- Email: [email protected]
Measurement of fission cross section for 232Th(n,x)89Rb reaction induced by neutrons around 14 MeV
Applied Radiation and Isotopes 70 (2012) 2295–2297
Contents lists available at SciVerse ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Measurement of fission cross section for neutrons around 14 MeV
232
Th(n,x)89Rb reaction induced by
Kaihong Fang n, Changlin Lan, Yupeng He, Xiangzhong Kong School of Nuclear Science and Technology, Lanzhou University, Lanzhou, Gansu Province 730000, PR China
H I G H L I G H T S c c c
Using the activation technique, cross section of 232Th(n,x)89Rb was measured. Neutron energies were measured by the cross-section ratio method. Deduced cross sections were 14.0 and 13.2 mb at 14.7 and 14.1 MeV, respectively.
a r t i c l e i n f o
abstract
Article history: Received 23 December 2011 Received in revised form 1 June 2012 Accepted 6 June 2012 Available online 15 June 2012
In order to investigate the fission process in more detail, and to compare with the measurement of cumulative fission yields, the fission cross section of the 232Th(n,x)89Rb reaction induced by 14 MeV neutron was measured using the activation technique. In our measurement the neutron flux was determined using the monitor 27Al(n,a)24Na reaction, and the neutron energies were measured by the method of cross-section ratios of 90Zr(n,2n)89Zr to 93Nb(n,2n)92mNb reactions. The cross sections were deduced as 14.0 7 0.9 mb at En ¼ 14.7 7 0.3 MeV and 13.2 7 1.0 mb at En ¼ 14.1 7 0.3 MeV. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Thorium Neutron Fission cross section Activation technique
1. Introduction The cross section of a nuclear reaction is fundamental to nuclear phenomena and basic for the application of nuclear technologies. The database of cross sections for the reactions induced by neutrons around 14 MeV plays a key role in the design of nuclear reactors. Meanwhile, the values are essential input parameters to estimate induced radioactivity, nuclear transmutation, radiation damage and other parameters (Robert and Larry, 1984; Cheng, 1989; Markovskij et al., 2000; Igashira and Ohsaki, 2002). In the case of fission reactions, the cross section of each fission channel is very important to study the symmetric/asymmetric fission model (Turkevich and Niday, 1951; Maslov, 2007) in detail. For the 232Th(n,f) reaction, many authors have measured the accumulative fission yields, while the literature (Chouak et al., 1995) contributing to the fission-yield measurement revealed a deficiency for the 232Th(n,f) reaction induced by 14 MeV neutrons, that was also pointed out in the compilation of Lammer (1991).
n
Corresponding author. Tel.: þ86 931 891 3572; fax: þ 86 931 891 3573. E-mail address: [email protected] (K. Fang).
0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.06.006
Especially, the measurement of fission cross section for each isotopic product has not been investigated adequately; thus the precise database of cross sections for all isotopic products requires further investigations. In this paper we present the result of the fission cross section of 232Th(n,x)89Rb reaction as a preliminary test.
2. Experiment The irradiations were carried out at the K-400 Intense Neutron Generator at the Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, and the bombardment lasted for about 1 h with a flux rate yield of about 3 1010–4 1010 n/s. Neutrons in the 14 MeV region were produced by means of the T(d,n)4He reaction with a deuteron beam of 220 keV and beam current of 350 mA. The solid tritium–titanium (T–Ti) target used in the neutron generator was about 2.18 mg/cm2 thick. The details were described in previous articles (Kaihong et al., 2008, 2009). The two samples (ThO2 powder of 99.5% purity) and monitor (Wagner et al., 1990) aluminum (thin Al foil of 99.99% purity) were made into round disks with a diameter of 2.0 cm; the thickness of samples was 1.0 mm and 1.3 mm,and the thickness
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K. Fang et al. / Applied Radiation and Isotopes 70 (2012) 2295–2297
of niobium and zirconium was 0.3–0.5 mm. Each of the samples was sandwiched between two Al foils. The samples were placed at 50 1351 angle relative to the deuteron beam direction and centered about the T–Ti target at distances of 3.5 cm. During the irradiation, neutron flux was monitored by accompanying aparticles so that the corrections could be made for small variations in the yield. The neutron energies in the measurements were determined by the cross-section ratio of the 93 Nb(n,2n)92mNb to 90Zr(n,2n)89Zr reactions (Lewis and Zieba, 1980). After the bombardment, the activated samples were cooled off for 3 min; then the g-activities were measured for 10 min to study the short half-life products by a low background, high efficiency g-ray spectrometer, using a well calibrated GEM-60P coaxial High-Purity Germanium (HPGe) detector (crystal diameter: 70.1 mm, crystal length: 72.3 mm;ORTEC, made in USA) with a relative efficiency of 68% and an energy resolution of 1.7 keV (FWHM) at 1.33 MeV. The uncertainty in the absolute efficiency curve at 5.5 cm was estimated to be 2%, while the uncertainty of the activity of the standard source was 1%.
3. Results and discussion 3.1. Formulation The cross section (sx) of 232Th(n,x)89Rb reaction was determined by the activation formula (Kong et al., 1999), as follows:
sx ¼
½eIg ZKSMDm ½lAFCx sm , ½eIg ZKSMDx ½lAFCm
ð1Þ
where the footnotes m and x represent the terms corresponding to the monitor and measured reactions, respectively, sm is the cross section of the monitor reaction induced at the same neutron energy as that of the sandwiched sample, e is the full-energy peak efficiency of the measured characteristic g-ray, Ig is the g-ray intensity, Z is the isotopic abundance of the target nuclide, S is the growth factor of the product nuclide which can be expressed as 1 e lT, where l is the decay constant (T1/2 ¼15.15 min;Browne and Firestone, 1996), T is the total irradiation time, M is the weight of sample, D is the counting collection factor which is expressed as elt1 elt2 , where t1 and t2 correspond to the time intervals from the end of the irradiation to the start and finish of the counting, respectively. A is the atomic weight, and C is the measured full-energy peak area. The correction factor (F in Eq. (1)) includes three elements, i.e., the self-absorption of the sample at a given g-energy (fs), the coincidence sum effect of cascade g-rays (fc), and geometry correction factor (fg), thus the F factor is expressed as F¼fsfcfg. Meanwhile, the neutron-fluctuation correction factor (K in Eq. (1)) is shown as to be " # L X K¼ Fi ð1elD ti ÞelT i FS ð2Þ i
Here, the total irradiation time was divided into L parts, where L is the number of time intervals. Dti is the duration of the ith time interval, Ti is the time interval from the end of the ith interval to the end of irradiation, F i is the neutron flux averaged over the sample during the Dti, and F is the neutron flux averaged over the sample during the total irradiation time T with the corresponding growth factor (S) defined above. 3.2. Results Unlike a general cross-section measurement, the 232Th target generated a large number of radioactive fission products under
Table 1 The associated database (Browne et al., 1996) of radioactive product from the 232 Th(n,f)89Rb reaction and the summary of the deduced cross sections in the present measurement. Characteristic g Eg (keV)
g-ray intensity
657.8 (E1)
10.0
1031.9 (E2)
58.0
1248.1 (E3)
42.6
Ig (%)
Energy En (MeV)
Cross-section sx (mb)
14.77 0.3 14.17 0.3 14.77 0.3 14.17 0.3 14.77 0.3 14.17 0.3
18.0 7 2.1 17.3 7 2.2 14.1 7 1.1 12.7 7 1.3 13.9 7 1.4 13.7 7 1.5
bombardment by the neutron beam; thus it is necessary to distinguish the special product (89Rb in this work) from the large number of candidates carefully. The decay characteristic g-rays which were used to discriminate the radioactive product nuclide have been chosen as Eg ¼ 657.8 keV (E1), 1031.9 keV (E2) and 1248.1 keV (E3) with their corresponding deduced intensities shown in Table 1. The values of cross-section deduced from each characteristic g-ray are 17.372.2 (E1), 12.771.3 (E2) and 13.771.5 (E3) mb at En ¼14.1 MeV which agree with each other within the error. For En ¼14.7 MeV, the deduced values are 18.072.1, 14.171.1 and 13.9 71.4 mb. All of them are listed in Table 1. Although the values of cross-section deduced from different characteristic g-rays of 89Rb are consistent with each other, the values deduced from Eg ¼657.8 keV are slightly larger than the others. This might be due to the low g-ray intensity (Ig) and the cumulative effect of overlapping from other products which have similar g-rays energy. The simple averaged value from E2 and E3 results in 14.070.9 mb at En ¼14.7 70.3 MeV and 13.271.0 mb at En ¼14.170.3 MeV.
4. Discussion The present work tried to deduce the cross section of short half-life (several minutes) products from the 232Th(n,f) reaction; thus the schedule of bombardment (1 h), cooling (3 min) and g-ray accumulation (10 min) can filter out the effect from many other products, i.e., long half-life or very short half-life nuclides. Meanwhile, to measure the cross section of a selected reaction, i.e., the 232Th(n,x)89Rb reaction, the cumulative effect from the precursor nuclide which decays to 89Rb should be deducted. For instance, the possible fission product 89Kr (T1/2 ¼3.15 min, Browne and Firestone, 1996) might be a precursor nuclide decaying to 89Rb. In the measurement, the g-spectra indicate few 89Kr in the activated samples. Due to the short cooling interval, the activation products made the deadtime of the detector to be about 5–10%. Thus, a practical deadtime correction for HPGe g-spectrometer system has to be reestimated. By using a strong (jamming) g-source, the relation between the percent deadtime and the correction of counting rate losses for the HPGe g-spectrometer system was found. Therefore, the activity measurement can be implemented at high count rate, i.e., a percent deadtime up to 15%. This work obtained the cross sections of the 232Th(n,x)89Rb reaction at En ¼14.1 MeV and 14.7 MeV. By using three characteristic g-rays emitted from 89Rb, the independently deduced values of cross section are consistent with each other within the error. So far the cumulative fission yields of the 232Th(n,f) reaction have been observed by many authors while the cross section for each activation production has not been studied adequately. In future work, the cross-section measurement for the 232Th(n,f) fission
K. Fang et al. / Applied Radiation and Isotopes 70 (2012) 2295–2297
reaction should be investigated more, i.e., long half-life activation productions.
Acknowledgments The authors are grateful to the personnel of the K-400 Neutron Generator at Institute of Nuclear Physics and Chemistry of China, Academy of Engineering Physics (CAEP), for their excellent support. This work was partly supported by the Fundamental Research Funds for the Central Universities. References Browne, E., Firestone, R.B., 1996. Table of Isotopes. Wiley, New York. Cheng, E.T., 1989. Radioactivity aspects of fusion reactors. Fusion Eng. Des. 10, 231–242. Chouak, A., Embarch, K., Berrada, M., 1995. Measurement of fission yields for 232 Th(n,f) at 14.7 MeV by direct gamma spectrometric method. Appl. Radiat. Isot. 46, 423–424. Igashira, M., Ohsaki, T., 2002. Neutron economy and nuclear data for transmutation of long-lived fission products. Prog. Nucl. Energy 40, 555–560.
2297
Kaihong, Fang, Shiwei, Xu, Changlin, Lan, Xiaosan, Xu, Xiangzhong, Kong, Rong, Liu, Li, Jiang, 2008. Cross-section measurement for the reactions producing shortlived nuclei induced by neutrons around 14 MeV. Appl. Radiat. Isot. 66, 1104–1107. Kaihong, Fang, Yang, Xiang, Yuncheng, Han, Xiangzhong, Kong, Tieshan, Wang, Rong, Liu, Li, Jiang, 2009. Measurements of activation cross-sections for 165 Ho(n,2n)164gHo and 180W(n,2n)179gW reactions induced by neutrons around 14 MeV. Radiat. Meas. 44, 68–71. Kong, X.Z., Wang, R., Wang, Y.C., Yang, J.K., 1999. Cross sections for 13.5–14.7 MeV neutron induced reactions on palladium isotopes. Appl. Radiat. Isot. 50, 361–364. Lammer, M., 1991. Compilation and Evaluation of Fission Yield Nuclear Data. IAEA, Vienna. Lewis, V.E., Zieba, K.J., 1980. A transfer standard for d þt neutron fluence and energy. Nucl. Instrum. Methods 174, 141–144. Markovskij, D.V., Forrest, R.A., Freiesleben, H., Kovalchuk, V.D., Richter, D., Seidel, K., Tereshkin, V.I., Unholzer, S., 2000. Experimental investigation of radioactivities induced in fusion reactor structural materials by 14 MeV neutrons. Fusion Eng. Des. 51, 695–700. Maslov, V.M., 2007. Symmetric vs asymmetric nucleon-induced fission of thorium up to 200 MeV. Phys. Lett. B 649, 376–383. Robert, K.S., Larry, R.G., 1984. Measurement of the 27Al(n,2n)26Al reaction cross section for fusion reactor applications. J. Nucl. Mater. 123, 1071–1077. Turkevich, A., Niday, J.B., 1951. Radiochemical studies on the fission of 232Th with pile neutrons. Phys. Rev. 84, 52–60. Wagner, M., Vonach, H., Pavlik, A., 1990. Physics data, evaluation of cross sections for 14 MeV important neutron. Dosimetry React. 13, 5.
Contents lists available at SciVerse ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Measurement of fission cross section for neutrons around 14 MeV
232
Th(n,x)89Rb reaction induced by
Kaihong Fang n, Changlin Lan, Yupeng He, Xiangzhong Kong School of Nuclear Science and Technology, Lanzhou University, Lanzhou, Gansu Province 730000, PR China
H I G H L I G H T S c c c
Using the activation technique, cross section of 232Th(n,x)89Rb was measured. Neutron energies were measured by the cross-section ratio method. Deduced cross sections were 14.0 and 13.2 mb at 14.7 and 14.1 MeV, respectively.
a r t i c l e i n f o
abstract
Article history: Received 23 December 2011 Received in revised form 1 June 2012 Accepted 6 June 2012 Available online 15 June 2012
In order to investigate the fission process in more detail, and to compare with the measurement of cumulative fission yields, the fission cross section of the 232Th(n,x)89Rb reaction induced by 14 MeV neutron was measured using the activation technique. In our measurement the neutron flux was determined using the monitor 27Al(n,a)24Na reaction, and the neutron energies were measured by the method of cross-section ratios of 90Zr(n,2n)89Zr to 93Nb(n,2n)92mNb reactions. The cross sections were deduced as 14.0 7 0.9 mb at En ¼ 14.7 7 0.3 MeV and 13.2 7 1.0 mb at En ¼ 14.1 7 0.3 MeV. & 2012 Elsevier Ltd. All rights reserved.
Keywords: Thorium Neutron Fission cross section Activation technique
1. Introduction The cross section of a nuclear reaction is fundamental to nuclear phenomena and basic for the application of nuclear technologies. The database of cross sections for the reactions induced by neutrons around 14 MeV plays a key role in the design of nuclear reactors. Meanwhile, the values are essential input parameters to estimate induced radioactivity, nuclear transmutation, radiation damage and other parameters (Robert and Larry, 1984; Cheng, 1989; Markovskij et al., 2000; Igashira and Ohsaki, 2002). In the case of fission reactions, the cross section of each fission channel is very important to study the symmetric/asymmetric fission model (Turkevich and Niday, 1951; Maslov, 2007) in detail. For the 232Th(n,f) reaction, many authors have measured the accumulative fission yields, while the literature (Chouak et al., 1995) contributing to the fission-yield measurement revealed a deficiency for the 232Th(n,f) reaction induced by 14 MeV neutrons, that was also pointed out in the compilation of Lammer (1991).
n
Corresponding author. Tel.: þ86 931 891 3572; fax: þ 86 931 891 3573. E-mail address: [email protected] (K. Fang).
0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.06.006
Especially, the measurement of fission cross section for each isotopic product has not been investigated adequately; thus the precise database of cross sections for all isotopic products requires further investigations. In this paper we present the result of the fission cross section of 232Th(n,x)89Rb reaction as a preliminary test.
2. Experiment The irradiations were carried out at the K-400 Intense Neutron Generator at the Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, and the bombardment lasted for about 1 h with a flux rate yield of about 3 1010–4 1010 n/s. Neutrons in the 14 MeV region were produced by means of the T(d,n)4He reaction with a deuteron beam of 220 keV and beam current of 350 mA. The solid tritium–titanium (T–Ti) target used in the neutron generator was about 2.18 mg/cm2 thick. The details were described in previous articles (Kaihong et al., 2008, 2009). The two samples (ThO2 powder of 99.5% purity) and monitor (Wagner et al., 1990) aluminum (thin Al foil of 99.99% purity) were made into round disks with a diameter of 2.0 cm; the thickness of samples was 1.0 mm and 1.3 mm,and the thickness
2296
K. Fang et al. / Applied Radiation and Isotopes 70 (2012) 2295–2297
of niobium and zirconium was 0.3–0.5 mm. Each of the samples was sandwiched between two Al foils. The samples were placed at 50 1351 angle relative to the deuteron beam direction and centered about the T–Ti target at distances of 3.5 cm. During the irradiation, neutron flux was monitored by accompanying aparticles so that the corrections could be made for small variations in the yield. The neutron energies in the measurements were determined by the cross-section ratio of the 93 Nb(n,2n)92mNb to 90Zr(n,2n)89Zr reactions (Lewis and Zieba, 1980). After the bombardment, the activated samples were cooled off for 3 min; then the g-activities were measured for 10 min to study the short half-life products by a low background, high efficiency g-ray spectrometer, using a well calibrated GEM-60P coaxial High-Purity Germanium (HPGe) detector (crystal diameter: 70.1 mm, crystal length: 72.3 mm;ORTEC, made in USA) with a relative efficiency of 68% and an energy resolution of 1.7 keV (FWHM) at 1.33 MeV. The uncertainty in the absolute efficiency curve at 5.5 cm was estimated to be 2%, while the uncertainty of the activity of the standard source was 1%.
3. Results and discussion 3.1. Formulation The cross section (sx) of 232Th(n,x)89Rb reaction was determined by the activation formula (Kong et al., 1999), as follows:
sx ¼
½eIg ZKSMDm ½lAFCx sm , ½eIg ZKSMDx ½lAFCm
ð1Þ
where the footnotes m and x represent the terms corresponding to the monitor and measured reactions, respectively, sm is the cross section of the monitor reaction induced at the same neutron energy as that of the sandwiched sample, e is the full-energy peak efficiency of the measured characteristic g-ray, Ig is the g-ray intensity, Z is the isotopic abundance of the target nuclide, S is the growth factor of the product nuclide which can be expressed as 1 e lT, where l is the decay constant (T1/2 ¼15.15 min;Browne and Firestone, 1996), T is the total irradiation time, M is the weight of sample, D is the counting collection factor which is expressed as elt1 elt2 , where t1 and t2 correspond to the time intervals from the end of the irradiation to the start and finish of the counting, respectively. A is the atomic weight, and C is the measured full-energy peak area. The correction factor (F in Eq. (1)) includes three elements, i.e., the self-absorption of the sample at a given g-energy (fs), the coincidence sum effect of cascade g-rays (fc), and geometry correction factor (fg), thus the F factor is expressed as F¼fsfcfg. Meanwhile, the neutron-fluctuation correction factor (K in Eq. (1)) is shown as to be " # L X K¼ Fi ð1elD ti ÞelT i FS ð2Þ i
Here, the total irradiation time was divided into L parts, where L is the number of time intervals. Dti is the duration of the ith time interval, Ti is the time interval from the end of the ith interval to the end of irradiation, F i is the neutron flux averaged over the sample during the Dti, and F is the neutron flux averaged over the sample during the total irradiation time T with the corresponding growth factor (S) defined above. 3.2. Results Unlike a general cross-section measurement, the 232Th target generated a large number of radioactive fission products under
Table 1 The associated database (Browne et al., 1996) of radioactive product from the 232 Th(n,f)89Rb reaction and the summary of the deduced cross sections in the present measurement. Characteristic g Eg (keV)
g-ray intensity
657.8 (E1)
10.0
1031.9 (E2)
58.0
1248.1 (E3)
42.6
Ig (%)
Energy En (MeV)
Cross-section sx (mb)
14.77 0.3 14.17 0.3 14.77 0.3 14.17 0.3 14.77 0.3 14.17 0.3
18.0 7 2.1 17.3 7 2.2 14.1 7 1.1 12.7 7 1.3 13.9 7 1.4 13.7 7 1.5
bombardment by the neutron beam; thus it is necessary to distinguish the special product (89Rb in this work) from the large number of candidates carefully. The decay characteristic g-rays which were used to discriminate the radioactive product nuclide have been chosen as Eg ¼ 657.8 keV (E1), 1031.9 keV (E2) and 1248.1 keV (E3) with their corresponding deduced intensities shown in Table 1. The values of cross-section deduced from each characteristic g-ray are 17.372.2 (E1), 12.771.3 (E2) and 13.771.5 (E3) mb at En ¼14.1 MeV which agree with each other within the error. For En ¼14.7 MeV, the deduced values are 18.072.1, 14.171.1 and 13.9 71.4 mb. All of them are listed in Table 1. Although the values of cross-section deduced from different characteristic g-rays of 89Rb are consistent with each other, the values deduced from Eg ¼657.8 keV are slightly larger than the others. This might be due to the low g-ray intensity (Ig) and the cumulative effect of overlapping from other products which have similar g-rays energy. The simple averaged value from E2 and E3 results in 14.070.9 mb at En ¼14.7 70.3 MeV and 13.271.0 mb at En ¼14.170.3 MeV.
4. Discussion The present work tried to deduce the cross section of short half-life (several minutes) products from the 232Th(n,f) reaction; thus the schedule of bombardment (1 h), cooling (3 min) and g-ray accumulation (10 min) can filter out the effect from many other products, i.e., long half-life or very short half-life nuclides. Meanwhile, to measure the cross section of a selected reaction, i.e., the 232Th(n,x)89Rb reaction, the cumulative effect from the precursor nuclide which decays to 89Rb should be deducted. For instance, the possible fission product 89Kr (T1/2 ¼3.15 min, Browne and Firestone, 1996) might be a precursor nuclide decaying to 89Rb. In the measurement, the g-spectra indicate few 89Kr in the activated samples. Due to the short cooling interval, the activation products made the deadtime of the detector to be about 5–10%. Thus, a practical deadtime correction for HPGe g-spectrometer system has to be reestimated. By using a strong (jamming) g-source, the relation between the percent deadtime and the correction of counting rate losses for the HPGe g-spectrometer system was found. Therefore, the activity measurement can be implemented at high count rate, i.e., a percent deadtime up to 15%. This work obtained the cross sections of the 232Th(n,x)89Rb reaction at En ¼14.1 MeV and 14.7 MeV. By using three characteristic g-rays emitted from 89Rb, the independently deduced values of cross section are consistent with each other within the error. So far the cumulative fission yields of the 232Th(n,f) reaction have been observed by many authors while the cross section for each activation production has not been studied adequately. In future work, the cross-section measurement for the 232Th(n,f) fission
K. Fang et al. / Applied Radiation and Isotopes 70 (2012) 2295–2297
reaction should be investigated more, i.e., long half-life activation productions.
Acknowledgments The authors are grateful to the personnel of the K-400 Neutron Generator at Institute of Nuclear Physics and Chemistry of China, Academy of Engineering Physics (CAEP), for their excellent support. This work was partly supported by the Fundamental Research Funds for the Central Universities. References Browne, E., Firestone, R.B., 1996. Table of Isotopes. Wiley, New York. Cheng, E.T., 1989. Radioactivity aspects of fusion reactors. Fusion Eng. Des. 10, 231–242. Chouak, A., Embarch, K., Berrada, M., 1995. Measurement of fission yields for 232 Th(n,f) at 14.7 MeV by direct gamma spectrometric method. Appl. Radiat. Isot. 46, 423–424. Igashira, M., Ohsaki, T., 2002. Neutron economy and nuclear data for transmutation of long-lived fission products. Prog. Nucl. Energy 40, 555–560.
2297
Kaihong, Fang, Shiwei, Xu, Changlin, Lan, Xiaosan, Xu, Xiangzhong, Kong, Rong, Liu, Li, Jiang, 2008. Cross-section measurement for the reactions producing shortlived nuclei induced by neutrons around 14 MeV. Appl. Radiat. Isot. 66, 1104–1107. Kaihong, Fang, Yang, Xiang, Yuncheng, Han, Xiangzhong, Kong, Tieshan, Wang, Rong, Liu, Li, Jiang, 2009. Measurements of activation cross-sections for 165 Ho(n,2n)164gHo and 180W(n,2n)179gW reactions induced by neutrons around 14 MeV. Radiat. Meas. 44, 68–71. Kong, X.Z., Wang, R., Wang, Y.C., Yang, J.K., 1999. Cross sections for 13.5–14.7 MeV neutron induced reactions on palladium isotopes. Appl. Radiat. Isot. 50, 361–364. Lammer, M., 1991. Compilation and Evaluation of Fission Yield Nuclear Data. IAEA, Vienna. Lewis, V.E., Zieba, K.J., 1980. A transfer standard for d þt neutron fluence and energy. Nucl. Instrum. Methods 174, 141–144. Markovskij, D.V., Forrest, R.A., Freiesleben, H., Kovalchuk, V.D., Richter, D., Seidel, K., Tereshkin, V.I., Unholzer, S., 2000. Experimental investigation of radioactivities induced in fusion reactor structural materials by 14 MeV neutrons. Fusion Eng. Des. 51, 695–700. Maslov, V.M., 2007. Symmetric vs asymmetric nucleon-induced fission of thorium up to 200 MeV. Phys. Lett. B 649, 376–383. Robert, K.S., Larry, R.G., 1984. Measurement of the 27Al(n,2n)26Al reaction cross section for fusion reactor applications. J. Nucl. Mater. 123, 1071–1077. Turkevich, A., Niday, J.B., 1951. Radiochemical studies on the fission of 232Th with pile neutrons. Phys. Rev. 84, 52–60. Wagner, M., Vonach, H., Pavlik, A., 1990. Physics data, evaluation of cross sections for 14 MeV important neutron. Dosimetry React. 13, 5.