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A Review of the Recent Studies on the Dosimetric Issues Tatsuhiko Sato Japan Atomic Energy Agency (JAEA), Japan 1 SATIF10, June 2-4, 2010, CERN Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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2 BackgroundBackground ICRP Publication 103 Definition of the effective dose (E) was revised Update of the radiation weighting factor w R Update of the tissue weighting factor w T Introduction of the ICRP/ICRU authorized voxel phantoms to represent reference male and female Numerical values of E is subjected to be changed when ICPR103 is introduced in the radiation protection system Evaluation of dose conversion coefficients (DCCs) based on ICRP103 is urgently requested

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Task Group on Radiation Exposures of Astronauts in Space (TG67) 3 ICRP C2 Task Groups Task Group on Dose Calculation (DOCAL) W. Bolch (chair), V. Berkovskyy, L. Bertelli, K. Eckerman, A. Endo, T. Fell, N. Hertel, J. Hunt, N. Ishigure, D. Nosske, M. Pelliccioni, N. Petoussi-Henss, M. Zankl Full Members Nuclear decay data for dosimetric calculations (ICRP107) Reference voxel phantoms for adult male and female (ICRP110) DCCs for exposures to external radiation and intake of radionuclides Publish the reference values of DCCs as the revision of ICRP74 G. Dietze (chair), D. Bartlett, F. Cucinotta, L. Junli, I. McAulay, M. Pelliccioni, V. Petrov, G. Reitz, T. Sato Full Members Guidance for assessment of radiation exposure of astronauts in space Publish the reference values of DCCs for heavy ions

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4 Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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Calculation of DCCs by DOCAL 5 ParticleEnergyGeometrySimulation Code Photon* 10keV-10GeVAP, PA, LLAT, RLAT, ISO, ROT EGS, GEANT, MCNPX Neutron* 1meV-10GeVAP, PA, LLAT, RLAT, ISO, ROT FLUKA, GEANT, MCNPX, PHITS Electron*/ Positron 50keV-10GeVAP, PA, ISO EGS, GEANT, MCNPX Proton 1MeV-10GeVAP, PA, LLAT, RLAT, ISO, ROT FLUKA, GEANT, MCNPX, PHITS Charged pion 1MeV-10GeVAP, PA, ISO FLUKA, GEANT, MCNPX, PHITS Muon 1MeV-10GeVAP, PA, ISO FLUKA, GEANT Calculation of DCCs under the framework of DOCAL Cover almost all particles that should be considered in practical RP Reference values will be determined, simply taking the mean values *included in ICRP74, but their energies are limited

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Organ dose conversion coefficients for 30 organs or tissues, D T Particle transport simulation inside phantoms using Monte Carlo codes Calculation Procedures ICRP/ICRU adult reference computational phantoms (ICRP110) 6 w R and w T defined in ICRP103 Effective dose conversion coefficients based on ICRP103, E ICRP103 Effective dose conversion coefficients based on ICRP103, E ICRP103

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7 Comparison with E ICRP60 and H*(10) E ICRP60 E ICRP103 > w R for lower & higher energy neutrons were reduced in ICRP103 Numerical compatibility between w R and Q(L) relationship w R for lower & higher energy neutrons were reduced in ICRP103 Numerical compatibility between w R and Q(L) relationship High energy neutrons deposit more energy at deeper locations in ICRU sphere 10mm is too shallow to represent the dose in human body High energy neutrons deposit more energy at deeper locations in ICRU sphere 10mm is too shallow to represent the dose in human body E ICRP60 E ICRP103 > E ICRP60 E ICRP103 ≈ H*(10) > 0.2 50 H*(10) ≥ ≥ CCs for E ICRP103 and E ICRP60 for neutrons for AP geometry (ICRP74 + PHITS) (PHITS)

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8 Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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Calculation Conditions 9 FacilityLocationSpectrum dataDose type CERNConcrete shield (top)IAEA 403 [1]H*(10) & E AP CERNIron shield (top)IAEA 403 [1]H*(10) & E AP IHEP 70GeV sync.Filtered by concreteIAEA 403 [1]H*(10) & E AP KEK 12GeV sync.Location 1IAEA 403 [1]H*(10) & E AP Tohoku 35MeV cyc.UnderpassIAEA 403 [1]H*(10) & E AP SSRL LinacDiagnostic roomIAEA 403 [1]H*(10) & E AP PWR in USAContainmentIAEA 403 [1]H*(10) & E AP AmBe source facilityGloveboxIAEA 403 [1]H*(10) & E AP Aircraft12km @ polar regionEXPACS 2.16 [2]H*(10) & E ISO [1] Compendium of neutron spectra and detector responses for radiation protection purposes, Technical report series 403, IAEA (2001) [2] EXcel-based Program for calculating Atmospheric Cosmic-ray Spectrum, http://phits.jaea.go.jp/expacs/

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10 Results of the dose estimation Ratios of effective doses to H*(10) E / H*(10) > 1 for high-energy neutron fields Not so significant by considering the uncertainty in measurements E / H*(10) > 1 for high-energy neutron fields Not so significant by considering the uncertainty in measurements Introduction of ICRP103 results in the decrease of the effective doses Reduction of w R for lower and higher energy neutrons Introduction of ICRP103 results in the decrease of the effective doses Reduction of w R for lower and higher energy neutrons 1.06 E / H*(10) < 1 for other neutron fields H*(10) can be adequately used

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11 Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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Fluence-to-dose conversion coefficients for various particles were calculated by several codes, following the instruction given in ICRP103 Reference values of dose conversion coefficients will be published as the revision of ICRP74 Summary of Computational Dosimetry 12 We estimated neutron doses for various conditions … We concluded … Current radiological protection system can be maintained after the introduction of ICRP103, with respect to neutron dosimetry Introduction of ICRP103 results in the decrease of the effective dose E ICRP103 / H*(10) ≤ 1.06 The use of H*(10) is fairly adequate even in high-energy accelerator facilities DOCAL Activity Personnel Work

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13 Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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14 BackgroundBackground Differences of radiation fields in high-energy accelerators in comparison to conventional nuclear facilities Existence of high-energy neutron doses Existence of pulsed time structure (pulsed beam accelerator) Neutron below 20 MeV Neutron above 20 MeV Photon Muon Dose, H*(10), contributions behind shield of accelerator underestimated by conventional survey-meter underestimated by conventional moderator-based survey-meter (rem-counter) Existence of muon doses Improvement of active dosimeters is necessary for ensuring radiation safety in HE accelerators Improvement of active dosimeters is necessary for ensuring radiation safety in HE accelerators

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High Energy Neutron Dose 15 Tungsten powder 3 He counter Polyethylene moderator Structure of WENDI-II Applicable energy: ~ 5 GeV Weight: 14 kg Olsher et al Health Phys. 79, 170 (2000) Rem-counter implemented with heavy metal layer Profile of WENDI-II Response / H*(10) Conventional type WENDI-II Dose measured at CERF Mayer et al RPD125, 289 (2007) 2 times Neutron Energy (MeV) Response of WENDI-II & conventional rem-counter normalized to H*(10) CCs

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16 Muon Dose Dose rates behind rock at Fermilab Calculated dose ratio: : e : : n = 0.68 : 0.28 : 0.03 : 0.01 Muon has the dominant contribution Experiment ≈ Calculation Total Muon e-e- Neutron Sanami et al, ISORD5 (2009) *calculations were done by MARS Muon dose at a certain location H*(10) or Effective dose ≠ CC for H*(10) & E ICPR103 for - in comparison with stopping power , e, doses must be distinguished New device must be developed

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Pulsed-Time-Structure Field 17 Generated by pulsed beam with low frequency Dose rates at a certain moment >> Average dose rates Dead time of active dosimeters becomes significant Profile of pulsed-time-structure field Pulse counting Current readout Reference neutron dose rate ( Sv/h) Measured dose rate ( Sv/h) Dose rates around KEK synchrotron measured by rem-counter (SARM) Iijima et al 2009 Pulse counting mode Current readout mode contamination cannot be excluded Saturation effect is occurred Pulse interval = 2.2 sec ≠ Above 2 Sv/h Data are rather scattered Some improvements are still needed to measure neutron dose precisely at pulsed-time-structure fields

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18 Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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19 Whole System System of DARWIN Phoswitch-type Detector BC501A 5×5φinch PM ZnS(Ag)+ 6 Li BC501A ： fast neutron, photon & muon 6 Li doped ZnS(Ag) sheet : thermal neutron Digital Waveform Analyzer 6 Li(n,α) 3 H p e-e- Fast neutron Thermal neutron Photon Dose monitoring system Applicable to various Radiations over WIde energy raNges 125 MHz 14bit ADC x 8 FPGA Fast & slow components of light output Maximum count rate: 100,000 cps ! Tablet PC Incident particle type: Pulse-shape-discrimination Corresponding dose: G-function method Draw trend of dose rates in real time DARWIN

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20 Features of DARWIN 1 ． Capable of monitoring doses, H*(10), from Neutron ： Photon: Muon ： ~ 1 GeV ~ 100 MeV ~ 100 GeV all particles that should be practically considered in radiation protection in high energy accelerator facilities 2 ． High sensitivity 5 ． Applicable to pulsed-time-structure fields 10 times higher sensitivity to neutron compared with conventional rem-counter 3 ． Applicable to wide dose-rate range Neutron ： Background (10 nSv/h) ~ 10 mSv/h Photon: Background (70 nSv/h) ~ 100 Sv/h 4 ． Function to Determine energy spectrum Unfolding technique based on the MAXED code* (UMG Package 3.2) * Courtesy of Dr. Reginatto, PTB short dead time of the detector compared with gas counters 6 ． Easy to use LabVEIW-based graphical user interface Relatively light weight (~7kg)

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21 Table of Contents 1.Computational Dosimetry 2.Experimental Dosimetry 1.1 Calculation of Dose Conversion Coefficient (DCC) 1.2 Neutron Dose Estimation Using DCCs 1.3 Summary 2.1 Review of Current Status 2.2 Development of Dose Monitor DARWIN 2.3 Summary

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Summary of Experimental Dosimetry 22 Radiation fields are different from those in conventional nuclear facilities Radiation Protection in High-Energy Accelerator Existence of high-energy neutron doses Existence of pulsed time structure Existence of muon doses inserting heavy metal layer into their moderator: WENDI-II current-readout circuit was installed in their data analysis process Conventional active dosimeters are not adequately used for ensuring the radiation safety Several new devices have been invented Rem-counters have been improved … As a different approach … Liquid-organic scintillator based dose monitor DARWIN was developed, using the latest digital pulse shape analysis techniques DARWIN can improve the radiation safety in accelerator facilities

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23 AcknowledgementAcknowledgement DOCAL members for their discussion in calculating dose conversion coefficients Dr. D. Satoh, Dr. A. Endo and Dr. N. Shigyo for their support in developing DARWIN Dr. M. Hagiwara and Dr. H. Nakashima for their support in performing J-PARC experiment Dr. T. Sanami, Dr. M. Hagiwara, Dr. M. Harada and Dr. H. Nakashima for their support in preparing this presentation material I am thankful to Thank you very much for your attention !

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