Recent Activities of the neutron standardization at KRISS

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1 Recent Activities of the neutron standardization at KRISS Hyeonseo Park, Jungho Kim Korea Research Institute of Standards and Science (KRISS), Korea Thermal neutron field Graphite pile We have constructed the thermal neutron field using a graphite pile and 241 Am-Be neutron source (Fig. 1). The graphite pile is 1.4 m long, 1.2 m wide, and 1.2 m high and the neutron source position is 35 cm off-centered in length to increase thermal neutron fraction. Total 139 pure graphite blocks of cm 3 are used and the mass of each block is measured on by one. Boron concentration in the graphite was measured with 16 samples by the PGAA(prompt gamma activation analysis) method in NG7 neutron beam line at NCNR of NIST. The average and standard deviation of 16 measurements are μg/g and μg/g. The impurities were checked by GDMS analysis and all impurities are below 0.1 μg/g. The density of the graphite block is determined by the measured mass and the size and it is ± g/cm 3. The emission rate of neutron from 241 Am-Be source is s -1. Neutron fluence measurement The thermal neutron fluence was measured by neutron activation method with thin gold foil through Westcott convention. The gold foil is 50 µm thick and 2 cm in diameter. To measure the cadmium ratio, two sets of foil case made by aluminum and cadmium of same dimension were used during the activation. The most of correction factors like self-shieling factor or cross-section differences were evaluated by MCNPX calculation. The neutron energy distribution at 70 cm position from the source center is calculated by MCNPX, shown in Fig. 2. The temperature of our system is determined by maximum likelihood fit for the neutron spectrum estimated by MCNPX calculation and is 307 K with the uncertainty of about 2 %. Gold activity determination The activity of gold foil activated by neutrons were measured by well-type NaI(Tl) scintillation detector (φ19.0 cm 19.8 cm) (Fig. 3). Figure 4 shows the gamma energy spectrum from 198 Au decay measured by well-type NaI(Tl) scintillation detector. The 1

411.8 kev gamma peak is clearly seen. The efficiency calibration is done with standard Gold foil activated in NPL thermal neutron field. The efficiency for 411.8 kev gamma is 0.766 (0.13 %, k=2).

2 411.8 kev gamma peak is clearly seen. The efficiency calibration is done with standard Gold foil activated in NPL thermal neutron field. The efficiency for kev gamma is (0.13 %, k=2). Now, we are developing β-γ coincidence counting methods using this well-type NaI(Tl) detector for γ counting and plastic scintillation counter for β counting. After this work, we will have our own traceability. Thermal neutron fluence at the reference position The reference position for thermal neutron standards is the 70 cm position from the neutron source. This position is selected because of the reasonably good thermal neutron fraction(about 0.96 %) and the acceptable amount of thermal neutron fluence (about 3000 n/s) if 241 Am-Be source of s -1 emission rate is used. The evaluated neutron fluence below cadmium cutoff energy at the reference position is n/s (1.8 %, k=1) and the temperature of Maxwell distribution is 307 K. Figure 1. Graphite pile to produce thermal neutron field 2

Figure 2. Neutron energy spectrum at 70 c m from the source estimated by MCNPX calculation Figure 3. Shielding system for well-type NaI(Tl) scintillation detector Figure 4.

3 Figure 2. Neutron energy spectrum at 70 c m from the source estimated by MCNPX calculation Figure 3. Shielding system for well-type NaI(Tl) scintillation detector Figure 4. γ energy spectrum from 198 Au decay measured by well-type NaI(Tl) scintillation detector Neutron Spectrometry with BSS KRISS has 10 Bonner spheres manufactured by Centronic Ltd., UK. It is consisted of 10 polyethylene spheres of 3", 3.5", 4", 4.5", 5", 6", 7", 8", 10", and 12" diameter. For the extension of the neutron energy up to 1 GeV, 4 multi-shell structure spheres with copper and lead were included. The response functions with the 3 He proportional counter SP9 and activation foils(gold and dysprosium) were calculated by using 3

MCNPX(Figure 5). The responses were found to be stable within 0.5 % for parallel, normal and isotropic incidence directions. Three sets of 197 Au foils were prepared for the measurements: φ12.7 mm 50.

4 MCNPX(Figure 5). The responses were found to be stable within 0.5 % for parallel, normal and isotropic incidence directions. Three sets of 197 Au foils were prepared for the measurements: φ12.7 mm 50.8 μm, φ15.0 mm 100 μm and φ20.0 mm 100 μm. The dimension of the natural abundant Dy foil is φ12.7 mm 25.4 μm. A well-type NaI(Tl) with φ17.78 cm cm is used for the activity measurements. We have measured the accelerator-produced neutrons with the extended BSS at three laboratories in Korea. Figure 5. Response functions of KRISS BSS with 197 Au foil (φ20.0 mm 100 μm) Neutron energy spectrum measurement at KIRAMS In 2013, we have measured neutrons from the 9 Be(p,n) 9 B reaction by 50-MeV cyclotron at Korea Institute of Radiological & Medical Sciences(KIRAMS). 197 Au and Dy foils were used as thermal detectors and the measurement were carried out using 11 spheres including 2 extended spheres. The incident proton energy was 30 MeV and the spheres were placed 100 cm from the 9 Be target at 0 o beam direction. The beam current was 10.0 μa and the fluctuation was stable within 1.5%(k=1). The saturation specific activities were measured by the φ17.78 cm cm well-type NaI(Tl) detector. Figure 6 shows the measurement at KIRAMS and the neutron energy spectra for both 197 Au and Dy foils. 4

10 MV and 18 MV modes. We have measured the secondary neutrons by X-rays from 18 MV mode in 2014.

5 Figure 6. Measurement at KIRAMS(left) and the energy spectra(right) Neutron energy spectrum measurement at KRISS KRISS has an electron LINAC manufactured by Elekta Synergy which could produce X-rays from 6 MV, 10 MV and 18 MV modes. We have measured the secondary neutrons by X-rays from 18 MV mode in The positions 50 cm from the isocenter and near the entrance gate were chosen to measure the accelerator-produced neutrons. 197 Au foils (φ20.0 mm 100 μm) and 9 Bonner spheres of 3", 3.5", 4", 4.5", 5", 6", 7", 8" and 10" diameter were used for the measurement. The total dose for each sphere was 10 Gy with the dose rate of 3 Gy/min. The beam size of X-ray was 10.0 cm 10.0 cm which is standard irradiation condition. Neutron dose were msv Gy -1 and msv Gy -1 for the isocenter 50 cm and the entrance gate. Figure 7 shows the measurement at KRISS and the neutron energy spectra. Figure 7 Measurement at KRISS(left) and the energy spectra(right) 5

Neutron energy spectrum measurement at hospital Secondary neutrons during 230-MeV proton therapy was measured at Samsung Medical Center in 2015.

6 Neutron energy spectrum measurement at hospital Secondary neutrons during 230-MeV proton therapy was measured at Samsung Medical Center in The neutron spectrum at flat panel position was measured using an extended BSS while irradiating proton beam to plastic water phantom instead of patient at isocenter. The extended BSS used for this study comprises 14 detectors, i.e., a 3 He proportional counter SP9, 9 PE spheres (3", 3.5", 4", 4.5", 5", 6", 7", 8" and 10") and 4 modified multi-shell spheres. The proton beam was operated with wobbling mode (passive scattering method using ridge filter, MLC, compensator, block and etc.) using multipurpose nozzle of Sumitomo Heavy Industry and the beam size was set to 10.0 cm 10.0 cm. The total dose for each sphere was 0.03 Gy and the dose rate was set to 0.03 Gy/min in order to use active detector. Neutron dose were 2.22 msv Gy -1 and 2.46 msv Gy -1 for with phantom and without phantom. Figure 8 shows the measurement at KRISS and the neutron energy spectra. Figure 8. Measurement at Samsung Medical Center(left) and the energy spectra(right) Table 1. Summary of the accelerator-produced neutron measurements KIRAM KRISS Samsung Medical Center Accelerator Proton cyclotron Electron LINAC Proton cyclotron Primary radiation proton X-ray proton Primary energy 30 MeV 18 MV 230 MeV Beam size 9 Be(p,n) at 0 o 10.0 cm 10.0 cm 10.0 cm 10.0 cm Position 100 cm Isocenter 50 cm, gate flat panel position 6

7 Primary dose (rate) Bonner sphere Beam current 10.0 μa 10 Gy 0.03 Gy (3Gy/min) (0.03Gy/min) 9 PE and 2 multi-shell 9 PE 9 PE and 4 multi-shell 197 Au foils Thermal detector Neutron fluence (rate) (φ12.7 mm 50.8 μm) Dy foils (φ12.7 mm 25.4 μm) 197 Au foils (φ20.0 mm 100 μm) SP9 (200 kpa) cm -2 s -1 (A) cm -2 Gy -1 6 (C) cm -2 Gy -1 (B) cm -2 Gy -1 (D) cm -2 Gy -1 Neutron dose (A) msv Gy msv h -1 (rate) (B) msv Gy -1 (A) 50 cm from the isocenter (B) Near entrance gate (C) With phantom (D) Without phantom (C) 2.22 msv/gy (D) 2.45 msv/gy Plans 1. Neutron generator In this year, we will install DD neutron generator (DD-109, Adelphi) which has 10 9 n/s emission rate. This is purchased by Center for Underground Physics, Institute of Basic Science, Korea and will be used mainly for the quenching factor measurement of crystal detector for the Dark matter search. 2. Neutron Spectrometry with LSC(Liquid Scintillation Counter) Because the energy resolution of BSS is very much limited, we are preparing LSC (liquid scintillation counter) system for the high resolution neutron spectrometry. 3. Neutron emission rate measurement Present manganese bath can measure the neutron emission rate up to 10 5 n/s. In order to expand this range to 10 3 or 10 4 n/s, the mini-manganese bath will be constructed. 4. Workplace field The work place field to simulate nuclear power plant and also the neutron field produced around electron accelerator will be constructed. Staff Members 7

8 Three research scientists and one research associate are fully involved for the neutron standardization. - Hyeonseo Park, ph.d in Nuclear Physics - Jung Ho Kim, ph.d in Nuclear Physics Facilities - Radioactive neutron sources two 252 Cf source : the emission rates of ~2x10 7 n/s and ~2 x 10 5 n/s three 241 Am-Be source : the emission rate of two ~1.2x10 7 n/s, and ~2x10 5 n/s - Low background neutron irradiation room : size of 6.7x7.6x6.4 m 3 - Manganese Sulphate Bath system for neutron emission rate measurement - Bonner sphere system with 10 PE spheres - 4 extended Bonner spheres with Pb and Cu shells - Neutron detectors Long counter with one He-3 proportional counter and one BF 3 proportional counter three REM counter(two EG&G Ortec LB123 and one Studsvik 2002A), two H 2 proportional counter Liquid scintillation detector (BC501a) two BF 3 proportional counter 8

9 Publications and Communications of KRISS Measurement of the 250 Cf component in a 252 Cf neutron source at KRISS, Jungho Kim, Hyeonseo Park, Kil-Oung Choi, Radiation Protection Dosimetry 161, pp , Long counter and its application for the calibration of the neutron irradiators, Hyeonseo Park, Jungho Kim, Kil-Oung Choi, Radiation Protection Dosimetry 161, pp , Dose dependence and uncertainty evaluation of calibration factors for active neutron personal dosimeters, Jungho Kim, Hyeonseo Park, Kil-Oung Choi, Jiyeon Kwak, Progress in Nuclear Science and Technolgy 4, pp , Neutron spectrum at the underground laboratory for the ultra low background experiment, Hyeonseo Park, Jungho Kim, Y.M.Hwang, Kil-Oung Choi, Applied Radiation and Isotopes 81, pp , Measurement of cosmic-ray-induced neutrons using multi-shell Bonner spheres, Jungho Kim, Hyeonseo Park, Kil-Oung Choi, XX IMEKO World Congress, Busan, Repulic of Korea, 9-14 September Development of a neutron energy monitoring system, Jungho Kim, Hyeonseo Park, Progress in nuclear science and technology 3, pp , Characteristic of the 18-tube NM64-type Daejeon neutron monitor in Korea, Jeongsoo Kang, Doh Yun Jang, Yunho Kim, Byoung Hwi Kang, Youn-kyun Kim, Jungho Kim, Hyeonseo Park, Yu Yi, Jour. Korean Phys. Soc. 61, pp , Scintillation properties and internal background study of 40 Ca 100 MoO 4 crystal scintillators for neutrino-less double beta decay search, J.H.So, et al, IEEE Transactions on nuclear science 59, pp , International key comparison of measurements of neutron source emission rate ( )-CCRI(III)-K9.AmBe, N.J.Roberts, L.N.Jones, Z.Wang, Y.Liu, Q.Wang, X.Chen, H.Luo, C.Rong, M.Kralik, H.Park, K.O.Choi, W.W.Pereira, E.S.da Fonseca, P.Cassette, M.S.Dewey, N.N.Moiseev, I.A.Kharitonov, Metrologia 48 Tech. Suppl ,

10 - Calibration of neutron personal dosimeters in a realistically simulated neutron irradiation room, J.H. Kim, H. Park, K.-O. Choi, Radiation Measurements 45, pp , Activation cross section measurements of 16 O(n,t) above 18.1 MeV up to 33.1 MeV, J.H.Park, G.D.Kim, W.Hong, C.S.Lee, Y.K.Kwon, K.B.Lee, J.H.Kim, J Radioanal Nucl Chem 285, pp , Neutron Spectrometer with a Capture-Gated Liquid Scintillator, J.H. Kim, H. Park, K.-O. Choi, Jour. Korean Phys. Soc. 56, pp34-41, Calibration of neutron personal dosimeters in a realistic neutron irradiation room, J.H.Kim, H.Park, K.-O.Choi, 11 th Neutron and Ion Dosimetry symposium(neudos11), Cape Town, South Africa, October Neutron Spectra at the workplace of Korean Nuclear Power Plant with Bonner Sphere Spectrometer, H.Park, J.H.Kim, K.-O.Choi, 11 th Neutron and Ion Dosimetry symposium(neudos11), Cape Town, South Africa, October Response Calculations of the neutron ambient dosimeters, Jungho Kim, Hyeonseo Park, Kil-Oung Choi, The Fifth International Symposium on Radiation Safety and Detection Technology(ISORD-5), Kitakyushu, Japan, July Development of the multi-shell Bonner Spheres and their response functions, Jungho Kim, Hyeonseo Park, Kil-Oung Choi, The Fifth International Symposium on Radiation Safety and Detection Technology(ISORD-5), Kitakyushu, Japan, July The Determination of Neutron Dose for Accelerator-Produced Neutrons by Using a Bonner Sphere Spectrometer, J.H. Kim, H. Park, K.O. Choi, Journal of Nuclear Science and Technology, Supp.5, pp , Neutron Spectrum Measurement at the Workplace of Nuclear Power Plant with Bonner Sphere Spectrometer, H. Park, J.H. Kim, K.O. Choi, Journal of Nuclear Science and Technology, Supp.5, pp , Calibration Procedure for a neutron monitor at energies below 20 MeV, A. Ohrn, J. Blomgre, H. Park, S. Khurana, R. Nolte, D. Schmidt, K. Wilhelm, Nuclear Instruments and Methods A 592, pp , "A Monitor for Neutron Flux Measurements up to 20 MeV,, A. Ohrn, J. Blomgre, H. Park, S. Khurana, R. Nolte, D. Schmidt, Radiation Protection 2

11 Dosimetry 124, pp , Neutron dosimetry at the workplace field with neutron spectrometry, H.Park, J.H.Kim, K.O.Choi, 2007 International Symposium on Radiation Safety Management, Daejeon, Republic of Korea, November 7-9, Neutron Calibration Facility with Radioactive neutron Sources at KRISS, H. Park, J.H. Kim, K.O. Choi, Radiation Protection Dosimetry 124, pp , Neutron Dosimetry at the Workplace Field with Neutron Spectroscopy, H. Park, J.H. Kim, K.O. Choi, Proceedings of International symposium on radiation safety management, Daejeon, Republic of Korea, November 7-9, Calibration of neutron personal dosimeters in the realistic case, J.H. Kim, J.H. Kim, K.O. Choi, Proceedings of International symposium on radiation safety management, Daejeon, Republic of Korea, November 7-9, The neutron spectrum measurement at the workplace of nuclear power plant with Bonner sphere spectrometer, Hyeonseo Park, Jungho Kim, Kil-Oung Choi, The Fourth International Symposium on Radiation Safety and Detection Technology (ISORD-4), Seoul, Republic of Korea, July 18-20, The determination of neutron dose for accelerator-produced neutron using a Bonner sphere spectrometer, Jungho Kim, Hyeonseo Park, Kil-Oung Choi, The Fourth International Symposium on Radiation Safety and Detection Technology (ISORD-4), Seoul, Republic of Korea, July 18-20, Development of low-background CsI(Tl) crystals for WIMP search, H.S.Lee,H.Bhang,I.S.Hahn,M.J.Hwang,H.J.Kim,S.C.Kim,S.K.Kim,S.Y.Kim,T. Y.Kim,Y.D.Kim,J.W.Kwak,Y.J.Kwon,J.Lee,J.I.Lee,M.J.Lee,J.Li,S.S.Myung,H. Park,J.J.Zhu, Nucl. Instrum. Meth. A 571, pp , Neutron calibration facility with radioactive neutron sources at KRISS, H. Park, J.H. Kim, K.O. Choi, Tenth Symposium on Neutron Dosimetry (NEUDOS10), Uppsala, Sweden, June 12-16, "First limit on WIMP cross section with low background CsI(Tl) crystal detector,.s.lee,h.bhang,j.h.choi,i.s.hahn,d.he,m.j.hwang,h.j.kim,s.c.ki m,s.k.kim,s.y.kim,t.y.kim,y.d.kim,j.w.kwak,y.j.kwon,j.lee,j.h.lee,j.i. Lee,M.J.Lee,J.Li,S.S.Myung,H.Park,H.Y.Yang,J.J.Zhu, Phys. Lett. B 633, pp ,

12 - Development of a Respirator to Protection against Gaseous Tritium used for a Pressurized Heavy Water Reactor and Evaluation of its Performance, K.- O.Choi, H.Park, H.G.Kim, Canadian Radiation Protection Association and Campus Radiation Safety Officers Conference 2005, Canada, The Measurement of Neutron spectral fluence with Bonner Sphere spectrometer for the dosimetric purpose, H.Park, J.H.Kim, K.-O. Choi, Proceedings of Inernational symposium on radiation safety management, Daejeon, Republic of Korea, November 2-4, Monte Carlo calculation of the efficiency calibration curve for a HPGE detector, K.H.Ahn, J.K.Chun, J.M.Lee, K.B.Kee, H.Park, C.Y.Lee, NMIJ- BIPM Workshop on the impact of Information Technology in Metrology, Tsukuba, Japan, May 16,18-20, Inhibition of 137 Cs contamination in cesium iodide, Y.D.Kim, I.S.Hahn, M.J.Hwang, LiJin, W.G.Kang, H.J.Kim, S.C.Kim, S.K.Kim, T.Y.Kim, J.W.Kwak, Y.J.Kwon, E.K.Lee, H.S.Lee, J.I.Lee, M.J.Lee, S.S.Myung, H.Park, A.Schiedt, H.Y.Yang, J.J.Zhu, Nucl. Instrum. Meth. A 552, pp , Absolute Measurement of the Neutron Emission Rate with a Manganese Sulphate Bath System, H.Park, K.-O.Choi, J.M.Lee, K.B.Lee, M.S.Hahn, M.Kralik, Jour. Korean Phys. Soc., 47, pp , Activation Cross Section Measurements of 16 O(n, 3 He) 14 C and 16 O(n,t) 14 N above neutron Thrsholds up to 18.1 MeV, J.H.Park, C.S.Lee, Y.K.Kwon, J.H.Lee, J.Y.Kim, K.B.Lee, H.Park, Jour. Korean Phys. Soc. 47, pp23-27, A Monte-Carlo Intranuclear Cascade Calculation for the Propagation of Energetic Nucleons in the Nucleus, M.J.Kim, H.Bhang, J.H.Kim, Y.D.Kim, H.Park, J.Chang, Jour. Korean Phys. Soc. 46, pp , Development of a Polyethylene Proportional Counter and Cf-252 Neutron Absorbed Dose Measurement, K.-O. Choi et al, International Sym. on Radiation Safety and Detection Technology, Tsukuba, Japan., An Experience in the KRISS Cf-252 Source Calibration for Its Neutron Emission Rate Measurement, K.O.Choi et al, American Nuclear Society 2002 Annual Meeting "CARE for NPPs in Korea and RMS of NPPs in Illinois, USA", S.T. Hwang, 2000 U.S.-Korea Conference (UKC) on Science, Technology, Entrepreneurship, and Leadership,

13 - Correction equations of coincidence summing using 75 Se radionuclide in the efficiency of HPGe detector, Y. Lee et al, Jour. of Radioanalytical and Nuclear Chemistry 242, pp105, Impurity correction factor of MnSO 4 compound for the determination of neutron emission rate on the manganese bath method, K.-O. Choi et al, Jour. of radioanalytical and Nuclear Chemistry 239, pp605, Impurity Correction factor on MnSO 4 compound for the determination of neutron emission rate on the manganese bath method, K. O. Choi et al, Asia- Pacific Symposium on Radiochemistry '97 and 41st Symposium on Radiochemistry, Simulation of Prompt Gamma-ray Activation Analysis for the Determination of NaCl Concentration in concerts, W.S.Kim, Proceed. the 5th Asian Symposium on research Reactors 1, pp355, Collisional processes in muon catalyzed fusion as studied by the classical collision theory, G. P. Lee et al, Jour. of Radioanalytical & nuclear chemistry 178, pp121, Neutron Depth Profiling:Overview and Description of NIST Facilities, R. G. Downing et al, Jour. of Research of NIST 98, pp109, The New Cold Neutron Depth Profiling Instrument At NIST G.P. Lee et al, Jour. of radioanalytical and Nuclear chemistry 160, pp315, Ion Beam Induced Emissions from Solid Europium Compounds, G.P. Lee et al, J. of radioanalytical and nuclear chemistry articles 160, pp203, Spectroscopic studies of Sb3 + color centers in alkali halide single crystals, K.O. Choi, Jour. Chem. Phys. 94, pp6420, Determination of the Leachability Index of 137 Cs from Cement Solidified Radioactive Waste, E.H. Hwang et al, Jour. of Radioanalytical & Nuclear Chem. 140, pp155, Determination of the Ratio of the Hydrogen and Manganese Absorption Cross Sections by the Manganese Bath Technique, S.T. Hwang et al, Jour. of Radioanalytical and Nuclear Chem. 139, pp37, An Experience in the KRISS Cf-252 Source Calibration for Its Neutron Emission Rate Measurement, S.T. Hwang, Transactions of the American Nuclear Society 60, pp378, Absolute neutron emission rate measurement of a 252 Cf source by the manganese sulfate bath method, S.T. Hwang et al, Nucl. Instrum. and Meth. A 273, pp381,

14 - Measurement of Neutron Emission Rate of Cf-252 Source by the Comparative, S.T. Hwang, Japanese Radiation 13, pp138, Saturation Manganese Activity Measurement by Circulated Manganse Sulphate Bath Technique, S.T. Hwang, 32nd Health physics soc. salt lake city,

Activities of the neutron standardization. at the Korea Research Institute of Standards and Science (KRISS)

Activities of the neutron standardization at the Korea Research Institute of Standards and Science (KRISS) I. Introduction The activities of neutron standardization in KRISS have been continued for last