Polarized Radiative Capture Reactions below 100 keV, a New Laboratory for Nuclear Physics.

Details Polarized Radiative Capture Reactions below 100 keV, a New Laboratory for Nuclear Physics. Polarized Radiative Capture Reactions below 100 keV, a New Laboratory for Nuclear Physics.

May 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aps..may..l103w&link_type=abstract

American Physical Society, APS/AAPT Joint Meeting, May 2-5, 1996, abstract #L1.03

Astronomy and Astrophysics

Astrophysics

Scientific paper

Despite the importance of low energy radiative capture reactions in nuclear astrophysics, very little is known and very few measurements have been made below 100 keV. The energy change of a factor of 100 as we go from 1 to 100 keV can be accompanied by huge changes in proton penetrabilities (of the order of 10^8), making extrapolations difficult. Although meson-exchange current effects are known to be important at thermal energies, no studies of these effects have been performed at finite low-energies. The availability of large high-resolution Germanium detectors (HPGe) and high intensity polarized beams has made it possible to begin to study these reactions between 10 and 100 keV in considerable detail. Our study of the D(p, γ)^3He and the ^1H(d, γ)^3He reactions using polarized beams below 80 keV has revealed a wealth of new information. The energy dependence of the cross section below 80 keV was determined experimentally for the first time. Our results indicate an astrophysical S-factor which is 34% smaller than the presently accepted value. Our detailed measurements of cross section, vector and tensor analyzing powers, and gamma-ray polarizations as a function of energy and angle have been compared with the results of new few-body calculations by Schiavilla et al.(R. Schiavilla, CEBAF Theory Group, private communication (1995).) which include Coulomb and MEC effects. Dramatic effects due to the tensor force and the associated two-body currents are observed in the vector and tensor analyzing powers for the first time. A detailed study of the ^7Li(p, γ)^8Be reaction has revealed the presence of a significant p-wave capture amplitude at these energies which affects the extrapolation used to obtain the S-factor. A recent measurement of the ^7Li(p, γ_3)^8Be (2^+, T=0+1) reaction has been performed using polarized protons below 80 keV. This reaction is especially interesting due to its close relationship to the ^7Be(p, γ)^8B (2^+, T=1) reaction, the source of high energy solar neutrinos. The results of this work and preliminary studies of several other reactions below 80 keV will be described. Work partially supported by USDOE grant No. DEFG05-91-ER40619

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