Abstract
Kawai, Kerman, and McVoy have shown that a statistical treatment of many open channels that are coupled by direct reactions leads to modifications of the Hauser- Feshbach expression for energy-averaged cross section (Ann. of Phys. 75, 156 (1973)). The energy averaging interval for this cross section is on the order of the width of sin- gle particle resonances, 1 MeV, revealing only a gross structure in the cross section. When the energy-averaging interval is decreased down to a width of a doorway state, 0:1 MeV, a so-called intermediate structure may be observed in cross sections. We extend the Kawai-Kerman-McVoy theory into the intermediate structure by leveraging a theory of doorway states developed by Feshbach, Kerman, and Lemmer (Ann. of Phys. 41, 230 (1967)). As a by-product of the extension, an alternative derivation of the central result of the Kawai-Kerman-McVoy theory is suggested. We quantify the e ect of the ap- proximations used in derivation by performing numerical computations for a large set of compound nuclear states.
Highlights
Kerman, and McVoy have shown that a statistical treatment of many open channels that are coupled by direct reactions leads to modifications of the HauserFeshbach expression for energy-averaged cross section [Ann. of Phys. 75, 156 (1973)]
The energy averaging interval for this cross section is on the order of the width of single particle resonances, ≈ 1 MeV, revealing only a gross structure in the cross section
When the energy-averaging interval is decreased down to a width of a doorway state, ≈ 0.1 MeV, a so-called intermediate structure may be observed in cross sections
Summary
One way of analyzing low-energy nuclear cross sections is by varying the experimental energy resolution, or alternatively, by numerical energy-averaging of high-resolution data. It is known that different energy resolutions may reveal different features in the cross section. On the order of fraction of an eV, reveals compound nuclear resonances, often referred to as fine structure. For an intermediate energy resolution, on the order of 100 keV, a so-called intermediate structure emerges, for which a theory of doorway states was developed in [2]. Doorway state concept was used to construct a non-local optical potential in [6].
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