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A novel design of beam shaping assembly to use D-T neutron generator for BNCT
Author’s Accepted Manuscript A novel design of beam shaping assembly to use DT neutron generator for BNCT Y. Kasesaz, M. Karimy, M. Salehi Barough
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PII: DOI: Reference:
S0969-8043(16)30310-4 http://dx.doi.org/10.1016/j.apradiso.2016.09.029 ARI7619
To appear in: Applied Radiation and Isotopes Received date: 26 June 2016 Revised date: 27 August 2016 Accepted date: 27 September 2016 Cite this article as: Y. Kasesaz, M. Karimy and M. Salehi Barough, A novel design of beam shaping assembly to use D-T neutron generator for BNCT, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2016.09.029 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A novel design of beam shaping assembly to use D-T neutron generator for BNCT Y. Kasesaz2*, M. Karimy1, M. Salehi Barough1 1
Department of Medical Radiation, Islamic Azad University Central Tehran Branch, Tehran, Iran 2
Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran *
Email: [email protected]
Abstract In order to use 14.1 MeV neutrons produced by D-T neutron generators, two special and novel Beam Shaping Assemblies (BSA), including multi-layer and hexagonal lattice have been suggested and the effect of them has been investigated by MCNP4C Monte Carlo code. The results show that the proposed BSA can provide the qualified epithermal neutron beam for BNCT. The final epithermal neutron flux is about 6e9 n/cm2.s. The final proposed BSA has some different advantages: 1) it consists of usual and well-known materials (pb, Al, Fluental and Cd); 2) it has a simple geometry; 3) it does not need any additional gamma filter; 4) it can provide high flux of epithermal neutrons. As this type of neutron source is under development in the world, it seems that they can be used clinically in a hospital considering the proposed BSA. Keywords:BNCT; D-T neutron generator; MCNP4C Monte Carlo code, BSA
1. Introduction Boron Neutron Capture Therapy (BNCT) is a modern method of radiation therapy based on the 10B(n,α)7Li reaction. In this method a boron-containing compound is first infused into a peripheral vein, following which the compound accumulates in tumor tissue, the tumor is subsequently irradiated with neutrons.7Li and α particles as a result from a 10B neutron capture reaction release their energy within a tumor cells and destroy them (Sauerwein, 2012, Barth 2012). The qualified neutron beam for BNCT is determined by the International Atomic Energy Agency (IAEA). Table 1 shows the recommended parameters for the therapeutic neutron beam (IAEATECDOC-1223, 2001). In order to provide such a beam, a special Beam Shaping Assembly (BSA) must be designed based on the neutron source specifications. A typical BSA includes moderator, reflector, collimator, thermal neutron filter, and gamma filter. The role of the moderator is to moderate fast neutrons to epithermal neutrons and the role of the reflector is to prevent neutron leakage from the beam line. In common BSA, the reflector is considered as a layer which covers the sides of the moderator materials as shown in fig. 1 (Kasesaz, 2013).
Research reactors are the only used neutron source in the all reported clinical trials (Barth 2012). The most important challenge in development of this method is related to the social acceptance of nuclear reactors for treatment and so many efforts are underway to develop and use of nonreactor neutron source. These efforts are focused on use of accelerator-based neutron source (Sakurai et al, 2015, Cartelli et al, 2015, Kreiner et al, 2014). Another alternative neutron source is the neutron generators which can produce 2.45 MeV or 14.1 MeV neutrons via D-D or D-T reactions. These neutron sources are in focus for BNCT applications and some effort have been made to build a high current compact D-T neutron generator for BNCT (Lu 2016, Loong 214, Kasesaz 2013, Verbeke 2000) There are some different works about using D-T or D-D neutron generators for BNCT. In that works, a typical BSA was used to convert produced high energy neutrons to an appropriate epithermal BNCT beam (Cerullo et al 2004, Rasouli et al 2012, Montagnini et al 2002, Durisi, 2007, Kasesaz 2013) In one of these works, natural uranium was used as a neutron multiplier (Rasouli et al 2012) which is need some safety regards and also has delayed gamma rays problem. In the previous work (Kasesaz 2015), two new BSA configurations have been proposed and investigated for use in nuclear reactors-based neutron source. Fig. 2 shows a schematic view of the two proposed BSA configurations. The proposed configurations are very different to common configuration (B in fig. 2) and include multilayer and hexagonal lattice geometry. In multilayers geometry, there are some reflector layers and also some moderator layers which have been considered as every other layer (C in Fig. 2). In lattice geometry, rod reflectors in different radius have been placed in the moderator material in hexagonal lattice geometry (D in fig. 2). In the present work, these two novel geometries for BSA have been studied for used in D-T neutron generator using MCNP4C Monte Carlo code (Briesmeister, 2000). 2. Material and methods 2.1.
Specifications of D-T neutron source
Generated D-T neutron beam parameters are highly depending on the deuteron energy and its current as well as tritium thickness. The desired neutron beam parameters are the neutron yield, the angular distribution of the neutrons and the neutron energy in different angles. Fig. 3 shows the neutron yield as a function of deuteron energy (Csikai , 1987). As seen, for 200 keV deuteron energy the total neutron yield is about 1.45E11 n/mA.s. The neutron energy (En) vs. angle θ below 500 keV deuteron energy can be well approximated by the following simple formula (Csikai , 1987): 2
En ( Ed , ) E0 Ei cosi i 1
(1)
Which is valid both for thin and thick tritium target. In eq.1, the Ed is the deuteron energy. The Ei coefficient for different deuteron energies are summarized in table 2 for thick tritium target. The angular distributions of the emitted neutrons relative to those at a degree of 90 can be approximated by the following equation (Csikai , 1987):
R( Ed , )
2 Y ( ) 1 Ai cosi Y (90) i 1
(2)
Which is valid both for thin and thick tritium target. The Ai coefficient for different deuteron energies are summarized in table 2 for thick tritium target. Fig.4 and 5 show En(Ed,θ) and R(Ed,θ) corresponding to different deuteron energies. All required parameters for simulation have been set for thick tritium target and 200 keV deuterons. Other properties such as deuteron current (1A) and dimensions have been considered as by Rasouli (Rasouli et al 2012). 2.2.
MCNP calculations
Fig. 6 presents a schematic view of the common BSA and two new BSA. Fluental alloy (69% Al, 30% AlF3, 1% LiF) and Pb have been used as the moderator and reflector, respectively. These materials are widely used in different BNCT facilities (IAEA-TECDOC-1223, 2001, Kasesaz 2014, Monshizadeh 2015). Initial assessments have been shown that 70 cm of Fluental can provide an epithermal beam which can then be modified by additional materials to achieve the qualified neutron beam, so the total length of the moderator/reflector has been set to 70 cm in the all calculations. At the first step, In order to analyse the effect of these new BSAs, a typical configurations have been designed and desired neutron parameters have been calculated at the beam exit. Fig. 4 shows a MCNP model of these configurations. In order to focusing the neutrons on the tumor area, a collimator has been assumed after the moderator/reflector assembly. The collimator was a slab of Pb including an incomplete air-filled cone, as shown in fig. 6. In the next step, the two new BSAs have been modified to provide desired neutron beam. The main modification was the considering an additional moderator layer at the beginning or at the end of the moderator/reflector assembly without any changes in the total length of the system, as shown in fig.7. Different materials have been tested for this additional moderator including Al, AlF3, MgF2, CF2, Fe, Ti, Al2O3, Fluental, TiF3, Pb, Bi and BeO. The goal of this phase was to achieve the qualified epithermal neutron beam as recommended by IAEA (table 1). The results show that adding this layer is not lead to achieve the required BNCT beam but it can improve the neutron beam parameters. In this phase, among the all tested cases the ones which can provide
the neutron beam with the following limitations have been selected: 1) φepi>6e9 (n/cm2.s), 2) Df/φepi<4e-13 (Gy.cm2), 3) Dg/φepi <2e-13 (Gy.cm2), and 4) φepi/φtotal>0.6. In the next step, the second moderator layer has been added in the beam line which has been considered in the collimator at the beginning of it, as shown in fig. 7. This modification has been done only for four selected cases which have the highest value of φepi/φthermal value. The maximum length of the additional moderator in the collimator was 10 cm. in this step, seven cases with the best beam parameter values have been selected and finally a 2 mm Cd layer has been added to them to reduce thermal neutron contamination of the final epithermal beam.
3. Resutls and disscussion Table 3 shows the neutron beam parameters related to four considered moderator/reflector configurations. As seen, the values of desired parameters corresponding to the new proposed configurations (i.e. C and D) are better than the configuration B. Fig. 8 presents the neutron energy spectrum corresponding to each configuration. As seen, the neutron energy spectrum is highly dependent on the moderator/reflector configuration. The results of adding the additional moderator layer at the end or at the beginning of the moderator/reflector assembly (see fig. 7) are shown in figs. 9, 10 and 11 corresponding to φepi, Df/φepi and φepi/φtotal respectively. As seen, the additional moderator layer has the significant effect on the neutron beam parameters but as mentioned above, adding this layer is not lead to achieve the required BNCT beam but it can improve the beam parameters. Table 4 shows the selected cases which they can provide the neutron beam with the mentioned limitations (φepi >6e9 (n/cm2.s), Df/φepi <4e-13 (Gy.cm2), Dg/φepi<2e-13 (Gy.cm2), and φepi/φtotal>0.6). Fig. 12 shows the neutron energy spectrum related to each selected case. It shows the effect of the adding the additional moderator layer and its position. These selected cases can categorised in four different groups considering their geometries and also the material of the additional moderator as presented in table 4. In each group, the ones which have the highest value of φepi/φthermal parameter and the lowest gamma dose rate have been selected for the next step including case no. 1, 6, 11 and 12. In the next step, the second moderator layer which is located at the beginning of the collimator has been assumed (see fig. 7). For each selected case in the previous step, among all the tested cases the ones which provide the epithermal neutron beam with the best values of desired beam parameters have been selected which are presented in table 5. The neutron energy spectrum related to each case is shown in fig. 13. As seen, considering the IAEA recommendation, all of these seven configurations can provide the required epithermal BNCT beam but to compare the results with the other works, it was try to reduce thermal neutron contamination in the beam. To do this, a 2 mm Cd layer have been added to the beam line. Table 6 and fig. 13 presents the results of adding the Cd filter to the seven selected cases in the previous step in comparison to some other works. As seen, the configuration no. 4 (see fig. 14) can provide the best epithermal beam in comparison with the other works. The most important advantage of the final BSA, is
that it not include any natural or enriched uranium as it used by Rasouli et. al. on the other hand, the used material in the final geometry is very simple and accessible (Pb, Al, Fluental and Cd).
4. Conclussion A novel design of BSA for use D-T neutron generators in BNCT applications has been proposed. The results show that the proposed BSA can provide the qualified epithermal neutron beam for BNCT. The final epithermal neutron flux is about 6e9 n/cm2.s. According to IAEA recommendation the epithermal neutron flux suitable for BNCT should be in the range of 5e81e9 n/cm2.s. It indicates that the assumed deuteron current can reduce form 1 A to 0.1 A. the proposed BSA has some different advantages: 1) it consists of usual and well-known materials (pb, Al, Fluental alloy and Cd); 2) it has a simple geometry; 3) it does not need any additional gamma filter; 4) it can provide high flux of epithermal neutrons. as this type of neutron source is under development, it seems that they can be used clinically in a hospital considering the proposed BSA.
References Barth, R.F., Vicente, M.H., Harling, O.K., Kiger, W.S., Riley, K.J., Binns, P.J., Wagner, F.M., Suzuki, M., Aihara, T., Kato, I. and Kawabata, S., 2012. Current status of boron neutron capture therapy of high grade gliomas and recurrent head and neck cancer. Radiation Oncology, 7(1), p.1. Briesmeister,J.F.E.,2000.MCNP—A 4C.LA-13709M.
GeneralMonteCarloN-ParticleTransportCode.
Version
Cartelli, D., Capoulat, M.E., Bergueiro, J., Gagetti, L., Anzorena, M.S., Del Grosso, M.F., Baldo, M., Castell, W., Padulo, J., Sandín, J.S. and Igarzabal, M., 2015. Present status of accelerator-based BNCT: Focus on developments in Argentina. Applied Radiation and Isotopes, 106, pp.18-21. Cerullo, N., Esposito, J. and Daquino, G.G., 2004. Spectrum shaping assessment of acceleratorbased fusion neutron sources to be used in BNCT treatment. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 213, pp.641-645. Csikai, G.J., 1987. CRC handbook of fast neutron generators.CRC Press.
Durisi, E., Zanini, A., Manfredotti, C., Palamara, F., Sarotto, M., Visca, L. and Nastasi, U., 2007. Design of an epithermal column for BNCT based on D–D fusion neutron facility. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 574(2), pp.363-369. IAEA-TECDOC-1223,2001.Current Status of Neutron Capture Therapy. Kasesaz, Y., Khalafi, H. and Rahmani, F., 2013. Optimization of the beam shaping assembly in the D–D neutron generators-based BNCT using the response matrix method. Applied Radiation and Isotopes, 82, pp.55-59. Kasesaz, Y., Khalafi, H. and Rahmani, F., 2014. Design of an epithermal neutron beam for BNCT in thermal column of Tehran research reactor. Annals of Nuclear Energy, 68, pp.234-238. Kasesaz, Y., Rahmani, F. and Khalafi, H., 2015. Investigation on the reflector/moderator geometry and its effect on the neutron beam design in BNCT. Applied Radiation and Isotopes, 106, pp.34-37. Kreiner, A.J., Baldo, M., Bergueiro, J.R., Cartelli, D., Castell, W., Vento, V.T., Asoia, J.G., Mercuri, D., Padulo, J., Sandin, J.S. and Erhardt, J., 2014. Accelerator-based BNCT. Applied Radiation and Isotopes, 88, pp.185-189. Loong, C-K., et al. "The Pros and Cons of Preliminary R&D of Boron Neutron Capture Therapy Based on Compact Neutron Generators: A Plan of Collaboration." Physics Procedia 60 (2014): 264-270. Lu, Xiaolong, et al. "Design of a high-current low-energy beam transport line for an intense DT/DD neutron generator." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 811 (2016): 76-81. Monshizadeh, M., Kasesaz, Y., Khalafi, H. and Hamidi, S., 2015. MCNP design of thermal and epithermal neutron beam for BNCT at the Isfahan MNSR. Progress in Nuclear Energy, 83, pp.427-432. Montagnini, B., Cerullo, N., Esposito, J., Giusti, V., Mattioda, F. and Varone, R., 2002. Spectrum shaping of accelerator-based neutron beams for BNCT. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 476(1), pp.90-98. Rasouli, F.S., Masoudi, S.F. and Kasesaz, Y., 2012. Design of a model for BSA to meet free beam parameters for BNCT based on multiplier system for D–T neutron source. Annals of Nuclear Energy, 39(1), pp.18-25. Sakurai, Y., Tanaka, H., Takata, T., Fujimoto, N., Suzuki, M., Masunaga, S., Kinashi, Y., Kondo, N., Narabayashi, M., Nakagawa, Y. and Watanabe, T., 2015. Advances in boron
neutron capture therapy (BNCT) at kyoto university-From reactor-based BNCT to accelerator-based BNCT. Journal of the Korean Physical Society, 67(1), pp.76-81. Sauerwein, W.A., Wittig, A., Moss, R. and Nakagawa, Y. eds., 2012. Neutron capture therapy: principles and applications. Springer Science & Business Media. Verbeke, J. M., K. N. Leung, and J. Vujic. "Development of a sealed-accelerator-tube neutron generator." Applied Radiation and Isotopes 53.4 (2000): 801-809.
Figure captions:
Fig. 1 a common BSA for BNCT: 1) reflector; 2) moderator; 3) collimator and 4) gamma shield (Kasesaz, 2013)
A
B
C
D
Fig. 2 a schematic view of the two proposed (C and D) and the common (B) BSA configurations: reflector, green: moderator
Fig. 3 the neutron yield as a function of deuteron energy for D-D and D-T reactions (Csikai , 1987)
15.0
50 keV 100 keV 200 keV 300 keV
14.8
Neutron Energy (MeV)
14.6 14.4 14.2 14.0 13.8 13.6 13.4 13.2 0
30
60
90
120
150
180
Emission Angle in LAB. system
Fig. 4 neutron energy vs. emission angle for different deuteron energies (see Eq.1)
1.07 1.06 1.05
50 keV 100 keV 200 keV 300 keV
Relative Neutron Yield
1.04 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0
30
60
90
120
150
180
Emission Angle in LAB. system
Fig. 5 neutron yield vs. emission angle for different deuteron energies (see Eq.2)
T D+
A: without reflector
B: 10 cm Pb as reflector (common geometry)
C: multi-layers: thickness of each layer is 2 cm
D: hexagonal geometry: pitch= 2 cm and the radius of moderator rods= 2 cm
Fig. 6 MCNP model of the different configurations. Total length of reflector/moderator assembly is 70 cm, the length of the collimator is 20 cm and the radius of BSA is 90 cm.
1
2
after the reflector/moderator assembly
2
1
before the reflector/moderator assembly
Fig. 7 different position of the additional moderator layer in the beam line: 1) reflector/moderator assembly; 2) additional moderator layer
Fig. 8 the neutron energy spectrum corresponding to each configuration
Fig. 9 the φepi after adding the additional moderator layer before or after the C and D moderator/reflector assembly (see fig. 7)
Fig. 10 the Df/φepi after adding the additional moderator layer before or after the C and D moderator/reflector assembly (see fig. 7)
Fig. 11 the φepi/φtotal after adding the additional moderator layer before or after the C and D moderator/reflector assembly (see fig. 7)
Fig. 12 the neutron energy spectrum related to each selected case (see table 4)
Fig. 13 the neutron energy spectrum before and after adding Cd layer as the thermal neutron filter (see table 5 ,6)
10 cm
15 cm
45 cm
6 cm
13.8 cm
Fig. 14 final design of BSA (case no.4 intabe 6): 1) Pb as the additional moderator (20 cm); 2) Pb and Fluental reflector/moderator assembly based on the C configuration (50 cm); 3) Al as the second moderator layer (6 cm); 4) Cd (2 mm); 5) air-filled collimator (13.8 cm)
Table captions: Table 1 BNCT neutron beam parameters recommended by IAEA for BNCT (IAEA-TECDOC1223, 2001) BNCT beam port parameters -2
-1
Recommended value
φepi (n.cm .s )
>109
Df/φepi (Gy.cm2)
<2×10-13
Dg/φepi (Gy.cm2)
<2×10-13
φepi /φthermal Fast energy group
>20
E > 10 keV
Epithermal energy group
1 eV < E <10 keV
Thermal energy group
E < 1 eV
Table 2 the recommended values for Ei and Ai coefficients for different deuteron energies related to thick target (Csikai , 1987) Ed E0 E1 E2 A1 A2 (keV) 50 14.06520 0.42329 0.00682 0.03003 0.00035 100 14.07883 0.57613 0.01222 0.04087 0.00062 200 14.09680 0.72427 0.01908 0.05124 0.00096 300 14.10803 0.80001 0.02374 0.05651 0.00119 Table 3 the neutron beam parameters related to four considered moderator/reflector configurations (see fig. 2) Configuration
φepi Df/φepi (×109 cm-2.s-1) (×10-13 Gy.cm2)
A B C D
2.90 3.20 5.65 5.48
5.40 4.92 2.85 5.03
Dg/φepi
φepi /φthermal
5.50 5.39 0.53 0.37
6 5 15 68
(×10-13 Gy.cm2)
Table 4 the selected cases after adding the additional moderator which they can provide the neutron beam with the following conditions: φepi>6e9 (n/cm2.s), Df/φepi<4e-13 (Gy.cm2), Dg/φepi <2e-13 (Gy.cm2), and φepi/φtotal>0.6. φepi (×109 cm-2.s-1)
Df/φepi (×10-13 Gy.cm2)
Dg/φepi (×10-13 Gy.cm2)
φepi /φthermal
φepi /φtotal
Fluental (5)
6.18
3.50
0.78
45
66
after (D)
Fluental (10)
6.77
2.61
1.01
32
71
after (D)
Fluental (15)
6.91
2.30
1.21
22
75
4
after (D)
Fluental (20)
6.99
2.03
1.48
15
77
5
after (D)
Fluental (25)
6.91
2.02
1.74
13
79
6
after (D)
MgF2 (5)
6.44
3.08
0.68
30
69
7
after (D)
MgF2 (10)
6.98
2.20
0.83
14
75
8
after (D)
MgF2 (15)
6.85
1.98
1.16
8
76
9
before (C)
Pb (5)
6.64
2.40
0.46
16
77
10
before (C)
Pb (10)
6.99
2.24
0.42
18
77
11
before (C)
Pb (15)
7.19
2.26
0.40
21
75
12
before (C)
Pb (20)
7.11
2.35
0.40
26
73
No.
Position (configuration)
1
after (D)
2 3
Material (thickness (cm))
Table 5 the selected cases after considdering the second moderator layer in the collimator Case no. according to Material φepi Df/φepi Dg/φepi Confi φepi table 2 (thickness (×109 cm(×10-13 (×10-13 g. No. /φthermal 2 -1 2 2 (configuratio (cm)) .s ) Gy.cm ) Gy.cm ) n) 1 Fluental (10) 1.82 0.82 39 4.83 1 2 MgF2 (10) 1.67 0.5 21 4.67 3 Al (8) 1.47 0.83 28 6.55 4 12 Al (6) 1.59 0.81 28 6.75 5 AlF3 (2) 1.87 0.43 24 7.03 6 11 Al (6) 1.6 0.75 23 6.71 7 6 Fluental (6) 1.85 0.92 20 5.99 Table 6 the final result (after adding 2 mm Cd filter) in comparison with some other works Config. Neutron No. φepi Df/φepi Dg/φepi Yield φ /φ 9 -2 -1 -13 2 according (×10 cm .s ) (×10 Gy.cm ) (×10-13 Gy.cm2) epi thermal (×1014 n.s-1) to table 5 1 1.34 0.96 74 5.02 2 1.25 0.71 73 4.61 3 1.56 0.73 100 6.19 This 4 1.45 1.72 0.60 114 6.26 work 5 2.11 0.45 126 6.49 6 1.70 0.68 99 6.36 7 1.79 0.70 96 5.54 Rasouli et al. 2012 1.45 0.59 1.98 121 4.43 Cerullo et al. 2004 4 3.45 0.21 115 2.51 Montagnini et al. 0.2 6.3 7.3 16.6 2002 0.29 Highlights
D-T neutron generator for BNCT. A new and novel design of beam shaping assembly. Simple and accessible assembly.
www.elsevier.com/locate/apradiso
PII: DOI: Reference:
S0969-8043(16)30310-4 http://dx.doi.org/10.1016/j.apradiso.2016.09.029 ARI7619
To appear in: Applied Radiation and Isotopes Received date: 26 June 2016 Revised date: 27 August 2016 Accepted date: 27 September 2016 Cite this article as: Y. Kasesaz, M. Karimy and M. Salehi Barough, A novel design of beam shaping assembly to use D-T neutron generator for BNCT, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2016.09.029 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A novel design of beam shaping assembly to use D-T neutron generator for BNCT Y. Kasesaz2*, M. Karimy1, M. Salehi Barough1 1
Department of Medical Radiation, Islamic Azad University Central Tehran Branch, Tehran, Iran 2
Nuclear Science and Technology Research Institute (NSTRI), Tehran, Iran *
Email: [email protected]
Abstract In order to use 14.1 MeV neutrons produced by D-T neutron generators, two special and novel Beam Shaping Assemblies (BSA), including multi-layer and hexagonal lattice have been suggested and the effect of them has been investigated by MCNP4C Monte Carlo code. The results show that the proposed BSA can provide the qualified epithermal neutron beam for BNCT. The final epithermal neutron flux is about 6e9 n/cm2.s. The final proposed BSA has some different advantages: 1) it consists of usual and well-known materials (pb, Al, Fluental and Cd); 2) it has a simple geometry; 3) it does not need any additional gamma filter; 4) it can provide high flux of epithermal neutrons. As this type of neutron source is under development in the world, it seems that they can be used clinically in a hospital considering the proposed BSA. Keywords:BNCT; D-T neutron generator; MCNP4C Monte Carlo code, BSA
1. Introduction Boron Neutron Capture Therapy (BNCT) is a modern method of radiation therapy based on the 10B(n,α)7Li reaction. In this method a boron-containing compound is first infused into a peripheral vein, following which the compound accumulates in tumor tissue, the tumor is subsequently irradiated with neutrons.7Li and α particles as a result from a 10B neutron capture reaction release their energy within a tumor cells and destroy them (Sauerwein, 2012, Barth 2012). The qualified neutron beam for BNCT is determined by the International Atomic Energy Agency (IAEA). Table 1 shows the recommended parameters for the therapeutic neutron beam (IAEATECDOC-1223, 2001). In order to provide such a beam, a special Beam Shaping Assembly (BSA) must be designed based on the neutron source specifications. A typical BSA includes moderator, reflector, collimator, thermal neutron filter, and gamma filter. The role of the moderator is to moderate fast neutrons to epithermal neutrons and the role of the reflector is to prevent neutron leakage from the beam line. In common BSA, the reflector is considered as a layer which covers the sides of the moderator materials as shown in fig. 1 (Kasesaz, 2013).
Research reactors are the only used neutron source in the all reported clinical trials (Barth 2012). The most important challenge in development of this method is related to the social acceptance of nuclear reactors for treatment and so many efforts are underway to develop and use of nonreactor neutron source. These efforts are focused on use of accelerator-based neutron source (Sakurai et al, 2015, Cartelli et al, 2015, Kreiner et al, 2014). Another alternative neutron source is the neutron generators which can produce 2.45 MeV or 14.1 MeV neutrons via D-D or D-T reactions. These neutron sources are in focus for BNCT applications and some effort have been made to build a high current compact D-T neutron generator for BNCT (Lu 2016, Loong 214, Kasesaz 2013, Verbeke 2000) There are some different works about using D-T or D-D neutron generators for BNCT. In that works, a typical BSA was used to convert produced high energy neutrons to an appropriate epithermal BNCT beam (Cerullo et al 2004, Rasouli et al 2012, Montagnini et al 2002, Durisi, 2007, Kasesaz 2013) In one of these works, natural uranium was used as a neutron multiplier (Rasouli et al 2012) which is need some safety regards and also has delayed gamma rays problem. In the previous work (Kasesaz 2015), two new BSA configurations have been proposed and investigated for use in nuclear reactors-based neutron source. Fig. 2 shows a schematic view of the two proposed BSA configurations. The proposed configurations are very different to common configuration (B in fig. 2) and include multilayer and hexagonal lattice geometry. In multilayers geometry, there are some reflector layers and also some moderator layers which have been considered as every other layer (C in Fig. 2). In lattice geometry, rod reflectors in different radius have been placed in the moderator material in hexagonal lattice geometry (D in fig. 2). In the present work, these two novel geometries for BSA have been studied for used in D-T neutron generator using MCNP4C Monte Carlo code (Briesmeister, 2000). 2. Material and methods 2.1.
Specifications of D-T neutron source
Generated D-T neutron beam parameters are highly depending on the deuteron energy and its current as well as tritium thickness. The desired neutron beam parameters are the neutron yield, the angular distribution of the neutrons and the neutron energy in different angles. Fig. 3 shows the neutron yield as a function of deuteron energy (Csikai , 1987). As seen, for 200 keV deuteron energy the total neutron yield is about 1.45E11 n/mA.s. The neutron energy (En) vs. angle θ below 500 keV deuteron energy can be well approximated by the following simple formula (Csikai , 1987): 2
En ( Ed , ) E0 Ei cosi i 1
(1)
Which is valid both for thin and thick tritium target. In eq.1, the Ed is the deuteron energy. The Ei coefficient for different deuteron energies are summarized in table 2 for thick tritium target. The angular distributions of the emitted neutrons relative to those at a degree of 90 can be approximated by the following equation (Csikai , 1987):
R( Ed , )
2 Y ( ) 1 Ai cosi Y (90) i 1
(2)
Which is valid both for thin and thick tritium target. The Ai coefficient for different deuteron energies are summarized in table 2 for thick tritium target. Fig.4 and 5 show En(Ed,θ) and R(Ed,θ) corresponding to different deuteron energies. All required parameters for simulation have been set for thick tritium target and 200 keV deuterons. Other properties such as deuteron current (1A) and dimensions have been considered as by Rasouli (Rasouli et al 2012). 2.2.
MCNP calculations
Fig. 6 presents a schematic view of the common BSA and two new BSA. Fluental alloy (69% Al, 30% AlF3, 1% LiF) and Pb have been used as the moderator and reflector, respectively. These materials are widely used in different BNCT facilities (IAEA-TECDOC-1223, 2001, Kasesaz 2014, Monshizadeh 2015). Initial assessments have been shown that 70 cm of Fluental can provide an epithermal beam which can then be modified by additional materials to achieve the qualified neutron beam, so the total length of the moderator/reflector has been set to 70 cm in the all calculations. At the first step, In order to analyse the effect of these new BSAs, a typical configurations have been designed and desired neutron parameters have been calculated at the beam exit. Fig. 4 shows a MCNP model of these configurations. In order to focusing the neutrons on the tumor area, a collimator has been assumed after the moderator/reflector assembly. The collimator was a slab of Pb including an incomplete air-filled cone, as shown in fig. 6. In the next step, the two new BSAs have been modified to provide desired neutron beam. The main modification was the considering an additional moderator layer at the beginning or at the end of the moderator/reflector assembly without any changes in the total length of the system, as shown in fig.7. Different materials have been tested for this additional moderator including Al, AlF3, MgF2, CF2, Fe, Ti, Al2O3, Fluental, TiF3, Pb, Bi and BeO. The goal of this phase was to achieve the qualified epithermal neutron beam as recommended by IAEA (table 1). The results show that adding this layer is not lead to achieve the required BNCT beam but it can improve the neutron beam parameters. In this phase, among the all tested cases the ones which can provide
the neutron beam with the following limitations have been selected: 1) φepi>6e9 (n/cm2.s), 2) Df/φepi<4e-13 (Gy.cm2), 3) Dg/φepi <2e-13 (Gy.cm2), and 4) φepi/φtotal>0.6. In the next step, the second moderator layer has been added in the beam line which has been considered in the collimator at the beginning of it, as shown in fig. 7. This modification has been done only for four selected cases which have the highest value of φepi/φthermal value. The maximum length of the additional moderator in the collimator was 10 cm. in this step, seven cases with the best beam parameter values have been selected and finally a 2 mm Cd layer has been added to them to reduce thermal neutron contamination of the final epithermal beam.
3. Resutls and disscussion Table 3 shows the neutron beam parameters related to four considered moderator/reflector configurations. As seen, the values of desired parameters corresponding to the new proposed configurations (i.e. C and D) are better than the configuration B. Fig. 8 presents the neutron energy spectrum corresponding to each configuration. As seen, the neutron energy spectrum is highly dependent on the moderator/reflector configuration. The results of adding the additional moderator layer at the end or at the beginning of the moderator/reflector assembly (see fig. 7) are shown in figs. 9, 10 and 11 corresponding to φepi, Df/φepi and φepi/φtotal respectively. As seen, the additional moderator layer has the significant effect on the neutron beam parameters but as mentioned above, adding this layer is not lead to achieve the required BNCT beam but it can improve the beam parameters. Table 4 shows the selected cases which they can provide the neutron beam with the mentioned limitations (φepi >6e9 (n/cm2.s), Df/φepi <4e-13 (Gy.cm2), Dg/φepi<2e-13 (Gy.cm2), and φepi/φtotal>0.6). Fig. 12 shows the neutron energy spectrum related to each selected case. It shows the effect of the adding the additional moderator layer and its position. These selected cases can categorised in four different groups considering their geometries and also the material of the additional moderator as presented in table 4. In each group, the ones which have the highest value of φepi/φthermal parameter and the lowest gamma dose rate have been selected for the next step including case no. 1, 6, 11 and 12. In the next step, the second moderator layer which is located at the beginning of the collimator has been assumed (see fig. 7). For each selected case in the previous step, among all the tested cases the ones which provide the epithermal neutron beam with the best values of desired beam parameters have been selected which are presented in table 5. The neutron energy spectrum related to each case is shown in fig. 13. As seen, considering the IAEA recommendation, all of these seven configurations can provide the required epithermal BNCT beam but to compare the results with the other works, it was try to reduce thermal neutron contamination in the beam. To do this, a 2 mm Cd layer have been added to the beam line. Table 6 and fig. 13 presents the results of adding the Cd filter to the seven selected cases in the previous step in comparison to some other works. As seen, the configuration no. 4 (see fig. 14) can provide the best epithermal beam in comparison with the other works. The most important advantage of the final BSA, is
that it not include any natural or enriched uranium as it used by Rasouli et. al. on the other hand, the used material in the final geometry is very simple and accessible (Pb, Al, Fluental and Cd).
4. Conclussion A novel design of BSA for use D-T neutron generators in BNCT applications has been proposed. The results show that the proposed BSA can provide the qualified epithermal neutron beam for BNCT. The final epithermal neutron flux is about 6e9 n/cm2.s. According to IAEA recommendation the epithermal neutron flux suitable for BNCT should be in the range of 5e81e9 n/cm2.s. It indicates that the assumed deuteron current can reduce form 1 A to 0.1 A. the proposed BSA has some different advantages: 1) it consists of usual and well-known materials (pb, Al, Fluental alloy and Cd); 2) it has a simple geometry; 3) it does not need any additional gamma filter; 4) it can provide high flux of epithermal neutrons. as this type of neutron source is under development, it seems that they can be used clinically in a hospital considering the proposed BSA.
References Barth, R.F., Vicente, M.H., Harling, O.K., Kiger, W.S., Riley, K.J., Binns, P.J., Wagner, F.M., Suzuki, M., Aihara, T., Kato, I. and Kawabata, S., 2012. Current status of boron neutron capture therapy of high grade gliomas and recurrent head and neck cancer. Radiation Oncology, 7(1), p.1. Briesmeister,J.F.E.,2000.MCNP—A 4C.LA-13709M.
GeneralMonteCarloN-ParticleTransportCode.
Version
Cartelli, D., Capoulat, M.E., Bergueiro, J., Gagetti, L., Anzorena, M.S., Del Grosso, M.F., Baldo, M., Castell, W., Padulo, J., Sandín, J.S. and Igarzabal, M., 2015. Present status of accelerator-based BNCT: Focus on developments in Argentina. Applied Radiation and Isotopes, 106, pp.18-21. Cerullo, N., Esposito, J. and Daquino, G.G., 2004. Spectrum shaping assessment of acceleratorbased fusion neutron sources to be used in BNCT treatment. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 213, pp.641-645. Csikai, G.J., 1987. CRC handbook of fast neutron generators.CRC Press.
Durisi, E., Zanini, A., Manfredotti, C., Palamara, F., Sarotto, M., Visca, L. and Nastasi, U., 2007. Design of an epithermal column for BNCT based on D–D fusion neutron facility. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 574(2), pp.363-369. IAEA-TECDOC-1223,2001.Current Status of Neutron Capture Therapy. Kasesaz, Y., Khalafi, H. and Rahmani, F., 2013. Optimization of the beam shaping assembly in the D–D neutron generators-based BNCT using the response matrix method. Applied Radiation and Isotopes, 82, pp.55-59. Kasesaz, Y., Khalafi, H. and Rahmani, F., 2014. Design of an epithermal neutron beam for BNCT in thermal column of Tehran research reactor. Annals of Nuclear Energy, 68, pp.234-238. Kasesaz, Y., Rahmani, F. and Khalafi, H., 2015. Investigation on the reflector/moderator geometry and its effect on the neutron beam design in BNCT. Applied Radiation and Isotopes, 106, pp.34-37. Kreiner, A.J., Baldo, M., Bergueiro, J.R., Cartelli, D., Castell, W., Vento, V.T., Asoia, J.G., Mercuri, D., Padulo, J., Sandin, J.S. and Erhardt, J., 2014. Accelerator-based BNCT. Applied Radiation and Isotopes, 88, pp.185-189. Loong, C-K., et al. "The Pros and Cons of Preliminary R&D of Boron Neutron Capture Therapy Based on Compact Neutron Generators: A Plan of Collaboration." Physics Procedia 60 (2014): 264-270. Lu, Xiaolong, et al. "Design of a high-current low-energy beam transport line for an intense DT/DD neutron generator." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 811 (2016): 76-81. Monshizadeh, M., Kasesaz, Y., Khalafi, H. and Hamidi, S., 2015. MCNP design of thermal and epithermal neutron beam for BNCT at the Isfahan MNSR. Progress in Nuclear Energy, 83, pp.427-432. Montagnini, B., Cerullo, N., Esposito, J., Giusti, V., Mattioda, F. and Varone, R., 2002. Spectrum shaping of accelerator-based neutron beams for BNCT. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 476(1), pp.90-98. Rasouli, F.S., Masoudi, S.F. and Kasesaz, Y., 2012. Design of a model for BSA to meet free beam parameters for BNCT based on multiplier system for D–T neutron source. Annals of Nuclear Energy, 39(1), pp.18-25. Sakurai, Y., Tanaka, H., Takata, T., Fujimoto, N., Suzuki, M., Masunaga, S., Kinashi, Y., Kondo, N., Narabayashi, M., Nakagawa, Y. and Watanabe, T., 2015. Advances in boron
neutron capture therapy (BNCT) at kyoto university-From reactor-based BNCT to accelerator-based BNCT. Journal of the Korean Physical Society, 67(1), pp.76-81. Sauerwein, W.A., Wittig, A., Moss, R. and Nakagawa, Y. eds., 2012. Neutron capture therapy: principles and applications. Springer Science & Business Media. Verbeke, J. M., K. N. Leung, and J. Vujic. "Development of a sealed-accelerator-tube neutron generator." Applied Radiation and Isotopes 53.4 (2000): 801-809.
Figure captions:
Fig. 1 a common BSA for BNCT: 1) reflector; 2) moderator; 3) collimator and 4) gamma shield (Kasesaz, 2013)
A
B
C
D
Fig. 2 a schematic view of the two proposed (C and D) and the common (B) BSA configurations: reflector, green: moderator
Fig. 3 the neutron yield as a function of deuteron energy for D-D and D-T reactions (Csikai , 1987)
15.0
50 keV 100 keV 200 keV 300 keV
14.8
Neutron Energy (MeV)
14.6 14.4 14.2 14.0 13.8 13.6 13.4 13.2 0
30
60
90
120
150
180
Emission Angle in LAB. system
Fig. 4 neutron energy vs. emission angle for different deuteron energies (see Eq.1)
1.07 1.06 1.05
50 keV 100 keV 200 keV 300 keV
Relative Neutron Yield
1.04 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0
30
60
90
120
150
180
Emission Angle in LAB. system
Fig. 5 neutron yield vs. emission angle for different deuteron energies (see Eq.2)
T D+
A: without reflector
B: 10 cm Pb as reflector (common geometry)
C: multi-layers: thickness of each layer is 2 cm
D: hexagonal geometry: pitch= 2 cm and the radius of moderator rods= 2 cm
Fig. 6 MCNP model of the different configurations. Total length of reflector/moderator assembly is 70 cm, the length of the collimator is 20 cm and the radius of BSA is 90 cm.
1
2
after the reflector/moderator assembly
2
1
before the reflector/moderator assembly
Fig. 7 different position of the additional moderator layer in the beam line: 1) reflector/moderator assembly; 2) additional moderator layer
Fig. 8 the neutron energy spectrum corresponding to each configuration
Fig. 9 the φepi after adding the additional moderator layer before or after the C and D moderator/reflector assembly (see fig. 7)
Fig. 10 the Df/φepi after adding the additional moderator layer before or after the C and D moderator/reflector assembly (see fig. 7)
Fig. 11 the φepi/φtotal after adding the additional moderator layer before or after the C and D moderator/reflector assembly (see fig. 7)
Fig. 12 the neutron energy spectrum related to each selected case (see table 4)
Fig. 13 the neutron energy spectrum before and after adding Cd layer as the thermal neutron filter (see table 5 ,6)
10 cm
15 cm
45 cm
6 cm
13.8 cm
Fig. 14 final design of BSA (case no.4 intabe 6): 1) Pb as the additional moderator (20 cm); 2) Pb and Fluental reflector/moderator assembly based on the C configuration (50 cm); 3) Al as the second moderator layer (6 cm); 4) Cd (2 mm); 5) air-filled collimator (13.8 cm)
Table captions: Table 1 BNCT neutron beam parameters recommended by IAEA for BNCT (IAEA-TECDOC1223, 2001) BNCT beam port parameters -2
-1
Recommended value
φepi (n.cm .s )
>109
Df/φepi (Gy.cm2)
<2×10-13
Dg/φepi (Gy.cm2)
<2×10-13
φepi /φthermal Fast energy group
>20
E > 10 keV
Epithermal energy group
1 eV < E <10 keV
Thermal energy group
E < 1 eV
Table 2 the recommended values for Ei and Ai coefficients for different deuteron energies related to thick target (Csikai , 1987) Ed E0 E1 E2 A1 A2 (keV) 50 14.06520 0.42329 0.00682 0.03003 0.00035 100 14.07883 0.57613 0.01222 0.04087 0.00062 200 14.09680 0.72427 0.01908 0.05124 0.00096 300 14.10803 0.80001 0.02374 0.05651 0.00119 Table 3 the neutron beam parameters related to four considered moderator/reflector configurations (see fig. 2) Configuration
φepi Df/φepi (×109 cm-2.s-1) (×10-13 Gy.cm2)
A B C D
2.90 3.20 5.65 5.48
5.40 4.92 2.85 5.03
Dg/φepi
φepi /φthermal
5.50 5.39 0.53 0.37
6 5 15 68
(×10-13 Gy.cm2)
Table 4 the selected cases after adding the additional moderator which they can provide the neutron beam with the following conditions: φepi>6e9 (n/cm2.s), Df/φepi<4e-13 (Gy.cm2), Dg/φepi <2e-13 (Gy.cm2), and φepi/φtotal>0.6. φepi (×109 cm-2.s-1)
Df/φepi (×10-13 Gy.cm2)
Dg/φepi (×10-13 Gy.cm2)
φepi /φthermal
φepi /φtotal
Fluental (5)
6.18
3.50
0.78
45
66
after (D)
Fluental (10)
6.77
2.61
1.01
32
71
after (D)
Fluental (15)
6.91
2.30
1.21
22
75
4
after (D)
Fluental (20)
6.99
2.03
1.48
15
77
5
after (D)
Fluental (25)
6.91
2.02
1.74
13
79
6
after (D)
MgF2 (5)
6.44
3.08
0.68
30
69
7
after (D)
MgF2 (10)
6.98
2.20
0.83
14
75
8
after (D)
MgF2 (15)
6.85
1.98
1.16
8
76
9
before (C)
Pb (5)
6.64
2.40
0.46
16
77
10
before (C)
Pb (10)
6.99
2.24
0.42
18
77
11
before (C)
Pb (15)
7.19
2.26
0.40
21
75
12
before (C)
Pb (20)
7.11
2.35
0.40
26
73
No.
Position (configuration)
1
after (D)
2 3
Material (thickness (cm))
Table 5 the selected cases after considdering the second moderator layer in the collimator Case no. according to Material φepi Df/φepi Dg/φepi Confi φepi table 2 (thickness (×109 cm(×10-13 (×10-13 g. No. /φthermal 2 -1 2 2 (configuratio (cm)) .s ) Gy.cm ) Gy.cm ) n) 1 Fluental (10) 1.82 0.82 39 4.83 1 2 MgF2 (10) 1.67 0.5 21 4.67 3 Al (8) 1.47 0.83 28 6.55 4 12 Al (6) 1.59 0.81 28 6.75 5 AlF3 (2) 1.87 0.43 24 7.03 6 11 Al (6) 1.6 0.75 23 6.71 7 6 Fluental (6) 1.85 0.92 20 5.99 Table 6 the final result (after adding 2 mm Cd filter) in comparison with some other works Config. Neutron No. φepi Df/φepi Dg/φepi Yield φ /φ 9 -2 -1 -13 2 according (×10 cm .s ) (×10 Gy.cm ) (×10-13 Gy.cm2) epi thermal (×1014 n.s-1) to table 5 1 1.34 0.96 74 5.02 2 1.25 0.71 73 4.61 3 1.56 0.73 100 6.19 This 4 1.45 1.72 0.60 114 6.26 work 5 2.11 0.45 126 6.49 6 1.70 0.68 99 6.36 7 1.79 0.70 96 5.54 Rasouli et al. 2012 1.45 0.59 1.98 121 4.43 Cerullo et al. 2004 4 3.45 0.21 115 2.51 Montagnini et al. 0.2 6.3 7.3 16.6 2002 0.29 Highlights
D-T neutron generator for BNCT. A new and novel design of beam shaping assembly. Simple and accessible assembly.