TUNL Research Groups

Current Research Endeavors

The Radiative-Capture Group has been engaged in studies of few-nucleon radiative-capture reactions using the 80 keV polarized beams directly out of the TUNL polarized ion source. In the past few years, we have concentrated on the p-d and d-p capture reactions. Measurements of all of the vector and tensor polarization observables, as well as the gamma-ray polarization, have led to a determination of the individual transition-matrix elements involved in the reaction at these energies. Recent studies have focused on A=4 (d-d capture and p-T capture reactions). Likewise, measurements of all of the relevant vector and tensor polarization observables are being made.

Future Studies

• Measurement of the analyzing powers of the n-p capture reaction using 300--500 keV polarized neutrons. This will be the first test of the GDH sum-rule integral strength of the deuteron predicted in this energy region. It will also test other theoretical predictions of the M1/E1 ratio in n-p capture, or deuteron photo-disintegration. This energy regime is important to Big Bang nucleosynthesis. A knowledge of the M1/E1 ratio will help determine the cross section in this region to the precision needed for accurate predictions of the abundances of elements.
• A determination of the quantity sigma_P - sigma_A for ³He using the p-d and the d-p radiative capture reactions at E_p(E_e) = 1(2), 2(4), and 3(6) MeV. This experiment will determine the value of the GDH sum rule integral for ³He below 3N breakup threshold. It will test the ability of 3N theory to predict this quantity, especially the difference between the S = 1/2 E1 amplitudes, observed to be discrepant with data in the region of 80 keV and lower.
• Measurements of the analyzing powers and cross sections of the ³H(p,gamma)⁴He and the ²H(d,gamma)⁴He reactions. These experiments are already underway. They are designed to test emerging 4N theory. They are, as in the case of ²H(p,gamma)³He, expected to be sensitive to MEC effects near threshold. The ²H(d,gamma)⁴He results should resolve the present discrepancy on the interpretation of the low-energy behavior of this reaction. Accurate astrophysical S factors will also result in both cases.