Polarized proton capture on tritium at proton energies below 80 keV

The 3H4He reaction was studied at energies below E_p = 80 keV at Triangle Universities Nuclear Laboratory (TUNL) using the polarized ion source. The current study was the logical progression of a previous study of the 2H3He reaction done by the radiative capture group at TUNL. One result from that study was the recognition of the importance of meson exchange currents (MEC) in that reaction. In fact, theoretical calculations have shown that approximately 50% of the magnetic dipole transition strength observed in that reaction at E_p = 80 keV can be attributed to MECs. The contribution of MECs to the M1 strength in the 3H4He reaction at very low energies is expected to be even stronger.; The use of a polarized proton beam allows for the observation of the analyzing power in this reaction. The angular distribution of the cross section, σ(&thetas;), and the analyzing power, Ay(&thetas;), were measured at incident proton beam energies of 40 keV and 80 keV. In both cases the beam was stopped in the target. The angular distribution in the cross section and analyzing power were fit to a Legendre and Associated Legendre polynomial expansion, respectively. A transition matrix element analysis, which expands all of the observables as a set of amplitudes and phases, was performed on the data as well. The magnetic dipole transition strength was determined from this analysis. The explicit MEC effects are contained in this strength. By comparing this strength with similar reactions in the case of three-bodies, we are able to interpret the MEC origin of this strength.; In addition, the absolute cross section has been determined. A parameterization of the Astrophysical S-factor, which factors out the rapidly varying effects due to the Coulomb potential from the cross section, has been performed. Previous measurements of the absolute cross section extended down to beam energies of 100 keV. The present study extends the measured cross section data closer to zero energy and, therefore, makes the extrapolation into the energy regime typically of interest to astrophysicists more reliable.; Finally, this reaction can be used as a source of 20 MeV γ-rays. A reliable measurement of the cross-section at low energies will be very useful in future designs of sources using high-voltage power supplies to accelerate the proton beam.