EGGER, CLAUDINE

GUNTEN, H. R. VON

PKUTS, H . S.

SCHMID, A.

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Radiochimica Acta 21, 200—202 (1974) © by Akademische Verlagsgesellschaft, Frankfurt am Main 1974 Absolute Yields of "Mo in the Thermal Neutron-Induced Fission of 288U and 289Pu By CLAUDINE E G G E R + , H . R. VON GUNTEN+*, A. SCHMID* and H . S. PKUTS*, + Anorganisch-Chemisches Institut, Universität Bern, CH-3000 Bern, Switzerland and *Eidg. Institut für Reaktorforschung, CH-6303 Wiirenlingen, Switzerland (Received June 5, 1974) Summary Absolute yields of "Mo were redetermined in the thermal neutron-induced fission o f m ü and ^ P u . (4.75 ± 0.11)% and (6.22 ± 0.14)% were obtained, respectively, for the yields of 233U and ^»Pu. Zusammenfassung Die absoluten Ausbeuten von "Mo wurden bei der thermischen Neutronenspaltung von m U und 239Pu neu bestimmt. Es wurden die folgenden Werte erhalten: ^ U : (4,75 ± 0,11)%; ¡»»Pu: (6,22 ± 0,14)%. Résumé La production du "Mo dans la fission du a í U et du 239Pu par les neutrons thermiques a été redeterminée. Les valeurs suivantes ont été trouvées: a 3U:(4,75 ± 0,11)% et ^»Pu: (6,22 ± 0,14)'%. Molybdenum-99 is an important standard nuclide for the determination of fission yields. Whereas general agreement has been reached for its yield in the thermal neutron fission of 23BU [1-7], there exist still large dis-crepancies between different measurements for 233U and especially for 239Pu [8-15]. The variations in the experimental values are of course reflected in the eva-luations of fission yields which recommend different "best" values [1-6]. An attempt for a reliable redeter-mination of the absolute fission yields of "Mo in the thermal neutron-induced fission of 233U and 239Pu seemed justified. Our absolute method was successfully used for the determination of "Mo and 139Ba in the thermal neutron-induced fission of 236U, and was described in detail in an earlier publication [7], Sample preparation, irradiation, fission counting and chemical separation for the 233U and 239Pu were performed similar to the measurements for 236U fission. The isolated molybde-num samples were counted on calibrated Nal(Tl)-, Ge(Li)-, and proportional counters. The calibration was performed with two standard solutions of "Mo from the Radiochemical Centre Amersham (England). Furthermore, the Ge(Li)-detector (resolution 1.95 keV for 1332 keV) was also calibrated with other standard nuclides from the IAEA, Vienna and from the Radio-chemical Centre Amersham. For the measurements on the Nal (TI)-detector the area under the 140 keV photo-peak of " m T c was calculated after reaching transient equilibrium with "Mo. For the measurements on the Ge(Li)-detector the gamma-lines a t 140.5 keV (99mTc) and 181.1 keV were used, with intensivities of (89.6 ± 0.5)°/0 and (6.7 ± 0.2)% [16], respectively. These abundances include corrections for the "Mo— 99mTc equilibrium and for conversion electrons. Cor-rections for self absorption were made for the propor-tional counter. The decay of the molybdenum samples was followed on all three detection systems in order to check for radiochemical purity. The results of the determinations of the fission yield of "Mo are shown in Tables 1 and 2. Ten determina-tions were performed for 233U and nine for 239Pu. The fission rate Rf in the tables includes a correction for counting efficiency and for counting losses. Rf is multiplied by the saturation factor (1 — e~Ai). A half-life of 66.7 hrs [17] was used for "Mo. The irradiation times t were of the order of 70 to 80 hrs. The activities in Tables 1 and 2 are corrected for chemical yield, detector efficiencies and decay properties of "Mo. If the measurements were performed on several detection systems mean values of the different determinations were used to compute the activity of the samples. The statistical error in the fission counting, including corrections for efficiency and coincidence losses is believed to be much smaller than ±l° /o · The neutron 1. S. KATCOFF, Nucleonics 18, No. 11, 201 (1960). 2. I. F. CROALL, AERE-R-5086 (1967). 3. E. A. C. CROUCH, AERE-R-7209 (1973). 4. M. E . MEEK a n d B. F . RIDER, N E D O - 1 2 1 5 4 (1972). 5. M. LAMMER a n d 0 . J . EDER, Proc. I A E A Conf. on Nuclear Data in Science and Technology, Vol. 1, 505, IAEA Vienna (1973). 6. W. H. WALKER, Preprint of Review Paper 11a, IAEA Panel on Fission Product Nuclear Data, Bologna (1973). 7. H . R . VON GTTNTEN and H . HERMANN, Radiochim. Acta 8, 112 (1967). 8. E . P . STEINBERG a n d L. E . GLENDENIN, Proc. o f 1st Inter-national Conf. on the Peaceful Uses of Atomic Energy, Vol. 7,3, United Nations, New York 1956. 9. G. P . FORD a n d J . S. GILMORE, LA-1997 (1956). 10. D . A. MARSDEN and L. Y AFFÉ, Can. J . Chem. 43 , 249 (1965). 11. H . R . FICKEL and R . H . TOMLINSON, Can. J . P h y s . 87, 916 (1959). 12. L. J. KIRBY, HW-77609 (1963). 13. F . L. LISMAN, R. Μ. ABERNATHEY, W . J . MAECK a n d J . E . REIN, Nucl . Sci. Eng . 42 , 191 (1970). 14. A . V. SOROKINA, N . V . SKOVORODKIN, S. S. BUGORKOV, A. S. RRIVOKHATSKII a n d H. A. PETRZHAK, A t o m n a y a Energiya 81, 99 (1971). 15. H . C. JAIN a n d M. V. RAMANIAH, Radiochim. A c t a 19, 90 (1973). 16. M. J . MARTIN and P. H . BLICHERT-TOFT, Nuclear D a t a Tables, Section A, 8, 74 (1970). 17. W . SEELMANN-EGGEBERT, G. PFENNIG and H . MUNZEL, Nuklidkarte, 3. Auflage, Bundesminister für wissenschaftliche Forschung, Bonn 1968. Absolute Yields of "Mo in the Thermal Neutron-Induced Fission of ^ U and M8Pu 201 Table 1. Summary of the experiments for the determination of "Mo in the thermal neutron-induced fission of ^ U Experiment Fission rate Activity of "Mo at end of irradiation Fission yield R r { 1 disintegrations/min »/ 10 fissions/min Proportional Nal-detector Ge(Li)-detector counter 140 keV 181 keV 1 352'822 17'234 4.88 2 188'572 8'994 4.77 3 302'761 14'275 4.71 4 335'955 16'219 4.83 5 209'273 9'603 4.59 6 240'481 11'402 4.74 7 265'657 12'534 4.72 8 365'755 16'585 16'984 15'901 4.51 9 428'873 21'483 19'551 18'812 4.65 10 441Ό70 22'182 23Ό55 22'603 5.13 Average: (4.75 ±0 .11)%» » Including systematic error of 2%. flux was stable to < ± 2 % during all the measure-ments. The errors in the activity measurements are of the order of ±5°/ 0 , this including statistical errors in the β- and y-counting of the samples ( < ± 1 % ) , an estimated error in the detector efficiency calibration of about ± 4 % , estimated errors in the decay schemes ( i 2 %) and errors in the determination of the chemi-cal yield ( ± 2 % ) . As only the fission rate and the activ-ity were determined in our straight-forward method no errors due to measurements of the neutron flux, the amount of fissionable material and uncertainties in the fission cross-sections (variations with the neutron temperature) are introduced. Systematic errors could occur in the calibration of the detectors. However, they are expected to be small, since the results obtained with the different detection systems are in agreement and do not show a systematic deviation. Furthermore, an independent calibration with a set of different standard samples was performed for the Ge(Li)-detector. Systematic errors should cancel out in this Table 2. Summary of the experiments for the determination of "Mo in the thermal neutron-induced fission of ^Pu Ex- Fission peri- rate ment £ / · (1 — θ~Λί) fissions/min Activity of "Mo at end of irradiation disintegrations/min Fission yield o/ 10 Propor-tional Ge(Li)-detector counter 140 keV 181 keV 1 88'565 5'539 5'399 6.18 2 71'570 4'335 6.06 3 325'545 20' 988 22'039 20'311 6.49 4 325'952 20'610 20'483 19'170 6.16 5 173'212 11'617 11'218 8'912 6.11 6 227'563 15'711 15'568 14' 300 6.68 7 405'688 24'465 24'494 24'934 6.07 8 461Ό15 28Ό80 27'884 26' 760 5.98 9 248'882 15'730 15'597 15'628 6.29 Average: (6.22 ± 0.14)% calibration. We believe that the main source of systematic errors lies in uncertainties of the decay schemes. The use of additional D20-moderators in the neutron beam did not affect the measurements. There-fore, systematic errors due to non-thermality of the neutron spectrum ought to be small. The errors indicated for the average of the different determinations in Tables 1 and 2 are one standard deviation. They were calculated on the basis of the spread of the individual measurements and on the estimated systematic error in the decay schemes of 2 % . Table 3 shows a comparison of the published values for the fission yield of ββΜο in the fission of 2S3U and 239Pu. Our result of (4.75 ± 0 . 1 1 ) % for 233U is outside of one standard deviation of the mean of all the former Table 3. Published values'for the yields of "Mo in the thermal neutron-induced fission of 2a3U and ^ P u Authors °/o Fission yield of "Mo 233U 23»pu a) Measurements Steinberg and Glendenin [8] Ford and Gilmobe [9] Mabsden and Y a i t e [10] Fickel and Tomlinson [11] Kibby [12] T.TSMAU et al. [ 1 3 ] SOROKINA et al. [14] Jain and Ramaniah [15] This work b) Evaluations Katcof f [1] Cboall [2] Cbotjch [3] Meek and Rider [4] TíAmmutr and Edeb [5] Walker [6] Recommended value this work 5.1 4 .96 ± 0 .15 5 .16 ± 0 .07 4 .75 ± 0 .11 4 . 8 0 4 .96 ± 0 .25 5 .08 ± 0 .15 5 .02 ± 0 .10 4 .89 4 .99 ± 0 .10 6.1 6.02 ± 0.18 5.61 ± 0 .33 6.44» 6.10 6.59 ± 0 .18 6 .17 ± 0 .19 6 .82 ± 0 .15 6 .22 ± 0 . 1 4 6.10 5 .86 ± 0 .18 6 .20 ± 0 .19 6 .43 ± 0 .13 6 .33 6 .32 ± 0 . 2 0 4 . 9 0 ± 0 .08 6 .23 ± 0 .13 4 Including systematic error of 2%. 14 Kadioohimlca Acta, Band 21, Heft 3/4 a Interpolated value. 202 CLAUDINE EOOEE, H . R . TON GTINTEN, A . SCHMID a n d H . S . PBFYS experimental determinations (5.07 ± 0.06)°/0. A value of 4.80 °/0, which is often found in the literature was not used for this average, because it was already updated in the paper of S T E I N B E R G and G L E N D E N I N [8]. Our value for M9Pu of (6.22 ± 0.14) °/0 is in perfect agreement with the mean of the former experimental results of (6.23 ± 0.13)°/0. The recent publication of J A I N and R A M A N I A H [ 1 5 ] gives a value of 6.82°/0 for the yield of "Mo in the fission of 23ePu. This result was mainly based on a determination of "Mo relative to the yield in the fission of 235U. L Ä M M E R and E D E R [ 5 ] have recalculated the result of J A I N and R A M A N I A H , taking into account the influence of different neutron temperatures on the cross-sections used and show that the value of 6.82 °/0 can be in considerable error. Based on the mean of the earlier measurements and on our new experimental results we recommend values of (4.90 ± 0.08) °/0 and (6.23 ± 0.13)% for the yield of "Mo in the thermal neutron-induced fission of 233U and 239Pu, respectively. Acknowledgement The authors thank Drs. P. B A E R T S C H I and M . R A J A -GOPALAN for valuable discussions. The help of the DIORIT-reactor-team during the irradiations is ac-knowledged. The plutonium was supplied by the plutonium group of the hot laboratory at EIR. Par t of the work was supported by the Swiss National Science Foundation. 

Absolute Yields of 99Mo in the Thermal Neutron-Induced Fission of 288U and 289Pu

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