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A Review of the Recent Studies on the Dosimetric Issues

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Presentation on theme: "A Review of the Recent Studies on the Dosimetric Issues"— Presentation transcript:

1 A Review of the Recent Studies on the Dosimetric Issues
Tatsuhiko Sato Japan Atomic Energy Agency (JAEA), Japan Table of Contents Computational Dosimetry 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 SATIF10, June 2-4, 2010, CERN

2 Background ICRP Publication 103
Definition of the effective dose (E) was revised Update of the radiation weighting factor wR Update of the tissue weighting factor wT 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

3 ICRP C2 Task Groups Task Group on Dose Calculation (DOCAL)
Full Members 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 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 Task Group on Radiation Exposures of Astronauts in Space (TG67) Full Members G. Dietze (chair), D. Bartlett, F. Cucinotta, L. Junli, I. McAulay, M. Pelliccioni, V. Petrov, G. Reitz, T. Sato Guidance for assessment of radiation exposure of astronauts in space Publish the reference values of DCCs for heavy ions

4 Computational Dosimetry
Table of Contents Computational Dosimetry 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

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

6 Calculation Procedures
Particle transport simulation inside phantoms using Monte Carlo codes Organ dose conversion coefficients for 30 organs or tissues, DT wR and wT defined in ICRP103 Effective dose conversion coefficients based on ICRP103, EICRP103 ICRP/ICRU adult reference computational phantoms (ICRP110)

7 Comparison with EICRP60 and H*(10)
(PHITS) (ICRP74 + PHITS) H*(10) (ICRP74 + PHITS) EICRP60 EICRP103 > EICRP60 EICRP103 > H*(10) EICRP60 EICRP103 > H*(10) 0.2 50 CCs for EICRP103 and EICRP60 for neutrons for AP geometry wR for lower & higher energy neutrons were reduced in ICRP103 Numerical compatibility between wR 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

8 Computational Dosimetry
Table of Contents Computational Dosimetry 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

9 Calculation Conditions
Facility Location Spectrum data Dose type CERN Concrete shield (top) IAEA 403 [1] H*(10) & EAP Iron shield (top) IHEP 70GeV sync. Filtered by concrete KEK 12GeV sync. Location 1 Tohoku 35MeV cyc. Underpass SSRL Linac Diagnostic room PWR in USA Containment AmBe source facility Glovebox Aircraft polar region EXPACS 2.16 [2] H*(10) & EISO [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,

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

11 Computational Dosimetry
Table of Contents Computational Dosimetry 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

12 We estimated neutron doses for various conditions …
Summary of Computational Dosimetry DOCAL Activity 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 Personnel Work We estimated neutron doses for various conditions … Introduction of ICRP103 results in the decrease of the effective dose EICRP103 / H*(10) ≤ 1.06 The use of H*(10) is fairly adequate even in high-energy accelerator facilities We concluded … Current radiological protection system can be maintained after the introduction of ICRP103, with respect to neutron dosimetry

13 Computational Dosimetry
Table of Contents Computational Dosimetry 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

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

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

16 m, e, g doses must be distinguished New device must be developed
Muon Dose Muon dose at a certain location H*(10) or Effective dose Total Muon e- g Neutron Dose rates behind rock at Fermilab CC for H*(10) & EICPR103 for m- in comparison with stopping power Calculated dose ratio: m: e : g : n = 0.68 : 0.28 : 0.03 : 0.01 Muon has the dominant contribution Experiment ≈ Calculation m, e, g doses must be distinguished Sanami et al, ISORD5 (2009) *calculations were done by MARS New device must be developed

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

18 Computational Dosimetry
Table of Contents Computational Dosimetry 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

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

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 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 mSv/h 4.Function to Determine energy spectrum Unfolding technique based on the MAXED code* (UMG Package 3.2) 5.Applicable to pulsed-time-structure fields short dead time of the detector compared with gas counters 6.Easy to use LabVEIW-based graphical user interface Relatively light weight (~7kg) * Courtesy of Dr. Reginatto, PTB

21 Computational Dosimetry
Table of Contents Computational Dosimetry 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

22 Summary of Experimental Dosimetry
Radiation Protection in High-Energy Accelerator Radiation fields are different from those in conventional nuclear facilities Existence of high-energy neutron doses Existence of muon doses Existence of pulsed time structure Conventional active dosimeters are not adequately used for ensuring the radiation safety Several new devices have been invented Rem-counters have been improved … inserting heavy metal layer into their moderator: WENDI-II current-readout circuit was installed in their data analysis process 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

23 Thank you very much for your attention !
Acknowledgement I am thankful to 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 Thank you very much for your attention !


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