R.W. Kavanagh

Solar fusion cross-sections

We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates.

Enhanced electron screening in d(d, p)t for deuterated Ta

Abstract:The recent observation of a large electron screening effect in the d(d, p)t reaction using a deuterated Ta target has been confirmed using somewhat different experimental approaches: Ue = 309±12 eV for the electron screening potential energy. The high Ue value arises from the environment of the deuterons in the Ta matrix, but a quantitative explanation is missing.

Laboratory for underground nuclear astrophysics(LUNA)

A compact high-current 50 kV ion accelerator facility including a windowless gas target system, a beam calorimeter, and detector telescopes in close geometry has been built and tested. The data acquisition and analysis involved a multiparameter system and a Monte Carlo program. The LUNA facility, presently installed at the Gran Sasso underground laboratory, is a pilot project focused initially on cross section measurements of the ^3He(^3He, 2p)^4He reaction within the thermal energy region of the sun. To achieve this goal, the experimental sensitivity has been improved by more than four orders of magnitude over that of previous work.

Proton capture in Be7

Abstract Cross sections for proton capture by Be 7 measured at bombarding energies of 800 keV and 1400 keV are 0.48±0.18 and 0.50±0.20 μ b, respectively, from which the corresponding cross section factors are S = 0.027±0.010 and 0.017±0.007 keV·b. The reaction is therefore important in stellar energy production only in stars operating on the proton-proton chain at temperatures greater than about 2×10 7 degrees Kelvin.

Masses and excitation energies of some proton-rich nuclei

Abstract The Q -values for seven ( 3 He, n) reactions have been measured, using a silicon semiconductor detector as a fast-neutron spectrometer, with the following results (final nuclei, Q -values in keV): 26 Si, 85±18; 30 S, −573±15; 34 Ar, −759±15; 42 Ti, −2865±6; 48 Cr, 5550±18; 56 Ni, 4513±14 and 60 Zn, 818±18. The following excited states (excitation energies in MeV) were also seen: 26 Si, 1.79, 2.80; 30 S, 2.19; 34 Ar, 2.06; 48 Cr, 0.72?, 56 Ni, 2.69, 3.95, 6.60 and 60 Zn, 1.02. Rough measurements of the 0°( 3 He,n) cross sections are given. Neutron angular distributions for 28 Si( 3 He, n) to the ground and first excited states of 30 S are consistent with assignments of 0 + and 2 + . Two gamma rays observed with energies 1.28±0.06 and 2.66±0.1 MeV are attributed to the reaction 54 Fe( 3 He, nγ) 56 Ni. The ( 3 He, p) Q -values of nuclear reactions forming 48 V, 56 Co and 60 Cu have been measured with a magnetic spectrometer. Ground state Q -values for 56 Co and 60 Cu are 7410±10 keV and 5770±12 keV. Many excited states were seen, viz. 48 V(3), 56 Co(15) and 60 Cu(23).

The 7Li(p, α)4 He cross section at low energies

Abstract The reaction cross section for 7Li(p, α)4He was obtained from Ec.m. = 25 to 873 keV corresponding to the temperature range T = (0.033 to 6.8) × 109 K. The data are in fair agreement with R-matrix calculations. Constraints drawn on the universal baryon density from the abundance of 7Li remain essentially unchanged by the present data.

Low-energy behavior of the 3He(α, γ)7Be cross section

Cross sections for the ^3He(α, γ)^7Be reaction have been measured at several energies from E_(c.m.) = 165 to 1169 keV by counting prompt γ-rays from a windowless, differentially pumped, recirculating, ^3He gas target. The cross-section factor S_(34)(E_(c.m.)) and branching ratio γ_1/γ_0 were determined at each energy. Cross sections were also measured at E_(c.m.) = 947 and 1255 keV by counting the γ-rays from the ^7Be produced in a ^3He gas cell with a Ni entrance foil. Combining the results of these two independent experiments yields a zero-energy intercept for the cross-section factor of S_(34)(0) = 0.53 ± 0.03 keV · b. The relationship between these measurements and several theoretical calculations, and the import of the extrapolated cross section for the solar-neutrino problem are discussed.

22Na(3He,d)23Mg reaction studies of states near the proton threshold and hydrogen burning of 22Na

Abstract The 22 Na( 3 He,d) 23 Mg reaction has been investigated at E τ = 30 MeV using a 22 Na implanted foil target and a Q3D spectrograph of high energy resolution. The angular distributions of deuteron groups corresponding to nineteen 23 Mg levels between E x = 6236 and 8076 keV have been measured at angles θ lab = 7.5° to 31° and lead to their proton spectroscopic factors using DWBA analysis. The 22 Na(p,γ) 23 Mg resonance strengths for unbound states near the proton threshold have been deduced. The resulting reaction rates significantly reduce previous uncertainties.

22Na(p,γ)23Mg resonant reaction at low energies

Abstract The 22 Na( p , γ ) 23 Mg reaction has been investigated in the energy range of E p = 0.20–0.63 MeV, using a 22 Na implanted target. A new resonance has been found at E p = 213 keV. The known resonances at E p = 290 and 613 keV have also been observed and have been used to determine the resonance strength ωγ of the new resonance. A new γ-branch for the E x = 7854 keV state in 23 Mg, corresponding to the E p = 290 keV resonance, has been found. The changes in the stellar reaction rates are discussed.

Resonances in the 22Na(p, γ)23Mg reaction

Abstract The reaction 22 Na(p,γ) 23 Mg has been investigated in the energy range E p = 0.17–1.29 MeV using a 22 Na implanted target, a D 2 O threshold detector, and NaI(Tl) and Ge detectors. Resonances in this reaction have been observed for the first time at E p = 290, 457, 503, 613, 740 and 796 keV. The strengths of these resonances, and upper limits on the strengths for expected resonances in the energy range covered, are given. The stellar reaction rates deduced from the present work are about one order of magnitude lower than previous theoretical estimates; they are however significantly higher than the upper limits from one previous measurement. Some astrophysical consequences are discussed.