectrum from gold excited with 16.6 MeV linearly polarized monoenergetic photons

Kirihara, Yoichi; Nakashima, Hiroshi; Sanami, Toshiya*; Namito, Yoshihito*; Itoga, Toshiro*; Miyamoto, Shuji*; Takemoto, Akinori*; Yamaguchi, Masashi*; Asano, Yoshihiro*

Journal of Nuclear Science and Technology, 57(4), p.444 - 456, 2020/04

https://doi.org/10.1080/00223131.2019.1691073

no abstracts in English

Degradation prediction of a gamma-ray radiation dosimeter using InGaP solar cells in a primary containment vessel of the Fukushima Daiichi Nuclear Power Station

Okuno, Yasuki; Yamaguchi, Masafumi*; Okubo, Nariaki; Imaizumi, Mitsuru*

Journal of Nuclear Science and Technology, 57(4), p.457 - 462, 2020/04

https://doi.org/10.1080/00223131.2019.1691072

Indium gallium phosphide (InGaP) solar cell with a superior high-radiation resistance is expected to be a powerful candidate for a dosimeter under a high-radiation dose rate environment. In this study, in order to predict the lifetime as the dosimeter using the InGaP solar cell, we clarify the effect of minority-carrier diffusion length () on a radiation-induced current as a dose signal in the InGaP solar cell by irradiation tests and empirical calculations. In the irradiation tests, the short circuit current density () as a function of the gamma-ray dose rate is measured to estimate the for the InGaP solar cell by irradiation tests. The operational lifetime as a detector using the InGaP solar cell under various dose rates is estimated by using the empirical calculations based on the relation between the L and absorbed dose. The results suggest that the dosimeter using InGaP solar cell is able to be used during more than 10 h in the primary containment vessel of the Fukushima Daiichi Nuclear Power Plant and it has a high potential of being a radiation-resistant dosimeter that would contribute to the decommissioning.

Material balance evaluation of pyroprocessing for minor actinide transmutation nitride fuel

Tateno, Haruka; Sato, Takumi; Tsubata, Yasuhiro; Hayashi, Hirokazu

Journal of Nuclear Science and Technology, 57(3), p.224 - 235, 2020/03

https://doi.org/10.1080/00223131.2019.1666056

Fuel cycle technology for the transmutation of long-lived minor actinides (MAs) using an accelerator-driven system has been developed using the double-strata fuel cycle concept. A mononitride solid solution of MAs and Pu diluted with ZrN is a prime fuel candidate for the accelerator-driven transmutation of MAs. Pyro-reprocessing is suitable for recycling the residual MAs in irradiated nitride fuel with high radiation doses and decay heat. Spent nitride fuel is anodically dissolved, and the actinides are recovered simultaneously into a liquid cadmium cathode via molten salt electrorefining. The process should be designed to achieve the target recovery yield of MAs and the acceptable impurity level of rare earths in the recovered material. We evaluated the material balance during the pyro-reprocessing of spent nitride fuel to gain important insight on the design process. We examined the effects of changing processing conditions on material flow and quantity of waste.

Estimation of uncertainty in lead spallation particle multiplicity and its propagation to a neutron energy spectrum

Iwamoto, Hiroki; Meigo, Shinichiro

Journal of Nuclear Science and Technology, 57(3), p.276 - 290, 2020/03

https://doi.org/10.1080/00223131.2019.1671912

This paper presents an approach to uncertainty estimation of spallation particle multiplicity of lead (Pb), primarily focusing on proton-induced spallation neutron multiplicity () and its propagation to a neutron energy spectrum. The uncertainty is estimated from experimental proton-induced neutron-production double-differential cross sections (DDXs) and model calculations with the Particle and Heavy Ion Transport code System (PHITS). Uncertainties in multiplicities for , , and reactions are then inferred from the estimated uncertainty and the PHITS calculation. Using these uncertainties, uncertainty in a neutron energy spectrum produced from a thick Pb target bombarded with 500 MeV proton beams, measured in a previous experiment, is quantified by a random sampling technique, and propagation to the neutron energy spectrum is examined. Relatively large uncertainty intervals (UIs) were observed outside the lower limit of the measurement range, which is prominent in the backward directions. Our findings suggest that a reliable assessment of spallation neutron energy spectra requires systematic DDX experiments for detector angles and incident energies below 100 MeV as well as neutron energy spectrum measurements at lower energies below 1.4 MeV with an accuracy below the quantified UIs.

Neutron capture cross-section measurement and resolved resonance analysis of Np

Rovira, G.*; Katabuchi, Tatsuya*; Tosaka, Kenichi*; Matsuura, Shota*; Terada, Kazushi*; Iwamoto, Osamu; Kimura, Atsushi; Nakamura, Shoji; Iwamoto, Nobuyuki; Segawa, Mariko; et al.

Journal of Nuclear Science and Technology, 57(1), p.24 - 39, 2020/01

https://doi.org/10.1080/00223131.2019.1651231