T.R. Donoghue

The 12C(α, γ)16O cross section at stellar energies☆

Abstract The capture reaction 12 C(α, γ) 16 O has been investigated at E = 0.94 to 2.84 MeV with the use of an intense α beam and implanted 12 C targets of high isotopic purity. The studies involved NaI(Tl) crystals and, for the first time, germanium detectors. The measurement of absolute cross sections, γ-ray angular distributions and excitation functions is reported. A cross section of 48 pb is found at E = 0.94 MeV. The data provide information on the E1 and E2 capture amplitudes involved in the transition to the ground state as well as to excited states. The S -factor at stellar energies has been determined by means of theoretical fits. The results verify the previous report of a substantial higher S -value compared to the value recommended in 1975. The present uncertainty in the S -value as well as possible improvements are discussed. This S -value is of crucial importance to nuclear astrophysics.

Proton-induced direct capture on 21Ne and 22Ne☆

Abstract The direct capture process in the reactions 21 Ne(p, γ) 22 Na and 22 Ne(p, γ) 23 Na has been investigated at E p = 0.3–1.6 MeV using neon gas enriched to 91 % in 21 Ne and to 99 % in 22 Ne, respectively. The gas was recirculated in a differentially pumped gas target system of the extended-static and quasi-point supersonic jet type. For 22 Ne(p, γ) 23 Na, the direct capture process has been observed to several final states in 23 Na up to E x = 8.83 MeV excitation energy. The deduced spectroscopic factors C 2 S are in fair agreement with the corresponding values from stripping reactions. The capture transition into the 23 Na ground state exhibits broad structures, which resemble Ericson fluctuations. The data remove the previously reported discrepancies in C 2 S for the 23 Na ground state. The excitation functions for the 21 Ne(p, γ) 22 Na reaction are dominated by broad and intense resonances, which hampered the measurement of the direct capture process. The nuclear and astrophysical aspects of the results are discussed.

The abundance of 26Al in the MgAl cycle

Abstract The capture reaction 26 Al(p, γ) 27 Si has been investigated in the energy range of E p = 0.17–1.58 MeV. High-spin resonances were found at E R = 287, 376, 719, 727, 790, 856 and 927 keV. Resonances for the reaction 26 Al(p, p 2 γ) 26 Al were observed at E R = 927, 1122, 1252 and 1363 keV. Information on resonance energies, total widths, branching ratios and resonance strengths is reported. The investigated energy range corresponds to the stellar temperature region of T = (0.2–1.0) × 10 9 K. The deduced stellar reaction rates are used to calculate the abundance of 26 Al in the hydrogen burning MgAl cycle.

Proton threshold states in 26Al

Abstract The energy levels of 26Al between Ex = 6.3 and 6.5 MeV, corresponding to proton threshold energies in the 25Mg + p reaction from E p = 0 to 200 keV , have been investigated using the reactions 27 Al(su3 He, α)26Al and 24Mg(3He, p)26Al. Despite early work reporting a doublet at Ex = 6346 keV and Ex = 6362 keV, most subsequent work reported a single state with conflicting spin and parity assignments. Our work clearly establishes the presence of the doublet and resolves the conflicts. We find that there are six states in this excitation energy region, including a new state at Ex = 6410 ± 5 keV. The l-values leading to possible spin and parity assignments for all these states have been made using DWBA. We conclude however that only three of these six states may contribute to the production of 26Al by the 25Mg(p, γ) reaction in the MgAl cycle and the new structure of 26Al reported here can substantially increase the production rate of 26Al in stellar reactions.

Difference between Polarization and Analyzing Power in the Reaction H 3 ( p , n ) He 3

We have examined the difference between polarization and analyzing power for the reaction

The 46, 48Ti(p, α)43,45Sc reaction at intermediate energy

^{3}mathrm{H}(p,n)^{3}mathrm{He}

Proton threshold states in 27Si and their implications on hydrogen burning of 26Al

. We find that this difference is due to the presence of

The mechanism of the 7Li(d, 2α)n reaction from Ed = 3 to 15 MeV☆

^{3}P_{2}ensuremath{leftrightarrow}^{3}F_{2}

Indirect investigation of proton capture reactions at stellar energies

transitions which are enhanced in the vicinity of the lowest

Analyzing power of proton-nucleus elastic scattering between 80 and 180 MeV

{2}^{ensuremath{-}}