Experimental neutron-activation cross-section data in the vicinity of 14 MeV are evaluated for several reactions of fusion-related interest using a least-squares method. New experimental measurements are performed at 14.7 MeV for all of these considered reactions and for some commonly-used standard reactions as well. Comparison is made between measured and evaluated results

Cox, S. A.

Meadows, J. W.

Smith, D. L.

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ICEIVED BY. flStI APR 2 4 1 3 8 5The submitted manuscript has been authoredby > contractor of the U. S. Governmentunder contract No. W-31-109-ENG-38.Accordingly, the U. S. Government retains anonexclusive. royalty-Ire* license to publishor reproduce the published form of thiscontribution, or allow others to do so, forU. S. Government purposes.CONF-850507—1DE85 010295MEASUREMENT AND EVALUATION OF SELECTED i4-MEV NEUTRONCROSS SECTIONS FOR FUSIONJ. W. MEADOWS, D. L. SMITH AND S. A. COXArgonne National Laboratory, Argonne, Illinois, U.S.A.Abstract Experimental neutron-activation cross-section datain the vicinity of 14 MeV are evaluated for several reactionsof fusion-related interest using a least-squares method. Newexperimental measurements are performed at 14.7 MeV for all ofthese considered reactions and for some commonly-used standardreactions as well. Comparison is made between measured andevaluated results.INTRODUCTIONIt Is generally assumed that the first generation of fusion-energyreactors will be based upon the H-3(d,n)He-4 reaction. Thus, know-ledge of a variety of reaction cross sections for neutrons at thesource energy around 14 MeV is very important (e.g., Refs. 1 and 2).A large body of neutron-cross-section data at this energy has al-ready been accumulated owing to the widespread availability of 14-MeV neutron generators (e.g., Refs. 3 and 4). However, knowledge ofthe pertinent cross sections is often confounded by the existenceof large discrepancies between the various reported results. Theproblem, then, is how to best deal with this dilemma. It is ourbelief that a reasonable approach is to: i) compile all the reporteddata, ii) adjust these data for revisions in nuclear standards andconstants, where possible, iii) evaluate the adjusted results us-ing modern and relatively-consistent procedures, and iv) test theevaluated results with some careful new measurements. Completionof this program in a comprehensive manner represents a formidabletask, but one which appears to be feasible provided that severallaboratories equipped for this purpose address the issue and co-ordinate their efforts. Our laboratory has undertaken a modestprogram along this line, and the present paper reports on some ofour work to date. We have performed measurements for the twentyreactions listed in Fig. 1. We have also compiled data and eval-uated sixteen of these, but have relied on recent high-qualityevaluation results from the literature for the other four, asdiscussed below. A detailed report of our evaluation work appearsin Ref. 5 so the present discussion is brief. The present experi-mental values are preliminary ones. Final values will be publish-ed upon completion of this phase of our investigation.DISCLAIMERThis report was prepared as an account of work sponsored by an agency of theUnited States Government. Neither the United States Government nor any agencythereof, nor any of their employees, makes any warranty, express or implied, orassumes any legal liability or responsibility for the accuracy, completeness, or use-fulness of any information, apparatus, product, or process disclosed, or representsthat its use would not infringe privately owned rights. Reference herein to any spe-cific commercial product, process, or service by trade name, trademark, manufac-turer, or otherwise does not necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof.The views and opinions of authors expressed herein do not necessarily state orreflect those of the United States Government or any agency thereof.J.W. MEADOWS, D.L. SMITH AND S.A. COXEVALUATIONSOur evaluation procedure, as described in Ref. 5, follows closelythe approach indicated above. The compiled data were adjustedfor nuclear-constant revisions (e.g., Ref. 6), and our choices ofstandard values were based upon state-of-the-art evaluation effortswhich preceded our work (7,8 and 9). We were satisfied with exist-ing evaluations for four of the reactions in Fig. 1 and did not re-peat them (8 and 9). A least-squares method was used to accountfor varying uncertainties and for correlations between the standardsand nuclear constants. However, we have not attempted to evaluateall reactions simultaneously (e.g., as done in Ref. 8). Simulta-neous evaluation appears to us to be a rather impractical approachexcept for a few standards. Our evaluation procedure, as well asthose of Refs. 7 and 8, lead to uncertainty predictions for theevaluations, as given in Fig. 1. For comparison, we have alsoshown the results of unweighted averaging of our selected, adjustedevaluation data base.MEASUREMENTSThe cross-section measurements were performed at Argonne NationalLaboratory using a Texas Nuclear Generator Model No. 9400 operat-ing at 150 ± 10 kV. Titanium-tritide targets were employed. Itwas determined that the average neutron energy was 14.74 ± 0.02MeV and the resolution was 0.324 MeV (FWHM). A low-mass fissionchamber containing depleted uranium (U-238) was used as a neutron-fluence monitor. All the indicated activities were measured bygamma-ray counting with a germanium detector. The experimentalprocedures used are described in more detail in Refs. 10 and 11.The errors in the measured cross-section ratios appear to be inthe range 2 to 5%. The uncertainty in the ENDF/B-V U-238 neutron-fission cross-section standard is taken to be 4.8% (7), so thetotal error in the measured cross sections is in the range 5.2to 7%. The preliminary experimental results are plotted in Fig.1.DISCUSSIONReferring to Fig. 1, we first note that the unweighted-average val-ues are generally in reasonable agreement with the more-rigorously-evaluated results, considering the combined errors. Thus, once theselection of the data base has been made and adjustments applied,the results of the evaluation seem not to be excessively dependentupon the particular algorithm used in the evaluation. It would ap-pear, then, that the most crucial part of an evaluation procedurecenters upon the selection or rejection of the available experi-mental data, and the adjustments made to the reported values. TheJ . W . MEADOWS, D . L . SMITH AND S . A . COX0.1 0.9 1 1.1Fe-56(n,P»Vi-56 ( A )C O - 5 9 ( N . P ) F E - 5 9CO-S9(N,2H)CO-S8Cc-59(n,AiPHiOfti-56( B )(7O.«)(113.1)(27.2){294.8 3(223.1)(60.61)< 31.17)(15.89)(72.1)9)< 815.6)(87.8S)(107.2)(58.60)(7H7.7)t 30.17 )(38.8!)(20.46)(967.8)(165.4)(162,2)(( MX))(OSO X))(( ltX»(( 17X))(( WI)>((>50 X))(( UX))(( <ax»(O50X))(( 25X))(( 50 X»(OSO I))(( SX»((>50X»«>5DXM((>50X))(( <6X))(( 39X))«>50X))(( 21X)>H - M HtESCNT INC1GMTED AVEXAC£ KITH-1- STAMMKC DEVIATICNI I HEASURED VAUX m m EWOR• M M frESEXT HEIGHT.-D EVAUWTION WITH EWCR ( . . . ) EvAU»TO VAUUEF.v«J*TED VtUUE FKH A W n O ( ( . . . ) ) R M M B I L I T V OF OCCUtEICEKVIATIQN K l t C W EXPCKIKNT «M> EVMJWTI0MFIGURE 1 Comparison of measured and evaluated 14.7-MeV crosssections. Evaluated values other than those from thepresent work are: (A) Ref. 8, (B) Ref. 9.REPRODUCED FROMBEST AVAILABLE COPYJ.W. MEADOWS, D.L. SMITH AND S.A. COXuncertainties in the evaluations (including those from Refs. 8 and9) range from 0.6 to 17.22. In '-ur opinion, evaluation errorssmaller than 1 to 27. are probably too optimistic in view of thehigh probability for systematic errors at this level. Clearly,new measurements intended to reduce uncertainty to this level willhave to be very accurate in order to have any substantive impact.Fig. 1 shows that, with few exceptions, the results of all ofthe present measurements are reasonably consistent with the eval-uated results. This has been quantified by calculating probabili-ties for the observed deviations, assuming the evaluated results tobe correct. These probabilities are shown by ((...)) in Fig. 1.In all instances the deviations are smaller than two combined(measurement and evaluation) standard deviations. The consistencyis even better for the four best-known reactions, thereby provid-ing confidence in our measurement procedures.This work was supported by the U.S. Department of Energy.REFERENCES1. O.N. Jarvis, European Applied Research Reports-Nuclear Scienceand Technology, Vol. 3, Ncs. I and 2, 127-352 (1981).2. E.T. Cheng, D.R. Mathews and K.R. Schultz, GA-17324, GeneralAtomic Company (1983).3. CINDA-A (1935-1976), Vols. I and II-June 1S79, CINDA-83 (1977-1983)-May 1983, CINDA-83 Supplement-November 1983, and CINDA-84 (1982-1984)-May 1984, International Atomic Energy Agency,Vienna, Austria.4. Experimental Data File, CSISRS, National Nuclear Data Center,Brookhaven National Laboratory, Upton, N.Y., U.S.A.5. B.P. Evain, D.L. Smith and P. Lucchese, ANL/NDM-89, ArgonneNational Laboratory (1985).6. Table of the Isotopes, 7th Edition, ed. CM. Lederer and V.S.Shirley (John Wiley and Sons, Inc., New York, 1978).7. Evaluated Neutron Data File, ENDF/B-V, Summary Documentation,compiled by R. Kinsey, ENDF-201, 3rd Edition, Brookhaven Na-tional Laboratory (1979).8. G. Winkler and T.B. Ryves, Annals of Nuclear Energy, 10, 601(1983).9. G. Winkler, A. Pavlik, H. Vonach, A. Paulsen and H. Liskien,Nuclear Science for Technology, ed. K. Boeckhoff (D. ReidelPublishing Company, Dordrecht, Holland, 1983) p. 400.10. D.L. Smith, J.W. Meadows, M.M. Bretscher and S.A. Cox, ANL/NDM-87, Argonne National Laboratory (1984).11. J.W. Meadows and D.L. Smith, ANL/NDM-60, Argonne National Lab-oratoty (1984).12. Handbook of Physics and Chemistry, 41st Edition, ed. C. H.Hodgraan (Chemical Rubber Pub. Co., Cleveland, Ohio, 1959) p.210.

Measurement and evaluation of selected 14-MeV neutron cross sections for fusion

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Measurement and evaluation of selected 14-MeV neutron cross sections for fusion

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