Status of the evaluated excitation function for the neutron-dosimetry reaction 93Nb(n,n′)93mNb

Ann. nucL Energy, Vol. 19, No. 8, p. 477, 1992 Printed in Great Britain. All rights reserved

LETTER

0306-4549/92 $5.00+0.00 Copyright © 1992 Pergamon Press Ltd

TO THE

EDITORS

STATUS OF THE EVALUATED EXCITATION FUNCTION FOR THE NEUTRON-DOSIMETRY REACTION 93Nb(n,n')93mNb This letter refers to the article "The determination of the 93Nb(n,n')93rnNb cross-section in the neutron energy range 145 MeV" by K. Randle, D. B. Gayther, M. F. Murphy and C. A. Uttley [Ann. Nucl. Energy 18, 677 (1991)]. The reaction 93Nb(n,n')93mNb is of interest as a long-term activation monitor in reactor dosimetry. In recent years considerable efforts, both in the experimental and the theoretical area, have been concentrated on establishing the excitation function of this reaction. Since no activation measurements of the cross-section of this reaction existed before 1981, its first evaluation at the IRK (Strohmaier et al., 1980) was based on nuclear model calculations only. These results were later included in the IRDF-82 (Cullen et al., 1982). The calculated cross-sections for the 93Nb(n,n')93mNb reaction used then were essentially the same as those published in the frame of a more comprehensive calculational study of neutron-induced reactions on 93Nb (Strohmaier, 1982). Since 1980, a number of activation measurements of the 93Nb(n,n')93~Nb cross-section have been carried out, namely at 14.3 MeV (Ryves and Kolkowski, 1981) and in the energy range 1-8 MeV (Gayther et al., 1986-1988 ; Wagner et al., 1988a,b). Making use of this extended data base, a new excitation function for this reaction was evaluated in 1989 (Strohmaier, 1989) by means of statistical model calculations, together with those for other neutron-induced reactions on 93Nb up to 20 MeV incident neutron energy. In the 1989 publication, the results for the 93Nb(n,n')93mNb excitation function of the previous evaluation (Strohmaier et al., 1980; Strohmaier, 1982) were declared obsolete due to the use of erratic branching ratios for two levels of 93Nb, which explains the unrealistic shape of the cross-section in the incident energy range between 2 and 4 MeV. Apart from the elimination of this computational error, the level scheme used in the 1989 calculations was that of Demanins et al. (1988) rather than that of Van Heerden et al. (1973) used in the older evaluation (Strohmaier et al., 1980; Strohmaier, 1982). In the summary publication (Randle et al., 1991) on their activation measurements o f the 93Nb(n,n')93mNb cross-section in the neutron energy range 145 MeV, Gayther's group presents a comparison of their results with the superseded evaluation o f the 93Nb(n,n')93mNb cross-section contained in IRDF-82 and hence going back to the I R K evaluation (Strohmaier et al., 1980). The successor of this evaluation, the IRDF-90 (Wagner et al., 1990) is mentioned as being in better agreement with the data of Randle and coworkers (Randle et al., 1991). This is clear since the IRDF-90 evalu-

ation (Wagner et al., 1990) was based entirely on experimental data for 93Nb(n,n')93mNb in the energy range 0.736.0 MeV, among them those by Randle et al. according to their previous publications (Gayther et al., 1986-1988). Also, the revised calculations (Strohmaier, 1989) which provide the recommended cross-sections of IRDF-90 in the energy range below 0.73 MeV and above 6.0 MeV incident neutron energy, are in reasonable agreement with the results of the British group as these represented part of the data base for the validation of the parameters for the model calculations. The use of the more recent calculations (Strohmaier, 1989) as well as of the data by Gayther and collaborators (Gayther et al., 1986-1988) for the IRDF-90 evaluation are described in the corresponding paper (Wagner et al., 1990).

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REFERENCES

Cullen D. E., Kocherov N. and McLaulin P. M. (Eds) (1982) Report IAEA-NDS-41/R, IAEA, Vienna. Demanins F., Abbondano U. and Raicich F. (1988) Report INFN(REP)-014/88, Istituto Nazionale de Legnaro (Padova), Italy (Annual Report 1987). Gayther D. B. et al. (1986) In Nuclear Data f o r Basic and Applied Science ; Proc. Int. Conf., Santa F~, New Mexico, M a y 13-17, 1985 (P. Young et al., Eds), p. 521. Gordon & Breach, New York. Gayther D. B. et al. (1987) Report AERE-R-12612, U K A E A , Harwell. Gayther D. B. et al. (1988) In Nuclear Data f o r Science and Technology ; Proc. Int. Conf. Mito, Japan, M a y 30-June 3, 1988 (S. Igarasi, Ed.), p. 1057. Saikon, Tokyo. Randle K. et al. (1991) Ann. Nucl. Energy 18, 677. Ryves T. B. and Kolkowski P. (1981) J. Phys. GT, 52. Strohmaier B., Tagesen S. and Vonach H. (1980) Phys. Data 13(2), 130. Strohmaier B. (1982) Ann. Nucl. Energy 9, 397. Strohmaier B. (1989) Ann. Nucl. Energy 16, 461. Van Heerden I. J., McMurray W. R. and Saayman R. (1973) Z. Phys. 260, 9. Wagner M. et al. (1988a) Ann. Nucl. Energy 15, 363. Wagner M. et al. (1988b) In Nuclear Data f o r Science and Technology ; Proc. lnt. Conf. Mito, Japan, M a y 30-June 3, 1988 (S. Igarasi, Ed.), p. 1049. Saikon, Tokyo. Wagner M. et al. (1990) Phys. Data 13(5), 135. Institut fiir Radiumforschung und Kernphysik der Universitdt Wien (IRK) Boltzmanngasse 3, A-1090 Vienna Austria

B. STROHMAIER