T. Mayer-Kuckuk

The statistical character of the reaction 37Cl(p, α)34S at 21–22 MeV excitation energy of the compound nucleus

Abstract For the reaction 37 Cl(p, α) 34 S excitation functions and angular distributions have been measured in steps of 8 keV in the energy range between 11 and 11.952 MeV. The transitions to the ground state and to the first and second excited states of 34 S have been analysed. The cross section as a function of energy as well as angle shows strong fluctuations. For the analysis, correlation functions and probability distributions have been calculated according to the statistical theory of Ericson and of Brink and Stephen. The results are in good agreement with the predictions of the theory. The average coherence energy Γ of 18 keV corresponds to a lifetime of 3.7 × 10 −20 sec for the compound nucleus 38 Ar excited at 21 MeV. Estimations of the number of effective channels and the amount of direct interaction are given. The level spacing D 0 in the compound nucleus has been estimated to lie between 0.53 keV and 0.90 keV.

An analysis of cross-section fluctuations in the reaction 26Mg(p, α)23Na

Abstract The reaction 26 Mg(p, α) 23 Na was studied as a quantitative test of fluctuation theory. Excitation functions and angular distributions were measured using protons of energy 9 to 13.26 MeV in 20 keV steps. Good overall energy resolution was achieved and α-particles corresponding to the ground state and first three excited states in 23 Na were studied. All the excitation functions show marked fluctuations and were analysed in terms of the auto-correlation function and the angular and group cross-correlation functions. The results do not agree with conventional statistical theory. Corrections have been made to the simple theory to take account of the finite range of the data, and the presence of non-statistical variations in the cross section. A “modulated fluctuation” analysis was made of the excitation functions and the results obtained agree well with the corrected theory. The implication is that the gross and probably intermediate structure of the compound state exerts a serious influence on the cross sections, and thereby invalidates the basis of the statistical description. It is possible to extract some information about this structure.

Statistical fluctuations in the cross sections of the reactions Cl35 (p, α)S32 and Cl37 (p, α)S34

Measurements of the excitation function of the differential cross section for the reactions /sup 35/Cl(p, alpha )/sup 32/S and /sup 37/Cl(p, alpha ) /sup 34/S at bombarding energies between 9.6 and 10.4 Mev in steps of 9 kev at several backward angles are reported. The marked fluctuations in the excitation functions of compound nucleus reactions in the region of overlapping levels of the compound nucleus are investigated. (C.E.S.)