||Nayuta Nagatomo, Genichiro Wakabayashi, Akihiro Nohtomi, Masakazu Horiuchi, Riku Matsumura, Measurement of Thermal Neutron Flux in Thermal Reactor by Using Activation of a CsI Scintillator, IEEE 2021 NSS/MIC/RTSD, 2021.10, A new technique to measure thermal neutron fluxes in a thermal reactor was developed. This technique uses a CsI(Tl) scintillator as a activation detector for neutron irradiation. Taking advantage of the fact that the neutron flux spectrum of a thermal reactor is approximated by the sum of a Maxwellian distribution and 1/E distribution, the thermal neutron flux at the irradiation site can be deduced from the activities of Cs-134m and I-128 produced in the scintillator without using the cadmium filter method. Large activities are produced in the scintillator by a short-time irradiation due to the short half-lives of Cs-134m and I-128, and they are measured with very high efficiency because the conversion electrons from Cs-134m and beta-rays from I-128 are fully stopped and counted in the scintillator. We applied this technique to the measurement of a thermal neutron flux in the irradiation hole of the research reactor UTR-KINKI with a power of 1W. This low power reactor has small excess reactivity and uses cadmium plates as the neutron absorber of its regulating rods. Therefore, the presence of the additional cadmium for the cadmium filter method can easily distort the neutron flux to be measured, and depending on the experimental condition, the reactor cannot be critical due to the negative reactivity of the additional cadmium. The activities of Cs-134m and I-128 in the scintillator were measured and used to deduce the thermal neutron flux from the relationship with the activation cross sections and resonance integrals. The result was agreed well with the known thermal neutron flux measured at the same position by another method. In conclusion, thermal neutron fluxes in a thermal reactor can be measured without cadmium filters by irradiating a single CsI(Tl) scintillator for a short time and applying the new technique..
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||Akihiro Nohtomi, A method of high-sensitive neutron detection by using a self-activated scintillator, International Workshop on Individual Radiation Monitoring 13, 2017.12.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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.
||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..
||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..
||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.
||Hiroyuki Kinoshita, Eriko Yahiro, Akihiro Nohtomi, Daiki Nakanishi, Genichiro Wakabayashi, Toshioh Fujibuchi, High sensitive neutron-detection by a self-activation method  Measurement at a research reactor, The 9th International Workshop on Ionizing Radiation Monitoring, 2013.11.
||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  Measurement at 10MV clinical linac, The 9th International Workshop on Ionizing Radiation Monitoring, 2013.11.
||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.