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Akihiro Nohtomi Last modified date:2021.09.22

Associate Professor / Quantum Radiation Sciences
Department of Health Sciences
Faculty of Medical Sciences




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Homepage
https://kyushu-u.pure.elsevier.com/en/persons/akihiro-nohtomi
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http://web.shs.kyushu-u.ac.jp/~nohtomi/
Web-site of Akihiro Nohtomi .
Phone
092-642-6722
Academic Degree
Ph. D. "Study on Operation Mechanism of Gas Counters in Self-quenching Streamer Mode"  Kyushu University 1995
Country of degree conferring institution (Overseas)
No
Field of Specialization
Radiation detection and measurement related to medical applications
Total Priod of education and research career in the foreign country
00years03months
Outline Activities
・Fundamental studies on Radiation Detection & Measurement and Radiation Dosimetry.
・Development of novel techniques for Neutrons Measurement and Dosimetry.
Research
Research Interests
  • Study of engineering aspect of BNCT
    keyword : BNCT, QA/QC, Energy measurement , dosimetry
    2016.04~2021.06.
  • ・Fundamental studies on Radiation Detection & Measurement and Radiation Dosimetry.
    ・Development of novel techniques for Neutrons Dosimetry.
    ・Development of high-sensitive neutron detection method for medical purposes.
    keyword : Neutron, Energy evaluation, Detection Efficiency, Position Distribution of Recoil Protons, Imaging Plate、Self activation of iodine-containing scintillator
    2011.04~2019.03.
Academic Activities
Books
1. Radiation Measurement ( Medical Physics Textbooks).
Papers
1. Akihiro Nohtomi, Yui Kanzaki, Naoya Sakamoto, Hideya Maeda, Observation of water luminescence for diagnostic 120-kV X-rays by using PMT and CCD camera, Nuclear Instruments and Methods in Physics Research A, 988 , 164935, 2021.01, Luminescence emitted from water was recently observed by Yamamoto et al. for X-rays with lower energy than the Cerenkov-light threshold. This phenomenon contradicts the conventional consensus that such low-energy photons cannot generate luminescence. Because properties and mechanism of this phenomenon have not been revealed yet, we carried out a series of observations of water luminescence during irradiation of diagnostic 120-kV X-rays by using a photomultiplier tube (PMT) and a charge-coupled device (CCD) camera. As a result of PMT measurement, the light yields owing to luminescence per unit dose deposition to water decreased almost linearly with the increase in the pulse duration time; approximately 25 % reduction of light yield was observed as the duration time increased from 0.025 s to 0.5 s. Therefore, the luminance intensity was not simply proportional to the dose deposition to water. In addition to water, sulfuric acid was used for luminescence imaging by a CCD camera for comparison. The profile curve of luminance along the beam center axis for sulfuric acid showed a somewhat different tendency in comparison to that for water; a notable bump appeared in the entry region of the X-rays. Based on these observations, the possibility of the contribution of sonoluminescence to the water luminescence can be discussed..
2. Yumika Hanada, Akihiro Nohtomi, Junichi Fukunaga, Yoshiyuki Shioyama, DEVELOPMENT OF A NEUTRON DOSIMETRY SYSTEM BASED ON DOUBLE SELF-ACTIVATED CsI DETECTORS FOR MEDICAL LINAC ENVIRONMENTS, Radiation Protection Dosimetry, doi:10.1093/rpd/ncaa218, 1-9, 2020.11, In the present study, by using double self-activated CsI detectors, the development of a neutron dosemeter system whose response indicates better agreement with the International Commission on Radiological Protection-74 rem-response was carried out to simply evaluate the neutron dose with high accuracy. The present double neutron dosemeter system, using a slow-neutron dosemeter (thermal to 10 keV) and a fast-neutron dosemeter (above 10 keV), consists of CsI scintillators wrapped with two types of neutron energy filtering materials: polyethylene and B4C silicon rubber. After optimization of each filter thickness, to confirm the validity of our method, the neutron ambient dose equivalents under several operating conditions of medical linear accelerators (Linacs) were evaluated using a Monte Carlo simulation and an experiment with the present dosemeter. From these results, the present dosimetry system has enabled a more accurate neutron dose evaluation than our conventional dosemeter, and the present dosemeter was suitable for the neutron dosimetry for 10 MV Linac environments..
3. Taishi Ueki, Akihiro Nohtomi, Genichiro Wakabayashi, Junichi Fukunaga, Toyoyuki Kato, S. Ohga, A design study of application of the CsI self-activation method to the neutron rem-counter technique, Radiation Measurements, 10.1016/j.radmeas.2019.106181, 128, 2019.09, A design study of application of the CsI self-activation method to the “neutron rem-counter technique” was investigated. A CsI crystal served as both the main target material and 4π counter of neutron activation method in our proposed CsI self-activation method. A commercially available CsI gamma-ray dosimeter was selected as the neutron detector and surrounded with several neutron filters made of polyethylene and silicon rubber containing B4C. The geometric structure of these neutron filters was optimized by a Monte Carlo calculation to make the neutron response similar to the ICRP-74 rem-response. Optimization of this method, the residual sum of squares (RSS) of the calculated neutron response and the ICRP-74 rem-response were minimized by changing the thickness of each filter sequentially. In addition, experimental verification using a Pu–Be source and photoneutrons from a 10 MV-X medical linac has been conducted. From these results, it is concluded that it may be practical for evaluating neutron ambient dose-equivalent simply around medical linacs..
4. Akihiro NOHTOMI , Masaaki TOKUNAGA, Genichiro WAKABAYASHI, Kiyomitsu SHINSHO, Neutron Distribution Measurement by the Self-activation of a CsI Plate with CCD Camera using a Decaying Self-activation Imaging Technique, JPS Conf. Proc. 24, 1, 011041, 2019.01, Neutron intensity distribution on a CsI scintillator plate has been observed by a CCD camera and analyzed by using a “decaying self-activation imaging technique”. The decaying self-activation imaging, which has been proposed recently by our group, is based on the analysis of time variation of specific radio-activities generated and remained inside the CsI plate after the termination of neutron irradiation. The luminance distributions of a CsI plate are recorded every one minute as a series of images by a cooling type CCD camera with a telescope lens in a black box. Then the time variations of luminance (mean pixel values) of the images are fitted on a “pixel-by-pixel basis” with a multi-exponential function. By this, two components of 128I (half life : 25 min) and 134mCs (half life : 174 min) are extracted as the fitting curves. The initial luminance values of individual component of radioactivity, which correspond to the values at the termination of neutron irradiation, are plotted as separate images. A conversion factor between the generated activity in a CsI plate and the observed luminance value is evaluated as “light yield”..
5. Ryosuke Kurihara, Akihiro Nohtomi, Genichiro Wakabayashi, Yoshinori Sakurai, Hiroki Tanaka, Preliminary design study of a simple neutron energy spectrometer using a CsI self-activation method for daily QA of accelerator-based BNCT, journal of nuclear science and technology, 10.1080/00223131.2018.1523757, 56, 1, 70-77, 2019.01, For recent boron neutron capture therapy (BNCT), accelerator-based neutron sources have been actively developed in place of reactor-based neutron sources. In this study, a novel neutron energy spectrometer for the daily quality assurance (QA) of BNCT was designed on the basis of a CsI self-activation method for accelerator-based neutron sources. The spectrometer design was optimized in terms of its energy resolution. To verify its applicability to high-intensity BNCT neutron fields, some practical simulations were performed. It was shown that the designed spectrometer was able to evaluate a neutron energy spectrum in approximately 900 s after an instantaneous neutron irradiation. In addition, its energy resolution was sufficient for detecting an unexpected distortion in the spectrum. The results confirm that the designed spectrometer can be employed for the daily QA of BNCT to check that the expected spectrum remains unchanged..
6. Ryo Kakino, Akihiro Nohtomi, Genichiro Wakabayashi, Improvement of neutron spectrum unfolding based on three-group approximation using CsI self-activation method for evaluation of neutron dose around medical linacs, Radiation Measurements, 10.1016/j.radmeas.2018.06.021, 116, 40-45, 2018.09, We previously evaluated ambient neutron dose equivalent by using the self-activation of a CsI scintillator around a high-energy medical linear accelerator (linac) 128I saturated activities were successfully converted to neutron spectrum and ambient neutron dose equivalent by neutron spectrum unfolding with the “three-group approximation.” The principle of the three-group approximation is based on the assumption of fixed shapes of neutron energy spectra for each of the three energy regions to evaluate the neutron spectrum effectively. However, such a neutron dose evaluation with the unfolding method might be affected by the difference between the actual fast neutron energy spectrum and the assumed spectrum. In the present work, we modified the unfolding method by taking into account the differences in the shapes of fast neutron energy spectra for various medical linacs. We verified the unfolding method using Monte Carlo simulation with several neutron spectra obtained from published research articles. The modified three-group approximation evaluates the neutron doses more accurately than the conventional unfolding method..
7. Soichiro Honda, Akihiro Nohtomi, Keita Machidori, Genichiro Wakabayashi, Shape distortion of 128I ß- spectrum observed by a self-activated CsI(Tl) scintillator for high-sensitivity neutron measurements, Nuclear Instruments and Method in Physics Research A, 2017.04, The factors causing the distortion of the 128I ß- spectrum detected by a self-activated CsI(Tl) scintillator were studied to verify the correctness of the spectral shape and the appropriateness of the discrimination setting for ß-particle counting by the scintillator. These criteria are essential for the correct evaluation of radioactivity generated in a scintillator volume by the self-activation method, which was recently proposed by our group.
A pulse height defect caused by the partial escape of ß! particles from the surface of the scintillator crystal shifts the ß! spectrum toward the lower-energy region when smaller CsI(Tl) scintillators are used (the ß-escape effect). For larger CsI(Tl) scintillators, an increase in pulse height caused by the summing of 0.443 MeV prompt γ-rays from the excited state of the 128I daughter nuclide (128Xe) affects the shape of the ß! spectrum considerably, resulting in a shift toward the higher-energy region (the γ-summing effect). The extent of the contributions of these two effects was examined by a Monte Carlo simulation of various cubical CsI(Tl) crystals of different sizes. It was found that the distortions caused by those two effects effectively cancel each other out for a medium-size cubical CsI(Tl) crystal with a side length of approximately 3 cm. This finding is very useful for the practical applications of the self-activation method.
In addition to the factors mentioned above, the efficiency of scintillation light collection by the photodetectors also affects the shape distortion of the ß! spectrum slightly through spectral line broadening due to the degradation of the energy resolution. This effect was estimated using a simple model with different discrimination settings for ß pulse counting.
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8. Akihiro Nohtomi, Genichiro Wakabayashi, Hiroyuki Kinoshita, Soichiro Honda, Ryosuke Kurihara, Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura, Saiji Ohga, Katsumasa Nakamura, High Sensitive Neutron-detection by using a Self-activation of Iodine-containing Scintillators for the Photo-neutron Monitoring around X-ray Radiotherapy Machines, JPS Conf. Proc. 11, 050002 (2016), 2016.11, A novel method for evaluating the neutron dose-equivalent as well as neutron fluence around high-energy X-ray radiotherapy machines has been proposed and examined by using the self-activation of a CsI scintillator. Several filtering conditions were used to extract energy information of the neutron field. The shapes of neutron energy spectra were assumed to be practically unchanged at each three energy regions (thermal, epi-thermal and fast regions) for different irradiations around an X-ray linac whose acceleration potential was fixed to be a certain value. In order to know the actual neutron energy spectrum, an unfolding process was carried out for saturated activities of 128I generated inside the CsI scintillator under different filtering conditions; the response function matrix for each filtering condition was calculated by a Monte Carlo simulation. As the result, neutron dose-equivalent was estimated to be 0.14 [mSv/Gy] at 30 cm from the isocenter of linac. It has been revealed that fast neutron component dominated the total dose-equivalent..
9. Akihiro Nohtomi, Ryousuke Kurihara, Hiroyuki Kinoshita, Soichiro Honda, Masaaki Tokunaga, Heita Uno, Kiyomitsu Shinsho, Genichiro Wakabayashi, Yusuke Koba, Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura, Saiji Ohga, An application of CCD read-out technique to neutron distribution measurement using the self-activation method with a CsI scintillator plate, Nuclear Instruments and Method in Physics Research A, A832, 21-23, 2016.06, In our previous paper, the self-activation of an NaI scintillator had been successfully utilized for detecting photo-neutrons around a high-energy X-ray radiotherapy machine; individual optical pulses from the self-activated scintillator are read-out by photo sensors such as a photomultiplier tube (PMT). In the present work, preliminary observations have been performed in order to apply a direct CCD read-out technique to the self-activation method with a CsI scintillator plate using a Pu-Be source and a 10-MV linac. In conclusion, it has been revealed that the CCD read-out technique is applicable to neutron measurement around a high-energy X-ray radiotherapy machine with the self-activation of a CsI plate. Such application may provide a possibility of novel method for simple neutron dose-distribution mea- surement..
10. Akihiro Nohtomi, Yoko Ariyoshi, Momoko Yamauchi, Hiroyuki Kinoshita, Soichiro Honda, Genichiro Wakabayashi, Junichi Fukunaga, H. Akamine, Yoshiyuki Umezu, Yasuhiko Nakamura, Study on high-sensitive neutron-detection by the self-activation method with a CsI(Tl) scintillator, Radiation Detectors and Their Uses, Proceedings of the 29th Workshop on Radiation Detectors and Their Uses (KEK Proceedings 2015-8), 50-53, 2015.12.
11. Akihiro Nohtomi, Genichiro Wakabayashi, Accuracy of neutron self-activation method with iodine-containing scintillators for quantifying 128I generation using decay-fitting technique, Nuclear Instruments and Method in Physics Research A, A800, 2015.08, Decay curves of 128I activity were numerically simulated by a computer program for various conditions including different initial count rates (R0) and background rates (RB), as well as counting statistical fluctuations. .
12. Genichiro Wakabayashi, Akihiro Nohtomi, Eriko Yahiro, Fujibuchi Toshioh, Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura, Katsumasa Nakamura, Makoto Hosono, Tetsuo Itoh, Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine, Radiological Physics and Technology, 8, 1, 125-134, 2015.01, NaIシンチレータに含まれるヨウ素に自己放射化に基づく高感度中性子検出方法を提案し、研究用原子炉ならびにがん治療用X線発生装置で原理検証実験を行った。その結果、〜10^2[n/cm2/s]程度までの熱中性子束を測定可能であることが判明した。この装置を用いて、高エネルギーX線治療装置から発生する光中性子の量を、オンラインにてサブリアルタイムで測定出来るシステムが実現できることが示唆された。.
13. Daiki Nakanishi, Akihiro Nohtomi, Ryoji Tanaka, Genichro Wakabayashi, A method of neutron-energy evaluation based on the position distribution of recoil protons, Progress in Nuclear Science and Technology, 4, 653-656, 2014.03, Cone-like acryl converters have been used for transforming the energy-distribution information of incident fast neutrons into the spatial-distribution information of recoil protons. The characteristics of neutron–proton conversion have been studied up to around 10 MeV by using an imaging plate (IP). A notable and interesting signal enhancement due to recoil protons generated in an acryl converter was observed on IP images for irradiation with a 252Cf source. Similar experiments were also performed in the radiation field of a research nuclear reactor and an accelerator-based neutron generator. A Monte Carlo calculation was carried out in order to understand the spatial distributions of the signal enhancement by recoil protons; these distributions promisingly involve the energy information of incident neutrons in principle. Consequently, it has been revealed that the neutron energy evaluation is surely possible by analyzing the spatial distributions of signal enhancement that is caused by recoil protons..
14. Akihiro Nohtomi, , A method of neutron energy evaluation by using an imaging plate and cone-like acryl converters with a geometrical modulation concept, Nuclear Instruments and Method in Physics Research A , A633, 36, 2011.03, Cone-like acryl converters have been used for transforming the energy-distribution information of incident fast neutrons into the spatial-distribution information of recoil protons. The characteristics of neutron–proton conversion have been studied up to around 10 MeV by using an imaging plate (IP). A notable and interesting signal enhancement due to recoil protons generated in an acryl converter was observed on IP images for irradiation with a 252Cf source. Similar experiments were also performed in the radiation field of a research nuclear reactor and an accelerator-based neutron generator. A Monte Carlo calculation was carried out in order to understand the spatial distributions of the signal enhancement by recoil protons; these distributions promisingly involve the energy information of incident neutrons in principle. Consequently, it has been revealed that the neutron energy evaluation is surely possible by analyzing the spatial distributions of signal enhancement that is caused by recoil protons..
Presentations
1. Naoya Sakamoto, Akihiro Nohtomi, Yui Kanzaki, Hideya Maeda, Genichiro Wakabayashi, An evaluation of quenching effects and an analysis of a long half-life component for neutron measurement with iodine-added liquid scintillator, 第121回日本医学物理学会学術大会, 2021.04.
2. Hideya Maeda, Akihiro Nohtomi, Shunsuke Kurosawa, Shohei Kodama, Genichiro Wakabayashi, Miyu Shimazu, The activation properties of CaI2 crystal on neutron detection by the self-activation method with an iodine-containing scintillator, 第121回日本医学物理学会学術大会, 2021.04.
3. Yui Kanzaki, Akihiro Nohtomi, Junichi Fukunaga, Yoshiyuki Shioyama, An observation of luminescence imaging of water during irradiation by 10MV clinical linac using a CCD camera, IEEE 2020 NSS/MIC/RTSD, 2020.11.
4. Yui Kanzaki, Akihiro Nohtomi, Yoshinori Sakurai, Observation of neutron distribution at E3 port of KUR by the self-activation of a CsI plate with a CCD camera, 第119回日本医学物理学会学術大会, 2020.05.
5. Naoya Sakamoto, Akihiro Nohtomi, Yumika Hanada, Eimi Nagano, Genichiro Wakabayashi, Miyu Shimazu, Study of neutron detection based on the self-activation of iodobenzene added to liquid scintillator with different mass concentrations, 第119回日本医学物理学会学術大会, 2020.05.
6. Y. Hanada, A. Nohtomi, T. Ueki, R. Kurihara, A fundamental study of a development of neutron dosimeter using double self-activated CsI scintillator for neutron doses around clinical Linac, IEEE 2019 NSS/MIC/RTSD, 2019.10.
7. Y.Hanada, A.Nohtomi, T.Ueki, R.Kurihara, Fundamental study of the neutron ambient dose-equivalents measurements using two CsI self-activation sensors, 第117回医学物理学会学術大会, 2019.04.
8. M. Shimazu, M. Nakata, G. Wakabayashi, A. Nohtomi, Y. Koba and K. Shinsho, The measurement of thermal neutron flux for the irradiation filed with a Pu-Be neutron source by the activation of a CsI scintillator, 14th International Workshop on Ionizing Radiation Monitoring, 2018.12.
9. M. Shimazu, G. Wakabayashi, A. Nohtomi, Y. Koba, K Shinsho, Thermal Neutron Flux Measurement by Counting Conversion Electrons from 、134mCs Generated in a CsI Scintillator, IEEE 2018 NSS/MIC/RTSD, 2018.11.
10. T. Ueki, A. Nohtomi, G. Wakabayashi, A Design Study of an Application of the CsI Self-activation Method to the Neutron Rem-counter Technique, IEEE 2018 NSS/MIC/RTSD, 2018.11.
11. Akihiro Nohtomi, Masaaki Tokunaga, Genichiro Wakabayashi, Kiyomitsu Shinsho, Neutron distribution measurement by the self-activation of a CsI plate with CCD camera using a decaying self-activation imaging technique, ISRD 2018: International Symposium on Radiation Detectors and Their Uses, 2018.01.
12. Akihiro Nohtomi, A method of high-sensitive neutron detection by using a self-activated scintillator, International Workshop on Individual Radiation Monitoring 13, 2017.12.
13. R. Kurihara, A. Nohtomi, G.Wakabayashi, Y. Sakurai, H. Tanaka, A design study of a handy neutron energy spectrometer for BNCT daily QA procedure, IEEE 2017 NSS/MIC/RTSD, 2017.10.
14. M. Tokunaga, A. Nohtomi, J. Fukunaga, Y. Nakamura,Y. Umezu, S. Ohga, G.Wakabayashi, Y. Koba, K. Shinsho, An image analysis for neutron distribution measurement by CsI plates with CCD camera using a decaying self-activation imaging technique, IEEE 2017 NSS/MIC/RTSD, 2017.10.
15. R. Kakino, A. Nohtomi, G.Wakabayashi, J. Fukunaga, Y. Umezu, Y. Nakamura, S. Ohga, Simplification of Neutron-Monitoring System by Using Cs-134m Conversion Electrons in a Self-Activated CsI Scintillator, IEEE 2017 NSS/MIC/RTSD, 2017.10.
16. Ryo Kakino, Akihiro Nohtomi, Genichiro Wakabayashi, Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura, Saiji Ohga, A comparison of neutron generating properties between Varian Clinac 21EX and Varian TrueBeam by using a self-activation of CsI scintillator, The 12th International Workshop on Ionizing Radiation Monitoring, 2016.12.
17. Masaaki Tokunaga, Akihiro Nohtomi, Junichi Fukunaga, Yasuhiko Nakamura, Yoshiyuki Umezu, Saiji Ohga, Genichiro Wakabayashi, Yusuke Koba, Kiyomitsu Shinsyo, An image analysis for neutron distribution distribution measurement by CsI plates with CCD camera using a decaying self-activation imaging technique, The 12th International Workshop on Ionizing Radiation Monitoring, 2016.12.
18. Akihiro Nohtomi, Genichiro Wakabayashi, Hiroyuki Kinoshita, Soichiro Honda, Ryosuke Kurihara, Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura, Saiji Ohga, Katsumasa Nakamura, High Sensitive Neutron-detection by using a Self-activation of Iodine-containing Scintillators for the Photo-neutron Monitoring around X-ray Radiotherapy Machines, ISRD2016, 2016.01.
19. Ryoko Matsuo, Akihiro Nohtomi, Ryosuke Kurihara, Genichiro Wakabayashi, Application of Bayesian inference to the on-line n/γ discrimination with a recoil proton proportional counter, The 11th International Workshop on Ionizing Radiation Monitoring, 2015.12.
20. Akihiro Nohtomi, Hiroyuki Kinoshita, Soichiro Honda, Ryosuke Kurihara, Momoko Yamauchi, Yoko Ariyoshi, Junichi Fukunaga, H. Akamine, Yoshiyuki Umezu, Yasuhiko Nakamura, Katsumasa Nakamura, Genichiro Wakabayashi, On-line detection of neutrons by the self-activation of a CsI scintillator around an X-ray radiotherapy machine and an RI source., ICRR2015, 2015.05.
21. Ryosuke Kurihara, Akihiro Nohtomi, Genichiro Wakabayashi, RISE-TIMEDISTRIBUTIONSOFAPOLYETHYLENE-LINEDRECOILPROTONPROPORTIONALCOUNTERFORFAST NEUTRONSANDGAMMA-RAYS, The 7th Korea-Japan Joint Meeting on Medical Physics, 2014.09, [Purpose] Wehavebeendoingbasicinvestigationwithaimingatthedevelopmentoffast-neutronsurvey meterbyusingapolyethylene-linedrecoilprotonproportionalcounter.Whenrecoilproton proportionalcountersareappliedforfastneutronmeasurements,themostcriticalissuetobe solvedisaneliminationofgamma-rays.Untilnow,nocommonlyavailablemeanshasbeen establishedforthediscriminationoffastneutronfromgammasignalsbyusingthese detectors.However,forapolyethylene-linedproportionalcounterwithCH4filling, ourresearchhasrevealedthatitispossibletodiscriminatetwocomponentsbyusingrise- timediscriminationmethod.Inthisstudy,weobservedtherise-timedistributionsofaP-10 fillingcounterinthesamewayasourpreviousmeasurements.Theresultswerecomparedwith thoseofCH4filling.
[Method] Thedetectorusedinthisstudyispolyethylene-linedrecoilprotonproportionalcounter filledP-10gasin430Torr.252Cfasaneutronsourceand60Coand 137Csasgamma-rayssourceswereused.Thepulsesfromthecounterwerefedintoa chargesensitivepreamplifier.Theoutputofthepreamplifierwassenttoaspectroscopy amplifier.Afterashapingwiththetimeconstantof1μs,thebi-polaroutputwasconnected toarise-timetoheightconverterfortherise-timemeasurement.Pulseheightswererecorded bymulti-channelanalyzersystem.
[Results] Observedrise-timedistributionsforP-10showarathersimilartendencywiththosefor CH4;rise-timesarecommonlyshorterforgamma-rays.Thoseforneutronsarealmost identicalforbothgasfillings.Ontheotherhand,thoseofgamma-raysareclearly distinguishableeachother.
[Conclusion] P-10fillinghasbeenfoundtobealsoapplicableforthediscriminationbetweenfast-neutron andgamma-raysbyusingrise-timeinformationofaproportionalcounter..
22. Hiroyuki Kinoshita, Akihiro Nohtomi, Soichiro Honda, Ryosuke Kurihara, Genichiro Wakabayashi, Yauhiko Nakamura, Yoshiyuki Umezu, Junichi Fukunaga, HIGH SENSITIVE NEUTRON-DETECTION BY A SELF-ACTIVATION METHOD WITH A CSI(TL) SCINTILLATOR AROUND A CLINICAL LINAC, The 7th Korea-Japan Joint Meeting on Medical Physics, 2014.09, Purpose: The purpose of this study is to confirm usefulness of a CsI(Tl) scintillator as a self-activation neutron detector using the activation of iodine; the present application centers on high sensitive measurement of rather weak photo- neutron field around a clinical linac. Inside this detector, a neutron capture produces I-128, which emits β-rays with half- life of 25 minutes. Since the half-life is adequately short, the detector shows relatively high sensitivity for the short time irradiation, as well as quick reduction of activity after the termination of irradiation. Such property allows repeatable use of this detector at practically appropriate intervals.
Methods: A CsI(Tl) crystal (2.5×2.5×2.5 cm3), which was enclosed in a aluminum cover (thickness: 0.5mm), was used. This was irradiated at the top of a research reactor UTR-KINKI of Kinki University (thermal output: 1W) and near the primary radiation field of 10MV X-ray clinical linac, Valian Clinac 21EX of Kyushu University Hospital. Just after each irradiation, the self-activation was measured by the CsI(Tl) itself. Pulse height spectra were recorded every one minutes, and the decay curves were fitted with several exponentially-decreasing components and a constant background.
Results: From above measurements, it has been found that the contribution of I-128 was dominant. The observed energy spectra were almost identical to the theoretical spectrum of β-rays from I-128 given by ICRP-107. For the research-reactor measurement, total number of counts due to I-128 was about 93% of all counts during the first one minute of each measurement. That for the clinical linac was about 98%.
Conclusion: Neutrons around the research reactor and the clinical linac were successfully detected by the self-activation method with a CsI(Tl) scintillator. The present technique will be useful for the routine on-line evaluation of neutron dose around a clinical linac..
23. Soichiro Honda, Akihiro Nohtomi, Hiroyuki Kinoshita, Ryosuke Kurihara, Genichiro Wakabayashi, Yauhiko Nakamura, Yoshiyuki Umezu, Junichi Fukunaga, EVALUATION OF SELF-SHIELDING EFFECT AND Γ-RAY SUMMATION EFFECT IN A SELF-ACTIVATION METHOD WITH AN NAI(TL) SCINTILLATOR CONTAINING IODINE , The 7th Korea-Japan Joint Meeting on Medical Physics, 2014.09.
24. Hiroyuki Kinoshita, Eriko Yahiro, Akihiro Nohtomi, Daiki Nakanishi, Genichiro Wakabayashi, Toshioh Fujibuchi, High sensitive neutron-detection by a self-activation method [1] Measurement at a research reactor, The 9th International Workshop on Ionizing Radiation Monitoring, 2013.11.
25. Aina Takayama, Soichiro Honda, Eriko Yahiro, Akihiro Nohtomi, Daiki Nakanishi, Genichiro Wakabayashi, Toshioh Fujibuchi, Yoshiyuki Umezu, Jynichi Fukunaga, Syuji Nagamine, Yasuhiko Nakamura, High sensitive neutron-detection by a self-activation method [2] Measurement at 10MV clinical linac, The 9th International Workshop on Ionizing Radiation Monitoring, 2013.11.
26. Eriko Yahiro, Akihiro Nohtomi, Daiki Nakanishi, Genichiro Wakabayashi, Fujibuchi Toshioh, Yoshiyuki Umezu, Jyunichi Fukunaga, Syuji Nagamine, Yasuhiko Nakamura, High sensitive neutron-detection by an NaI(Tl) scintillator with a novel self-activation method
, 2013 Institute of Electrical and Electronics Engineers / Nuclear Science Symposium (IEEE/NSS), 2013.11.
Membership in Academic Society
  • The Society of Iodine Science
  • Japanese Society of Neutron Capture Therapy
  • Japan Health Physics Society
  • Atomic Energy Society of Japan
  • The Japan Society of Applied Physics
  • Japanese Society of Medical Physics
Awards
  • Fundamental study of the neutron ambient dose- equivalent measurement using two CsI self-activation sensor
  • A comparison of generating properties of I-128 and Cs-134m in a self-activated CsI scintillator for different energy neutron fields
  • (Outstanding Paper Published in 2015)
    "Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine"
  • "On-line Detection of Neutrons by the Self-activation of a CsI Scintillator around a X-ray Radiotherapy Machine and an RI Source"
  • High sensitive neutron-detection by an NaI scintillator (2) Measurement at clinical linac
  • n/γ discrimination of pulses from a polyethylene-lined proportional counter base on the rise-time analysis
Educational
Other Educational Activities
  • 2019.04.
  • 2013.01.