Neutronics Analyses of the Radiation Field at the Accelerator-Based Neutron Source of Nagoya University for the BNCT Study
, Sachiko Yoshihashi 1, Yuuki Tanagami 1, Kazuki Tsuchida 1, Shogo Honda 1, Atsushi Yamazaki 1, Kenichi Watanabe 2, Yoshiaki Kiyanagi 3 and Akira Uritani 1Round 1
Reviewer 1 Report
Takeo Nishitani et al, present the radiation analysis generated with the beam shaping assembly (BSA) at the accelerator-based neutron source of Nagoya University (NUANS) in the context of Boron Neutron Capture Therapy (BNCT). The study of the shielding efficiency at mitigating radiation in the vicinity of the device, as well as the expected dose used to irradiates biological sample is entirely based on the results generated from a Monte-Carlo simulation, PHITS.
The authors first describe with great details the NUANS facility. It is composed of an accelerator generating a 2.8 MeV, 15 mA, proton beam which produces a neutron beam when irradiating a solid Lithium converter, and a BSA to shape the neutron beam, as well as a water phantom that contains the vials samples for irradiation studies. After a brief description of the neutron and gamma source terms used in the simulation, the authors present the resulting radiation fields obtained in the radiation room at the outlet of the BSA, in its vicinity and behind it. While the zone around the proton inlet is insufficiently shielded and suffers from neutron backscattering and gamma-radiation emitted in the shielding material, the rest of the room is well-shielded. The neutron beam generated at the outlet of the BSA is in overall found compliant with IAEA recommendations for a standard BNCT source. The last part of the paper presents the irradiation recorded in 9 vials located in a water phantom model at the exit of the BSA. The simulation results indicate that the dose after a 20 min irradiation agrees with what is required for a typical in-vitro cell-based irradiation test, but that the non-uniformity of the dose deposited between the vials prevents simultaneous irradiation of 9 samples under the same field.
The manuscript is clear and thorough. If the authors address my comments below, it will be suitable for publication in the Journal of Nuclear Engineering.
Suggested major revisions:
1. The abstract states that the PHITS simulation results is “confirmed with some measurements” and the end of the introduction indicates that “some of the calculation results are validated with some experimental values”. Despite being vague, these two statements are promising as this is an important aspect to validate the entire simulation effort. However, the only mention of experimental validation in the ms. can be found at lines 370-374 and refers to results published elsewhere. The authors do not present any experimental values, draw any comparison with the simulation, not to mention a discussion. This needs to be addressed by providing numbers, error bars and discussing any difference.
2. In part 2.2 and Figure 2, the clarity of the BSA model could be greatly improved by:
a. Using colors easier to distinguish and/or adding label on the model: for instance, MgF2, Bi, PE-B20-2nd colors are very similar
b. Using similar naming in the text and in the legend of Figure 2. e.g. on line 96, write “using boron-doped polyethylene, PE-B(10%), and LiF-doped polyethylene, PE-LiF,”
Suggested minor revisions:
1. Typo:
a. Line 88: BAS instead of BSA
b. Line 236: ICRP [X]
2. The English can be improved as some wordings are not used properly and can be misleading, e.g., “considered” is often used incorrectly in the ms.
3. Line 162: What does “the proton beam is caned on the lithium target surface” mean? Please rephrase.
4. Line 280: add the reference of the IAEA TECDOC-1223
5. Table 1: you forgot to change the default name of the 2nd column corresponding to the simulation results.
Author Response
Reviewer(s)' Comments to Author:
Reviewer: 1
Comments and Suggestions for Authors
Takeo Nishitani et al, present the radiation analysis generated with the beam shaping assembly (BSA) at the accelerator-based neutron source of Nagoya University (NUANS) in the context of Boron Neutron Capture Therapy (BNCT). The study of the shielding efficiency at mitigating radiation in the vicinity of the device, as well as the expected dose used to irradiates biological sample is entirely based on the results generated from a Monte-Carlo simulation, PHITS.
The authors first describe with great details the NUANS facility. It is composed of an accelerator generating a 2.8 MeV, 15 mA, proton beam which produces a neutron beam when irradiating a solid Lithium converter, and a BSA to shape the neutron beam, as well as a water phantom that contains the vials samples for irradiation studies. After a brief description of the neutron and gamma source terms used in the simulation, the authors present the resulting radiation fields obtained in the radiation room at the outlet of the BSA, in its vicinity and behind it. While the zone around the proton inlet is insufficiently shielded and suffers from neutron backscattering and gamma-radiation emitted in the shielding material, the rest of the room is well-shielded. The neutron beam generated at the outlet of the BSA is in overall found compliant with IAEA recommendations for a standard BNCT source. The last part of the paper presents the irradiation recorded in 9 vials located in a water phantom model at the exit of the BSA. The simulation results indicate that the dose after a 20 min irradiation agrees with what is required for a typical in-vitro cell-based irradiation test, but that the non-uniformity of the dose deposited between the vials prevents simultaneous irradiation of 9 samples under the same field.
The manuscript is clear and thorough. If the authors address my comments below, it will be suitable for publication in the Journal of Nuclear Engineering.
Suggested major revisions:
- The abstract states that the PHITS simulation results is “confirmed with some measurements” and the end of the introduction indicates that “some of the calculation results are validated with some experimental values”. Despite being vague, these two statements are promising as this is an important aspect to validate the entire simulation effort. However, the only mention of experimental validation in the ms. can be found at lines 370-374 and refers to results published elsewhere. The authors do not present any experimental values, draw any comparison with the simulation, not to mention a discussion. This needs to be addressed by providing numbers, error bars and discussing any difference.
Response: Discussion on the comparison between experimental values and the simulation will be submitted by my colleague soon. I do not want to duplicate the discussion. Therefore, I deleted “which has been confirmed with some measurements” in Abstract.
- In part 2.2 and Figure 2, the clarity of the BSA model could be greatly improved by:
- Using colors easier to distinguish and/or adding label on the model: for instance, MgF2, Bi, PE-B20-2ndcolors are very similar
Response: Figure2 is revised. Colors of Bi, PE-B20-2nd were changed.
- Using similar naming in the text and in the legend of Figure 2. e.g. on line 96, write “using boron-doped polyethylene, PE-B(10%),and LiF-doped polyethylene, PE-LiF,”
Response: “using boron-doped polyethylene, and LiF-doped polyethylene” is changed to “using boron-doped polyethylene, PE-B(10%), and LiF-doped polyethylene, PE-LiF”
Suggested minor revisions:
- Typo:
- Line 88: BAS instead of BSA
Response: “BAS” is changed to “BSA”
- Line 236: ICRP [X]
Response: “ICRP60 [X]” is changed to “ICRP60 [19]”
“19. ICRP. 1990 Recommendation of International Commission on Radiological Protection, Publication 60 (Pergamon Press, Oxford, UK) 1991.” Is added in Reference.
- The English can be improved as some wordings are not used properly and can be misleading, e.g., “considered” is often used incorrectly in the ms.
Response:
Line 165 “is considered to be reasonable.” is changed to “is reasonable.”.
Line 197 “It is considered” is changed to “We consider”.
Line 231 “which is considered to be” is changed to “which is”.
Line 240 “which is considered to be” is changed to “which is”.
Line 249 “It is considered that gamma-ray of 10B(n, a) are mainly ” is changed to “The gamma-rays of 10B(n, a) are believed to be primarily”.
Line 252 “8 MeV is considered to be” is changed to “8 MeV is presumed to be”.
Line 290 “it is considered” is changed to “we believe”.
Line 295 “we consider” is changed to “we believe”.
Line ３１２ “which is considered to be due“which is be due”.
- Line 162: What does “the proton beam is caned on the lithium target surface” mean? Please rephrase.
Response: It means that we can the proton beam on the lithium target surface by the staring magnet. “the proton beam is caned” is changed to “the proton beam is scanned by the staring magnets”.
- Line 280: add the reference of the IAEA TECDOC-1223
Response: “IAEA TECDOC-1223” is changed to “IAEA TECDOC-1223 [1]”
- Table 1: you forgot to change the default name of the 2ndcolumn corresponding to the simulation results.
Response: There is no recommendation for the absolute values of the fast and thermal neutron fluxes. “None recommendation” is added on 2nd and 3rd columns.
Reviewer 2 Report
1， why do you choose the BSA model shown in Figure 2? What is the design principle of the BSA in this paper?
2， “The calculation model of the Lithium target is a lithium disk with 100mm in diameter and 100 mm in thickness covered with a 5mm thick Titanium foil.” Is the Lithium target connected directly with the copper substrate in this paper? Why do you choose Titanium foil to cover the lithium target in this paper?
3， “The radiation field at the BSA outlet meets almost all the IAEA recommendations.” Could you explain “almost” in details?
Author Response
Reviewer: 2
Comments and Suggestions for Authors
- why do you choose the BSA model shown in Figure 2? What is the design principle of the BSA in this paper?
Response: The design principle was discusses in Ref.[9]. “The basic concept of this BSA is described in Ref.[9].” Is added.
- “The calculation model of the Lithium target is a lithium disk with 100mm in diameter and 100 mm in thickness covered with a 5mm thick Titanium foil.” Is the Lithium target connected directly with the copper substrate in this paper? Why do you choose Titanium foil to cover the lithium target in this paper?
Response: In the source term calculation (Section 2.3), the calculation model is a lithium disk and titanium foil. Incident protons are fully stopped in the lithium disk. Therefore, we do not need model the copper substrate. Off course, we modeled the cupper substrate in the neutron transport calculation of the BSA.
The cover foil need tolerate the heat deposition by the proton beam. We chouse Titanium by its high melting temperature. “The cover foil need tolerate the heat deposition by the proton beam. Titanium foil is suitable material for its high melting temperature of 1941 K.” is added.
- “The radiation field at the BSA outlet meets almost all the IAEA recommendations.” Could you explain “almost” in details?
Response: “almost” is deleted. To make the conclusion clear, we revised as
“Consequently, we evaluate that the radiation field at the BSA outlet of NUANS meets of the IAEA recommendations except epithermal neutron flux and fast neutron dose per epithermal neutron flux, however, those two values are acceptable level.”
“18. Hiraga, F, Ooieb, T. Synergistic effects of fast-neutron dose per epithermal neutron and 10B concentration on rela-tive-biological-effectiveness dose for accelerator-based boron neutron capture therapy. Appl. Rad. Isotopes 2019, 144, pp. 1–4.” is added as reference for the importance of the fast neutron dose per epithermal neutron flux
Reviewer 3 Report
This manuscript is well written and only a few minor corrections are needed before it can be published.
line 154 - Specify what was the energy spread of the proton beam and its spatial profile (e.g. pencil, Gaussian).
line 224 - Replace "visinity" with "vicinity".
line 236 - Add missing reference to ICRP60.
line 253 - Replace "ion" with "iron".
Table 1 - Replace "Title 2" with a correct term (e.g. "PHITS calculation"). Add uncertainties of the calculated values.
line 313 - Define the energy boundaries of thermal, epithermal and fast neutrons.
Fig. 9 - Consider adding the reaction rate of 10B(n,alpha).
line 359 - Replace "flues" with "fluxes".
line 373 - Quantify "a good agreement".
Discussion - You calculated the prompt dose rates. Discuss how big contribution the delayed dose rates from the activation could bring.
Author Response
Reviewer: 3
Comments and Suggestions for Authors
This manuscript is well written and only a few minor corrections are needed before it can be published.
line 154 - Specify what was the energy spread of the proton beam and its spatial profile (e.g. pencil, Gaussian).
Response: The energy spread of the proton beam is approximately 30 keV and the spatial profile is assumed to be pensile beam.
“The spatial profile is assumed to be a pensile beam” is added.
“The energy spread of the 2.8 MeV proton beam by the titanium foil is approximately 30 keV.” is added.
line 224 - Replace "visinity" with "vicinity".
Response: "visinity" is changed to "vicinity
line 236 - Add missing reference to ICRP60.
Response: “ICRP60 [X]” is changed to “ICRP60 [19]”
line 253 - Replace "ion" with "iron".
Response: “ion” is changed to “iron”
Table 1 - Replace "Title 2" with a correct term (e.g. "PHITS calculation"). Add uncertainties of the calculated values.
Response: “Title 2” is changed to “PHITS calculation”. Uncertainties of the calculated values are added.
line 313 - Define the energy boundaries of thermal, epithermal and fast neutrons.
Response: In the main text (line 246-247), definitions of thermal, epithermal and fast neutrons are described as “Here, the energy ranges of thermal neutron, epithermal neutron, and fast neutron are < 0.5 eV, 0.5eV- 10 keV, and > 10 keV, respectively.”
Fig. 9 - Consider adding the reaction rate of 10B(n,alpha).
Response: Fig.9 is revised, where the reaction rate of 10B(n,alpha) is added.
line 359 - Replace "flues" with "fluxes".
Response: “flues” is changed to “fluxes"”.
line 373 - Quantify "a good agreement".
Response:”, typically within 6% deviation,” is added.
Discussion - You calculated the prompt dose rates. Discuss how big contribution the delayed dose rates from the activation could bring.
Response: We added following sentences to discuss the delayed dose rates from the activated materials. “We chose low-activation materials for the BSA. The gamma-ray dose measurement by an ionization chamber located at the BSA outlet confirmed that the gamma-ray dose due to activated materials was negligibly small compared with the prompt gamma-ray dose by the comparison of the doses during proton beam on and just beam off.”
