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Measurement of the cross-section for the 115in(n, n′) 115min reaction
Journal
of Nuclear Energy,Vol. 27,
pp. 741 tct 745.
PergamonPress1973.Printedin Northern Ireland
MEASUREMENT OF THE CROSS-SECTION THE Wn(n, n’) llsmln REACTION
FOR
KATSUHEI KOBAYASHI and ITSURO KIMURA Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu, Japan and HIROSHI GOTOH and HIDEYUKI YAGI Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken, Japan (Received 19 March 1973)
Abstract-The energy dependent cross-section for the 1*5In(n, n)’*lb”In reaction was measured in the neutron energy region from 3.37 to 4.89 MeV with a 2 MeV van de Graaff accelerator. A pair of semiconductor proton recoil counters composed of a polyethylene radiator and a silicon detector was used for the absolute measurement of the neutron flux at the indium sample. A comparison of the average cross section, 175 f 6 mb, which was measured with a fission
plate, with the average cross-sectioncalculated with the energy dependent cross-sectionand the Maxwellianfissionneutron spectrumis presentedand discussed. ALTHOUGH a number of measurements (MARTINet al., 1954; HEERTJE et al., 1964; BUTLER and SANTRY, 1967; MENLOVE et al., 1967; GRENCH and MENLOVE, 1968 ; PAUW et al., 1971) and evaluations (BRESESTIet al., 1970; UKNDL-70) of the energy
dependent cross section of the well known threshold reaction l151n(n, n’) 115mInhave been reported, there still exist somewhat large discrepancies between them, especially in the energy region above about 2.5 MeV. The main origin of the discrepancies is thought to be systematic errors of the neutron flux estimations in the cross-section measurements, which have overridden the uncertainties claimed by the experimenters. The present authors tried to making some contribution in solving this problem under their experimental conditions. The experimental arrangement shown in Fig. 1 was used. Monochromatic neutrons were produced by the D(d, n)3He reaction with the 2 MeV van de Graaff accelerator at JAERI. The energy of neutrons was calculated with the kinematics (BROLLEY and FOWLER, 1960) of the reaction from the acceleration energy of the deuteron beam with the consideration of the energy loss of the beam in the nickel foil and the gas target and of the angular spread. For absolute measurement of the neutron flux at the indium foil, a pair of semiconductor proton recoil counters, as shown in Fig. 1, composed of a polyethylene radiator about 30 pm thick and a silicon detector was used. By opening or closing the shutter of the front counter which measured the neutron flux at the irradiation sample, net counts from the polyethylene were obtained from the difference of totaland background-counts which were alternately measured in every 1000 ,uC preset counts of deuteron beam current. The rear counter worked as an incident neutron monitor of the front counter when the shutter was opened or closed. The radiator of the front counter was attached to just behind the induim sample. Sample distance from the mean neutron source position was about 50 mm, and the distance between the sample and the front detector was about 14 mm. The neutron flux at the sample was calculated from the net count with the detection efficiency of the proton recoil 741
742
K. KOBAYASHI, I. KIMURA, H. Goro~ and H. YAGI
FIG.
T X
Target Sample
B
Au Backing
R
Radiator
S M
Shutter Mask
D
Si Detectaf
I.-Schematic
figure of a semiconductor proton recoil counter.
counter described elsewhere (GOTOH et al., 1972; GOTOH and YAGI, 1972; GOTOH et al., 1973 ; GOTOH et al. to be published). Indium samples were about 14 mm in diameter and about 0.4 mm in thickness. Induced activities of l15?n were measured with a 3 in. in diameter and 3 in. thick NaI(TI) scintillation counter whose photopeak efficiency had been calibrated with the standard gamma-ray sources manufactured at IAEA. From the results of the response function and the pulse height distribution to monochromatic neutrons during the experiment, the fact that the background neutrons seemed to hardly contribute to the total was experimentally confirmed. The obtained results of the cross-section for the ll%r(n, n’) l15Yn reaction are shown in Table 1 and Fig. 2. The previous data are also plotted in Fig. 2. The errors estimated in the present experiment are listed in Table 2. The uncertainty of the detection efficiency of the proton recoil counter includes the correction for detector and sample distances from the mean neutron source position. The uncertainty of the counter efficiency of the NaI(T1) scintillator includes the error derived from the difference in shape and size between the standard sources and sample foils. These errors were added quadratically to give a total error of 3.7 N 4-O per cent. Moreover, the uncertainty of about 2 per cent exists in the decay scheme but internal conversion coefficient of llKnzIn (LEDERER et al., 1967). Since the neutron flux is monitored with TABLE
l.--PRFSENTVALUESOFTHECROSS-SECTION FOR THE "%(?Z, d)"6mkl REACTION
Neutron energy* (MeV) 3.37 f 3.42 f 3.52 f 3.80 f 3.80 f 3.95 f 4.17 f 4.54 f 4.59 f 4.89 f
0.016 0.016 0.017 0.016 0.015 0.016 0.018 0.011 0.018 0.024
Cross-section (mb) 346 351 339 333 332 314 334 328 317 314
rt 13 5 14 i 13 & 13 f 13 * 12 f 13 f 13 f 12 f 12
* Calculated mean energy considering energy spread derived from the angles subtended by the indium foil.
143
Measurement for the llQr (n, n’) llsmIn reaction
Neutron
energy (MeV)
FIG. 2.-Cross-section for Yn(n,
n’)116mInreaction.
Measurements: t A
_---
t d
Evaluations :
Present works (1954) (1964) BUTLER and SANTRY (1967) MARTIN et al. HEERTJE et al.
MENLOVE~~
al. (1967)
-o-
GRENCH and MENLOVE(~~~~) PAUW el al. (1971)
-___ ~
UKNDL-70
BRE~ESTI et al.
(1970)
TABLE 2.--SUMMARYOFTHEESTIMATED ERRORSFROMTHEPRESENTCROSS-SECTION MEASUREMENT
Elastic scattering cross-section of hydrogen Geometry and efficiency of the semiconductor proton recoil counter Multiple neutron scattering in the counter system Statistics of proton recoil counting Weighing of radiator Efficiency of the NaI(T1) scintillator Statistics of induced activity measurement of 115mIn Weighing of indium foil Irradiation and counting time Total
-1% 1.5% <0*5% &I% 1% 2.0 2.5 % 0.1% 0.3 % 3.1 N 4.0 %
the proton recoil counter in this experiment, it may be considered that the systematic error is smaller than the previous values. The present results agree with BUTLER and SANTRY’S data (1967) in the energy region from about 3.9 MeV to 4.9 MeV, while the values around 3.5 MeV are rather close to those of MENLOVE ef al. (1967). Data of MARTIN er al. (1954) and UKNDL-70 are markedly lower than the values of the present and other reported results in the
744
K.
KOBAYASHI, I. KIMURA, H. GOTOH and
H. YACI
energy region above 4 MeV. On the contrary the results of HEERTJE et al. (1964) and of PAUW et al. (1971) are generally larger than those of the present and others. In order to compare with the integral value, the authors calculated the fission average cross-section for the l151n(n, n’)115m In reaction, making use of the Maxwellian fission neutron spectrum (CRANBERG et al., 1956) and the energy dependent crosssection of the present data and BUTLER and SANTRY’S (1967) in the energy region where the cross-section was not measured in the present experiment. The average cross-section has become to be 176 mb. The average cross-section for this reaction was measured with a fission plate of 90 per cent enriched uranium installed at the thermal neutron facility of the Kyoto University Reactor. The fast neutron flux monitored with the 5sNi(n,p)58Co, 24Mg(n, p)24Na and 27Al(n, a)24Na reactions agreed with each other within 2-3 per cent in error (KIMURA et al., 1971). The present measured average cross-section, which agreed with the previous works except FABRY’S (1967) within the limits of error as TABLE 3.--COMPARISON OF FISSIONAVERAGECROSS-SECTIONS FOR THE “%(n, “‘“%I REACIION
Cross-section tmb)
?I’)
Reference
177 f 10 171*5 177 5 6 174
Present work, measured with a fission plate Present work, calculated with the energy dependent cross-section and the Maxwellian fission spectrum KIMURA et al. (1969) KANDA et al. (1971) BRESESTIet al. (1970) SIMONSand MCELROY (1970)
200 *
FABRY
175 i 6 176
10
(1967)
shown in Table 3, agreed satisfactorily with the above calculated average crosssection. This fact would suggest the propriety of the results of the energy dependent In reaction, assuming the Maxwellian form as cross-section for the lr51n(n, n’)115m the 235Ufission neutron spectrum. By monitoring the fast neutron flux with the proton recoil counters, the measurement of the cross-section for the li51n(n, n ’) 115mInreaction has been carried out successfully with a little systematic error. This method is applicable to other crosssection measurements. Acknowledgments-The authors wish to express their sincere thanks to Prof. T. SHIBATA of Kyoto University for his invaluable guidance and encouragement. Thanks are also due to Messrs. C. The authors KOBAYASHI and S. KANDA of JAERI for the operation of the van de Graaff accelerator. are much indebted to the staff members of the Nuclear Data Laboratory at JAERI and of CCDN for providing us the UKNDL-70 available for this study. REFERENCES BRESIXSTI A. M., BRESESTIM., ROTA A., RYDIN R. BROLLEY J. E., JR. and FOWLER J. L. (1960) Fast
A. and LESCA L. (1970) Nuci. Sci. Eng 40, 331. Neutron Physics, part I, p. 73. Interscience, New
York. BUTLER J. P. and SANTRYD. C. (1967) B&I. Am. Phys. Sot. 12,547. Cited by BRESESTIet CRANBERG L. et al. (1956) Phys. Rev. 103,662. FABRY D. (1967) Nukleonik 10, 280. GoTon H., YAGI H. and KOBAYASHI K. (1972) Nucl. Instrum. Methods, 100,473. GOTOH H. and YAGI H. (1972) ibid, 101,395.
al. (1970).
Measurement for the llSIn(n, n’)l15mIn reaction
145
GOTOI~ H., YAGI H. and HARAYAMA Y. (1973) ibid, 110. GOTOH H., YAGI H., KIMURA I. and KOBAYASHIK., to be published. GRENCH H. A. and MENLOVEH. 0. (1968) Phys. Reu. 165, 1298. HEERTJEI., NAGEL W. and ATEN A. H. W., JR. (1964) Physica 30, 775. KANDA K. et al. (1971) Ann. Rep. KURRI 4,94. KIMURA. I., KOBAYASHIK. and SHIBATAT. (1969) J. Nucl. Sci. Technol. 6,485. KIMURA I., KOBAYASH~K. and SHIBATAT. (1971) J. Nucl. Sci. Technol. 8,59. LEDERER,C. M., HOLLANDER, J. M. and PERLMAN, 1. (1967) Table of Isotopes, 6th edn. J. Wiley, New York. MARTIN H., DIVEN V. and TASCHEKR. F. (1954) Phys. Rev. 93, 199. MENLOVEH. O., COOP K. L., GRENCH H. A. and SHER R. (1967) Phys. Reo. 163,1308. PAUW H. and ATEN A. H. W., JR. (1971) J. nucl. Energy 25,459. SIMONSR. L. and MCELROY W. N. (1970) BNWL-1312. United Kingdom Nuclear Data Library-70.
of Nuclear Energy,Vol. 27,
pp. 741 tct 745.
PergamonPress1973.Printedin Northern Ireland
MEASUREMENT OF THE CROSS-SECTION THE Wn(n, n’) llsmln REACTION
FOR
KATSUHEI KOBAYASHI and ITSURO KIMURA Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu, Japan and HIROSHI GOTOH and HIDEYUKI YAGI Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken, Japan (Received 19 March 1973)
Abstract-The energy dependent cross-section for the 1*5In(n, n)’*lb”In reaction was measured in the neutron energy region from 3.37 to 4.89 MeV with a 2 MeV van de Graaff accelerator. A pair of semiconductor proton recoil counters composed of a polyethylene radiator and a silicon detector was used for the absolute measurement of the neutron flux at the indium sample. A comparison of the average cross section, 175 f 6 mb, which was measured with a fission
plate, with the average cross-sectioncalculated with the energy dependent cross-sectionand the Maxwellianfissionneutron spectrumis presentedand discussed. ALTHOUGH a number of measurements (MARTINet al., 1954; HEERTJE et al., 1964; BUTLER and SANTRY, 1967; MENLOVE et al., 1967; GRENCH and MENLOVE, 1968 ; PAUW et al., 1971) and evaluations (BRESESTIet al., 1970; UKNDL-70) of the energy
dependent cross section of the well known threshold reaction l151n(n, n’) 115mInhave been reported, there still exist somewhat large discrepancies between them, especially in the energy region above about 2.5 MeV. The main origin of the discrepancies is thought to be systematic errors of the neutron flux estimations in the cross-section measurements, which have overridden the uncertainties claimed by the experimenters. The present authors tried to making some contribution in solving this problem under their experimental conditions. The experimental arrangement shown in Fig. 1 was used. Monochromatic neutrons were produced by the D(d, n)3He reaction with the 2 MeV van de Graaff accelerator at JAERI. The energy of neutrons was calculated with the kinematics (BROLLEY and FOWLER, 1960) of the reaction from the acceleration energy of the deuteron beam with the consideration of the energy loss of the beam in the nickel foil and the gas target and of the angular spread. For absolute measurement of the neutron flux at the indium foil, a pair of semiconductor proton recoil counters, as shown in Fig. 1, composed of a polyethylene radiator about 30 pm thick and a silicon detector was used. By opening or closing the shutter of the front counter which measured the neutron flux at the irradiation sample, net counts from the polyethylene were obtained from the difference of totaland background-counts which were alternately measured in every 1000 ,uC preset counts of deuteron beam current. The rear counter worked as an incident neutron monitor of the front counter when the shutter was opened or closed. The radiator of the front counter was attached to just behind the induim sample. Sample distance from the mean neutron source position was about 50 mm, and the distance between the sample and the front detector was about 14 mm. The neutron flux at the sample was calculated from the net count with the detection efficiency of the proton recoil 741
742
K. KOBAYASHI, I. KIMURA, H. Goro~ and H. YAGI
FIG.
T X
Target Sample
B
Au Backing
R
Radiator
S M
Shutter Mask
D
Si Detectaf
I.-Schematic
figure of a semiconductor proton recoil counter.
counter described elsewhere (GOTOH et al., 1972; GOTOH and YAGI, 1972; GOTOH et al., 1973 ; GOTOH et al. to be published). Indium samples were about 14 mm in diameter and about 0.4 mm in thickness. Induced activities of l15?n were measured with a 3 in. in diameter and 3 in. thick NaI(TI) scintillation counter whose photopeak efficiency had been calibrated with the standard gamma-ray sources manufactured at IAEA. From the results of the response function and the pulse height distribution to monochromatic neutrons during the experiment, the fact that the background neutrons seemed to hardly contribute to the total was experimentally confirmed. The obtained results of the cross-section for the ll%r(n, n’) l15Yn reaction are shown in Table 1 and Fig. 2. The previous data are also plotted in Fig. 2. The errors estimated in the present experiment are listed in Table 2. The uncertainty of the detection efficiency of the proton recoil counter includes the correction for detector and sample distances from the mean neutron source position. The uncertainty of the counter efficiency of the NaI(T1) scintillator includes the error derived from the difference in shape and size between the standard sources and sample foils. These errors were added quadratically to give a total error of 3.7 N 4-O per cent. Moreover, the uncertainty of about 2 per cent exists in the decay scheme but internal conversion coefficient of llKnzIn (LEDERER et al., 1967). Since the neutron flux is monitored with TABLE
l.--PRFSENTVALUESOFTHECROSS-SECTION FOR THE "%(?Z, d)"6mkl REACTION
Neutron energy* (MeV) 3.37 f 3.42 f 3.52 f 3.80 f 3.80 f 3.95 f 4.17 f 4.54 f 4.59 f 4.89 f
0.016 0.016 0.017 0.016 0.015 0.016 0.018 0.011 0.018 0.024
Cross-section (mb) 346 351 339 333 332 314 334 328 317 314
rt 13 5 14 i 13 & 13 f 13 * 12 f 13 f 13 f 12 f 12
* Calculated mean energy considering energy spread derived from the angles subtended by the indium foil.
143
Measurement for the llQr (n, n’) llsmIn reaction
Neutron
energy (MeV)
FIG. 2.-Cross-section for Yn(n,
n’)116mInreaction.
Measurements: t A
_---
t d
Evaluations :
Present works (1954) (1964) BUTLER and SANTRY (1967) MARTIN et al. HEERTJE et al.
MENLOVE~~
al. (1967)
-o-
GRENCH and MENLOVE(~~~~) PAUW el al. (1971)
-___ ~
UKNDL-70
BRE~ESTI et al.
(1970)
TABLE 2.--SUMMARYOFTHEESTIMATED ERRORSFROMTHEPRESENTCROSS-SECTION MEASUREMENT
Elastic scattering cross-section of hydrogen Geometry and efficiency of the semiconductor proton recoil counter Multiple neutron scattering in the counter system Statistics of proton recoil counting Weighing of radiator Efficiency of the NaI(T1) scintillator Statistics of induced activity measurement of 115mIn Weighing of indium foil Irradiation and counting time Total
-1% 1.5% <0*5% &I% 1% 2.0 2.5 % 0.1% 0.3 % 3.1 N 4.0 %
the proton recoil counter in this experiment, it may be considered that the systematic error is smaller than the previous values. The present results agree with BUTLER and SANTRY’S data (1967) in the energy region from about 3.9 MeV to 4.9 MeV, while the values around 3.5 MeV are rather close to those of MENLOVE ef al. (1967). Data of MARTIN er al. (1954) and UKNDL-70 are markedly lower than the values of the present and other reported results in the
744
K.
KOBAYASHI, I. KIMURA, H. GOTOH and
H. YACI
energy region above 4 MeV. On the contrary the results of HEERTJE et al. (1964) and of PAUW et al. (1971) are generally larger than those of the present and others. In order to compare with the integral value, the authors calculated the fission average cross-section for the l151n(n, n’)115m In reaction, making use of the Maxwellian fission neutron spectrum (CRANBERG et al., 1956) and the energy dependent crosssection of the present data and BUTLER and SANTRY’S (1967) in the energy region where the cross-section was not measured in the present experiment. The average cross-section has become to be 176 mb. The average cross-section for this reaction was measured with a fission plate of 90 per cent enriched uranium installed at the thermal neutron facility of the Kyoto University Reactor. The fast neutron flux monitored with the 5sNi(n,p)58Co, 24Mg(n, p)24Na and 27Al(n, a)24Na reactions agreed with each other within 2-3 per cent in error (KIMURA et al., 1971). The present measured average cross-section, which agreed with the previous works except FABRY’S (1967) within the limits of error as TABLE 3.--COMPARISON OF FISSIONAVERAGECROSS-SECTIONS FOR THE “%(n, “‘“%I REACIION
Cross-section tmb)
?I’)
Reference
177 f 10 171*5 177 5 6 174
Present work, measured with a fission plate Present work, calculated with the energy dependent cross-section and the Maxwellian fission spectrum KIMURA et al. (1969) KANDA et al. (1971) BRESESTIet al. (1970) SIMONSand MCELROY (1970)
200 *
FABRY
175 i 6 176
10
(1967)
shown in Table 3, agreed satisfactorily with the above calculated average crosssection. This fact would suggest the propriety of the results of the energy dependent In reaction, assuming the Maxwellian form as cross-section for the lr51n(n, n’)115m the 235Ufission neutron spectrum. By monitoring the fast neutron flux with the proton recoil counters, the measurement of the cross-section for the li51n(n, n ’) 115mInreaction has been carried out successfully with a little systematic error. This method is applicable to other crosssection measurements. Acknowledgments-The authors wish to express their sincere thanks to Prof. T. SHIBATA of Kyoto University for his invaluable guidance and encouragement. Thanks are also due to Messrs. C. The authors KOBAYASHI and S. KANDA of JAERI for the operation of the van de Graaff accelerator. are much indebted to the staff members of the Nuclear Data Laboratory at JAERI and of CCDN for providing us the UKNDL-70 available for this study. REFERENCES BRESIXSTI A. M., BRESESTIM., ROTA A., RYDIN R. BROLLEY J. E., JR. and FOWLER J. L. (1960) Fast
A. and LESCA L. (1970) Nuci. Sci. Eng 40, 331. Neutron Physics, part I, p. 73. Interscience, New
York. BUTLER J. P. and SANTRYD. C. (1967) B&I. Am. Phys. Sot. 12,547. Cited by BRESESTIet CRANBERG L. et al. (1956) Phys. Rev. 103,662. FABRY D. (1967) Nukleonik 10, 280. GoTon H., YAGI H. and KOBAYASHI K. (1972) Nucl. Instrum. Methods, 100,473. GOTOH H. and YAGI H. (1972) ibid, 101,395.
al. (1970).
Measurement for the llSIn(n, n’)l15mIn reaction
145
GOTOI~ H., YAGI H. and HARAYAMA Y. (1973) ibid, 110. GOTOH H., YAGI H., KIMURA I. and KOBAYASHIK., to be published. GRENCH H. A. and MENLOVEH. 0. (1968) Phys. Reu. 165, 1298. HEERTJEI., NAGEL W. and ATEN A. H. W., JR. (1964) Physica 30, 775. KANDA K. et al. (1971) Ann. Rep. KURRI 4,94. KIMURA. I., KOBAYASHIK. and SHIBATAT. (1969) J. Nucl. Sci. Technol. 6,485. KIMURA I., KOBAYASH~K. and SHIBATAT. (1971) J. Nucl. Sci. Technol. 8,59. LEDERER,C. M., HOLLANDER, J. M. and PERLMAN, 1. (1967) Table of Isotopes, 6th edn. J. Wiley, New York. MARTIN H., DIVEN V. and TASCHEKR. F. (1954) Phys. Rev. 93, 199. MENLOVEH. O., COOP K. L., GRENCH H. A. and SHER R. (1967) Phys. Reo. 163,1308. PAUW H. and ATEN A. H. W., JR. (1971) J. nucl. Energy 25,459. SIMONSR. L. and MCELROY W. N. (1970) BNWL-1312. United Kingdom Nuclear Data Library-70.