Microscopic substructure effects in nucleon capture reactions
Abstract
Nucleon capture reactions at low energies, such as ^7Be(p,γ)^8B, ^16O(p,γ)^17F, or ^7Li (n,γ)^8Li, play an important role in our understanding of astrophysical phenomena. For example, exact knowledge of the first two reaction rates is necessary for modeling the energy generation and evolution of hydrogen-burning stars. In addition, the ^7Be(p,γ)^8B reaction at solar energies (E_cm<= 20 keV) plays a key role in the `solar neutrino puzzle' since the neutrino event rate in the existing chlorine and water Cerenkov detectors is dominated by the high-energy neutrinos produced in the subsequent β decay of ^8B. The ^7Li (n,γ)^8Li reaction is a key element of primordial nucleosynthesis in inhomogeneous Big Bang scenarios. Direct measurements of capture reactions at energies corresponding to astrophysically relevant temperatures are often very difficult, since the cross sections diminish exponentially at low energies. Thus, theoretical studies of these processes become very valuable. Cross sections of external capture reactions depend primarily on the asymptotic normalization of the final bound-state wave function. The asymptotic normalization, however, is in turn connected to the short-distance behavior of the wave function through the bound-state Lippmann-Schwinger equation. We discuss the implications of this connection for theoretical determinations of the low-energy S factor. In particular, we study the role that microscopic substructure effects play in the low-energy cross sections of capture reactions. We discuss various approximation schemes for the full many-body problem and clarify the role of one-body models in the description of direct capture reactions. We illustrate how microscopic substructure effects arise naturally in the relevant transition matrix element and can be (in part) accounted for via a spectroscopic factor.
- Publication:
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APS Meeting Abstracts
- Pub Date:
- October 2001
- Bibcode:
- 2001APS..HAW.FF003E