“…Alpha particles are distributed throughout the image. The distribution of alpha particles of 222 Rn was different from the PuO 2 particles, which correlated well with the results obtained from other alpha imaging detectors 21 . Figure 6 Alpha particles emitted from the 222 Rn progeny with a zoom range of 5 × using the 30-min acquisition.…”
The internal exposure of workers who inhale plutonium dioxide particles in nuclear facilities is a crucial matter for human protection from radiation. To determine the activity median aerodynamic diameter values at the working sites of nuclear facilities in real time, we developed a high-resolution alpha imager using a ZnS(Ag) scintillator sheet, an optical microscope, and an electron-multiplying charge-coupled device camera. Then, we designed and applied a setup to measure a plutonium dioxide particle and identify the locations of the individual alpha particles in real time. Employing a Gaussian fitting, we evaluated the average spatial resolution of the multiple alpha particles was evaluated to be 16.2 ± 2.2 μmFWHM with a zoom range of 5 ×. Also, the spatial resolution for the plutonium dioxide particle was 302.7 ± 4.6 µmFWHM due to the distance between the plutonium dioxide particle and the ZnS(Ag) scintillator. The influence of beta particles was negligible, and alpha particles were discernible in the alpha–beta particle contamination. The equivalent volume diameter of the plutonium dioxide particle was calculated from the measured count rate. These results indicate that the developed alpha imager is effective in the plutonium dioxide particle measurements at the working sites of nuclear facilities for internal exposure dose evaluation.
“…Alpha particles are distributed throughout the image. The distribution of alpha particles of 222 Rn was different from the PuO 2 particles, which correlated well with the results obtained from other alpha imaging detectors 21 . Figure 6 Alpha particles emitted from the 222 Rn progeny with a zoom range of 5 × using the 30-min acquisition.…”
The internal exposure of workers who inhale plutonium dioxide particles in nuclear facilities is a crucial matter for human protection from radiation. To determine the activity median aerodynamic diameter values at the working sites of nuclear facilities in real time, we developed a high-resolution alpha imager using a ZnS(Ag) scintillator sheet, an optical microscope, and an electron-multiplying charge-coupled device camera. Then, we designed and applied a setup to measure a plutonium dioxide particle and identify the locations of the individual alpha particles in real time. Employing a Gaussian fitting, we evaluated the average spatial resolution of the multiple alpha particles was evaluated to be 16.2 ± 2.2 μmFWHM with a zoom range of 5 ×. Also, the spatial resolution for the plutonium dioxide particle was 302.7 ± 4.6 µmFWHM due to the distance between the plutonium dioxide particle and the ZnS(Ag) scintillator. The influence of beta particles was negligible, and alpha particles were discernible in the alpha–beta particle contamination. The equivalent volume diameter of the plutonium dioxide particle was calculated from the measured count rate. These results indicate that the developed alpha imager is effective in the plutonium dioxide particle measurements at the working sites of nuclear facilities for internal exposure dose evaluation.
“…Another aim of measuring alpha emitters is obtaining information about the two-dimensional distribution of alpha emitters. In the previous study, alpha particles from Pu characteristically show up as spots in the two-dimensional distributions 20 . Information about the size and distribution of alpha emitters is very useful for radiation protection.…”
Section: Introductionmentioning
confidence: 76%
“…Figure 6 shows comparisons of the energy spectra of the smear papers and the Pu sample measured at the nuclear fuel facility 20 . The energy spectrum of smear papers no.…”
Section: Resultsmentioning
confidence: 99%
“…Figure 16 shows a photograph of the alpha particle imaging detector and the data acquisition system. The data acquisition system is the same as that in the previous alpha imaging system 20 . High voltage (HV) was adjusted to −67 V, and the temperature of the SiPM circuit was monitored to compensate for temperature-dependent changes in gain.…”
Section: Methodsmentioning
confidence: 99%
“…For example, the particle size of alpha emitters is important for estimating internal exposure to a worker 12 . Moreover, information about the two-dimensional distribution of alpha emitters is valuable for distinguishing Pu from Rn progeny because the distributions of alpha particles between them are different 20,23,24 . An imaging plate (IP) has been widely used to obtain the two-dimensional distribution of alpha emitters 25,26 , but this plate is sensitive to beta particles and gamma rays as well.…”
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 Gd3(Ga,Al)5O12 (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 238Pu) 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 238Pu (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 241Am was identified by gamma spectrum measurement. Based on these results, we report actual findings of alpha emitters in the FDNPP reactor buildings originating from nuclear fuels. The surface contamination level of alpha emitters exceeded 4 Bq/cm2.
A new method has been developed to image surface contamination on-site by short range radiation emitters (such as alpha or beta particle emitters). The measurement is performed in direct contact with the contaminated surface and uses a solid scintillator coupled with Silicon Photomultiplier (SiPM) arrays. The signal readout is processed using a dedicated electronic.The experimental setup used to acquire the data, as well as the analysis procedure, are described and the results are discussed with regard to dismantling requirements. Image reconstruction is investigated using various algorithms. A proof of principle is performed in laboratory using a simple prototype and multiple alpha and beta sources. All the common beta and alpha emitters are detected (including tritium) and tests on gamma radiation are also performed. The minimum detectable activity is estimated to be 0.4 Bq/cm² for beta radiations ( 14 C) and 0.3 Bq/cm² for alpha radiations ( 239 Pu). Finally, promising discrimination capability of the prototype is highlighted.
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