K. A. Snover

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.

Solar fusion cross sections II: the pp chain and CNO cycles

The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for {sup 8}B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.

7Be(p,gamma)8B astrophysical S factor from precision cross section measurements.

We measured the 7Be(p,gamma)8B cross section from E(c.m.) = 186 to 1200 keV, with a statistical-plus-systematic precision per point of better than +/-5%. All important systematic errors were measured including 8B backscattering losses. We obtain S17(0) = 22.3+/-0.7(expt)+/-0.5(theor) eV b from our data at E(c.m.)< or =300 keV and the theory of Descouvemont and Baye.

The He-3 + He-4 ---> Be-7 astrophysical S-factor

We present precision measurements of the 3He + 4He --> 7Be reaction in the range ECM = 0.33 to 1.23 MeV using a small gas cell and detection of both prompt gamma rays and 7Be activity. Our prompt and activity measurements are in good agreement within an experimental uncertainty of several percent. We find S(0) = 0.595 +/- 0.018 keV b from fits of the Kajino theory to our data. We compare our results with published measurements, and we discuss the consequences for Big Bang Nucleosynthesis and for solar neutrino flux calculations.

Search for a phase transition in the nuclear shape at finite temperature and rapid rotation

Abstract At high spin the strength function for γ-decay of the Giant Dipole Resonance in highly excited 45 Sc compound nuclei exhibits a shoulder at E γ ≈ 25 MeV, in addition to the main peak at E γ ≈ 16 MeV, suggesting the presence of large deformations β > 0.45. Calculated spectral shapes including thermal shape fluctuations provide a good description of the data when the nuclear potential energy surface includes the oblate → triaxial phase transition predicted by the rotating liquid drop model at high spin.

The fabrication of metallic 7Be targets with a small diameter for 7Be(p,γ)8B measurements

Abstract The fabrication process for a metallic 7 Be target of small diameter is described. Targets fabricated in this manner have been subjected to systematic tests and one of them has been used in a 7 Be(p,γ) 8 B measurement at the University of Washington. Target properties have been determined including the total amount of 7 Be, the 7 Be distribution over the target area derived via a decay γ-scan and the 7 Be depth profile. The latter has been measured with the E α =1376 keV resonance in the 7 Be ( α , γ ) 11 C reaction.

The 3He + 4He --> 7Be Astrophysical S-factor

We present precision measurements of the 3He + 4He --> 7Be reaction in the range ECM = 0.33 to 1.23 MeV using a small gas cell and detection of both prompt gamma rays and 7Be activity. Our prompt and activity measurements are in good agreement within an experimental uncertainty of several percent. We find S(0) = 0.595 +/- 0.018 keV b from fits of the Kajino theory to our data. We compare our results with published measurements, and we discuss the consequences for Big Bang Nucleosynthesis and for solar neutrino flux calculations.

A new measurement of 7Be(p,γ)8B cross section and its astrophysical meaning

Abstract We measured the 7Be(p,γ)8B cross section from Ep = 221 keV to 1376 keV. A uniformly distributed beam that illuminated the whole area of a small diameter target was used to eliminate systematic error from 7Be target non-uniformity. The energy loss profile of the target to the incident beam was measured using the 7Be(α,γ)11C resonance at Eα = 1376 keV. The (α,γ) measurement also demonstrated that the target had a high 7Be atomic purity. The measured yield of the detected 8B was normalized to the activity of the target and the solid angle of the counting detector. Corrections for 8B decay during bombardment and arm rotation were applied. For the first time, the correction due to lost 8B from backscattering was determined experimentally. A new experiment is presently underway, extending to lower proton energy. Due to a problem in the determination of the α-detector solid angle in the first measurement, the solid angle in the new measurement will be determined by a different technique using a 148Gd α source and a silicon detector whose distance to the source can be precisely adjusted.

Solar fusion cross sections. II. Theppchain and CNO cycles

The available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production are summarized and critically evaluated. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for {sup 8}B solar neutrinos. Opportunities for further increasing the precision of key rates are also discussed, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to 1998, Rev. Mod. Phys. 70, 1265.

E0 emission in a + 12C fusion at astrophysical energies

We show that E0 emission in alpha + ^12C fusion at astrophysically interesting energies is negligible compared to E1 and E2 emission.