質子治療設施與其他高能輻射環境的中子偵測是一個重要且困難的問題。由於傳統緩速型中子劑量計的原理特性，通率劑量轉換係數與偵檢器的偵測效率在高能中子能量區間(> 10 MeV)有著相反的趨勢，若直接應用會嚴重低估中子劑量的測量結果。為了彌補此一低估的問題，本研究藉由分析IAEA-TRS-403報告中超過200種的輻射工作場所的中子能譜，以及八類超過50種的中子偵檢器，比較利用252Cf射源校正之偵檢器響應函數所計算出來的劑量，以及直接利用通率劑量轉換係數得到的劑量，建立用於校正傳統緩速型中子劑量計的能譜修正因子。為了改進以及延伸此能譜修正因子的應用範圍，亦進行一系列的靈敏度分析，包括：(1)探討使用不同的偵檢器校正射源(252Cf, 241Am-Be, 239Pu-Be等)對於能譜修正因子的影響、(2)探討使用不同尺寸之緩速型中子劑量計(6吋至9吋波那球)對於能譜修正因子的影響、(3)探討使用不同類型之中子偵檢器對於能譜修正因子的影響。最後，以國內第一座質子治療設施：林口長庚醫院質子加速器為案例，討論此能譜修正因子的實際應用情形，以利此能譜修正因子的實務應用。本研究的成果可提供國內高能加速器設施與主管機關參考，提升國內在高能中子輻射場所的劑量測量技術水準。

This study aimed at improving and extending results of our previous study on corrections for conventional neutron dose meters used in environments with high-energy neutrons (E > 10 MeV). Moderated-type neutron dose meters tend to underestimate the dose contribution of high-energy neutrons because of the opposite trends of dose conversion coefficients and detection efficiencies as the neutron energy increases. A practical correction scheme has been proposed based on analysis of hundreds of neutron spectra and more than 50 kinds of neutron detectors in the IAEA-TRS-403 report. By comparing 252Cf-calibrated dose responses with reference values derived from fluence-to-dose conversion coefficients, this study provided recommendations for neutron field characterization and the corresponding dose correction factors. Further sensitivity studies addressed three important issues. (1) If the spectral correction factors are independent of the selection of three commonly used calibration sources: 252Cf, 241Am-Be, 239Pu-Be or other commonly-used calibration sources? (2) If the derived correction factors for different sizes of moderated-type neutron dose meters, such as Bonner spheres of various sizes (6” to 9”), are similar in trend? (3) If the derived correction factors for different kinds of neutron detectors, such as different type survey instruments or other detectors with different principle, are still applicable? Finally, use the proton accelerator of Chang Gung Hospital, the first proton therapy center in Taiwan as an example, to confirm the feasibility of spectral correction factors in the practical application.

[1] Hankins, D. E., “Determination of the Neutron Contribution to the Rem Dose.”, USAEC Report LA-DC-7323A, Los Alamos Scientific Laboratory, 1965, p. 9
[2] Olsher, R. H., Hsu, H. H., Beverding, A., Kleck, J. H., Casson, W. H., Vasilik, D. G. and Devine, R. T., “WENDI: an improved neutron rem meter.”, Health Phys, 79(2), 2000, pp. 170-181
[3] Klett, A., Mayer, S., Theis, C. and Vincke, H., “A neutron dose rate monitor for high energies.“, Rad. Meas., 41, 2007, S279-S282
[4] Wiegel, B. and Alevera, A.V., “NEMUS-the PTB neutron multisphere spectrometer: Bonner spheres and more.”, Nucl. Instrum. Method A, 476, 2002, pp. 36-42
[5] Pelowitz, D.B., Eds., “MCNPX user’s manual, Version 2.7.0”, LA-CP-11-00438, Los Alamos National Laboratory, 2011
[6] International Organization for Standardization, Reference Neutron Radiations—Part 1: Characteristics and methods of product. International Organization for Standardization, ISO 8529-1, 2001
[7] Fassò, A., Liu, J. C. and Rokni, S. H., “Neutron spectra and dosimetric quantities outside typical concrete shielding of synchrotron facilities.”, ICRS-12 & RPSD-2012, paper ID 2C-21, 2012
[8] Bedogni, R., “Neutron spectrometry with Bonner Spheres for area monitoring in particle accelerators.”, Radiation Protection Dosimetry, 146, 2011, pp. 383-394
[9] Naismith, O. F. and Siebert, B. R., “A Database of Neutron Spectra, Instrument Response Functions, and Dosimetric Conversion Factors for Radiation Protection Applications.”, Radiat. Prot. Dosim., 70(1-4), 1997, pp.241-245
[10] Tanner, R. J. Thomas, D. J. Bartlett, D. T., et al. Effect of the energy dependence of response of neutron personal dosemeters routinely used in the UK on the accuracy of dose estimation., NRPB-W25, UK, 2002
[11] Lee, K. W. and Sheu, R. J., “Spectral correction factors for conventional neutron dose meters used in high-energy neutron environments.”, Radiat. Prot. Dosim. 164, 2015, pp. 210-218
[12] International Atomic Energy Agency., Compendium of neutron spectra and detector responses for radiation protection purposes., Technical Reports Series No. 403., IAEA, Vienna, 2001
[13] Piesch, E. and Burgkhardt, B., “Albedo Neutron Dosimetry.”, Radiation Protection Dosimetry, 10(1-4), 1985, pp. 175-188
[14] 蔡宜璇, 傳統中子偵檢器用於高能中子輻射場的劑量低估修正研究, 國立清華大學核子工程與科學研究所, 碩士論文, 2014
[15] Oparaji, U. Tsai, Y. H. Liu, Y. C. Lee, K. W. Patelli, E. and Sheu, R. J., “Spectral correction factors for conventional neutron dose meters used in high-energy neutron environments—improved and extended results based on a complete survey of all neutron spectra in IAEA-TRS-403.”, Radiation Protection Dosimetry, 175(1), 2017, pp. 87-95
[16] Valérie De Smet., Neutron measurements in a proton therapy facility and comparison with Monte Carlo shielding simulations. UNIVERSITÉ LIBRE DE BRUXELLES, Brussels, 2016
[17] Kase, K. R., Bjärngard, B. E. and Attix, F. H., The Dosimetry of ionizing radiation, Vol. I, Academic Press, Inc., 1985
[18] Kase, K. R., Bjärngard, B. E. and Attix, F. H., The Dosimetry of ionizing radiation, Vol. II, Academic Press, Inc., 1987
[19] Kase, K. R., Bjärngard, B. E. and Attix, F. H., The Dosimetry of ionizing radiation, Vol. III, Academic Press, Inc., 1990
[20] Patterson, H. W. and Thomas, R. H., Accelerator Health Physics., Academic Press, Inc., 1973
[21] Ferrari, A. Sala, P. R. Fassò, A. and Ranft, J., Fluka: a multi-particle transport code (Program version 2011). CERN, Geneva, 2005
[22] Shani, G., Radiation Dosimetry, Instrumentation and Methods, second Edition., CRC Press, 2001