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Applicability of the statistical model for explaining the ratio of the (n, n′) to (n, 2n) cross sections

Применимость статистической модели для оБъяснения отношения поперечного сечения (n,n′) к сечению (n, 2n)

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Acta Physica Academiae Scientiarum Hungaricae

Abstract

The cross sections for the reactions Tl203(n, 2n)Tl202, Hg204(n, 2n)Hg203, Pb204(n, 2n)Pb203m Y89(n, n′)Y89m, Zr91(n, 2n)+Zr90(n, n′)Zr90m, Au197(n, n′)Au197m, and Pb208(n, 2n)+Pb207(n, n′)Pb207m have been measured at neutron energy 15±0,3 MeV, the results are 1680±210, 2230±300, 860±180, 594±130, 820±200, 280±64, and 1340±174 mb respectively. The cross section ratios of (n, n′) to (n, 2n) reactions are considerably higher than the values predicted by the statistical model. Features of (n, 2n) reactions are in agreement with evaporation mechanism, so the most probable explanation of these disagreements is the deviation of the actual spectrum from the evaporation spectrum supposed in the calculations. According to the present results, the competition of inelastic scattering can be important in the case of the heaviest elements too, so theWeisskopf assumptions are not applicable for nuclei with relatively low neutron excess.

For the interpretation of theN−Z dependence of (n, 2n) reactions it is necessary to investigate the mechanism of the competing (n, n′) processes.

Резюме

Измерялись поперечные сечения для реакций Tl203 (n, 2n) Tl202, Hg204 (n, 2n) Hg203 Pb204 (n, 2n) Pb203m Y89 (n, n′) Y89m, Zr91 (n, 2n)+Zr90 (n, n′) Zr90m, Au117 (n, n′) Au197m и Pb208 (n, 2n)+Pb207 (n, n′) P207m при нейтронной энергии 15±0,3 Мэв, для чего получены значения 1680±210, 2230±300, 860±180, 594±130, 820±200, 280±64 и 1340±174 мб соответственно. Отношение поперечных сечений реакций (n, n′) и (n, 2n) значительно больше полученного на основе статистической модели. Характер реакций (n, 2n) согласуется с механизмом испарения, таким образом более надежное объяснение данного несоответствия заключается в расхождении действительного спектра от спектра испарения, предположенного при вычислениях.

По отношению данных результатов можно установить, что конкуренция неупругого рассеяния может быть значительной и в случае более тяжелых элементов, и так предположения Вейскопфа неприменимы для ядер с относительно небольшим избытком нейтронов

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Authors and Affiliations

  1. Institute for Experimental Physics, Debrecen

    G. Pető

  2. Institute of Nuclear Research of the Hungarian Academy of Sciences, Debrecen

    P. Bornemisza-Pauspertl & J. Károlyi

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  1. G. Pető
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  2. P. Bornemisza-Pauspertl
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  3. J. Károlyi
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Pető, G., Bornemisza-Pauspertl, P. & Károlyi, J. Applicability of the statistical model for explaining the ratio of the (n, n′) to (n, 2n) cross sections. Acta Physica 25, 91–97 (1968). https://doi.org/10.1007/BF03159213

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