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[en] The ¹⁴N(p,γ)¹⁵O reaction is the slowest reaction in the hydrogen burning CNO cycle and thus of high astrophysical interest. The reaction rate determines the CNO neutrino spectrum of our sun and sensitively influences the age determination of globular clusters. A recent work done at the LUNA facility at the Laboratori Nazionali del Gran Sasso at energies below 400 keV shows that R-matrix fits to the existing data reveal good agreement for the energy regime below 500 keV. Nevertheless, a precise determination of the astrophysical S factor at zero energy depends strongly on the data above 500 keV. Therefore a new measurement of ¹⁴N(p,γ)¹⁵O in the energy range of 500 and 1500 keV was performed at the Dynamitron Tandem Laboratory (DTL) of the Ruhr-Universitaet Bochum in order to remove systematic uncertainties in the existing data, e.g. summing corrections. (author)

[en] We report on a new lifetime measurement of the E_x=6792 keV state in ¹⁵O via the Doppler-shift attenuation method at the E=259 keV resonance in the reaction ¹⁴N(p,γ)¹⁵O. This subthreshold state is of particular importance for the determination of the ground state astrophysical S factor of ¹⁴N(p,γ)¹⁵O 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_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(τ)>0.98 for the E_x=6172 and 6792 keV states, respectively, corresponding to τ<0.77 fs. The attenuation factor for the E_x=5181 keV state results in F(τ)=0.78±0.02 corresponding to τ=8.4±1.0 fs, which is in excellent agreement with literature

[en] For improved measurements of the key astrophysical reaction ¹²C(α, γ)¹⁶O in inverse kinematics, a recoil separator ERNA is developed to detect directly the ¹⁶O recoils with nearly 100% efficiency. Since the ¹²C projectiles and the ¹⁶O recoils have essentially the same momentum and since the ¹²C ion beam emerging from an accelerator usually passes through a momentum filter, a sufficient absence of an ¹⁶O beam contaminant in the ¹²C ion beam is of utmost importance for ERNA. In the present work, a Wien filter together with a ΔE-E telescope are used to investigate the beam contaminants accompanying a momentum-filtered ¹²C ion beam and to measure the level of ion beam purification achievable with the Wien filter

[en] Complete text of publication follows. The ⁷Be produced in the ³He(α,γ)⁷Be reaction of the pp-chain is essential for predicting the ⁸B solar neutrino flux. The termination of the pp-II chain can proceed via two di rent paths: the reaction ⁷Be(p,γ)⁸B, which indeed produces the high energy solar neutrinos, and in competition, the ⁷Be decay to ⁷Li. The half-life of radioactive nuclei decaying only by electron capture depends on the electron density at the nucleus. Therefore, these isotopes are expected to have a different half-life in a stellar plasma. The recently observed enhanced electron screening in metals might connect the stellar plasma to metals, because in both environments free electrons play the dominant role. We started to search for the changes in the half-life of ⁷Be implanted into various metals at room temperature. The implanted samples are prepared for the first time using a high purity radioactive ⁷Be ion beam. The ⁷Be was produced by the ⁷Li(p,n)⁷Be reaction on ⁷Li metallic targets at the ATOMKI cyclotron, Debrecen, with a 11.4MeV proton beam of typically 20 μA intensity. The radiochemical separation of the ⁷Be from the carrier material and the preparation for the use of the sample in a sputter source were carried out by the isotopic laboratory of the Ruhr-Universitaet Bochum. Finally, the high purity ⁷Be radioactive beam was accelerated at the Naples tandem accelerator and the ⁷Be nuclei were implanted into di rent metals such as Pd, Zr, W and Ta, resulting in activities between 3.6 and 36 kBq. The decay curve of the implanted sources was measured by well shielded HPGe detectors. To reduce the systematic errors, the half- life of ⁷Be was determined relative to that of well known sources. Directly at the back of the ⁷Be sample, a ⁶⁰Co source is mounted. Any possible movement of the ⁷Be source during the counting can easily be seen by the change of the measured ⁶⁰Co intensity. Additionally, an extended ⁴⁰K source is fixed inside the lead cage allowing for the control of the long term stability of the system. Fig. 1 shows a γ-spectrum measured on the implanted tungsten sample for 12 hours. The 478 keV ⁷Be peak as well as the peaks of the reference sources can clearly be seen. The preliminary results show no change in the half-life within the experimental errors achieved (0.3-0.4%). This is compatible with the predictions of the Debye model applied to the free electrons in metals. (author)

[en] The LUNA Collaboration has provided the first cross section measurements of the key reaction ³He(³He,2p)⁴He of the proton-proton chain at the thermal energy of the Sun. This successful project has shown that, by going underground and by using the typical techniques of the low background physics, it is possible to measure down to the energy of the nucleosynthesis inside the stars

[en] The LUNA Collaboration has recently completed the first measurement of the ³He(³He,2p)⁴He reaction in the Gamow peak region. A new phase, based on a new, 400 kV accelerator, has started and it is aimed to the study, at very low energy, of other relevant reactions of the p-p chain and of the CNO cycle. Measurements of electron screening effects are also planned

[en] An exclusive measurement of the Coulomb breakup of B⁸ into Be⁷+p at 254A MeV allowed the study of the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates and that E2 multipolarity can be neglected. By using a simple single-particle model for B⁸ and treating the breakup in first-order perturbation theory, we extract a zero-energy S factor of S₁₇(0)=18.6±1.2±1.0 eV b, where the first error is experimental and the second one reflects the theoretical uncertainty in the extrapolation

[en] An exclusive measurement of the Coulomb breakup of ⁸B into ⁷Be+p at 254A MeV was used to infer the low-energy ⁷Be(p,γ)⁸B cross section. The radioactive ⁸B beam was produced by projectile fragmentation of 350A MeV ¹²C and separated with the FRagment Separator (FRS) at Gesellschaft fuer Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S₁₇ factors exhibit good agreement with the most recent direct ⁷Be(p,γ)⁸B measurements. By using the energy dependence of S₁₇ according to the recently refined cluster model for ⁸B of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S₁₇(0)=20.6±0.8(stat)±1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%