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Neutron Induced Fission Cross-Sections of 240Pu and 243Am in the Energy Range 1 - 200 MeV
Nuclear Physics A 734 (2004) E45–E48 www.elsevier.com/locate/npe
Neutron Induced Fission Cross-Sections of in the Energy Range 1 - 200 MeV
240
Pu and
243
Am
A. B. Lapteva, A. Yu. Donetsb, A. V. Fomichevb, A. A. Fomichevc, R. C. Haightd, O. A. Shcherbakova,e, S. M. Solovievb, Yu. V. Tuboltsevf and A. S. Vorobyeva a
Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300, Russia
b
V.G. Khlopin Radium Institute, St. Petersburg, 194021, Russia
c
Saint Petersburg State University, St. Petersburg, 198504, Russia
d
Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
e
Japan Nuclear Cycle Development Institute, Tokai-mura, Ibaraki 319-1194, Japan
f
A.F. Ioffe Physico-Technical Institute, St. Petersburg, 194021, Russia
During the last several years, the measurements of neutron-induced fission cross-sections of actinides and stable isotopes have been performed at the GNEIS facility. At present moment, the new series of experiments for measurements of fission cross-section ratios relative to 235U have been began for 240Pu, 243Am and natW in a wide energy range of incident neutrons from 1 MeV to 200 MeV. The measurements were performed using the multiplate ionization chamber and time-of-flight technique. The first results of this measurement in case of 240Pu and 243Am are presented in comparison with the other data.
1. INTRODUCTION There is a long-standing need for information about fission reactions of heavy nuclei induced by particles at intermediate energies. But regular experimental studies of fission and the evaluations of nuclear data in this energy region have begun comparatively recently. Among new applications, the most important for fission at intermediate energies are accelerator-driven systems such as those proposed for transmuting nuclear waste, especially actinides, and for energy generation. The solution of these tasks leads to increased requirements on accuracy and reliability of relevant nuclear data, which are not fulfilled as yet [1]. Fission cross sections in the energy range 20 to several hundred MeV have been measured with spallation neutron sources at the WNR/LANSCE facility at Los Alamos and at the GNEIS facility [2]. At GNEIS, the fission cross-sections of 233U, 238U, 232Th, 237Np, 239Pu, nat Pb and 209Bi have been measured relative to 235U in the energy range 1-200 MeV [3]. The purpose of present investigation is to measure neutron-induced fission cross-sections of 240Pu, 243Am and natW relative to 235U in the energy range from 1 to 200 MeV at the neutron spectrometer GNEIS. Measurements are performed in the framework of new ISTC Project 1971. The first new results of this measurement for 240Pu and 243Am are presented in this article in comparison with the other data. The very first results of this measurement in the case of 240Pu have been published earlier [4].
0375-9474/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2004.03.016
E46
A.B. Laptev et al. / Nuclear Physics A 734 (2004) E45–E48
2. EXPERIMENTAL PROCEDURE The fission cross-section ratios for 240Pu and 243Am relative to 235U have been measured using the neutron time-of-flight spectrometer GNEIS [2]. This facility is based on the 1 GeV proton synchrocyclotron of PNPI (Gatchina) and has average intensity 3.1014 n/s (at internal proton current ~3 ȝA), a burst duration 10 ns and repetition rate up to 50 Hz. A flight path was 48.5 m. A system of iron, brass and lead collimators gives the beam diameter of 18 cm at the fission detector location. The measurements were carried out with the use of a sweeping magnet placed at 30 m from the source-target. Schematic layout of the GNEIS facility and experimental arrangement for fission cross-section measurements are shown in Figure 1. The fission reaction rate was measured using a fast parallel plate ionization chamber filled with methane working gas at the absolute pressure of 3 atm. The ionization chamber has a total of 6 sections, every one containing one pair of cathode and anode plates spaced by 5 mm. The painting technique with high quality fissionable materials has been used for actinide targets production. The target foils were about 5-7 ȝg/cm2 thick in case of 240Pu or 243Am and 150 ȝg/cm2 thick in case of 235U and were deposited Figure 1. Schematic layout of the GNEIS facility on 0.05-mm-thick Al backings. and experimental arrangement for fission crossFor each nucleus under investigation, section measurements. the time-of-flight and pulse height spectra were accumulated using the data acquisition system based on a 100-MHz FLASH-ADC in each measuring channel. The start signal was provided by gamma flash detector – the bare PMT placed in the neutron beam. This signal was also used to control a single-turn deflection of the proton beam to the neutron-producing target. 3. DATA PROCESSING The initial stage of the raw data reduction included the digital processing of the data from FLASH-ADCs and re-arranging of the data into pulse height (Figure 2), TOF-spectra (Figure 3) and 2-dimensional matrix consisting of 512 TOF channels by 128 amplitude channels. Identification of start (gamma flash) and stop (fission) signals on the background of electronic noise, alpha- and pile-up events has been made by a method of digital filtering [5]. The “time-of-flight vs neutron energy” calibration with an accuracy 0.03 % has been made using a position of the lead total cross section resonances and weak gamma-flash peak observed in the TOF-spectra and used as a true time-zero (v. inserts to Figure 3). In the data reduction process, the fission event counting rates were corrected for background events, the neutron flux attenuation for investigated and reference nuclei and fragment losses in the targets due to finite deposit thickness, neutron momentum transfer and angular anisotropy of fission fragments. The attenuation correction was calculated using the neutron total cross-sections from ENDF/B-VI. A correction for the energy dependent linear-momentum and angular-momentum effects were calculated following a method of G. Carlson [6].
A.B. Laptev et al. / Nuclear Physics A 734 (2004) E45–E48
E47
Neutron Energy, MeV 1000
800 600
240
bias
200 50 20 10
800
Pu
40
600
0 1500
243
400
bias
Counts / channel
Counts / channel
0 600
Am
200
0 15000
40
50
1000
0 30
420
440
40
50
400
420
440
Am
0 20000
2000
1000
821 keV
1500
γ - peak
723 keV
1000
0 30
40
400
50
420
440
235
5000
0
Pu
243
10000
5000
400
500
15000
bias
0.6
80 60 40 20 0
γ - peak
50
2000
U
1.0 0.8
240
100
235
10000
γ - peak
30
1.5 100 80 60 40 20
0
400 200
2
20
400 200
3
5
60
U
0
100
200
300
400
500
Pulse height channel
Figure 2. Pulse height spectra observed for 240 Pu, 243Am and 235U targets in the neutron energy range 1 – 200 MeV, an arrows show the biases used for discrimination.
100
200
300
400
500
TOF channel
Figure 3. Time-of-flight spectra (10 ns channel width) obtained for 240Pu, 243Am and 235U targets with the pulse height biases as shown in Figure 2. Inserts show TOF-spectra in regions of gamma-flash and lead resonances in more details.
The fission cross-section ratios for 240Pu and 243Am and the reference nucleus 235U obtained in the “shape” measurements have been normalized using the existing data of Staples et al. [7] and Behrens et al. [8] in the energy range about 1-2 MeV. Finally, the normalized fission cross-section ratios have been converted to the cross-sections using fission cross-section of 235U from JENDL-3.2 [9] below 20 MeV and the recommended data of A. Carlson et al. [10] above 20 MeV. 4. RESULTS AND CONCLUSIONS The results of present fission cross-sections measurements are shown in Figures 4 and 5 in comparison with experimental data of Staples et al. [7] and Behrens et al. [8]. For clarity of the comparison, only small part of the known data of other authors is presented. The error bars of our data represent the statistical errors only (one standard deviation) and these uncertainties are ~3% above 1 MeV. Detailed analysis of systematic errors is under performing. For 240Pu (Figure 4), there is good agreement between the present data and those of Staples et al. [7] up to 100 MeV, but there are disagreements in the energy range of 100-200 MeV. Solid line demonstrates result of a Hauser-Feshbach statistical model calculation of Maslov [11] and shows a rough agreement with our data. For 243Am (Figure 5), a comparison of the present data with data set of LLNL [8] shows a good agreement of both data sets below ~8 MeV, while at higher energies the present data lie above the data of Behrens et al. (up to 10 % at 8-20 MeV). There are no known previous data for fission cross-section of 243Am above ~40 MeV, such data have been obtained for the first time.
E48
A.B. Laptev et al. / Nuclear Physics A 734 (2004) E45–E48
2.8
3.0
2.6
240
2.4
243
Pu
2.5
Am
Fission cross-section, b
Fission cross-section, b
2.2 2.0 1.8 1.6 1.4
Present data Staples&Morley Maslov
1.2 1.0
2.0
1.5
Present data Behrens&Browne
1.0
0.5
0.8 0.6
0.0 1
10
100
1
Neutron energy, MeV
Figure 4. Fission cross-section of energy range up to 200 MeV.
10
100
Neutron energy, MeV
240
Pu in the
Figure 5. Fission cross-section of energy range up to 200 MeV.
243
Am in the
In general, in the overlapping energy regions (below 20 MeV) our data are in reasonable agreement with previous data obtained mainly at electron linacs. But in case of 243Am situation is not so clear. There are some 2.8 disagreements between previous data. At 2.6 Am Figure 6 cross-section of 243Am is shown 2.4 more detailed in the energy range 3 - 13 2.2 MeV. There are two groups of data with 2.0 different absolute values. Our data did not 1.8 confirm wave-shape energy dependence of fission cross-section demonstrated by 1.6 data of Knitter et al. [12]. 1.4 Measurement of neutron-induced 1.2 3 4 5 6 7 8 9 10 11 12 13 fission cross-sections of 240Pu and 243Am at the GNEIS facility are continuing now and will be extended to sub-actinides Figure 6. Measured fission cross-section of 243Am in comparison with other data in the energy range such as tungsten. Fission cross-section, b
243
Present data Behrens&Browne [12] Knitter&Budtz-Jorgensen [16] Goverdovskiy et al. [17] Kanda et al. [18] Fursov et al. [19]
Neutron energy, MeV
3 – 13 MeV.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
M. Salvatores, J. Nucl. Sci. Tech., Suppl. 2, 1, 4 (2002). N.K. Abrosimov, G.Z. Borukhovich, A.B. Laptev et al., Nucl. Instr. Meth., A242, 121 (1985). O. Shcherbakov, A. Donets, A. Evdokimov et al., J. Nucl. Sci. Tech., Suppl. 2, 1, 230 (2002). O.A. Shcherbakov, A.Yu. Donets, A.V. Fomichev et al., Proc. of IX Int. Seminar on Interaction of Neutrons with Nuclei (ISINN-9), Dubna, May 23-26, 2001. Dubna, JINR, E3-2001-192, p.271 (2001). D.D. Burgess and R.J. Tervo, Nucl. Instr. Meth., 214, 431 (1983). G.W. Carlson, Nucl. Instr. Meth., 119, 97 (1974). P. Staples, K. Morley, Nucl. Sci. Eng., 129, 149 (1998). J.W. Behrens, J.C. Browne, Nucl. Sci. Eng., 77, 444 (1981). T. Nakagawa, S. Shibata, S. Chiba et al., J. Nucl. Sci. Tech., 32(12), 1259 (1995). A.D. Carlson, S. Chiba, F.-J. Hambsch et al., Summary Report of a Consultants’ Meeting held in Vienna, Austria, December 2-6, 1996. INDC(NDC)-368, IAEA, Vienna, p.23 (1997). V. Maslov, Yu. Porodzinskij, M. Baba, A. Hasegawa, J. Nucl. Sci. Tech., Suppl. 2, 1, 80 (2002). H.-H. Knitter, C. Budtz-Jorgensen, Nucl. Sci. Eng., 99, 1 (1988). A.A. Goverdovskiy, A.K. Gordyushin, B.D. Kuz'minov et al., Atomnaya Energiya, 67, 30 (1989). K. Kanda, H. Imaruoka, H. Terayama et al., J. Nucl. Sci. Tech., 24, 423 (1987). B.I. Fursov, E.Ju. Baranov, M.P. Klemyshev et al., Atomnaya Energiya, 59, 339 (1985).
Neutron Induced Fission Cross-Sections of in the Energy Range 1 - 200 MeV
240
Pu and
243
Am
A. B. Lapteva, A. Yu. Donetsb, A. V. Fomichevb, A. A. Fomichevc, R. C. Haightd, O. A. Shcherbakova,e, S. M. Solovievb, Yu. V. Tuboltsevf and A. S. Vorobyeva a
Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188300, Russia
b
V.G. Khlopin Radium Institute, St. Petersburg, 194021, Russia
c
Saint Petersburg State University, St. Petersburg, 198504, Russia
d
Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
e
Japan Nuclear Cycle Development Institute, Tokai-mura, Ibaraki 319-1194, Japan
f
A.F. Ioffe Physico-Technical Institute, St. Petersburg, 194021, Russia
During the last several years, the measurements of neutron-induced fission cross-sections of actinides and stable isotopes have been performed at the GNEIS facility. At present moment, the new series of experiments for measurements of fission cross-section ratios relative to 235U have been began for 240Pu, 243Am and natW in a wide energy range of incident neutrons from 1 MeV to 200 MeV. The measurements were performed using the multiplate ionization chamber and time-of-flight technique. The first results of this measurement in case of 240Pu and 243Am are presented in comparison with the other data.
1. INTRODUCTION There is a long-standing need for information about fission reactions of heavy nuclei induced by particles at intermediate energies. But regular experimental studies of fission and the evaluations of nuclear data in this energy region have begun comparatively recently. Among new applications, the most important for fission at intermediate energies are accelerator-driven systems such as those proposed for transmuting nuclear waste, especially actinides, and for energy generation. The solution of these tasks leads to increased requirements on accuracy and reliability of relevant nuclear data, which are not fulfilled as yet [1]. Fission cross sections in the energy range 20 to several hundred MeV have been measured with spallation neutron sources at the WNR/LANSCE facility at Los Alamos and at the GNEIS facility [2]. At GNEIS, the fission cross-sections of 233U, 238U, 232Th, 237Np, 239Pu, nat Pb and 209Bi have been measured relative to 235U in the energy range 1-200 MeV [3]. The purpose of present investigation is to measure neutron-induced fission cross-sections of 240Pu, 243Am and natW relative to 235U in the energy range from 1 to 200 MeV at the neutron spectrometer GNEIS. Measurements are performed in the framework of new ISTC Project 1971. The first new results of this measurement for 240Pu and 243Am are presented in this article in comparison with the other data. The very first results of this measurement in the case of 240Pu have been published earlier [4].
0375-9474/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2004.03.016
E46
A.B. Laptev et al. / Nuclear Physics A 734 (2004) E45–E48
2. EXPERIMENTAL PROCEDURE The fission cross-section ratios for 240Pu and 243Am relative to 235U have been measured using the neutron time-of-flight spectrometer GNEIS [2]. This facility is based on the 1 GeV proton synchrocyclotron of PNPI (Gatchina) and has average intensity 3.1014 n/s (at internal proton current ~3 ȝA), a burst duration 10 ns and repetition rate up to 50 Hz. A flight path was 48.5 m. A system of iron, brass and lead collimators gives the beam diameter of 18 cm at the fission detector location. The measurements were carried out with the use of a sweeping magnet placed at 30 m from the source-target. Schematic layout of the GNEIS facility and experimental arrangement for fission cross-section measurements are shown in Figure 1. The fission reaction rate was measured using a fast parallel plate ionization chamber filled with methane working gas at the absolute pressure of 3 atm. The ionization chamber has a total of 6 sections, every one containing one pair of cathode and anode plates spaced by 5 mm. The painting technique with high quality fissionable materials has been used for actinide targets production. The target foils were about 5-7 ȝg/cm2 thick in case of 240Pu or 243Am and 150 ȝg/cm2 thick in case of 235U and were deposited Figure 1. Schematic layout of the GNEIS facility on 0.05-mm-thick Al backings. and experimental arrangement for fission crossFor each nucleus under investigation, section measurements. the time-of-flight and pulse height spectra were accumulated using the data acquisition system based on a 100-MHz FLASH-ADC in each measuring channel. The start signal was provided by gamma flash detector – the bare PMT placed in the neutron beam. This signal was also used to control a single-turn deflection of the proton beam to the neutron-producing target. 3. DATA PROCESSING The initial stage of the raw data reduction included the digital processing of the data from FLASH-ADCs and re-arranging of the data into pulse height (Figure 2), TOF-spectra (Figure 3) and 2-dimensional matrix consisting of 512 TOF channels by 128 amplitude channels. Identification of start (gamma flash) and stop (fission) signals on the background of electronic noise, alpha- and pile-up events has been made by a method of digital filtering [5]. The “time-of-flight vs neutron energy” calibration with an accuracy 0.03 % has been made using a position of the lead total cross section resonances and weak gamma-flash peak observed in the TOF-spectra and used as a true time-zero (v. inserts to Figure 3). In the data reduction process, the fission event counting rates were corrected for background events, the neutron flux attenuation for investigated and reference nuclei and fragment losses in the targets due to finite deposit thickness, neutron momentum transfer and angular anisotropy of fission fragments. The attenuation correction was calculated using the neutron total cross-sections from ENDF/B-VI. A correction for the energy dependent linear-momentum and angular-momentum effects were calculated following a method of G. Carlson [6].
A.B. Laptev et al. / Nuclear Physics A 734 (2004) E45–E48
E47
Neutron Energy, MeV 1000
800 600
240
bias
200 50 20 10
800
Pu
40
600
0 1500
243
400
bias
Counts / channel
Counts / channel
0 600
Am
200
0 15000
40
50
1000
0 30
420
440
40
50
400
420
440
Am
0 20000
2000
1000
821 keV
1500
γ - peak
723 keV
1000
0 30
40
400
50
420
440
235
5000
0
Pu
243
10000
5000
400
500
15000
bias
0.6
80 60 40 20 0
γ - peak
50
2000
U
1.0 0.8
240
100
235
10000
γ - peak
30
1.5 100 80 60 40 20
0
400 200
2
20
400 200
3
5
60
U
0
100
200
300
400
500
Pulse height channel
Figure 2. Pulse height spectra observed for 240 Pu, 243Am and 235U targets in the neutron energy range 1 – 200 MeV, an arrows show the biases used for discrimination.
100
200
300
400
500
TOF channel
Figure 3. Time-of-flight spectra (10 ns channel width) obtained for 240Pu, 243Am and 235U targets with the pulse height biases as shown in Figure 2. Inserts show TOF-spectra in regions of gamma-flash and lead resonances in more details.
The fission cross-section ratios for 240Pu and 243Am and the reference nucleus 235U obtained in the “shape” measurements have been normalized using the existing data of Staples et al. [7] and Behrens et al. [8] in the energy range about 1-2 MeV. Finally, the normalized fission cross-section ratios have been converted to the cross-sections using fission cross-section of 235U from JENDL-3.2 [9] below 20 MeV and the recommended data of A. Carlson et al. [10] above 20 MeV. 4. RESULTS AND CONCLUSIONS The results of present fission cross-sections measurements are shown in Figures 4 and 5 in comparison with experimental data of Staples et al. [7] and Behrens et al. [8]. For clarity of the comparison, only small part of the known data of other authors is presented. The error bars of our data represent the statistical errors only (one standard deviation) and these uncertainties are ~3% above 1 MeV. Detailed analysis of systematic errors is under performing. For 240Pu (Figure 4), there is good agreement between the present data and those of Staples et al. [7] up to 100 MeV, but there are disagreements in the energy range of 100-200 MeV. Solid line demonstrates result of a Hauser-Feshbach statistical model calculation of Maslov [11] and shows a rough agreement with our data. For 243Am (Figure 5), a comparison of the present data with data set of LLNL [8] shows a good agreement of both data sets below ~8 MeV, while at higher energies the present data lie above the data of Behrens et al. (up to 10 % at 8-20 MeV). There are no known previous data for fission cross-section of 243Am above ~40 MeV, such data have been obtained for the first time.
E48
A.B. Laptev et al. / Nuclear Physics A 734 (2004) E45–E48
2.8
3.0
2.6
240
2.4
243
Pu
2.5
Am
Fission cross-section, b
Fission cross-section, b
2.2 2.0 1.8 1.6 1.4
Present data Staples&Morley Maslov
1.2 1.0
2.0
1.5
Present data Behrens&Browne
1.0
0.5
0.8 0.6
0.0 1
10
100
1
Neutron energy, MeV
Figure 4. Fission cross-section of energy range up to 200 MeV.
10
100
Neutron energy, MeV
240
Pu in the
Figure 5. Fission cross-section of energy range up to 200 MeV.
243
Am in the
In general, in the overlapping energy regions (below 20 MeV) our data are in reasonable agreement with previous data obtained mainly at electron linacs. But in case of 243Am situation is not so clear. There are some 2.8 disagreements between previous data. At 2.6 Am Figure 6 cross-section of 243Am is shown 2.4 more detailed in the energy range 3 - 13 2.2 MeV. There are two groups of data with 2.0 different absolute values. Our data did not 1.8 confirm wave-shape energy dependence of fission cross-section demonstrated by 1.6 data of Knitter et al. [12]. 1.4 Measurement of neutron-induced 1.2 3 4 5 6 7 8 9 10 11 12 13 fission cross-sections of 240Pu and 243Am at the GNEIS facility are continuing now and will be extended to sub-actinides Figure 6. Measured fission cross-section of 243Am in comparison with other data in the energy range such as tungsten. Fission cross-section, b
243
Present data Behrens&Browne [12] Knitter&Budtz-Jorgensen [16] Goverdovskiy et al. [17] Kanda et al. [18] Fursov et al. [19]
Neutron energy, MeV
3 – 13 MeV.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
M. Salvatores, J. Nucl. Sci. Tech., Suppl. 2, 1, 4 (2002). N.K. Abrosimov, G.Z. Borukhovich, A.B. Laptev et al., Nucl. Instr. Meth., A242, 121 (1985). O. Shcherbakov, A. Donets, A. Evdokimov et al., J. Nucl. Sci. Tech., Suppl. 2, 1, 230 (2002). O.A. Shcherbakov, A.Yu. Donets, A.V. Fomichev et al., Proc. of IX Int. Seminar on Interaction of Neutrons with Nuclei (ISINN-9), Dubna, May 23-26, 2001. Dubna, JINR, E3-2001-192, p.271 (2001). D.D. Burgess and R.J. Tervo, Nucl. Instr. Meth., 214, 431 (1983). G.W. Carlson, Nucl. Instr. Meth., 119, 97 (1974). P. Staples, K. Morley, Nucl. Sci. Eng., 129, 149 (1998). J.W. Behrens, J.C. Browne, Nucl. Sci. Eng., 77, 444 (1981). T. Nakagawa, S. Shibata, S. Chiba et al., J. Nucl. Sci. Tech., 32(12), 1259 (1995). A.D. Carlson, S. Chiba, F.-J. Hambsch et al., Summary Report of a Consultants’ Meeting held in Vienna, Austria, December 2-6, 1996. INDC(NDC)-368, IAEA, Vienna, p.23 (1997). V. Maslov, Yu. Porodzinskij, M. Baba, A. Hasegawa, J. Nucl. Sci. Tech., Suppl. 2, 1, 80 (2002). H.-H. Knitter, C. Budtz-Jorgensen, Nucl. Sci. Eng., 99, 1 (1988). A.A. Goverdovskiy, A.K. Gordyushin, B.D. Kuz'minov et al., Atomnaya Energiya, 67, 30 (1989). K. Kanda, H. Imaruoka, H. Terayama et al., J. Nucl. Sci. Tech., 24, 423 (1987). B.I. Fursov, E.Ju. Baranov, M.P. Klemyshev et al., Atomnaya Energiya, 59, 339 (1985).