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A Review of the Recent Studies on the Dosimetric Issues

This article reviews recent studies on dosimetric issues, focusing on computational and experimental dosimetry. It discusses the calculation of dose conversion coefficients, neutron dose estimation, and the development of dose monitors. The article also highlights the updates in the definition of effective dose and the evaluation of dose conversion coefficients based on ICRP103. The findings suggest that the current radiological protection system can be maintained after the introduction of ICRP103.

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A Review of the Recent Studies on the Dosimetric Issues

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  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. 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 *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/ICRUadult reference computational phantoms (ICRP110)

  7. Comparison with EICRP60 and H*(10) (PHITS) (ICRP74 + PHITS) H*(10) (ICRP74 + PHITS) ≥ EICRP60 EICRP103 EICRP60 EICRP103 EICRP60 EICRP103 H*(10) ≈ > > ≥ > 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. 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 [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/

  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

  11. 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. 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. 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) Muon Neutron above 20 MeV underestimated by conventional moderator-based survey-meter (rem-counter) underestimated by conventional survey-meter Photon Neutron below 20 MeV Improvement of active dosimeters is necessary for ensuring radiation safety in HE accelerators Dose, H*(10), contributions behind shield of accelerator

  15. 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. 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. Pulsed-Time-Structure Field 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. 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. 6Li(n,α)3H Thermal neutron e- Photon Fast neutron p System of DARWIN Phoswitch-type Detector Whole System ZnS(Ag)+6Li 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. all particles that should be practically considered in radiation protection in high energy accelerator facilities Features of DARWIN 1．Capable of monitoring doses, H*(10), from • Neutron： • Photon: • Muon： ~ 1 GeV ~ 100 MeV ~ 100 GeV 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. 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. 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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