C. Rolfs

A compilation of charged-particle induced thermonuclear reaction rates

Low-energy cross section data for 86 charged-particle induced reactions involving light (1 less than or equal to Z less than or equal to 14), mostly stable, nuclei are compiled. The corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 10(6) K to 10(10) K are calculated. These evaluations assume either that the target nuclei are in their ground state, or that the target states are thermally populated following a Maxwell-Boltzmann distribution, except in some cases involving isomeric states. Adopted values complemented with lower and upper limits of the rates are presented in tabular form. Analytical approximations to the adopted rates, as well as to the inverse/direct rate ratios, are provided

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.

Low-energy fusion cross sections of D + D and D + 3He reactions

Abstract The D(d, n) 3 He and D(d, p)T reactions have been investigated at E c.m = 2.98 to 162.5 keV and the 3 He(d, p) 4 He reaction at E c.m. = 6.95 to 141.8 keV. The studies involved high-current accelerators with well-known beam characteristics and windowless gas target systems of the extended and quasi-point supersonic jet type. The measurement of absolute cross sections, angular distributions and excitation functions is reported. The data extend into the thermal energy region of future fusion reactors. The results for the D(d, n) 3 He and D(d, p)T reactions are in good agreement with previous work, while substantial differences are found for 3 He(d, p) 4 He.

First Measurement of the 3 He ( 3 He , 2 p ) 4 He Cross Section down to the Lower Edge of the Solar Gamow Peak

We give the LUNA results on the cross section measurement of a key reaction of the proton-proton chain strongly affecting the calculated neutrino luminosity from the Sun: He3+He3-->He4+2p. Due to the cosmic ray suppression provided by the Gran Sasso underground laboratory it has been possible to measure the cross section down to the lower edge of the solar Gamow peak, i.e. as low as 16.5 keV centre of mass energy. The data clearly show the cross section increase due to the electron screening effect but they do not exhibit any evidence for a narrow resonance suggested to explain the observed solar neutrino flux.

Oppenheimer-Phillips effect and electron screening ind+ d fusion reactions

Thed(d, n)3He andd(d,p)t fusion reactions have been studied at center-of-mass energies E=1.6 to 130 keV using intense beam currents from 30, 100, and 450 kV accelerators in combination with detectors in close and far geometry. The cross sesction ratio,R(E)=σ(d,n)/σ(d, p), approaches unity (within 2%) at low energies; thus there is no experimental evidence for the Oppenheimer-Phillips effect at subcoulomb energies. The cross sections of d(d, p)t at E≦10keV show clear evidence for electron screening effects. However, the observed cross section enhancement is significantly larger than can be accounted for from available atomic physics models.

The LUNA II 400 kV accelerator

A second high current accelerator of 400 kV has been installed at the underground laboratory of Gran Sasso, called LUNA II. We describe this new facility as well as measurements of the proton beam characteristics: absolute energy, energy spread, and long-term energy stability. The absolute energy was determined to a precision of 7300 eV at Ep ¼ 130–400 keV using the energy of the capture g-ray transition of 12 Cðp;gÞ 13 N as well as resonance energies at Ep ¼ 309–389 keV of 23 Naðp;gÞ 24 Mg; 26 Mgðp;gÞ 27 Al; and 25 Mgðp;gÞ 26 Al: The resonance studies led to a proton energy

Effects of electron screening on the 3He(d, p)4He low-energy cross sections☆

The reaction 3He(d, p)4He has been investigated for ECM = 5.9−41.6 keV with the use of D projectiles and 3He atomic gas target nuclides as well as with 3He projectiles and D2 molecular gas target nuclides. These studies show for the first time the effects of electron screening on low-energy fusion cross sections, i.e. a nearly exponential enhancement of the cross sections compared to the case of bare nuclei. The enhancement is about a factor 2 smaller for the case d(3He, p)4He due to the molecular nature of the D2 target nuclides.

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.

The Bare Astrophysical S(E) Factor of the 7Li(p, α)α Reaction

The astrophysically important 7Li(p, α)α reaction has been studied via the Trojan horse method in the energy range E = 10-400 keV. A new theoretical description, based on the distorted-wave Born approximation approach, allows one to extract information on the bare astrophysical S-factor, Sb(E), with Sb(0) = 55 ± 3 keV barns. The results are compared with direct experimental data leading to a model-independent value of the electron screening potential energy, Ue = 330 ± 40 eV, much higher than the adiabatic limit Uad = 175 eV.

Stellar reaction rate of 14N(p, γ)15O and hydrogen burning in massive stars

Abstract The capture reaction 14 N(p, γ) 15 O has been investigated in the energy range E p = 0.2 to 3.6 MeV with the use of windowless gas targets as well as implanted 14 N solid targets of high isotopic purity. The measurement of absolute cross sections, γ-ray angular distributions and excitation functions is reported. The data provide information on the capture amplitudes involved in the transitions to all bound states of 15 O. The astrophysical S -factor at stellar energies has been determined by means of theoretical fits. The result of S (0) = 3.20 keV · b is in good agreement with the value incorporated in the compilations. Also discussed are the nuclear physics aspects of the data.