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Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept
Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept Isao Murata n, Yuki Otani, Fuminobu Sato Graduate School of Engineering, Osaka University, Yamada-oka 2-1, Suita, Osaka 565-0871, Japan
H I G H L I G H T S
Proton-lithium (p-Li) reaction is a candidate nuclear production reaction for ABNS for BNCT. The number of neutrons produced by the reaction cannot be known easily. A simple method was investigated to monitor it by isomer production reaction. Numerical examination showed 107Ag, 115In and 189Os were feasible, i.e., 107Ag is the most convenient foil, 115In is the best at 0° and 189Os is only suitable in backward angles.
art ic l e i nf o
a b s t r a c t
Article history: Received 7 February 2015 Received in revised form 17 July 2015 Accepted 25 July 2015
Proton-lithium (p-Li) reaction is being examined worldwide as a candidate nuclear production reaction for accelerator based neutron source (ABNS) for BNCT. In this reaction, the emitted neutron energy is not so high, below 1 MeV, and especially in backward angles the energy is as low as about 100 keV. The intensity measurement was thus known to be difficult so far. In the present study, a simple method was investigated to monitor the absolute neutron intensity of the p-Li neutron source by employing the foil activation method based on isomer production reactions in order to cover around several hundreds keV. As a result of numerical examination, it was found that 107Ag, 115In and 189Os would be feasible. Their features found out are summarized as follows: 107Ag: The most convenient foil, since the half life is short. 115 In: The accuracy is the best at 0°, though it cannot be used for backward angles. And 189Os: Suitable nuclide which can be used in backward angles, though the gamma-ray energy is a little too low. These would be used for p-Li source monitoring depending on measuring purposes in real BNCT scenes. & 2015 Elsevier Ltd. All rights reserved.
Keywords: BNCT p-Li reaction Foil activation method Isomer production reaction Source intensity
1. Introduction Proton-lithium (p-Li) reaction of Eq. (1) is a promising candidate nuclear reaction for accelerator based neutron source (ABNS) for Boron Neutron Capture Therapy (BNCT). 7
Li + p → n + 7Be + Q (Q = −1. 88 MeV)
(1)
It creates several tens to 800 keV neutrons for the proton energy of 2.5 MeV and the produced neutrons are moderated to become epithermal neutrons suitable for irradiation. However, such energetic neutrons have not frequently been utilized in practical engineering applications with the exception BNCT. Recently BNCT has been recognized as a promising cancer therapy among radiation therapies. And as a result, we should characterize the neutron source precisely n
Corresponding author. Fax: þ 81 6 6879 7899. E-mail address: [email protected] (I. Murata).
especially in neutron energies less than 1 MeV when the p-Li neutron source is utilized as a neutron source for BNCT. Normally, the number of neutrons produced by p-Li reaction can easily be confirmed by measuring radioactivity of the target (7Be). Practically, gamma-rays emitted from 7Be are measured after irradiation by means of gamma-ray spectrometry using a Ge semiconductor detector. However, in an actual BNCT, it is not so easy, because it is not straightforward to remove the target after irradiation in order to measure the radioactivity of the target. Since detectors like scintillators are also difficult to be applied because the neutron intensity is too strong and the energy of the source neutrons is not suitable for accurate detection by such detectors. We, then, focused on the foil activation method, being a well-known method to measure intensity of fast neutrons or slow neutrons. Concretely, for fast neutrons higher than 1 MeV appropriate threshold reactions exist for the activation method. And for slow neutrons below keV region, resonance reactions and neutron capture reactions can be applied to measure epi-thermal and thermal neutrons, respectively.
http://dx.doi.org/10.1016/j.apradiso.2015.07.034 0969-8043/& 2015 Elsevier Ltd. All rights reserved.
Please cite this article as: Murata, I., et al., Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept. Appl. Radiat. Isotopes (2015), http://dx.doi.org/10.1016/j.apradiso.2015.07.034i
I. Murata et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
However, for several tens to hundreds keV (below 1 MeV) neutrons, it was known to be difficult to apply the foil activation method to neutron intensity characterization. In the present study, we utilized isomer production reaction induced by neutrons so as to cover neutron energy of interest, i.e., several tens to hundreds keV. The objectives of the present study are to establish a simple method to easily monitor the absolute neutron intensity of the p-Li neutron source by the foil activation method based on the isomer production reaction.
Table 1 Abundance of
113
In,
115
In and
135
Ba and half-lives of their isomers.
Nucleus
Abundance
Half-life
113
4.3 95.7 6.6
1.66 h 4.48 h 28.8 h
In In 135 Ba 115
2. Selection of activation material
Eex is from several tens keV to 800 keV, the reaction can be used for the present purpose, and the emitted gamma-rays can be measured because the energies are suitable for gamma-ray spectrometry.
2.1. p-Li neutron spectrum
2.3. Material selection result
Proton-lithium (p-Li) reaction is a source neutron producing reaction in BNCT similar to p-Be reaction. In the authors' group a p-liquid Li neutron source is designed and developed at present (Sauerwein et al., 2012). As is well known, the p-Li reaction cross section is rapidly increasing just after the threshold of 1.88 MeV. It means even by a low energy proton an intense neutron yield could be expected. In addition in this case the emitted neutron energy is relatively low, which is quite suitable for BNCT. Normally protons of around 2.5 MeV are utilized, which are just over the first resonance. The neutron energy can uniquely be fixed by kinematics if the proton energy and emission angle are given. However, in a real case the proton loses its energy in a lithium target gradually and continuously. As a result, the emitted neutron spectrum has an energy distribution for each emission angle as shown in Fig. 1, which is a calculation result for proton energy of 2.5 MeV by DROSG-2000 (Drosg, 2005). In this case the neutron energy is lower in backward and higher in forward angles. Energies to be measured are therefore from several tens keV to 800 keV.
To find possible activation materials for the present purpose, we extracted isomer production reactions induced by p-Li neutrons from Table of Isotopes (Firestone et al., 1996). The possible isomer nuclides we picked up are in the following 24 nuclei; 60mCo, 77m Se, 79mSe, 87mSr, 94mNb, 96mTc, 99mTc, 101mRh, 107mPb, 107mAg, 111m Cd, 113mIn, 115mIn, 117mSn, 133mBa, 134mCs, 135mBa, 154mEu, 158m Tb, 163mHo, 167mEr, 183mW, 189mOs, 193mPt. Among them, removing the ones having half-lives shorter than 30 s and taking into consideration the threshold energy, cross section value (Nakajima et al., 1991) and energy dependence, five nuclides were selected as 107Ag, 113In, 115In, 135Ba, 189Os. For 113In, 115In, 135Ba, since their cross sections and energy dependence are more-or-less the same, considering their half-lives and abundances shown in Table 1, 115In was finally chosen because the accuracy of measurement was expected to be the best among the three, because the expected number of counts is the largest. Finally, 107Ag, 115In and 189Os were selected as monitor candidates. Figs. 2 and 3 show their isomer production cross sections and isomeric transition schemes, respectively. Their basic information is summarized in Table 2.
2.2. Isomer production reaction
3. Examination of foil availability These candidate materials should be tested before practical use to confirm whether the absolute source intensity could really be estimated in p-Li neutron sources. If any discrepancy is found, we will need to check the cross section availability because especially 107 Ag and 189Os have not been used as activation foils so far. We expect, if necessary, the cross sections of these isomer production reactions should be measured by ourselves. Now we are planning to carry out test measurements with a dynamitron accelerator in Tohoku University, in which a beam current of 1 μA for proton energy of 2.5 MeV is available. In the present study, a feasibility
Cross secon (barn)
As mentioned in Section 1, it is normally difficult to measure neutrons of several tens to 800 keV. As for the foil activation method focused on in the present study, no available foils are known for that purpose. The reason is in the following: In this energy range (n,γ) and threshold reactions cannot be applied easily. The (n,γ) reaction has sensitivity on this energy range, however, quite a large sensitivity is seen also in thermal energy region. For the threshold reaction, the threshold energy is generally more than 1 MeV. In the present study, we thus focused on isomer production reaction via inelastic scattering. If an excited state of a nucleus by the isomer production reaction has a meaningfully long half-life, it could be utilized as an activation material. If the excited level energy is Eex, the reaction can be induced around or over the neutron energy of Eex. And the emitted gamma-ray energy is Eex. If
Fig. 1. Neutron spectrum of p-Li source as a function of emission angle.
0.5 0.4 107Ag
0.3
115In
0.2
189Os
0.1 0
0
500 Energy (keV)
Fig. 2. Isomer production cross sections of
1,000 107
Ag,
115
In and
189
Os.
Please cite this article as: Murata, I., et al., Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept. Appl. Radiat. Isotopes (2015), http://dx.doi.org/10.1016/j.apradiso.2015.07.034i
I. Murata et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Fig. 3. Isomeric transition schemes of Table 2 Selected isomer production reactions. Nuclide
Abundance (%)
Reaction
Excited level
Eγ (keV)
Half-life
107
51.8 95.7 16.1
(n,n′) (n,n′) (n,n′)
1st 1st 1st
93.1 226.2 30.8
44.3 s 4.48 h 5.8 h
Ag In 189 Os 115
Table 3 Irradiation condition at dynamitron accelerator in Tohoku University. 107
115
189
10 4 0.025
10 4 0.456
10 4 0.001
From the target
300 s 10 s 300 s 3.0 83
2τ 1τc 2τ 1.3 13,500
2τ 3000 sd 2τ 4.9 350
τ: half-life
Ag
Foil Position (cm) Area (cm2) Thickness (cm)a Irradiation conditionb Irradiation Cooling Measurement Ge efficiency (%) No. of counts a
In
Os
Description
3 cm from the detector 0° direction
Thickness corresponding to the thickness of 80% decay for measured gamma-
rays. b
1 μA on a LiF target. To wait for decay of 116In. d To wait for decay of 190Os. c
check was conducted under the condition listed in Table 3. The feasibility check calculation was carried out by a simple foil activation method with the physical conditions of neutron spectrum, energy dependent reaction cross section, foil thickness and so on. This result shows that measurements may be difficult for 189Os and 107 Ag. However, for 189Os the result would be improved if relaxing the gamma-ray self-shielding condition, i.e., if a thicker sample could be used. For 107Ag, since the half-life is short, repeated measurements are very effective to make the statistical accuracy acceptable. The above result also indicates that practical application in BNCT facilities is feasible, because normally the absolute source intensity of the BNCT facilities is extremely stronger than the dynamitron of Tohoku University, as high as over 1 1013 n/s. In this case it can be expected that for all the three foils high-precision measurements would be realized in an acceptably short measuring time.
4. Role of the foils in BNCT As shown in the previous section, these three foils can be used in the real BNCT facilities. And moreover these foils can selectively
107
Ag,
115
In and
3
189
Os.
be applied as a p-Li source monitor depending on measuring purposes in the real scene of BNCT as in the following: 107 Ag: Most convenient activation foil for actual BNCT facilities, because it has a short half-life. Irradiation and measurement can be finished in a short time. 115 In: Enables us to measure flux intensity in a high accuracy because of its high reaction rate. However, the cross section becomes small in the lower energy region. It means it is difficult to measure neutrons emitted in backward angles. Also, it may be necessary to wait for decay of 116In created parasitically. As mentioned in Section 2.3, disturbance of 113In is expected to be very small. 189 Os: Because of the large cross section in the lower energy region, it is possible to precisely measure neutrons emitted in backward angles. However, it would be difficult to prepare an Os foil because the emitted γ-ray energy is very low. In the measurement, we should wait for decay of 190Os.
5. Conclusion A simple method to monitor the absolute neutron intensity of p-Li neutron source especially for BNCT was investigated. The method is based on the foil activation method with isomer production reaction via inelastic scattering. As a result of numerical examination with evaluated nuclear data and Table of Isotope, it was found that 115In, 107Ag, and 189Os would be feasible. The three materials could be used effectively depending on measuring purposes in BNCT. Their features are summarized in the following: 107
Ag: The most convenient foil, since the half-life is short. In: Cannot be used for backward emission angles. However, the accuracy is the best at 0°. 189 Os: Suitable nuclide which can be used in backward angles. However, the gamma-ray energy is a little too low. 115
In the next step, validity of these foils will be examined experimentally using a p-Li neutron source.
References Drosg, M., 2005. DRORG-2000: Neutron Source Reactions, Nuclear Data Service, IAEA. Firestone, R.B., et al. (Eds.), 1996. Table of Isotopes. John Wiley and Sons, Inc. Nakajima, Y., et al., 1991. JENDL Activation Cross Section File. In: Proceedings of the 1990 Symposium on Nuclear Data, JAERI-M 91-032, 43. Sauerwein, W.A.G., Wittig, A., Moss, R., Nakagawa, Y. (Eds.), 2012. Neutron Capture Therapy: Principles and Applications. Springer.
Please cite this article as: Murata, I., et al., Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept. Appl. Radiat. Isotopes (2015), http://dx.doi.org/10.1016/j.apradiso.2015.07.034i
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept Isao Murata n, Yuki Otani, Fuminobu Sato Graduate School of Engineering, Osaka University, Yamada-oka 2-1, Suita, Osaka 565-0871, Japan
H I G H L I G H T S
Proton-lithium (p-Li) reaction is a candidate nuclear production reaction for ABNS for BNCT. The number of neutrons produced by the reaction cannot be known easily. A simple method was investigated to monitor it by isomer production reaction. Numerical examination showed 107Ag, 115In and 189Os were feasible, i.e., 107Ag is the most convenient foil, 115In is the best at 0° and 189Os is only suitable in backward angles.
art ic l e i nf o
a b s t r a c t
Article history: Received 7 February 2015 Received in revised form 17 July 2015 Accepted 25 July 2015
Proton-lithium (p-Li) reaction is being examined worldwide as a candidate nuclear production reaction for accelerator based neutron source (ABNS) for BNCT. In this reaction, the emitted neutron energy is not so high, below 1 MeV, and especially in backward angles the energy is as low as about 100 keV. The intensity measurement was thus known to be difficult so far. In the present study, a simple method was investigated to monitor the absolute neutron intensity of the p-Li neutron source by employing the foil activation method based on isomer production reactions in order to cover around several hundreds keV. As a result of numerical examination, it was found that 107Ag, 115In and 189Os would be feasible. Their features found out are summarized as follows: 107Ag: The most convenient foil, since the half life is short. 115 In: The accuracy is the best at 0°, though it cannot be used for backward angles. And 189Os: Suitable nuclide which can be used in backward angles, though the gamma-ray energy is a little too low. These would be used for p-Li source monitoring depending on measuring purposes in real BNCT scenes. & 2015 Elsevier Ltd. All rights reserved.
Keywords: BNCT p-Li reaction Foil activation method Isomer production reaction Source intensity
1. Introduction Proton-lithium (p-Li) reaction of Eq. (1) is a promising candidate nuclear reaction for accelerator based neutron source (ABNS) for Boron Neutron Capture Therapy (BNCT). 7
Li + p → n + 7Be + Q (Q = −1. 88 MeV)
(1)
It creates several tens to 800 keV neutrons for the proton energy of 2.5 MeV and the produced neutrons are moderated to become epithermal neutrons suitable for irradiation. However, such energetic neutrons have not frequently been utilized in practical engineering applications with the exception BNCT. Recently BNCT has been recognized as a promising cancer therapy among radiation therapies. And as a result, we should characterize the neutron source precisely n
Corresponding author. Fax: þ 81 6 6879 7899. E-mail address: [email protected] (I. Murata).
especially in neutron energies less than 1 MeV when the p-Li neutron source is utilized as a neutron source for BNCT. Normally, the number of neutrons produced by p-Li reaction can easily be confirmed by measuring radioactivity of the target (7Be). Practically, gamma-rays emitted from 7Be are measured after irradiation by means of gamma-ray spectrometry using a Ge semiconductor detector. However, in an actual BNCT, it is not so easy, because it is not straightforward to remove the target after irradiation in order to measure the radioactivity of the target. Since detectors like scintillators are also difficult to be applied because the neutron intensity is too strong and the energy of the source neutrons is not suitable for accurate detection by such detectors. We, then, focused on the foil activation method, being a well-known method to measure intensity of fast neutrons or slow neutrons. Concretely, for fast neutrons higher than 1 MeV appropriate threshold reactions exist for the activation method. And for slow neutrons below keV region, resonance reactions and neutron capture reactions can be applied to measure epi-thermal and thermal neutrons, respectively.
http://dx.doi.org/10.1016/j.apradiso.2015.07.034 0969-8043/& 2015 Elsevier Ltd. All rights reserved.
Please cite this article as: Murata, I., et al., Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept. Appl. Radiat. Isotopes (2015), http://dx.doi.org/10.1016/j.apradiso.2015.07.034i
I. Murata et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
However, for several tens to hundreds keV (below 1 MeV) neutrons, it was known to be difficult to apply the foil activation method to neutron intensity characterization. In the present study, we utilized isomer production reaction induced by neutrons so as to cover neutron energy of interest, i.e., several tens to hundreds keV. The objectives of the present study are to establish a simple method to easily monitor the absolute neutron intensity of the p-Li neutron source by the foil activation method based on the isomer production reaction.
Table 1 Abundance of
113
In,
115
In and
135
Ba and half-lives of their isomers.
Nucleus
Abundance
Half-life
113
4.3 95.7 6.6
1.66 h 4.48 h 28.8 h
In In 135 Ba 115
2. Selection of activation material
Eex is from several tens keV to 800 keV, the reaction can be used for the present purpose, and the emitted gamma-rays can be measured because the energies are suitable for gamma-ray spectrometry.
2.1. p-Li neutron spectrum
2.3. Material selection result
Proton-lithium (p-Li) reaction is a source neutron producing reaction in BNCT similar to p-Be reaction. In the authors' group a p-liquid Li neutron source is designed and developed at present (Sauerwein et al., 2012). As is well known, the p-Li reaction cross section is rapidly increasing just after the threshold of 1.88 MeV. It means even by a low energy proton an intense neutron yield could be expected. In addition in this case the emitted neutron energy is relatively low, which is quite suitable for BNCT. Normally protons of around 2.5 MeV are utilized, which are just over the first resonance. The neutron energy can uniquely be fixed by kinematics if the proton energy and emission angle are given. However, in a real case the proton loses its energy in a lithium target gradually and continuously. As a result, the emitted neutron spectrum has an energy distribution for each emission angle as shown in Fig. 1, which is a calculation result for proton energy of 2.5 MeV by DROSG-2000 (Drosg, 2005). In this case the neutron energy is lower in backward and higher in forward angles. Energies to be measured are therefore from several tens keV to 800 keV.
To find possible activation materials for the present purpose, we extracted isomer production reactions induced by p-Li neutrons from Table of Isotopes (Firestone et al., 1996). The possible isomer nuclides we picked up are in the following 24 nuclei; 60mCo, 77m Se, 79mSe, 87mSr, 94mNb, 96mTc, 99mTc, 101mRh, 107mPb, 107mAg, 111m Cd, 113mIn, 115mIn, 117mSn, 133mBa, 134mCs, 135mBa, 154mEu, 158m Tb, 163mHo, 167mEr, 183mW, 189mOs, 193mPt. Among them, removing the ones having half-lives shorter than 30 s and taking into consideration the threshold energy, cross section value (Nakajima et al., 1991) and energy dependence, five nuclides were selected as 107Ag, 113In, 115In, 135Ba, 189Os. For 113In, 115In, 135Ba, since their cross sections and energy dependence are more-or-less the same, considering their half-lives and abundances shown in Table 1, 115In was finally chosen because the accuracy of measurement was expected to be the best among the three, because the expected number of counts is the largest. Finally, 107Ag, 115In and 189Os were selected as monitor candidates. Figs. 2 and 3 show their isomer production cross sections and isomeric transition schemes, respectively. Their basic information is summarized in Table 2.
2.2. Isomer production reaction
3. Examination of foil availability These candidate materials should be tested before practical use to confirm whether the absolute source intensity could really be estimated in p-Li neutron sources. If any discrepancy is found, we will need to check the cross section availability because especially 107 Ag and 189Os have not been used as activation foils so far. We expect, if necessary, the cross sections of these isomer production reactions should be measured by ourselves. Now we are planning to carry out test measurements with a dynamitron accelerator in Tohoku University, in which a beam current of 1 μA for proton energy of 2.5 MeV is available. In the present study, a feasibility
Cross secon (barn)
As mentioned in Section 1, it is normally difficult to measure neutrons of several tens to 800 keV. As for the foil activation method focused on in the present study, no available foils are known for that purpose. The reason is in the following: In this energy range (n,γ) and threshold reactions cannot be applied easily. The (n,γ) reaction has sensitivity on this energy range, however, quite a large sensitivity is seen also in thermal energy region. For the threshold reaction, the threshold energy is generally more than 1 MeV. In the present study, we thus focused on isomer production reaction via inelastic scattering. If an excited state of a nucleus by the isomer production reaction has a meaningfully long half-life, it could be utilized as an activation material. If the excited level energy is Eex, the reaction can be induced around or over the neutron energy of Eex. And the emitted gamma-ray energy is Eex. If
Fig. 1. Neutron spectrum of p-Li source as a function of emission angle.
0.5 0.4 107Ag
0.3
115In
0.2
189Os
0.1 0
0
500 Energy (keV)
Fig. 2. Isomer production cross sections of
1,000 107
Ag,
115
In and
189
Os.
Please cite this article as: Murata, I., et al., Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept. Appl. Radiat. Isotopes (2015), http://dx.doi.org/10.1016/j.apradiso.2015.07.034i
I. Murata et al. / Applied Radiation and Isotopes ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Fig. 3. Isomeric transition schemes of Table 2 Selected isomer production reactions. Nuclide
Abundance (%)
Reaction
Excited level
Eγ (keV)
Half-life
107
51.8 95.7 16.1
(n,n′) (n,n′) (n,n′)
1st 1st 1st
93.1 226.2 30.8
44.3 s 4.48 h 5.8 h
Ag In 189 Os 115
Table 3 Irradiation condition at dynamitron accelerator in Tohoku University. 107
115
189
10 4 0.025
10 4 0.456
10 4 0.001
From the target
300 s 10 s 300 s 3.0 83
2τ 1τc 2τ 1.3 13,500
2τ 3000 sd 2τ 4.9 350
τ: half-life
Ag
Foil Position (cm) Area (cm2) Thickness (cm)a Irradiation conditionb Irradiation Cooling Measurement Ge efficiency (%) No. of counts a
In
Os
Description
3 cm from the detector 0° direction
Thickness corresponding to the thickness of 80% decay for measured gamma-
rays. b
1 μA on a LiF target. To wait for decay of 116In. d To wait for decay of 190Os. c
check was conducted under the condition listed in Table 3. The feasibility check calculation was carried out by a simple foil activation method with the physical conditions of neutron spectrum, energy dependent reaction cross section, foil thickness and so on. This result shows that measurements may be difficult for 189Os and 107 Ag. However, for 189Os the result would be improved if relaxing the gamma-ray self-shielding condition, i.e., if a thicker sample could be used. For 107Ag, since the half-life is short, repeated measurements are very effective to make the statistical accuracy acceptable. The above result also indicates that practical application in BNCT facilities is feasible, because normally the absolute source intensity of the BNCT facilities is extremely stronger than the dynamitron of Tohoku University, as high as over 1 1013 n/s. In this case it can be expected that for all the three foils high-precision measurements would be realized in an acceptably short measuring time.
4. Role of the foils in BNCT As shown in the previous section, these three foils can be used in the real BNCT facilities. And moreover these foils can selectively
107
Ag,
115
In and
3
189
Os.
be applied as a p-Li source monitor depending on measuring purposes in the real scene of BNCT as in the following: 107 Ag: Most convenient activation foil for actual BNCT facilities, because it has a short half-life. Irradiation and measurement can be finished in a short time. 115 In: Enables us to measure flux intensity in a high accuracy because of its high reaction rate. However, the cross section becomes small in the lower energy region. It means it is difficult to measure neutrons emitted in backward angles. Also, it may be necessary to wait for decay of 116In created parasitically. As mentioned in Section 2.3, disturbance of 113In is expected to be very small. 189 Os: Because of the large cross section in the lower energy region, it is possible to precisely measure neutrons emitted in backward angles. However, it would be difficult to prepare an Os foil because the emitted γ-ray energy is very low. In the measurement, we should wait for decay of 190Os.
5. Conclusion A simple method to monitor the absolute neutron intensity of p-Li neutron source especially for BNCT was investigated. The method is based on the foil activation method with isomer production reaction via inelastic scattering. As a result of numerical examination with evaluated nuclear data and Table of Isotope, it was found that 115In, 107Ag, and 189Os would be feasible. The three materials could be used effectively depending on measuring purposes in BNCT. Their features are summarized in the following: 107
Ag: The most convenient foil, since the half-life is short. In: Cannot be used for backward emission angles. However, the accuracy is the best at 0°. 189 Os: Suitable nuclide which can be used in backward angles. However, the gamma-ray energy is a little too low. 115
In the next step, validity of these foils will be examined experimentally using a p-Li neutron source.
References Drosg, M., 2005. DRORG-2000: Neutron Source Reactions, Nuclear Data Service, IAEA. Firestone, R.B., et al. (Eds.), 1996. Table of Isotopes. John Wiley and Sons, Inc. Nakajima, Y., et al., 1991. JENDL Activation Cross Section File. In: Proceedings of the 1990 Symposium on Nuclear Data, JAERI-M 91-032, 43. Sauerwein, W.A.G., Wittig, A., Moss, R., Nakagawa, Y. (Eds.), 2012. Neutron Capture Therapy: Principles and Applications. Springer.
Please cite this article as: Murata, I., et al., Neutron intensity monitor with activation foil for p-Li neutron source for BNCT – Feasibility test of the concept. Appl. Radiat. Isotopes (2015), http://dx.doi.org/10.1016/j.apradiso.2015.07.034i