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Cobalt cross sections for 14 MeV neutrons
Ann. nucL Energy, Vol. 15, No. 12, pp. 561-565, 1988
0306-4549/88 $3.00+0.00 Pergamon Press plc
Printed in Great Britain.
C O B A L T CROSS SECTIONS F O R 14 MeV N E U T R O N S T. B. RYVES, P. KOLKOWSKIand S. M. JUDGE Division of Radiation Science and Acoustics, National Physical Laboratory, Teddington, Middlesex TW11 0LW, U.K. (Received 6 June 1988) A b s t r a c t - - 1 4 MeV cross sections for the reactions 59Co(n,2n) SSm+gCo,59Co(n,p) 59Fe and 59Co(n,~)56Mn were measured relative to the 56Fe(n,p)56Mn reaction employing the activation technique. Accuracies of about 1% were achieved for the (n,~) reaction and 2% for the others. The isomeric cross section ratio was measured for the 59Co(n,2n) reactions.
reactions-SqCo(n,2n)SSm+gCo, 59Co(n,p)SgFe, 59Co(n,~)56Mn,E,, = 14.3, 14.7 MeV; measured activation cross sections relative to 56Fe(n,p)56Mn. 59Co(n,2n) 58m'gCo,E, = 14.3 MeV; measured isomeric cross section ratio. Natural targets. Ge, NaI and 4r~fl detectors. Nuclear
1. INTRODUCTION Cross section data for reactions of d + T neutrons with energies between 14 and 15 MeV are needed for dosimetry, and for calculating the activation of materials to be used in future fusion reactors. For many reactions which are impossible to measure or predict from theory, a semiempirical approach is used, e.g. by Forrest (1986), based on the systematics of existing data for the different types of reaction, of which the (n,2n), (n,p) and (n,~) reactions are the most important. For this approach to succeed, additions to the existing pool of accurate data are needed. The main purpose of this work was to measure by the activation technique the ratio of the 59Co(n,~) to the 56Fe(n,p) cross sections to the highest possible accuracy (i.e. ~ 1%). This ratio was required as an essential part of the database for a simultaneous evaluation of cross sections at 14.7 MeV for 12 reactions being done by Ryves (1989). In the course of this work it was also possible to measure the 59Co(n,2n) and 59Co(n,p) cross sections with high accuracy, and also the isomeric cross section ratio for the 59Co(n,2n) reactions. The 59Co(n,2n)58~+gCo reaction has recently been recommended by the N E A N D C Standards Subcommittee, Young (1987), as a secondary standard for the measurement of neutron fluence. 2. EXPERIMENTAL DETAILS
2.1. Neutron irradiations
Neutrons with energies of about 14 MeV were produced using the NPL SAMES accelerator, employing
the d + T reaction. Activation samples consisted of uniform thin 25 mm dia discs of Co (thickness 80 and 100 mg cm -2) and of natural Fe (thickness 80 mg cm 2). The purities of metals were better than 99.99%. The experimental details have been described previously by Ryves and Kolkowski (1981), including the technique whereby many of the foil irradiations were performed in contact with the neutron-producing target to obtain the maximum neutron fluence rate. The neutron ftuences were determined using activation from the 56Fe(n, p)56Mn reaction, using a pair of Fe foils to sandwich each Co foil. The reference cross section was taken as (108.4 +_0.5) mbarn at 14.70 MeV from the recent evaluation by Ryves (1989). 2.2. Activity measurements
The activities induced in the Co foils were assayed with NaI(T1), 4r~fl proportional counter with 7 coincidence, and/or Ge or Ge(Li) detectors. The observed activities are shown in Table 1, together with the relevant nuclear data. In the case of the 59Co(n,e)56Mn reaction, using the 56Fe(n,p)56Mn reaction as a fluence monitor, the induced 56Mn activity is common to both, and hence the final accuracy in the cross section ratio depends almost entirely on the statistical accuracy, which is typically ~<1%. For the 4~fly coincidence-measurements the masses of the Fe and Co foils were closely matched, so that the small correction for y-ray interaction in the foils (which produces counts in the 4z/3 counter) cancels in the ratio. It was however necessary to make careful corrections for the 58gCo y-rays which also occur in the y-gate set for the 56Mn photopeak, 561
562
T. B. RYVES et al.
Table 1. Adopted nuclear data
~6Mn 5SmCo 58~Co 59Fe
Half-life
v-energy (keY)
Iv (%)
Reference
2.5785(2) h 9.15(10) h 70.82(3) days 44.496(7) days (44.51(2) days) ~
846 IT 810 1099 1291
98.87(3)
Huo et al. (1987) Peker (1984) Peker (1984) Andersson et al. (1983) adopted half-life
99.453(10) 56.5(15) 43.2(11)
aLagoutine et al. (1984).
and cause small contributions to the fl, y and coincidence channels, and which are partly time-dependent on the decay of the 58mCo parent. A small contribution from the 59Fe activity is also present. These corrections were readily achieved by analyzing the fl, y and coincidence channel decays of the Co samples, followed over several days in the 4~zflyequipment. For the ratio of the production of 58mCo and 58~Co from the Co(n,2n) reaction, it is necessary to analyze the shape of the complex decay over a period of several days, with subsequent measurements after several months to estimate the small 44 d half-life 59Fe component. To obtain maximum activity, the Co foils were irradiated in contact with the neutron-producing target, and the induced y-activity measured with two 7.5 x 7.5 cm NaI (Tl) crystals, which have a much higher y-detection efficiency than Ge(Li) devices. Since the ratio depends only on the shape of the decaying y-activity, it was unnecessary to know the neutron fluence and the absolute calibration of the NaI detectors.
3. RESULTS
Experimental results and uncertainties (one standard deviation) are given in Table 2. For the 59Co(n,p)59Fe and 59Co(n,2n)58m+gCo reactions at
14.3 MeV, each cross section was measured twice (as a ratio to the 56Fe(n,p)56Mn cross section) using a calibrated Ge detector. In addition, the ratio of the two cross sections was measured many times in a completely separate set of foil irradiations using a Ge(Li) detector, obtaining two different average values depending on the two principal y-rays (1099 and 1291keV) of 59Fe. The least-squares analysis including covariances of the results is given in the Appendix.
4. DISCUSSION
In Table 3 the results of some recently published measurements and evaluations are given, adjusted to a common energy of 14.7 MeV for the purpose of comparison with the present results.
4.1. 59Co(n, c~)S6Mn From Fig. 1, taken from the recent simultaneous evaluation of Ryves (1989), it can be seen that the present 4nfly coincidence measurement is about 2 standard deviations (i.e. 2%) above the evaluated mean of (31.6___0.3) mbarn. This measurement formed an important part of the database for the evaluation due to its very small uncertainty and hence large statistical weight. The independent Ge(Li)
Table 2 Results 1 a-uncertainties (%) Referenceb cross section
E,, (MeV)
na
Statistical
59Co(n,p) 59Co(n,2n)
14.67 14.3 14.3 14.3
4 2 ---
1.0 1.0 See Appendix
0.5 0.8 0.8 0.8
1.1 1.3 2.0 1.7
58mCO/58gCoC
14.3
4
14
--
14
Reaction 59Co(n, 0t)
aNO. of measurements. h56Fe(n,p) 56Mn, a - (I 12.9_+0.9) mbarn at 14.3 MeV, = (108.4+0.5) mbarn at 14.7 MeV. ~Production ratio for isomers "~mCo/~eCo from 59Co(n.2n) reaction.
Total
tr (mbarn)
Detector system
32.3 + 0.4 32.1 +0.4 51.9 -+ 1.1 753-+ 13 Isomeric ratio 2.1 +0.3
4rr/~V Ge Ge, Ge(Li) Ge, Ge(Li) NaI(T1)
C o b a l t cross sections for 14 MeV n e u t r o n s
563
Table 3. Recent literature results adjusted to 14.7 MeV" Reference
59C0 (n, ~) 56Mn a
59Co(n, p) 59Fe
59C0 (n, 2n) 58m +gCo
-32.8 + 1.7 30.2_+2.1 30.9_+ 1.2 -30.8 + 0.7 30.1 + 1.5 -32.3 _+0.4b
-48.9 _+3.4 -45.9_+4.05 -44.8 -+2.3 46.0-+2.3 46.7_+2.2 49.9+_ 1.1
699 _+27 c 783 _+55 754_+36 769+_38 ~ 807-+ 18~ 751 -+ 35 721 _+25 780_+8 799 + 16
-2.1 2.22+0.12 2.1 _+0.3
30.0+0.4 r 31.6 _+0.3
56.6_+9.2 --
747.7_+ 17.7 --
---
Decowski et al. (1968) Garlea et al. (1985) Ghorai et al. (1980) Ikeda et al. (1987) Lu et al. (1980) Meadows et al. (1987a) Pepelnik et al. (1984) Hasan et al. (1986) Present work
58mCO/ 588CO
1.9 -1.8_+0.1 --
Evaluations Evain et al. (1985) Ryves (1988)
Results: (a) averaged; (b) adjusted to standard reference cross sections; (c) adiusted to 14.70 MeV assuming a linear variation of cross section with energy between 14 and 15 MeV of 10.3% MeV ~ for '~Co(n,p) and + 15.3% MeV ~ for 59Co(n,2n) from model calculation of Hasan et al. (1986), see Ryves (1989) for 59Co(n,Gt). b4n[~7 result [the Ge(Li) result is 31.8 _+0.4 mbarn] Evaluated by Evain et al. (1985). d ~9Co(n,c~) cross sections used in the evaluation by Ryves (1989). ° Assume 93Nb(n ' 2n)92mNb reference cross section of 464 mbarn. f Evaluation by Meadows et al. (1987b).
measurement more
reported in this paper would agree much
closely with
tunately
not
the evaluation,
available
at that
but
time.
was
unfor-
Several other
experimentalists in the past have also taken advantage of the 59Co(n,~)/S6Fe(n,p) cross section ratio involving the common
product
not include some of the recent accurate measurements, is s i g n i f i c a n t l y l o w e r a t ( 3 0 , 2 + 0.4) m b a r n .
56Mn activity, to produce
4.2. S9Co(n,p) S9Fe
e x c e p t i o n a l l y a c c u r a t e v a l u e s f o r t h e r a t i o , e.g. A g r a -
O u r c r o s s s e c t i o n v a l u e is t h e m o s t p r e c i s e m e a s u r e ment to date, but considerably higher (by 7-11%)
w a l e t al. ( 1 9 8 4 ) . The evaluation
than the best previous results which carry errors of about 5%. However, it lies more than 10% below the
o f E v a i n e t al. ( 1 9 8 5 ) , w h i c h d o e s
El Present 4~'/~T m e a s u r e m e n t * Huang e / a t . [1981) • Roberston et at. (19751 AgrawaL e t a l . (1984) V Meadows e t o/.. ( 1 9 8 7 0 ) b. Achour e t a l . (1996) ¢ Ikeda et at. (1987l t~ Zupranska et al.. (1990) Santry and ButLer (1964l A PepeLnlk et oL. (1984) Bormann e t oL. (1961) I= Fischer e t or. (19861
oli-o 0
# I
,
I
--20
=
I
i
I
-10
J
I
,o
I 20
o I~ I~ e # $
GorLeo et al. 11985l Bormann e t o L . (1965) Ghorai et ol. (1980) Liskien and PouLsen (19651 G a b b a r d nnd Kern (1962l BLosser et at. (1958l
from the mean
59Co (n, a )56Mn
Fig. 1. G r a p h i c a l fit given by the e v a l u a t i o n of Ryves (1988).
564
T . B . RvvEs et al.
Evain et al. (1985) evaluation, which has a large error of 16%, but is based on old data, mostly pre-1970. 4.3. 59Co(n,2n) SSm+gCo O u r result agrees with the other most accurate values o f L u et al. (1980) a n d H a s a n et al. (1986), but is 7 % a b o v e the evaluation by E v a i n et al. (1985), a discrepancy in excess of 3 s t a n d a r d deviations. 4.4. ss"co/59gCo f r o m (n, 2n) reaction O u r result is in reasonable agreement with other measurements. The large uncertainty is p r o b a b l y due to the difficulty is estimating the 44 d c o m p o n e n t from 59Fe which interferes with the y-counting.
5. CONCLUSIONS The activation cross sections of several reactions of d + T n e u t r o n s with 59Co have been m e a s u r e d to a n improved accuracy. The ratio of the 59Co(n,~) to the 56Fe(n,p) cross section at 14.7 M e V was m e a s u r e d with particular precision (_+1%) a n d formed a n i m p o r t a n t part o f the d a t a b a s e for a recent simultaneous evaluation o f 12 cross sections by Ryves (1989). Both the 59Co(n,p) and 59Co(n,2n) cross sections were significantly higher t h a n most previous measurements, a n d suggest t h a t there is a need for several more m e a s u r e m e n t s of high precision to establish the values. Acknowledgements--We are grateful to A. Hooley for help with the data processing, and J. R. Winnington and A. Bennett for running the SAMES accelerator.
REFERENCES
Achour M., Ait Haddou A., Berrada M., Boufraqech A., Chiadli A., Chouak A., Reggoug A. and Viennot M. (1986) Report INDC (MOR)-003/GI/1NT(86)-I 1. Agrawal H. M., Zasadny K. R. and Knoll G. F. (1984) Trans Am. nucl. Soc. 117, 431.
Andersson P., Ekstr6m L. P. and Lyttkens J. (1983) Nucl. Data Sheets 39, 641. Blosser H. G., Goodman C. D. and Handley T. H. (1958) Phys. Rev. 110, 531. Bormann M., Dreyer F., Fretwurst E. and Schenka P. (1965) Report EANDC(E) 57 "U". Bormann M., Cierjacks S., Langkau R., Neuert H. and Pollehn H. (1961) J. Phys. Radium 22, 602. Decowski P., Grochulski W., Marcinkowski A., Siwek K., Sledzinska I. and Wilhelm Z. (1968) Nuel. Phys. All2, 513. Evain B. P., Smith D. L. and Lucchese P. (1985) Report ANL/NDM-89. Fischer R., Traxler G., Uhl M., Vonach H. and MaierKomor P. (1986) Phys. Rev. C34, 460. Forrest R. A. (1986) Report AERE 12419. Gabbard F. and Kern B. D. (1962) Phys Rev. 128, 1276. Garlea I., Garlea C., Dobrea D., Roth C., Rosu H. N. and Rapeanu S. (1985) Rev. Roum. Phys 30, 673. Ghorai S. K., Gaiser J. E. and Alford W. L. (1980) Ann. nucL Energy 7, 41. Hasan S. J., Pavlik A., Winkler G., Uhl M. and Kaba M. (1986) J. Phys G: Nuel. Phys 12, 397. Huang J. Z., Lu H., Li J. and Fan P. (1981) ChineseJ. nucl Phys 3, 59. Huo J., Hu D., Zhou C., Han X., Hu B. and Wu Y. (1987) Nucl. Data Sheets 51, 1. Ikeda Y., Konno C., Oishi K., Nakamura T., Miyade H., Kawade K., Yamamoto H. and Katoh T. (1987) JAERI Report, to be published. Lagoutine F., Coursol N. and Legrand J. (1984) Table de Radionucleides. CEA. Liskien H. and Paulsen A. (1965) J. nucl. Energy 19, 73. Lu H., Huang J., Fan P., Cui Y. and Zhao W. (1980) Chinese J. nucl. Phys 2, 286. Meadows J. W., Smith D. L., Bretscher M. M. and Cox S. A. (1987a) Ann. nucl. Energy 14, 489. Meadows J. W., Smith D. L. and Lawson R. D. (1987b) Ann. nucl. Energy 14, 603. Peker L. K. (1984) Nucl. Data Sheets 42, 457. Pepelnik R., Anders B., Fanger H.-U. and Michaelis W. (1984) Report INDC (GER)-27/LN + Special. Robertson J. C., Audric B. and Kolkowski P. (1973) J. nuel. Energy 27, 531. Ryves T. B. and Kolkowski P. (1981) J. Phys. G : Nuel Phys 7, 529. Ryves T. B. (1989) European Applied Research Report, to be published.
Table 4.59Co(n,p) and 59Co(n,2n) uncertainties 1-auncertainties (%) Measurement
Foil
59Co(n,p)
Statistical 59Co(n,2n)
1 2 3 4
Col0 ColO Col 1 Co 11
-3.01 -5.05
1.41 -1.49 -59Co(n, 2n)/SgCo(n,P) statistical
5 6
('05,' Co10
Parenthesis indicate covariant errors.
0.77 0.93
56Fe(n,p) 1.I0 1.10 1.20 1.20
59Co(n,p) -['0.35 4-{ 0.35 7 efficiency ratio {2.0 2.0
7 efficiency 59Co(n,2n) f053 / {. 0.53 --
S6Fe(n,p) [0.51 )0.51 ] 0.51 10.51
/~59Fe { 2.6 (1099 keY) 2.6 (1291 keV)
565
Cobalt cross sections for 14 MeV neutrons Table 5. Measurement data and error matrix Measurement 1 3 2 4 5 6
Cross section ratio
Result
59Co(n,2n)/56Fe(n,p) 59Co(n,2n)/56Fe(n,p) 59Co(n,p)/S6Fe(n,p) 59Co(n,p)/56Fe(n,p) "9Co(n,2n)/SqCo(n,p) ~Co(n,2n)/~gCo(n,p)
6.7920 6.5580 0.4747 0.4660 14.75 14.48
Error matrix (%) 1.934 0.736 1.212 0.510 2.050 0.510 1.304 3.264 0.619 5.225
0 0 0 0 3.370
0 0 0 0 0 3.410
Table 6. Results of least-squares analysis Cross section ratio
Result
59Co(n,2n)/56Fe(n,p) 6.710+1.49% 59Co(n,p)/56Fe(n,p) 0.4601+ 1.85%
Correlation
matrix
100 17
17 100
~(2/DF = 0.71
Santry D. C. and Butler J. P. (1964) Can. J. Phys. 42, 1030. Young P. G. (1987) Report NEANDC-U-242. Zupranska E., Rusek K., Turkiewicz J. and Zupranski P. (1980) Acta phys. Polonica B l l , 853. APPENDIX
Least-squares Analysis (~["Cross Section Ratios ~f 5~Co(n,2n) and 5~Co(n,p) to 5~Fe(n,p) at 14.3 M e V Both cross section ratios were measured twice by irra-
diating Co foils sandwiched between Fe monitor foils (measurements 1-4). In addition, the ratio of the 59Co(n, 2n) to 59Co(n,p) cross sections was measured directly by irradiating Co foils alone, and using a Ge(Li) detector to assay the two principal 7-rays (1099 and 1291 keV) of 59Fe and the 810 keV of sSgCo (measurements 5 and 6). The errors and correlations are listed in Table 4, from which the error matrix of Table 5 was constructed, and the least-squares analysis is given in Table 6. The value of)~2/DF ~ 0.71 indicated a good fit to the data.
0306-4549/88 $3.00+0.00 Pergamon Press plc
Printed in Great Britain.
C O B A L T CROSS SECTIONS F O R 14 MeV N E U T R O N S T. B. RYVES, P. KOLKOWSKIand S. M. JUDGE Division of Radiation Science and Acoustics, National Physical Laboratory, Teddington, Middlesex TW11 0LW, U.K. (Received 6 June 1988) A b s t r a c t - - 1 4 MeV cross sections for the reactions 59Co(n,2n) SSm+gCo,59Co(n,p) 59Fe and 59Co(n,~)56Mn were measured relative to the 56Fe(n,p)56Mn reaction employing the activation technique. Accuracies of about 1% were achieved for the (n,~) reaction and 2% for the others. The isomeric cross section ratio was measured for the 59Co(n,2n) reactions.
reactions-SqCo(n,2n)SSm+gCo, 59Co(n,p)SgFe, 59Co(n,~)56Mn,E,, = 14.3, 14.7 MeV; measured activation cross sections relative to 56Fe(n,p)56Mn. 59Co(n,2n) 58m'gCo,E, = 14.3 MeV; measured isomeric cross section ratio. Natural targets. Ge, NaI and 4r~fl detectors. Nuclear
1. INTRODUCTION Cross section data for reactions of d + T neutrons with energies between 14 and 15 MeV are needed for dosimetry, and for calculating the activation of materials to be used in future fusion reactors. For many reactions which are impossible to measure or predict from theory, a semiempirical approach is used, e.g. by Forrest (1986), based on the systematics of existing data for the different types of reaction, of which the (n,2n), (n,p) and (n,~) reactions are the most important. For this approach to succeed, additions to the existing pool of accurate data are needed. The main purpose of this work was to measure by the activation technique the ratio of the 59Co(n,~) to the 56Fe(n,p) cross sections to the highest possible accuracy (i.e. ~ 1%). This ratio was required as an essential part of the database for a simultaneous evaluation of cross sections at 14.7 MeV for 12 reactions being done by Ryves (1989). In the course of this work it was also possible to measure the 59Co(n,2n) and 59Co(n,p) cross sections with high accuracy, and also the isomeric cross section ratio for the 59Co(n,2n) reactions. The 59Co(n,2n)58~+gCo reaction has recently been recommended by the N E A N D C Standards Subcommittee, Young (1987), as a secondary standard for the measurement of neutron fluence. 2. EXPERIMENTAL DETAILS
2.1. Neutron irradiations
Neutrons with energies of about 14 MeV were produced using the NPL SAMES accelerator, employing
the d + T reaction. Activation samples consisted of uniform thin 25 mm dia discs of Co (thickness 80 and 100 mg cm -2) and of natural Fe (thickness 80 mg cm 2). The purities of metals were better than 99.99%. The experimental details have been described previously by Ryves and Kolkowski (1981), including the technique whereby many of the foil irradiations were performed in contact with the neutron-producing target to obtain the maximum neutron fluence rate. The neutron ftuences were determined using activation from the 56Fe(n, p)56Mn reaction, using a pair of Fe foils to sandwich each Co foil. The reference cross section was taken as (108.4 +_0.5) mbarn at 14.70 MeV from the recent evaluation by Ryves (1989). 2.2. Activity measurements
The activities induced in the Co foils were assayed with NaI(T1), 4r~fl proportional counter with 7 coincidence, and/or Ge or Ge(Li) detectors. The observed activities are shown in Table 1, together with the relevant nuclear data. In the case of the 59Co(n,e)56Mn reaction, using the 56Fe(n,p)56Mn reaction as a fluence monitor, the induced 56Mn activity is common to both, and hence the final accuracy in the cross section ratio depends almost entirely on the statistical accuracy, which is typically ~<1%. For the 4~fly coincidence-measurements the masses of the Fe and Co foils were closely matched, so that the small correction for y-ray interaction in the foils (which produces counts in the 4z/3 counter) cancels in the ratio. It was however necessary to make careful corrections for the 58gCo y-rays which also occur in the y-gate set for the 56Mn photopeak, 561
562
T. B. RYVES et al.
Table 1. Adopted nuclear data
~6Mn 5SmCo 58~Co 59Fe
Half-life
v-energy (keY)
Iv (%)
Reference
2.5785(2) h 9.15(10) h 70.82(3) days 44.496(7) days (44.51(2) days) ~
846 IT 810 1099 1291
98.87(3)
Huo et al. (1987) Peker (1984) Peker (1984) Andersson et al. (1983) adopted half-life
99.453(10) 56.5(15) 43.2(11)
aLagoutine et al. (1984).
and cause small contributions to the fl, y and coincidence channels, and which are partly time-dependent on the decay of the 58mCo parent. A small contribution from the 59Fe activity is also present. These corrections were readily achieved by analyzing the fl, y and coincidence channel decays of the Co samples, followed over several days in the 4~zflyequipment. For the ratio of the production of 58mCo and 58~Co from the Co(n,2n) reaction, it is necessary to analyze the shape of the complex decay over a period of several days, with subsequent measurements after several months to estimate the small 44 d half-life 59Fe component. To obtain maximum activity, the Co foils were irradiated in contact with the neutron-producing target, and the induced y-activity measured with two 7.5 x 7.5 cm NaI (Tl) crystals, which have a much higher y-detection efficiency than Ge(Li) devices. Since the ratio depends only on the shape of the decaying y-activity, it was unnecessary to know the neutron fluence and the absolute calibration of the NaI detectors.
3. RESULTS
Experimental results and uncertainties (one standard deviation) are given in Table 2. For the 59Co(n,p)59Fe and 59Co(n,2n)58m+gCo reactions at
14.3 MeV, each cross section was measured twice (as a ratio to the 56Fe(n,p)56Mn cross section) using a calibrated Ge detector. In addition, the ratio of the two cross sections was measured many times in a completely separate set of foil irradiations using a Ge(Li) detector, obtaining two different average values depending on the two principal y-rays (1099 and 1291keV) of 59Fe. The least-squares analysis including covariances of the results is given in the Appendix.
4. DISCUSSION
In Table 3 the results of some recently published measurements and evaluations are given, adjusted to a common energy of 14.7 MeV for the purpose of comparison with the present results.
4.1. 59Co(n, c~)S6Mn From Fig. 1, taken from the recent simultaneous evaluation of Ryves (1989), it can be seen that the present 4nfly coincidence measurement is about 2 standard deviations (i.e. 2%) above the evaluated mean of (31.6___0.3) mbarn. This measurement formed an important part of the database for the evaluation due to its very small uncertainty and hence large statistical weight. The independent Ge(Li)
Table 2 Results 1 a-uncertainties (%) Referenceb cross section
E,, (MeV)
na
Statistical
59Co(n,p) 59Co(n,2n)
14.67 14.3 14.3 14.3
4 2 ---
1.0 1.0 See Appendix
0.5 0.8 0.8 0.8
1.1 1.3 2.0 1.7
58mCO/58gCoC
14.3
4
14
--
14
Reaction 59Co(n, 0t)
aNO. of measurements. h56Fe(n,p) 56Mn, a - (I 12.9_+0.9) mbarn at 14.3 MeV, = (108.4+0.5) mbarn at 14.7 MeV. ~Production ratio for isomers "~mCo/~eCo from 59Co(n.2n) reaction.
Total
tr (mbarn)
Detector system
32.3 + 0.4 32.1 +0.4 51.9 -+ 1.1 753-+ 13 Isomeric ratio 2.1 +0.3
4rr/~V Ge Ge, Ge(Li) Ge, Ge(Li) NaI(T1)
C o b a l t cross sections for 14 MeV n e u t r o n s
563
Table 3. Recent literature results adjusted to 14.7 MeV" Reference
59C0 (n, ~) 56Mn a
59Co(n, p) 59Fe
59C0 (n, 2n) 58m +gCo
-32.8 + 1.7 30.2_+2.1 30.9_+ 1.2 -30.8 + 0.7 30.1 + 1.5 -32.3 _+0.4b
-48.9 _+3.4 -45.9_+4.05 -44.8 -+2.3 46.0-+2.3 46.7_+2.2 49.9+_ 1.1
699 _+27 c 783 _+55 754_+36 769+_38 ~ 807-+ 18~ 751 -+ 35 721 _+25 780_+8 799 + 16
-2.1 2.22+0.12 2.1 _+0.3
30.0+0.4 r 31.6 _+0.3
56.6_+9.2 --
747.7_+ 17.7 --
---
Decowski et al. (1968) Garlea et al. (1985) Ghorai et al. (1980) Ikeda et al. (1987) Lu et al. (1980) Meadows et al. (1987a) Pepelnik et al. (1984) Hasan et al. (1986) Present work
58mCO/ 588CO
1.9 -1.8_+0.1 --
Evaluations Evain et al. (1985) Ryves (1988)
Results: (a) averaged; (b) adjusted to standard reference cross sections; (c) adiusted to 14.70 MeV assuming a linear variation of cross section with energy between 14 and 15 MeV of 10.3% MeV ~ for '~Co(n,p) and + 15.3% MeV ~ for 59Co(n,2n) from model calculation of Hasan et al. (1986), see Ryves (1989) for 59Co(n,Gt). b4n[~7 result [the Ge(Li) result is 31.8 _+0.4 mbarn] Evaluated by Evain et al. (1985). d ~9Co(n,c~) cross sections used in the evaluation by Ryves (1989). ° Assume 93Nb(n ' 2n)92mNb reference cross section of 464 mbarn. f Evaluation by Meadows et al. (1987b).
measurement more
reported in this paper would agree much
closely with
tunately
not
the evaluation,
available
at that
but
time.
was
unfor-
Several other
experimentalists in the past have also taken advantage of the 59Co(n,~)/S6Fe(n,p) cross section ratio involving the common
product
not include some of the recent accurate measurements, is s i g n i f i c a n t l y l o w e r a t ( 3 0 , 2 + 0.4) m b a r n .
56Mn activity, to produce
4.2. S9Co(n,p) S9Fe
e x c e p t i o n a l l y a c c u r a t e v a l u e s f o r t h e r a t i o , e.g. A g r a -
O u r c r o s s s e c t i o n v a l u e is t h e m o s t p r e c i s e m e a s u r e ment to date, but considerably higher (by 7-11%)
w a l e t al. ( 1 9 8 4 ) . The evaluation
than the best previous results which carry errors of about 5%. However, it lies more than 10% below the
o f E v a i n e t al. ( 1 9 8 5 ) , w h i c h d o e s
El Present 4~'/~T m e a s u r e m e n t * Huang e / a t . [1981) • Roberston et at. (19751 AgrawaL e t a l . (1984) V Meadows e t o/.. ( 1 9 8 7 0 ) b. Achour e t a l . (1996) ¢ Ikeda et at. (1987l t~ Zupranska et al.. (1990) Santry and ButLer (1964l A PepeLnlk et oL. (1984) Bormann e t oL. (1961) I= Fischer e t or. (19861
oli-o 0
# I
,
I
--20
=
I
i
I
-10
J
I
,o
I 20
o I~ I~ e # $
GorLeo et al. 11985l Bormann e t o L . (1965) Ghorai et ol. (1980) Liskien and PouLsen (19651 G a b b a r d nnd Kern (1962l BLosser et at. (1958l
from the mean
59Co (n, a )56Mn
Fig. 1. G r a p h i c a l fit given by the e v a l u a t i o n of Ryves (1988).
564
T . B . RvvEs et al.
Evain et al. (1985) evaluation, which has a large error of 16%, but is based on old data, mostly pre-1970. 4.3. 59Co(n,2n) SSm+gCo O u r result agrees with the other most accurate values o f L u et al. (1980) a n d H a s a n et al. (1986), but is 7 % a b o v e the evaluation by E v a i n et al. (1985), a discrepancy in excess of 3 s t a n d a r d deviations. 4.4. ss"co/59gCo f r o m (n, 2n) reaction O u r result is in reasonable agreement with other measurements. The large uncertainty is p r o b a b l y due to the difficulty is estimating the 44 d c o m p o n e n t from 59Fe which interferes with the y-counting.
5. CONCLUSIONS The activation cross sections of several reactions of d + T n e u t r o n s with 59Co have been m e a s u r e d to a n improved accuracy. The ratio of the 59Co(n,~) to the 56Fe(n,p) cross section at 14.7 M e V was m e a s u r e d with particular precision (_+1%) a n d formed a n i m p o r t a n t part o f the d a t a b a s e for a recent simultaneous evaluation o f 12 cross sections by Ryves (1989). Both the 59Co(n,p) and 59Co(n,2n) cross sections were significantly higher t h a n most previous measurements, a n d suggest t h a t there is a need for several more m e a s u r e m e n t s of high precision to establish the values. Acknowledgements--We are grateful to A. Hooley for help with the data processing, and J. R. Winnington and A. Bennett for running the SAMES accelerator.
REFERENCES
Achour M., Ait Haddou A., Berrada M., Boufraqech A., Chiadli A., Chouak A., Reggoug A. and Viennot M. (1986) Report INDC (MOR)-003/GI/1NT(86)-I 1. Agrawal H. M., Zasadny K. R. and Knoll G. F. (1984) Trans Am. nucl. Soc. 117, 431.
Andersson P., Ekstr6m L. P. and Lyttkens J. (1983) Nucl. Data Sheets 39, 641. Blosser H. G., Goodman C. D. and Handley T. H. (1958) Phys. Rev. 110, 531. Bormann M., Dreyer F., Fretwurst E. and Schenka P. (1965) Report EANDC(E) 57 "U". Bormann M., Cierjacks S., Langkau R., Neuert H. and Pollehn H. (1961) J. Phys. Radium 22, 602. Decowski P., Grochulski W., Marcinkowski A., Siwek K., Sledzinska I. and Wilhelm Z. (1968) Nuel. Phys. All2, 513. Evain B. P., Smith D. L. and Lucchese P. (1985) Report ANL/NDM-89. Fischer R., Traxler G., Uhl M., Vonach H. and MaierKomor P. (1986) Phys. Rev. C34, 460. Forrest R. A. (1986) Report AERE 12419. Gabbard F. and Kern B. D. (1962) Phys Rev. 128, 1276. Garlea I., Garlea C., Dobrea D., Roth C., Rosu H. N. and Rapeanu S. (1985) Rev. Roum. Phys 30, 673. Ghorai S. K., Gaiser J. E. and Alford W. L. (1980) Ann. nucL Energy 7, 41. Hasan S. J., Pavlik A., Winkler G., Uhl M. and Kaba M. (1986) J. Phys G: Nuel. Phys 12, 397. Huang J. Z., Lu H., Li J. and Fan P. (1981) ChineseJ. nucl Phys 3, 59. Huo J., Hu D., Zhou C., Han X., Hu B. and Wu Y. (1987) Nucl. Data Sheets 51, 1. Ikeda Y., Konno C., Oishi K., Nakamura T., Miyade H., Kawade K., Yamamoto H. and Katoh T. (1987) JAERI Report, to be published. Lagoutine F., Coursol N. and Legrand J. (1984) Table de Radionucleides. CEA. Liskien H. and Paulsen A. (1965) J. nucl. Energy 19, 73. Lu H., Huang J., Fan P., Cui Y. and Zhao W. (1980) Chinese J. nucl. Phys 2, 286. Meadows J. W., Smith D. L., Bretscher M. M. and Cox S. A. (1987a) Ann. nucl. Energy 14, 489. Meadows J. W., Smith D. L. and Lawson R. D. (1987b) Ann. nucl. Energy 14, 603. Peker L. K. (1984) Nucl. Data Sheets 42, 457. Pepelnik R., Anders B., Fanger H.-U. and Michaelis W. (1984) Report INDC (GER)-27/LN + Special. Robertson J. C., Audric B. and Kolkowski P. (1973) J. nuel. Energy 27, 531. Ryves T. B. and Kolkowski P. (1981) J. Phys. G : Nuel Phys 7, 529. Ryves T. B. (1989) European Applied Research Report, to be published.
Table 4.59Co(n,p) and 59Co(n,2n) uncertainties 1-auncertainties (%) Measurement
Foil
59Co(n,p)
Statistical 59Co(n,2n)
1 2 3 4
Col0 ColO Col 1 Co 11
-3.01 -5.05
1.41 -1.49 -59Co(n, 2n)/SgCo(n,P) statistical
5 6
('05,' Co10
Parenthesis indicate covariant errors.
0.77 0.93
56Fe(n,p) 1.I0 1.10 1.20 1.20
59Co(n,p) -['0.35 4-{ 0.35 7 efficiency ratio {2.0 2.0
7 efficiency 59Co(n,2n) f053 / {. 0.53 --
S6Fe(n,p) [0.51 )0.51 ] 0.51 10.51
/~59Fe { 2.6 (1099 keY) 2.6 (1291 keV)
565
Cobalt cross sections for 14 MeV neutrons Table 5. Measurement data and error matrix Measurement 1 3 2 4 5 6
Cross section ratio
Result
59Co(n,2n)/56Fe(n,p) 59Co(n,2n)/56Fe(n,p) 59Co(n,p)/S6Fe(n,p) 59Co(n,p)/56Fe(n,p) "9Co(n,2n)/SqCo(n,p) ~Co(n,2n)/~gCo(n,p)
6.7920 6.5580 0.4747 0.4660 14.75 14.48
Error matrix (%) 1.934 0.736 1.212 0.510 2.050 0.510 1.304 3.264 0.619 5.225
0 0 0 0 3.370
0 0 0 0 0 3.410
Table 6. Results of least-squares analysis Cross section ratio
Result
59Co(n,2n)/56Fe(n,p) 6.710+1.49% 59Co(n,p)/56Fe(n,p) 0.4601+ 1.85%
Correlation
matrix
100 17
17 100
~(2/DF = 0.71
Santry D. C. and Butler J. P. (1964) Can. J. Phys. 42, 1030. Young P. G. (1987) Report NEANDC-U-242. Zupranska E., Rusek K., Turkiewicz J. and Zupranski P. (1980) Acta phys. Polonica B l l , 853. APPENDIX
Least-squares Analysis (~["Cross Section Ratios ~f 5~Co(n,2n) and 5~Co(n,p) to 5~Fe(n,p) at 14.3 M e V Both cross section ratios were measured twice by irra-
diating Co foils sandwiched between Fe monitor foils (measurements 1-4). In addition, the ratio of the 59Co(n, 2n) to 59Co(n,p) cross sections was measured directly by irradiating Co foils alone, and using a Ge(Li) detector to assay the two principal 7-rays (1099 and 1291 keV) of 59Fe and the 810 keV of sSgCo (measurements 5 and 6). The errors and correlations are listed in Table 4, from which the error matrix of Table 5 was constructed, and the least-squares analysis is given in Table 6. The value of)~2/DF ~ 0.71 indicated a good fit to the data.