Reanalyses of certain nuclear evaporation spectra exhibiting anomalies

Ali, Shahida Parvin (1971) Reanalyses of certain nuclear evaporation spectra exhibiting anomalies. Masters thesis, Memorial University of Newfoundland.

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Abstract

The situation concerning the 'anomalous dependence of the shape of level density plots of nuclear evaporation spectra on the energy of the incident particle' is rather confusing. Some authors have reported observing this anomaly while others have claimed that their results did not indicate any anomaly. It is, however, not always clear if different incident energy spectra have been compared for the same excitation energy of the residual nucleus, as they should be for establishing the existence (or non-existence) of this type of anomaly. Moreover in some (n,α) and (p,n) spectra it has been reported that different choices of the inverse cross section σc lead to different conclusions concerning this anomaly. No thorough study of evaporation spectra with protons as emitted particles has been reported. A thorough examination of published (n,p) and (α,p) spectra was undertaken by us and those sets of spectra which were available for different incident energies were reanalyzed (using the method of least squares for straight line fitting) by us for the constant temperature model as well as for the Fermi gas model with n = 2, 1.67, 1.5, 1.25 and 0 in the expression -- [special characters omitted] -- and in each case we tried six different sets of σc; Blatt & Weisskopf (rₒ = 1.3, rₒ = 1.5), Shapiro (rₒ = 1.3, rₒ = 1.5), Lindner (optical model), and Mani et al (optical model). The aim was to find out if the conclusions concerning these spectra depended significantly on the choice of σc and of level density expression. In particular, it was hoped that some combination(s) of σc and level density expression(s) might lead to a more consistent and less anomalous description of these spectra. Our reanalysis did indicate in many cases significantly different results for different σc but no overall consistent and clearer pattern has emerged. In addition to the conventional analysis a 'level density independent' approach has also been employed by us. From the detailed results certain conclusions about the relative magnitudes of T and different level density parameters have been drawn.

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