R. Kunz

First direct measurement of the total cross-section of 12C(α,γ)16O

Abstract.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.

First direct measurement of the total cross section of 12C(alpha,gamma)16O

Abstract.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.The total cross-section of 12C(α,γ)16O was measured for the first time by a direct and ungated detection of the 16O recoils. This measurement in inverse kinematics using the recoil mass separator ERNA in combination with a windowless He gas target allowed to collect data with high precision in the energy range E = 1.9 to 4.9 MeV. The data represent new information for the determination of the astrophysical S(E) factor.

Precision study of ground state capture in the N-14(p, gamma)O-15 reaction

Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S-factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV centerof-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total Sfactor.

Lifetime measurement of the 6792-keV state in O-15, important for the astrophysical S factor extrapolation in N-14(p,gamma)O-15

We report on a new lifetime measurement of the E{sub x}=6792 keV state in {sup 15}O via the Doppler-shift attenuation method at the E=259 keV resonance in the reaction {sup 14}N(p,{gamma}){sup 15}O. This subthreshold state is of particular importance for the determination of the ground state astrophysical S factor of {sup 14}N(p,{gamma}){sup 15}O at stellar energies. The measurement technique has been significantly improved over that used in previous work. The conclusion of a finite lifetime drawn there cannot be confirmed with the present data. In addition, the lifetimes of the two states at E{sub x}=5181 and 6172 keV have been measured with the same technique in order to verify the experimental method. We observe an attenuation factor F({tau})>0.98 for the E{sub x}=6172 and 6792 keV states, respectively, corresponding to {tau}<0.77 fs. The attenuation factor for the E{sub x}=5181 keV state results in F({tau})=0.78{+-}0.02 corresponding to {tau}=8.4{+-}1.0 fs, which is in excellent agreement with literature.

The 198Au β− half-life in the metal Au revisited

Abstract.The half-life of the β− -decay of 198Au has been measured for room temperature and 12K. The resulting values of T1/2(RT) = 2.684±0.004 d and T1/2(12K) = 2.687±0.005 d agree well within statistical uncertainties. Evidence for the temperature dependence of the half-life was not observed.

Precision study of ground state capture in the 14N(p,γ)15O reaction

Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S-factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV centerof-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total Sfactor.

Stellar and Primordial Nucleosynthesis of {sup 7}Be: Measurement of {sup 3}He({alpha},{gamma}){sup 7}Be

The {sup 3}He({alpha},{gamma}){sup 7}Be reaction presently represents the largest nuclear uncertainty in the predicted solar neutrino flux and has important implications on the big bang nucleosynthesis, i.e., the production of primordial {sup 7}Li. We present here the results of an experiment using the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the {sup 7}Be ejectiles. In addition, off-beam activation and coincidence {gamma}-ray measurements were performed at selected energies. At energies above 1 MeV a large discrepancy compared to previous results is observed both in the absolute value and in the energy dependence of the cross section. Based on the available data and models, a robust estimate of the cross section at the astrophysical relevant energies is proposed.The 3He(α,γ)7Be reaction presently represents the largest nuclear uncertainty in the predicted solar neutrino flux and has important implications on the big bang nucleosynthesis, i.e., the production of primordial 7Li. We present here the results of an experiment using the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the 7Be ejectiles. In addition, off-beam activation and coincidence γ-ray measurements were performed at selected energies. At energies above 1 MeV a large discrepancy compared to previous results is observed both in the absolute value and in the energy dependence of the cross section. Based on the available data and models, a robust estimate of the cross section at the astrophysical relevant energies is proposed.

Measurement of 3He(α, γ)7Be with ERNA Recoil Separator

The 3He(α, γ)7Be reaction plays an important role in the interpretation of the results of the solar neutrino experiments, since the estimate of the oscillation parameters relies on the solar neutrino spectrum, calculated by solar models. The high energy component in this spectrum is mainly produced by the decay of 7Be and 8B. The uncertainty in the 3He(α, γ)7Be cross section is also one of the largest contributions to the uncertainty on the predicted primordial 7Li abundance in Big Bang Nucleosynthesis calculations.Previous measurements of the 3He(α, γ)7Be cross section have been performed detecting the capture γ‐rays or, alternatively, measuring the activity of the synthesized 7Be. While the results of the two different approaches agree on the energy dependence of the astrophysical S factor, they disagree in the extrapolated S34(0) value at a 3σ level.A novel approach uses the European Recoil separator for Nuclear Astrophysics (ERNA) to detect directly the 7Be ions produced in the reaction and, additiona...