Abstract
We have analyzed a large set of mean energies and angular anisotropies for evaporative4He emission to obtain barriers to evaporation,B. These exit channel barriers are often substantially smaller than the corresponding empirical s-wave fusion barriersE 0. The differences (E 0-B) are interpreted as indicators of the extent of distortion of the emitters. These distortions have in turn been characterized by the deformation parameter for a spheroid α20. ForZ=80 the dependence ofB or {α}20 on spin is somewhat suggestive of the superdeformed shapes predicted by the liquid drop model. ForZ>70 significant distortions are indicated for emitters of both large and small spin.
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Moretto has developed many aspects of the transition-state theory of evaporation, Moretto, L.G.: Nucl. Phys. A247, 211 (1975). In this approach the thermal contribution to the average energy 《ɛ》 depends on the number of “amplifying and nonamplifying modes” that are effective at the saddle point for evaporation. At this time it is not possible to choose this number unambiguously either from theory or from the empirical evidence. However it seems that (1) (from evaporation theory [3]) does correspond to a reasonable choice of modes in this transition-state theory. Other reasonable choices might give somewhat larger thermal contributions to 《ɛ》 and therefore somewhat smaller values ofB
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Alexander, J.M., Guerreau, D. & Vaz, L.C. Evaporation barriers for4He indicate very extended forms for many emitting nuclei. Z Physik A 305, 313–318 (1982). https://doi.org/10.1007/BF01419079
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DOI: https://doi.org/10.1007/BF01419079