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Recent nuclear data measurement at the Khlopin Radium Institute
Fusion Engineering and Design 37 (1997) 151 158
ELSEVIER
Fusion Engineen.'ng and Design
Recent nuclear data measurement at the Khlopin Radium Institute A . A . F i l a t e n k o v *, S.V. C h u v a e v , V . A . J a k o v l e v , V . P . P o p i k Khlopin Radium Institute, 2nd Murinski Ave., 28, I94 021 Saint Petersburg, Russia
Abstract
Results of activation cross section measurement curried out at the Khlopin Radium Institute in the second half of 1995 is reported in the paper. The data on isomeric ratio for 58Ni(n, p)58Co, and cross sections tbr J38Ba(n, X)I37Cs, 238U(n, 2n)237U and 241Am(n, 2n)24°Am are presented. © 1997 Elsevier Science S.A.
Keywords: Khlopin Radium Institute; Isomeric ratio; Neutron energy
I. Introduction Cross sections of reactions leading to activation of materials in fusion reactors have been measured at the Khlopin Radium Institute for several years. Most intensively, the cross section of nuclear reactions were studied at neutron energy around 14 MeV. For this, a computerised set-up of high productivity was used that is designated to carry out a large number of measurements with stable quality. A very important practical support of our activity was done by international organisations (IAEA, ISTC) and foreign Institutions (JAERI) as well as individual scientists. At present, about 300 cross sections were measured for approximately 50 reactions. Some of them were measured in the frame of international collaboration under the auspices of the IAEA and the correspondent results have been presented at previous IAEA meetings [1-4]. * Corresponding author.
The present paper describes the latest experiments carried out at the Khlopin Radium Institute during several months after the last IAEA Meetings on 'Activation Cross Section for the Generation of Long-lived Radionuclides of Importance in Fusion Reactor Technology' and 'Selection of Evaluations for the F E N D L / A - 2 Activation Cross Section Library' that were held in St. Petersburg, at June 19-23, 1995.
2. Experimental method Briefly, the experimental method that is used at the Khlopin Radium Institute for activation cross section measurements is as follows. Samples are irradiated using the Neutron generator NG-400 that has a maximal accelerating voltage of 350 kV and current up to 1.2 mA. To diminish the influence of scattered neutrons on the results of measurement, thin-wall constructions are used for the target chamber and sample
0920-3796/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 0 - 3 7 9 6 ( 9 7 ) 0 0 0 3 8 - 0
152
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151 158
Air Jet
j ~
~ ~ A //~y,,~ ' ~
j
Seanmng scintillator monitor
r
X
Samples
AI
- -
B
10 em
Fig. l, Near target arrangement at sample irradiation.
holders (Fig. 1). Typically the thickness of walls is 0.3 0.5 mm. In most cases, the target is cooled by the air jet. The sample positions are rigidly fixed relative to the target. This, along with standardisation of procedures of induced activity measurement and data processing leads to good reproducibility of data and to the reduction of many random components of experimental errors. Neutron fluence is determined by means of niobium and aluminium foils using reference data on the 93Nb(n, 2n)92mNb and 27Al(n, ~)24Na cross sections. Neutron flux variation is measured continuously by means of a scintillation detector that rotates around the target. The detector is connected to a computer that analyses the data on angular and energy distributions of neutrons that are displayed on the screen and saved on the hard disk. The induced gamma activity is counted by means of the Ge(Li) detector of large volume that is placed in a thick shield. The detector has a high sensitivity that allows the measurement of gamma activities of the order of 0.01 Bk. The data treatment takes into account the common decay of two generations of induced activity. It includes two integrals taken on the time of
irradiation and gamma counting. All the data that are necessary for calculations are extracted automatically from the structured data bank that contains full information about irradiations and sample characteristics as well as the reference data. Necessary corrections are calculated in the same procedure. There are corrections for the detector efficiency dependence on the sample size and position, for self-absorbtion, gamma cascading, etc. Neutron energy distribution inside samples are calculated using real experimental conditions. These include the finite size of the beam and the sample, inhomogeneity of tritium distribution in the target, the change of energetical and angular parameters of the beam during slowing down in the target, etc. The calculations are very important when the samples are placed in the close vicinity of the target which is necessary to do at the measurement of small cross sections leading to the generation of long lived radioactive nuclides. It is worth noticing that working near the target we can obtain the data avoiding excessive activation of target chamber, accelerator elements, etc. Some results of neutron field calculations are shown in Fig. 2(a-f).
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151 158
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Fig. 2. (a) Neutron spectra calculated for different deuteron energies. (b) Neutron spectra calculated for the target-sample distance of 5 mm. (c) Neutron spectra calculated for different sample diameters. (d) Energy dependence of the 4n-solid angle integrated neutron flux. (e) Target-sample distance dependence of the averaged neutron energy at Ed = 220 keV. (f) Target-sample distance dependence of the full width at half of maximum (FWHM) of the neutron spectrum at E d = 220 keV.
A.A. Filatenkov et al./'Fusion Engineering and Design 37 (1997) 151-158
154
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(e) I s o m e r i c r a t i o Crrd(Cm+cg) o f t h e 58Ni(n,p)SSm.gCo r e a c t i o n in n e u t r o n e n e r g y i n t e r v a l 0 - 16 M e V . Fig. 3. (a) Screen c o p y o f t h e p r o g r a m c a l c u l a t i n g the best i s o m e r i c ratio. (b) O u t p u t d a t a o f the p r o g r a m c a l c u l a t i n g e r r o r o f the i s o m e r i c ratio. (c,d) I s o m e r i c r a t i o a t n e u t r o n e n e r g y a r o u n d 3 a n d 14 M e V . (e) I s o m e r i c r a t i o O-m/(O"m -~- O'g) o f the 58Ni(n, p)58m'gCo r e a c t i o n in the n e u t r o n e n e r g y interval 0-..16 M e V .
155
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151-158
3. Results
3.2. Measurement of the 138Ba(n, n'p -t-d)137Cs
3.1. Isomeric ratio measurement for the
This reaction takes second priority in the IAEA list. Since the reaction was expected to have a small cross section (1 mb or less), and it leads to generation of the long lived 137Cs (TI/2 = 30.7 years), the large neutron fluence was necessary to put into the samples. The interfering reaction 137Ba(n, p)137Cs, having a larger cross section, excluded the possibility of using the natural barium where the abundance of 137Ba is 11.3%. Two samples made of the enriched 138Ba were irradiated by neutron fluences of 2.3 x 1014 and 8.2 x 1013 n I cm 2. The average neutron energy was 14.73 and 13.73 MeV, respectively. The data obtained are shown in Fig. 4. They are 0.36 + 0.07 nab at En = 13.73 MeV and 1.21 _+ 0.14 mb at En = 14.73 MeV. The data agree better with the EAF-4 evaluation and are several times higher than other evaluations (ADL/3T and JENDL-3).
5SNi(n, p)SSm,xCo
As a rule, the isomeric ratios are studied less than the reaction cross sections. At the same time, they are important for a more detailed understanding of the mechanism of nuclei deexcitation. The 58Ni(n, p)58m'gCo reaction takes first priority and is one of the important dosimetrical reactions with a low threshold that could be used in a wide range of neutron energy. Measurement of isomeric ratios for reactions leading to generation of 58Co, requires the long measurement of decay curve of the 58gCo, because the 58mCo has no gamma rays that are convenient to observation. The 58mCo decays with the halflife 9.15 h by the converted isomeric transition to the 58gCo (T1/2 = 70.8 days) that emits the gamma rays of 810.8 keV with the probability of 99.4%. The isomeric ratio of the SSNi(n, p)58m'gCO reaction was measured in eight points of the neutron energy interval of 2.0-3.0 MeV and at six values of neutron energy in the interval of 13.4-14.9 MeV. The decay curves were measured using four or six gamma spectrometers from different laboratories of the Radium Institute simultaneously. For the decay curve calculation, the main algorithm used for the activation cross section calculation was slightly modified considering the isomeric ratio as the variable. The best isomeric ratio was deduced by the least squares method. The error of the isomeric ratio was determined using the Monte-Carlo method where all the input data were varied inside errors suggesting that they have normal distribution. The work of the programs is illustrated in Fig. 3(a,b). The isomeric ratio data obtained are presented in Fig. 3(c-e). They have errors 1 3% at neutron energy 14 MeV and 2 5% at neutron energy 3 MeV. At neutron energy around 14 MeV, the data agree rather well with the calculated ones taken from the A D L / 3 T library but at neutron energy around 3 MeV, the experimental data are about 20% lower. The local minimum predicted by calculations at neutron energy about 2.4 MeV could be seen in the experimental data.
3.3. Measurement of the 238U(n, 2n)237U cross section The measurement was carried out in the standard, well studied conditions for eight neutron energies of interval 13.4-14.9 MeV. The samples of the natural metallic uranium were used that were 14 mm in diameter and 0.5 mm in thickness. The neutron fluence was determined, as usually, 1.5 . . . . . . . .
I .........
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Fig. 4. 138Ba(n,d + n'p)137Cs cross section.
15.0
156
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151 158 After the irradiation, the fast radiochemical cleaning of the solution was carried out. To count the induced g a m m a activity the samples were placed in an additional lead container with wall thickness of 5 mm. The lead container suppressed entirely the power g a m m a radiation of the 241Am with energy of 59.5 keV but weakly attenuated the g a m m a rays with energy of 987.8 keV belonging to the 24°Am (T1/2 = 50.9 h). The results are presented in Fig. 6.
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Fig. 5. 238U(n,2n)237U cross section. using the data on the 93Nb(n, 2n)92mNb cross section. The amount of the 237U was determined using the measured intensity of the 208.0 keV g a m m a peak. Self-absorbtion was calculated taking into account finite size of the sample and detector. It was 32.5%. The correctness of calculations was checked by the 185.0 keV g a m m a peak intensity which was emitted by the 235U contained in the natural uranium. The measured cross sections are presented in Fig. 5. They agree within errors with the data of Y. Ikeda [5] and with the JENDL-3 evaluation.
3.5. Measurement o f possible content o f the 179Hi" in samples o f natural tungsten that were used at the Is2W(n, n'cOI78m2Hf cross section measuremen t On the 3rd R C M on 'activation cross section for the generation of long-lived radionuclides of importance in fusion reactor technology', it was noted that experimental results on the 182W(n,n'~)J78m2Hf cross section measurement carried out by three experimental groups participating in the C R P agree satisfactory within errors (rather large) but disagree drastically upon results of theoretical calculations. Experimental data are hundreds times higher. One of the possible reasons for this disagreement could be the small, of the order of 0.1%, i.e. 400 .........
3.4. Measurement o f the 241Am(n, 2n)24°Am cross section The reaction is important for the problem of transmutation. This cross section was never measured before. As the 241Am is one of the most dangerous for health elements, we could use only a very small amount of this material. In the experiment, the water solution of the americium nitrate was used that contained about 3 mg of 241Am. The solution was grouted into the container that had three hermetic shells. Neutron fluence was determined by means of two niobium foils attached to the front and back surfaces of the container. The distance between the foils was 5 mm. The measurements were made at three neutron energies.
.
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I ........
Z4~m(n, 2n)Z4°Am
300
.2
I .........
+
.....+
200
• ....
100 -0
Present data Konshin 95' -- JENDL-3.2 - ENDF/B-6
IIIII,,~,I,L,,,,,,,I,,,,
13.0
.....
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13.5 14.0 14.5 Neutron Energy (MeV)
15.0
Fig. 6. 24~Am(n,2n)24°Am cross section. The data for curves were taken from [6].
A.A. Filatenkov et al./ Fusion Engineering and Design 37 (1997) 151-158
contamination of the 179Hf in the tungsten samples. Though both measured and calculated values are very small (about 10 gb experiment and 0.024 gb calculation) and therefore this reaction cannot have essential meaning in the problem of production and disposal of radioactive waste, nevertheless, for the right understanding of physical processes taking place in nuclei at these neutron energies, it is important to find out the cause of such remarkable disagreement. To check for possible contamination of the hafnium in the tungsten samples that were used in the experiment at the Khlopin Radium Institute, one of the samples was irradiated by thermal neutrons in the investigation nuclear reactor of the St. Petersburg Institute of Nuclear Physics. After the neutron capture by hafnium isotopes, the l~Hf could be produced that has a half-life of 42.4 days and emits gamma rays with energies of 133.0, 345.5 and 482.0 keV and with yields of 42, 14.0 and 86.0%, respectively. On the other hand, the tungsten isotopes capturing neutrons do not lead to the production of a large background in gamma spectra if they are measured with the cooling time of about 1 month because the only tungsten isotope, the 18vW, that could emit intensive gamma rays has a half-life of 23.9 h. The investigation made by us revealed that the contamination of the 179Hf in the tungsten isotopes used for the ~82W(n,n'e)~VSm2Hf cross section measurement did not exceed 0.0001%. It means that he possible presence of the 179Hf could not give essential contribution to the cross section measured. However, it should be noted that the errors of the experimental cross section remain very large still (60%). To clarify the situation finally, it is necessary to repeat the very long gamma counting of the tungsten samples irradiated by 14 MeV neutrons 4 years ago.
4. Plans for the near future
Plans for the near future are related to the ISTC Project. They include various investigations in which the peculiarities of the method
157
used a the Khlopin Radium Institute could be profitably used. These investigations incorporate: (i) a low level of contamination of scattered neutrons. This is important for the measurement of reactions with a low threshold; (ii) calculation of the neutron spectra in real experimental conditions and the continuous control of them by the scanning neutron monitor. This is necessary for the rapidly changed cross section (reactions with high threshold) and for work in close vicinity of the target. Both are of importance for the 27A1 cross section measurement that should be measured by spring 1998; (iii) computerised gamma spectrometer with low background and high sensitivity. This allows the measurement of small gamma activities, e.g. the 13SBa(n, np)137Cs. The gamma counting of tungsten samples irradiated 4 years ago should be repeated next year to obtain with higher accuracy the Js2W(n,n'~)wsm2Hf cross section; (iv) high accuracy of the isomeric ratio measurement and realistic estimation of the errors. There is a number of such reactions foreseen in the project. For instance, the 59Co(n, 2n)58m'gCo will be studied in January 1996; and (v) specialists and equipment for work with radioactive targets. This enabled us to measure the 241Amtn, 2n)24°Am cross section. Next year we plan to carry out the 241Am(n, 3n)239Am cross section measurement as well.
Acknowledgements
We would like to thank Donald Smith and Yujiro Ikeda for their contribution to the work on the ISTC Project, in particular their participation in the experiment on the 241Am(n, 2n)24°Am cross section measurement. The collaboration with Professor Julius Csikai who initiated our measurement of the isomeric ratio of the 5SNi(n, p) 58m'gCO reaction in region around 3 MeV was very fruitful. Authors would also like to thank personnel of the Neutron Generator and other participants of the work from different laboratories of the Radium Institute.
158
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151-158
References [1] M.V. Blinov, A.A. Filatenkov, B.M. Shiryaev, S.V. Chuvaev, Measurements of Cross Sections of the Ag109(n, 2n)Ag-108 m, Eu-151(n, 2n)Eu-150 m and Eu-153(n, 2n)Eu-152 Reactions at Neutron Energy 14 MeV, Proceedings of the IAEA Consultant's Meeting, Argonne, USA, 11-12 September, 1989, INDC(NDS)232L, 1990, pp. 87-94. [2] M.V. Blinov, A.A. Filatenkov, S.V. Chuvaev, Measurements of Activation Cross Sections for Some Long-lived Nuclides Important in Fusion Reactor Technology, Proceedings of the IAEA Consultant's Meeting on Longlived Activation for Fusion, Vienna, Austria, 11 13 November, 1991, INDC(NDS)-263, 1992, pp. 143-154. [3] M.V. Blinov, S.V. Chuvaev, A.A. Filatenkov, B.P. Gavrilov, Measurements of Some Activation Cross Sec-
tions for Generation of Long-lived Nuclides, Proceedings of the 2nd Research Meeting of IAEI Consultant's on Long-lived Activation for Fusion, Del Mar, USA, 29-30 April 1993, INDC(NDS)-286, 1993, pp. 61-66. [4] M.V. Blinov, S.V. Chuvaev, A.A. Filatenkov, V.A. Jakovlev, A.A. Rimski-Korsakov, Measurement of Cross Sections of Some Reactions of Importance in Fusion Reactor Technology, Proceedings of the 3rd IAEA Research Consultant's Meeting on Long-lived Activation for Fusion, St. Petersburg, Russia, 19-23 June, 1995. [5] Chikara Konno, Yujiro Ikeda, Koji Oishi et al., Activation Cross Section Measurement at Neutron Energy from 13.3-14.9 MeV using the FNS Facility, JAERI, 1993, pp. 1329.
[6] V.A. Konshin, Consistent Calculation of Fast Neutron Induced Fission, (n, 2n) and (n, 3n) Cross Sections for 71 Isotopes of Th, Pa, U, Np, Pu, Am, Cm, Bk and Cf: JAERI-Research 95-010, 1995.
ELSEVIER
Fusion Engineen.'ng and Design
Recent nuclear data measurement at the Khlopin Radium Institute A . A . F i l a t e n k o v *, S.V. C h u v a e v , V . A . J a k o v l e v , V . P . P o p i k Khlopin Radium Institute, 2nd Murinski Ave., 28, I94 021 Saint Petersburg, Russia
Abstract
Results of activation cross section measurement curried out at the Khlopin Radium Institute in the second half of 1995 is reported in the paper. The data on isomeric ratio for 58Ni(n, p)58Co, and cross sections tbr J38Ba(n, X)I37Cs, 238U(n, 2n)237U and 241Am(n, 2n)24°Am are presented. © 1997 Elsevier Science S.A.
Keywords: Khlopin Radium Institute; Isomeric ratio; Neutron energy
I. Introduction Cross sections of reactions leading to activation of materials in fusion reactors have been measured at the Khlopin Radium Institute for several years. Most intensively, the cross section of nuclear reactions were studied at neutron energy around 14 MeV. For this, a computerised set-up of high productivity was used that is designated to carry out a large number of measurements with stable quality. A very important practical support of our activity was done by international organisations (IAEA, ISTC) and foreign Institutions (JAERI) as well as individual scientists. At present, about 300 cross sections were measured for approximately 50 reactions. Some of them were measured in the frame of international collaboration under the auspices of the IAEA and the correspondent results have been presented at previous IAEA meetings [1-4]. * Corresponding author.
The present paper describes the latest experiments carried out at the Khlopin Radium Institute during several months after the last IAEA Meetings on 'Activation Cross Section for the Generation of Long-lived Radionuclides of Importance in Fusion Reactor Technology' and 'Selection of Evaluations for the F E N D L / A - 2 Activation Cross Section Library' that were held in St. Petersburg, at June 19-23, 1995.
2. Experimental method Briefly, the experimental method that is used at the Khlopin Radium Institute for activation cross section measurements is as follows. Samples are irradiated using the Neutron generator NG-400 that has a maximal accelerating voltage of 350 kV and current up to 1.2 mA. To diminish the influence of scattered neutrons on the results of measurement, thin-wall constructions are used for the target chamber and sample
0920-3796/97/$17.00 © 1997 Elsevier Science S.A. All rights reserved. PII S 0 9 2 0 - 3 7 9 6 ( 9 7 ) 0 0 0 3 8 - 0
152
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151 158
Air Jet
j ~
~ ~ A //~y,,~ ' ~
j
Seanmng scintillator monitor
r
X
Samples
AI
- -
B
10 em
Fig. l, Near target arrangement at sample irradiation.
holders (Fig. 1). Typically the thickness of walls is 0.3 0.5 mm. In most cases, the target is cooled by the air jet. The sample positions are rigidly fixed relative to the target. This, along with standardisation of procedures of induced activity measurement and data processing leads to good reproducibility of data and to the reduction of many random components of experimental errors. Neutron fluence is determined by means of niobium and aluminium foils using reference data on the 93Nb(n, 2n)92mNb and 27Al(n, ~)24Na cross sections. Neutron flux variation is measured continuously by means of a scintillation detector that rotates around the target. The detector is connected to a computer that analyses the data on angular and energy distributions of neutrons that are displayed on the screen and saved on the hard disk. The induced gamma activity is counted by means of the Ge(Li) detector of large volume that is placed in a thick shield. The detector has a high sensitivity that allows the measurement of gamma activities of the order of 0.01 Bk. The data treatment takes into account the common decay of two generations of induced activity. It includes two integrals taken on the time of
irradiation and gamma counting. All the data that are necessary for calculations are extracted automatically from the structured data bank that contains full information about irradiations and sample characteristics as well as the reference data. Necessary corrections are calculated in the same procedure. There are corrections for the detector efficiency dependence on the sample size and position, for self-absorbtion, gamma cascading, etc. Neutron energy distribution inside samples are calculated using real experimental conditions. These include the finite size of the beam and the sample, inhomogeneity of tritium distribution in the target, the change of energetical and angular parameters of the beam during slowing down in the target, etc. The calculations are very important when the samples are placed in the close vicinity of the target which is necessary to do at the measurement of small cross sections leading to the generation of long lived radioactive nuclides. It is worth noticing that working near the target we can obtain the data avoiding excessive activation of target chamber, accelerator elements, etc. Some results of neutron field calculations are shown in Fig. 2(a-f).
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151 158
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&
250
180 °
~"
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', 140 14.5 15.0 energy, MeV
T(d,n)4He,
40
E,~ =
220
1 800
0 .... L''''1''''1''''1 .... I'''' 0.05 0.10 0.15 0.20 0.25 0.30 Oeuteron energy, MeV
' 1'5.5
keY
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/
m 25
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.
.
.
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.
.
.
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mm
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, .......
~
, , ,,,,,u
--
fl~st. = .30 mt m 0~
= 3 mm
--~_-14m
I T 1o-
.... i 1ooo
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the averaged neutron energy at Ed = 220 keV.
12-
90 °
..... J 1oo
(e) Target-sample distance dependence of
target-sample distance of 5 mnt. T(d,n)'He,
11o
Sample-Target
(b) Neutron spectra calculated for the
~
=
1.0
mm
0.8
52~
T
~0.6 6-
c Io
i
14.5
o
2~
........
ooj
(3°
> :~ 14.0
20"Z c "
m
I
Di,t. - 5 turn
7
T
055
(d) Energy dependence of the 4n-solid angle integrated neutron flux.
7
~
~ ....
50-
(a) Neutron spectra calculated for different deuteron energies•
?"
, ....
fli!l~
I
T
, ....
,¢
0.5
T
....
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153
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0.4
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(3 °
(3o
0.2 o .... t, 12.5 13.0
, 13.5 Neutron
, ,r, 14.0 14.5 15.0 15.5 energy, MeV
(c) Neutron spectra calculated for different sample diameters.
o.o
180o , .......
i ........ 10 Sample-Target
1 ........ F 100 10{30 Distance, mrn
(f)Target-smnple distance dependence of the full width at half of maxn'num (FWHM) of the neutron spectrum at Ea = 220 keV.
Fig. 2. (a) Neutron spectra calculated for different deuteron energies. (b) Neutron spectra calculated for the target-sample distance of 5 mm. (c) Neutron spectra calculated for different sample diameters. (d) Energy dependence of the 4n-solid angle integrated neutron flux. (e) Target-sample distance dependence of the averaged neutron energy at Ed = 220 keV. (f) Target-sample distance dependence of the full width at half of maximum (FWHM) of the neutron spectrum at E d = 220 keV.
A.A. Filatenkov et al./'Fusion Engineering and Design 37 (1997) 151-158
154
0.4
I
I
1.0S ~tllllple N:34 I
0.3
n I e
n0.5s I t Y
~0.2 o
l'o
io
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~o
Oa)
io
o.g 0.52
_ __1 0.54 0.55 0.56 0.5 Isomeric Ratio (b) O u t p u t d a t a o f t h e p r o g r a m calculating error of the isomeric ratio.
(a)Screen copy of the program calculating the best isomeric ratio.
0.4
.........
J
0.1
IR = 0.572(6)
I .........
0.7
0.53
.........
i .........
t .........
I ........
58Ni(n,p) 58m'g Co
o0.3
00.6
+÷+ ÷ ÷ ÷l,
o
+
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~0.5 Present d a t a E
0.1
2.0
i
- -
i
i
t
i
i
i
•
Present d a t a ',
IL - -
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i
i
2.5 N e u t r o n E n e r g y (MeV)
1
........
I .........
0.4 13.0
3.0
ADL-3
I .........
1
I ........
13.5 14.0 14.5 N e u t r o n E n e r g y (MeV)
15.0
(c)-(d) I s o m e r i c r a t i o a t n e u t r o n e n e r g y a r o u n d 3 a n d 14 M e V . 0.7,-~,
, i , , , i , , , i , , , i , , , i , , , i , , , i , , ,
0.6
58 Ni(n,p)SSm,g C o
0.5
o g 0.4
~
~
•
Present data
0.2 Z
ADL-3
0.1 0.0 . . 0.0
- - . .
I
2.0
,
,
,
I
4.0
,
,
,
I
,
,
,
I
,
,
,
FENDL/PA-I.I I
6.0 8.0 10.0 Neutron Energy (MeV)
,
,
,
I
12.0
,
,
,
I
14.0
,
,
,
16.0
(e) I s o m e r i c r a t i o Crrd(Cm+cg) o f t h e 58Ni(n,p)SSm.gCo r e a c t i o n in n e u t r o n e n e r g y i n t e r v a l 0 - 16 M e V . Fig. 3. (a) Screen c o p y o f t h e p r o g r a m c a l c u l a t i n g the best i s o m e r i c ratio. (b) O u t p u t d a t a o f the p r o g r a m c a l c u l a t i n g e r r o r o f the i s o m e r i c ratio. (c,d) I s o m e r i c r a t i o a t n e u t r o n e n e r g y a r o u n d 3 a n d 14 M e V . (e) I s o m e r i c r a t i o O-m/(O"m -~- O'g) o f the 58Ni(n, p)58m'gCo r e a c t i o n in the n e u t r o n e n e r g y interval 0-..16 M e V .
155
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151-158
3. Results
3.2. Measurement of the 138Ba(n, n'p -t-d)137Cs
3.1. Isomeric ratio measurement for the
This reaction takes second priority in the IAEA list. Since the reaction was expected to have a small cross section (1 mb or less), and it leads to generation of the long lived 137Cs (TI/2 = 30.7 years), the large neutron fluence was necessary to put into the samples. The interfering reaction 137Ba(n, p)137Cs, having a larger cross section, excluded the possibility of using the natural barium where the abundance of 137Ba is 11.3%. Two samples made of the enriched 138Ba were irradiated by neutron fluences of 2.3 x 1014 and 8.2 x 1013 n I cm 2. The average neutron energy was 14.73 and 13.73 MeV, respectively. The data obtained are shown in Fig. 4. They are 0.36 + 0.07 nab at En = 13.73 MeV and 1.21 _+ 0.14 mb at En = 14.73 MeV. The data agree better with the EAF-4 evaluation and are several times higher than other evaluations (ADL/3T and JENDL-3).
5SNi(n, p)SSm,xCo
As a rule, the isomeric ratios are studied less than the reaction cross sections. At the same time, they are important for a more detailed understanding of the mechanism of nuclei deexcitation. The 58Ni(n, p)58m'gCo reaction takes first priority and is one of the important dosimetrical reactions with a low threshold that could be used in a wide range of neutron energy. Measurement of isomeric ratios for reactions leading to generation of 58Co, requires the long measurement of decay curve of the 58gCo, because the 58mCo has no gamma rays that are convenient to observation. The 58mCo decays with the halflife 9.15 h by the converted isomeric transition to the 58gCo (T1/2 = 70.8 days) that emits the gamma rays of 810.8 keV with the probability of 99.4%. The isomeric ratio of the SSNi(n, p)58m'gCO reaction was measured in eight points of the neutron energy interval of 2.0-3.0 MeV and at six values of neutron energy in the interval of 13.4-14.9 MeV. The decay curves were measured using four or six gamma spectrometers from different laboratories of the Radium Institute simultaneously. For the decay curve calculation, the main algorithm used for the activation cross section calculation was slightly modified considering the isomeric ratio as the variable. The best isomeric ratio was deduced by the least squares method. The error of the isomeric ratio was determined using the Monte-Carlo method where all the input data were varied inside errors suggesting that they have normal distribution. The work of the programs is illustrated in Fig. 3(a,b). The isomeric ratio data obtained are presented in Fig. 3(c-e). They have errors 1 3% at neutron energy 14 MeV and 2 5% at neutron energy 3 MeV. At neutron energy around 14 MeV, the data agree rather well with the calculated ones taken from the A D L / 3 T library but at neutron energy around 3 MeV, the experimental data are about 20% lower. The local minimum predicted by calculations at neutron energy about 2.4 MeV could be seen in the experimental data.
3.3. Measurement of the 238U(n, 2n)237U cross section The measurement was carried out in the standard, well studied conditions for eight neutron energies of interval 13.4-14.9 MeV. The samples of the natural metallic uranium were used that were 14 mm in diameter and 0.5 mm in thickness. The neutron fluence was determined, as usually, 1.5 . . . . . . . .
I .........
t .........
I .........
138Ba(n ' x)137Cs •
~1.0
EAF-4PresentAdata DL-3
+
/" /" /
©
/
/~
/
/ /
20.5 c..) _
/ /
z
/
, j
0.0 13.0
i,
i~tlllll
J
ii,i,qlllllll~llrl
13.5 14.0 14.5 Neutron Energy (MeV)
Fig. 4. 138Ba(n,d + n'p)137Cs cross section.
15.0
156
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151 158 After the irradiation, the fast radiochemical cleaning of the solution was carried out. To count the induced g a m m a activity the samples were placed in an additional lead container with wall thickness of 5 mm. The lead container suppressed entirely the power g a m m a radiation of the 241Am with energy of 59.5 keV but weakly attenuated the g a m m a rays with energy of 987.8 keV belonging to the 24°Am (T1/2 = 50.9 h). The results are presented in Fig. 6.
1500~. . . . . . . . . I . . . . . . . . . [ . . . . . . . . . I . . . . . . . . . ~ l O O O ~ Z 3 82n)237U U ( n '
5oo o
i_ •
Present data
A
Y.Ikeda93
-
0
i
13.0
~r~,~,,I
-
ENDF/B-V1 JENDL-3 ........
,1 . . . . . . . . .
] .....
13.5 14.0 14.5 Neutron Energy (MeV)
,,~
15.0
Fig. 5. 238U(n,2n)237U cross section. using the data on the 93Nb(n, 2n)92mNb cross section. The amount of the 237U was determined using the measured intensity of the 208.0 keV g a m m a peak. Self-absorbtion was calculated taking into account finite size of the sample and detector. It was 32.5%. The correctness of calculations was checked by the 185.0 keV g a m m a peak intensity which was emitted by the 235U contained in the natural uranium. The measured cross sections are presented in Fig. 5. They agree within errors with the data of Y. Ikeda [5] and with the JENDL-3 evaluation.
3.5. Measurement o f possible content o f the 179Hi" in samples o f natural tungsten that were used at the Is2W(n, n'cOI78m2Hf cross section measuremen t On the 3rd R C M on 'activation cross section for the generation of long-lived radionuclides of importance in fusion reactor technology', it was noted that experimental results on the 182W(n,n'~)J78m2Hf cross section measurement carried out by three experimental groups participating in the C R P agree satisfactory within errors (rather large) but disagree drastically upon results of theoretical calculations. Experimental data are hundreds times higher. One of the possible reasons for this disagreement could be the small, of the order of 0.1%, i.e. 400 .........
3.4. Measurement o f the 241Am(n, 2n)24°Am cross section The reaction is important for the problem of transmutation. This cross section was never measured before. As the 241Am is one of the most dangerous for health elements, we could use only a very small amount of this material. In the experiment, the water solution of the americium nitrate was used that contained about 3 mg of 241Am. The solution was grouted into the container that had three hermetic shells. Neutron fluence was determined by means of two niobium foils attached to the front and back surfaces of the container. The distance between the foils was 5 mm. The measurements were made at three neutron energies.
.
I .........
I ........
Z4~m(n, 2n)Z4°Am
300
.2
I .........
+
.....+
200
• ....
100 -0
Present data Konshin 95' -- JENDL-3.2 - ENDF/B-6
IIIII,,~,I,L,,,,,,,I,,,,
13.0
.....
[lllllll~
13.5 14.0 14.5 Neutron Energy (MeV)
15.0
Fig. 6. 24~Am(n,2n)24°Am cross section. The data for curves were taken from [6].
A.A. Filatenkov et al./ Fusion Engineering and Design 37 (1997) 151-158
contamination of the 179Hf in the tungsten samples. Though both measured and calculated values are very small (about 10 gb experiment and 0.024 gb calculation) and therefore this reaction cannot have essential meaning in the problem of production and disposal of radioactive waste, nevertheless, for the right understanding of physical processes taking place in nuclei at these neutron energies, it is important to find out the cause of such remarkable disagreement. To check for possible contamination of the hafnium in the tungsten samples that were used in the experiment at the Khlopin Radium Institute, one of the samples was irradiated by thermal neutrons in the investigation nuclear reactor of the St. Petersburg Institute of Nuclear Physics. After the neutron capture by hafnium isotopes, the l~Hf could be produced that has a half-life of 42.4 days and emits gamma rays with energies of 133.0, 345.5 and 482.0 keV and with yields of 42, 14.0 and 86.0%, respectively. On the other hand, the tungsten isotopes capturing neutrons do not lead to the production of a large background in gamma spectra if they are measured with the cooling time of about 1 month because the only tungsten isotope, the 18vW, that could emit intensive gamma rays has a half-life of 23.9 h. The investigation made by us revealed that the contamination of the 179Hf in the tungsten isotopes used for the ~82W(n,n'e)~VSm2Hf cross section measurement did not exceed 0.0001%. It means that he possible presence of the 179Hf could not give essential contribution to the cross section measured. However, it should be noted that the errors of the experimental cross section remain very large still (60%). To clarify the situation finally, it is necessary to repeat the very long gamma counting of the tungsten samples irradiated by 14 MeV neutrons 4 years ago.
4. Plans for the near future
Plans for the near future are related to the ISTC Project. They include various investigations in which the peculiarities of the method
157
used a the Khlopin Radium Institute could be profitably used. These investigations incorporate: (i) a low level of contamination of scattered neutrons. This is important for the measurement of reactions with a low threshold; (ii) calculation of the neutron spectra in real experimental conditions and the continuous control of them by the scanning neutron monitor. This is necessary for the rapidly changed cross section (reactions with high threshold) and for work in close vicinity of the target. Both are of importance for the 27A1 cross section measurement that should be measured by spring 1998; (iii) computerised gamma spectrometer with low background and high sensitivity. This allows the measurement of small gamma activities, e.g. the 13SBa(n, np)137Cs. The gamma counting of tungsten samples irradiated 4 years ago should be repeated next year to obtain with higher accuracy the Js2W(n,n'~)wsm2Hf cross section; (iv) high accuracy of the isomeric ratio measurement and realistic estimation of the errors. There is a number of such reactions foreseen in the project. For instance, the 59Co(n, 2n)58m'gCo will be studied in January 1996; and (v) specialists and equipment for work with radioactive targets. This enabled us to measure the 241Amtn, 2n)24°Am cross section. Next year we plan to carry out the 241Am(n, 3n)239Am cross section measurement as well.
Acknowledgements
We would like to thank Donald Smith and Yujiro Ikeda for their contribution to the work on the ISTC Project, in particular their participation in the experiment on the 241Am(n, 2n)24°Am cross section measurement. The collaboration with Professor Julius Csikai who initiated our measurement of the isomeric ratio of the 5SNi(n, p) 58m'gCO reaction in region around 3 MeV was very fruitful. Authors would also like to thank personnel of the Neutron Generator and other participants of the work from different laboratories of the Radium Institute.
158
A.A. Filatenkov et al./Fusion Engineering and Design 37 (1997) 151-158
References [1] M.V. Blinov, A.A. Filatenkov, B.M. Shiryaev, S.V. Chuvaev, Measurements of Cross Sections of the Ag109(n, 2n)Ag-108 m, Eu-151(n, 2n)Eu-150 m and Eu-153(n, 2n)Eu-152 Reactions at Neutron Energy 14 MeV, Proceedings of the IAEA Consultant's Meeting, Argonne, USA, 11-12 September, 1989, INDC(NDS)232L, 1990, pp. 87-94. [2] M.V. Blinov, A.A. Filatenkov, S.V. Chuvaev, Measurements of Activation Cross Sections for Some Long-lived Nuclides Important in Fusion Reactor Technology, Proceedings of the IAEA Consultant's Meeting on Longlived Activation for Fusion, Vienna, Austria, 11 13 November, 1991, INDC(NDS)-263, 1992, pp. 143-154. [3] M.V. Blinov, S.V. Chuvaev, A.A. Filatenkov, B.P. Gavrilov, Measurements of Some Activation Cross Sec-
tions for Generation of Long-lived Nuclides, Proceedings of the 2nd Research Meeting of IAEI Consultant's on Long-lived Activation for Fusion, Del Mar, USA, 29-30 April 1993, INDC(NDS)-286, 1993, pp. 61-66. [4] M.V. Blinov, S.V. Chuvaev, A.A. Filatenkov, V.A. Jakovlev, A.A. Rimski-Korsakov, Measurement of Cross Sections of Some Reactions of Importance in Fusion Reactor Technology, Proceedings of the 3rd IAEA Research Consultant's Meeting on Long-lived Activation for Fusion, St. Petersburg, Russia, 19-23 June, 1995. [5] Chikara Konno, Yujiro Ikeda, Koji Oishi et al., Activation Cross Section Measurement at Neutron Energy from 13.3-14.9 MeV using the FNS Facility, JAERI, 1993, pp. 1329.
[6] V.A. Konshin, Consistent Calculation of Fast Neutron Induced Fission, (n, 2n) and (n, 3n) Cross Sections for 71 Isotopes of Th, Pa, U, Np, Pu, Am, Cm, Bk and Cf: JAERI-Research 95-010, 1995.