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Journal Articles

Improvement of detection limit in differential die-away analysis system for nuclear non-proliferation and nuclear security

Ozu, Akira; Maeda, Makoto; Komeda, Masao; Toh, Yosuke

Proceedings of 2019 IEEE Nuclear Science Symposium and Medical Imaging Conference (IEEE NSS/MIC 2019), Vol.1, p.101 - 104, 2020/08

Oral presentation

System development and challenges for delayed gamma-ray nondestructive assay in safeguard verification of nuclear material

Rossi, F.; Rodriguez, D.; Seya, Michio; Takahashi, Toon; Koizumi, Mitsuo; Abbas, K.*; Crochemore, J.-M.*; Pedersen, B.*; Bogucarska, T.*; Varasano, G.*; et al.

no journal, , 

Oral presentation

Radon measurements in a small chamber using compact organic scintillator-based alpha/beta spectrometer

Morishita, Yuki; Ye, Y.*; Mata, L.*; Pozzi, S.*; Kearfott, K.*

no journal, , 

A compact organic scintillator-based $$alpha beta$$ spectrometer was developed and tested for radon measurements. The spectrometer was composed of a Through Silicon Via (TSV) silicon photomultiplier or SiPM and a 6 mm $$times$$ 6 mm $$times$$ 6 mm stilbene cube crystal. Analog signals from the SiPM were sent to a digitizer. The detector was placed in a light-tight box and a stacked air filter was embedded on the side surface of the light-tight box. A continuous radon monitor, the AlphaGUARD, and $$^{226}$$Ra sources were placed in a small radon chamber constructed using a cylindrical 0.57 m diameter, 0.88 m tall steel drum. By applying a pulse shape discrimination technique, alpha and beta spectra were simultaneously clearly separated and quantitatively measured. Two peaks were registered in the measured alpha spectrum: $$^{218}$$Po was registered in the lower peak and $$^{214}$$Po was registered in the higher peak. A linear relationship was observed between radon counts from the AlphaGUARD and count-rates from the stilbene-SiPM detector. The thickness of the stilbene-SiPM detector was less than 10 mm, thus easy increases insensitivity should be possible with future construction. Thus, the compact organic scintillator-based alpha/beta spectrometer shows promise for use in novel radon detection systems.

Oral presentation

Detection of alpha particle emitters originating from nuclear fuel inside reactor building of Fukushima Daiichi Nuclear Power Station

Morishita, Yuki; Torii, Tatsuo; Usami, Hiroshi; Kikuchi, Hiroyuki*; Utsugi, Wataru*; Takahira, Shiro*

no journal, , 

We measured alpha emitters obtained from a reactor building in the Fukushima Daiichi Nuclear Power Plant (FDNPP) by using an alpha particle imaging detector. For developing the detector, we used a very thin (0.05-mm-thick) a cerium-doped Gd$$_{3}$$(Ga,Al) $$_{5}$$O$$_{12}$$ (Ce GAGG) scintillator and silicon photomultiplier (SiPM) arrays as the photodetector. The floor of the reactor building in FDNPP was wiped off by using smear papers, and the radioactivity of these papers was measured by the alpha particle imaging detector. In addition, we measured a Plutonium (Pu) sample (mainly 5.5 MeV alpha particles from $$^{238}$$Pu) obtained from a nuclear fuel facility by using of the same detector for comparison with the smear papers. The alpha spectrum was in the energy range of 5-6 MeV, which corresponds to the alpha particle energy of $$^{238}$$Pu (5.5 MeV). The correlation coefficient of the alpha spectra of the smear papers and the Pu sample had a strong positive linear relation. Moreover, the peak of $$^{241}$$Am was identified by gamma spectrum measurement. Based on these results, it is highly likely that the alpha emitters in the reactor building of FDNPP are $$^{238}$$Pu and $$^{241}$$Am, which originated from the nuclear fuel. The surface contamination level of alpha emitters exceeded 4 Bq/cm$$^{2}$$.

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