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7Be(p, $\gamma$ )8B has an important role in nuclear astrophysics, having a direct impact on both the high energy component of solar neutrinos and the 7Li abundance after the Big Bang Nucleosynthesis. All direct measurements providing useful information on this reaction so far used the same approach, i.e. a proton beam on a radioactive 7Be target. The overall precision and accuracy of the estimate of the astrophysical rate of this reaction are limited by the discrepancy between the results of existing measurements, possibly due to the complicated stoichiometry and beam induced deterioration of the radioactive targets. The ERNA (European Recoil separator for Nuclear Astrophysics) collaboration planned a new experiment in inverse kinematics exploiting the intense 7Be beam available at CIRCE (Center for Isotopic Research on Cultural and Environmental heritage), Caserta, Italy. The 8B recoils are produced in a windowless hydrogen gas target and detected after the efficient mass separation provided by ERNA. Here we present the commissioning of the experimental setup and a first cross section measurement at $E_{\mathrm{cm}}\approx 812$ keV.

The astrophysical S-factor of 14N(p,gamma)15O has been measured for effective center-of-mass energies between E_eff = 119 and 367 keV at the LUNA facility using TiN solid targets and Ge detectors. The data are in good agreement with previous and recent work at overlapping energies. R-matrix analysis reveals that due to the complex level structure of 15O the extrapolated S(0) value is model dependent and calls for additional experimental efforts to reduce the present uncertainty in S(0) to a level of a few percent as required by astrophysical calculations., Comment: Eur. Phys. J. A, accepted. 17 pages, 15 figures

For improved cross-section measurements of the reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is developed at the 4MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. Due to the emission of the capture γ-rays, the kinematically forward directed 16O recoils are described by an angle and energy spread. Thus, the acceptances in angle and energy of ERNA must cover these spreads in order to extract reliable cross-section values. We report on such acceptance measurements over the energy range Ecm=0.7-5.0 MeV, using an 16O pilot beam. © 2003 Elsevier B.V. All rights reserved.

Non-radiative transitions in nuclear capture reactions between light nuclei play a relevant role in stellar nuclear astrophysics, where nuclear processes occur at typical energies from tens to hundreds of keV. At higher energies, instead, the E0 contributions may be shadowed by more intense transitions. The experimental study of E0 transitions requires a specific detection setup, able to uniquely identify events where an electron-positron pair is produced. A compact ΔE-E charged-particle spectrometer based on two silicon detectors has been designed to be installed in the jet gas target chamber of the recoil mass separator ERNA (European Recoil separator for Nuclear Astrophysics) at the CIRCE laboratory of Caserta, Italy. The detector design, its performances and the first foreseen applications are described.

Stellar models show an exceptional sensitivity on the cross section of 12C( α , γ )16O and a precision of about 10% is required to provide adequate constraints on stellar evolution. A measurement at the astrophysical energy, E 0 ≈ 300 keV , is unfeasible due to the extremely low cross section. Furthermore, the extrapolation of existing high-energy data is complicated by a complex reaction scheme. Besides direct measurements of 12C( α , γ )16O, the β-delayed α-decay of 16N and 12C + 4He elastic scattering provide additional information for the relevant 16O levels. In this Letter we present a new R-matrix analysis, where systematic uncertainties of the included data sets, in particular the absolute normalization, were treated in the fitting procedure. The data were selected according to rigorous criteria in order to reduce uncontrolled systematic effects and, finally, a Monte Carlo approach was used to evaluate the uncertainty at astrophysical energy. The resulting S factor, S ( 300 ) = 161 ± 19 stat − 2 sys + 8 keV b , is, for the first time, close to the required precision.

The radiative capture reaction C 12 ( α , γ ) O 16 has been investigated in the energy range E = 3.3 to 4.5 MeV. This experiment focused in particular on the cascade transition to the 0+ state at E x = 6.05 MeV in 16O and was performed by detecting the capture γ-rays with a NaI detector array at the windowless 4He gas target of the recoil mass separator ERNA in coincidence with the 16O ejectiles. The 6.05 MeV transition has been considered recently as a component accounting for up to 15% of the C 12 ( α , γ ) O 16 total cross section at astrophysical energies. The arrangement of the detector array yielded additional information on the γ-ray multipolarity, i.e. the ratio σ E 2 / σ E 1 , and it was found that the 6.05 MeV transition is entirely E2 in the studied energy range. The results for this transition are analyzed in an R-matrix formalism and extrapolated to the relevant Gamow energy of stellar helium burning, E 0 ≃ 300 keV . In contrast to a previous analysis, the present extrapolation suggests a negligible contribution from this amplitude, S 6.05 ( 300 ) 1 keV b . Additional data for cascade transitions to excited states at E x = 6.13 , 6.92, and 7.12 MeV, respectively, as well as to the ground state were obtained and the corresponding S factors in the studied energy range are given.

For improved measurements of the key astrophysical reaction C-12(alpha, gamma)O-16 in inverted kinematics, a recoil separator ERNA is being developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the O-16 recoils with about 50% efficiency. Calculations of the ion beam optics including all filtering and focusing elements of ERNA are presented. Since the C-12 projectiles and the O-16 recoils have essentially the same momentum, and since the C-12 ion beam emerging from the accelerator passes through a momentum filter (analysing magnet), the C-12 ion beam must be as free as possible from O-16 contamination for ERNA to succeed. In the present work, the O-16 contamination was reduced from a level of 1 x 10(-11) to a level below 2 x 10(-29) by the installation of Wien filters both before and after the analysing magnet. The measurement of these and other beam specifications involved other parts of the final ERNA layout - sequentially a Wien filter, a 60 degrees dipole magnet, another Wien filter, and a Delta E-E telescope. The setup led to a measured suppression factor of 5 x 10(-18) for the C-12 ion beam. The experiments also indicate that an almost free choice of the charge state for the O-16 recoils is possible in the separator.

(7)Be decays via electron capture and therefore its half-life is expected to depend on the electron density at the nucleus. We measured the (7)Be half-life in palladium, tungsten, zirconium and tantalum metals, in order to investigate the influence of the quasi-free electrons in metals on the probability of electron capture. The (7)Be samples were obtained implanting a 4.85 MeV pure radioactive (7)Be ion beam. The (7)Be half-life was determined measuring the 478 keV gamma decay following the electron capture by means of HPGe detectors. In order to reduce systematic errors, we planned to perform independent measurements in three different laboratories: Naples (Italy), Bochum (Germany) and Debrecen (Hungary). On the basis of the first results, we do not find a (7)Be half-life change within the experimental errors of 0.4%. RI Fulop, Zsolt/B-2262-2008

The electron screening in the 7Li ( p , α ) α reaction has been studied at E p = 30 to 100 keV for different environments: Li2WO4 insulator, Li metal, and PdLi alloys. For the insulator a screening potential energy of U e = 185 ± 150 eV was observed, consistent with previous work and the atomic adiabatic limit. However, for the Li metal and the PdLi alloys we find large values of U e = 1280 ± 60 and 3790 ± 330 eV , respectively: the values can be explained by the plasma model of Debye applied to the quasi-free metallic electrons in these samples. Similar results have been found for the 6Li ( p , α ) 3 He reaction supporting the hypothesis of the isotopic independence of the electron screening effect. The data together with previous studies of d ( d , p ) t and 9Be ( p , α ) 6 Li in metals verify the Debye model scaling U e ∝ Z t (charge number of target).

The astrophysically relevant 3 He ( d , p ) 4 He reaction was indirectly studied by means of the Trojan Horse Method applied to the 6 Li ( 3 He , pα ) 4 He three body process performed at 5 and 6 MeV. The bare astrophysical S(E)-factor extracted in Modified Plane Wave Born Approximation was compared with the free behaviour and an independent estimate of the screening potential was obtained, confirming the discrepancy with the adiabatic limit.

The reaction $^{17}$O$(p,\gamma)^{18}$F influences hydrogen-burning nucleosynthesis in several stellar sites, such as red giants, asymptotic giant branch (AGB) stars, massive stars and classical novae. In the relevant temperature range for these environments ($T_{9}=0.01-0.4), the main contributions to the rate of this reaction are the direct capture process, two low lying narrow resonances ($E_{r}=65.1$ and 183 keV) and the low-energy tails of two broad resonances ($E_{r}=557$ and 677 keV). Previous measurements and calculations give contradictory results for the direct capture contribution which in turn increases the uncertainty of the reaction rate. In addition, very few published cross section data exist for the high energy region that might affect the interpretation of the direct capture and the contributions of the broad resonances in the lower energy range. This work aims to address these issues. The reaction cross section was measured in a wide proton energy range ($E_{c.m.}=345$ - 1700 keV) and at several angles ($\theta_{lab}=0^{\circ},45^{\circ},90^{\circ},135^{\circ}$). The observed primary $\gamma$-transitions were used as input in an $R$-matrix code in order to obtain the contribution of the direct capture and the two broad resonances to the low-energy region. The extrapolated S-factor from the present data is in good agreement with the existing literature data in the low-energy region. A new reaction rate was calculated from the combined results of this work and literature S-factor determinations. Resonance strengths and branchings are reported for several $^{18}$F states. We were able to extrapolate the astrophysical S-factor of the reaction $^{17}$O$(p,\gamma)^{18}$F at low energies from cross section data taken at higher energies. No significant changes in the nucleosynthesis are expected from the newly calculated reaction rate., Comment: Accepted in Physical Review C

The recoil separator ERNA (European Recoil Separator for Nuclear Astrophysics) for improved measurements of the astrophysical key reaction C-12(alpha, gamma)O-16 is being developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the O-16 recoils. The total detection efficiency of about 50 % allows direct measurements in a much wider energy range than previously accessible. In addition this technique allows improved measurements not hampered by cosmic background problems when compared to gamma -ray detection.

The reaction He 3 ( α , γ ) Be 7 plays a key role for the understanding of the production of 7Li in Big Bang nucleosynthesis as well as for the high energy component of the solar neutrino spectrum. The uncertainty in its absolute cross-section arises from systematic differences of the available data sets. In various experiments the cross-section was measured by the detection of the prompt γ -rays or by the off-line observation of the γ -rays following the 7Be electron capture; in a few cases both observations were carried out. We report on a new approach based on the use of the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the 7Be recoils as well as the prompt γ -rays in coincidence with the recoils. We present technical details of the experimental setup, such as a recirculating 3He gas target, a TOF-E end detector, and a NaI detector array. In addition, the measurement of the separator acceptance is discussed and compared to the expected recoil emittance. The feasibility of the approach is demonstrated by sample spectra, indicating cross-section determinations of He 3 ( α , γ ) Be 7 in the energy range E cm = 0.7 – 3.3 MeV with high precision and accuracy.

The electron capture half life of 7 Be implanted into different metals has been measured with high precision in order to search for a possible dependence of the decay rate on the electron configuration around the 7 Be atoms. In order to reduce systematic errors, the half life in different metals is measured by three laboratories simultaneously using different experimental setups. The measurements and data analysis are in progress, preliminary results are presented.

The total cross section of 12C(alpha,gamma)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.

For improved cross-section measurements of the reaction 12C(α,γ)16O in inverted kinematics, a recoil separator ERNA is developed at the 4MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. The 16O recoils are produced by the 12C projectiles in a windowless 4He gas target. We report on the pressure profile of the gas target, the beam suppression by the separator, and the first observation of the 16O recoils at selected energies. © 2003 Elsevier B.V. All rights reserved.

For the electron capture of Be-7 in the metallic environments Pd and In the Be-7 half-life was observed to increase by 0.9 +/- 0.2 and 0.7 +/- 0.2%, respectively, while in the insulator Li2O it was unchanged within experimental error (all samples cooled to T = 12K). The observations are consistent with the predictions of the Debye plasma model applied to the quasi-free electrons in the metals.

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 +/-300 eV at E-p = 130-400 keV using the energy of the capture gamma-ray transition of C-12(p,gamma)N-13 as well as resonance energies at E-p = 309-389 keV of Na-23(p, gamma)Mg-24, Mg-26(p, gamma)Al-27, and Mg-25(p, gamma)Al-26. The resonance studies led to a proton energy spread of better than 100 eV and a long-term energy stability of 5 eV per hour.

A new measurement of the cross section of 7Be(p, $ \gamma$ )8B will be done in inverted kinematics with the recoil separator ERNA at the CIRCE laboratory in Caserta, Italy. The 8B recoils will be produced in a windowless hydrogen gas target. We report here on the construction and characterization of the gas cell. In detail we describe measurements for target density, the profile determination via the 7Li(p, p’)7Li* reaction as well as the role and performance of a gaseous post-stripper.

We report on a new lifetime measurement of the ${E}_{x}=6792$ keV state in $^{15}\mathrm{O}$ via the Doppler-shift attenuation method at the $E=259$ keV resonance in the reaction $^{14}\mathrm{N}$($p,\ensuremath{\gamma}$)$^{15}\mathrm{O}$. This subthreshold state is of particular importance for the determination of the ground state astrophysical $S$ factor of $^{14}\mathrm{N}$($p,\ensuremath{\gamma}$)$^{15}\mathrm{O}$ 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 ${E}_{x}=5181$ and 6172 keV have been measured with the same technique in order to verify the experimental method. We observe an attenuation factor $F(\ensuremath{\tau})g0.98$ for the ${E}_{x}=6172$ and 6792 keV states, respectively, corresponding to $\ensuremath{\tau}l0.77$ fs. The attenuation factor for the ${E}_{x}=5181$ keV state results in $F(\ensuremath{\tau})=0.78\ifmmode\pm\else\textpm\fi{}0.02$ corresponding to $\ensuremath{\tau}=8.4\ifmmode\pm\else\textpm\fi{}1.0$ fs, which is in excellent agreement with literature.

In the metal Cu cooled to T = 12K the alpha-decay half-life of Po-210 nuclides, located inside the metal, was measured to be shorter by 6.3 +/- 1.4% compared to that at room temperature. RI Aliotta, Marialuisa /H-2567-2012

For the β--decay of 198Au in a Au metallic environment the half-life was observed to be longer by 0.4±0.7% at room temperature (T = 293K) and by 4.0±0.7% when the metal was cooled to T = 12K, both compared to the literature value of T 1/2 = 2.6943±0.0008d.

The $^{3}\mathrm{He}$($d,p$)$^{4}\mathrm{He}$ reaction has been studied from ${E}_{c.m.}=600$ keV down to astrophysical energies by means of the ``Trojan horse'' method using the $^{6}\mathrm{Li}$($^{3}\mathrm{He}$,$p\ensuremath{\alpha}$)$^{4}\mathrm{He}$ three-body reaction at ${E}_{\mathrm{lab}}=5$ and 6 MeV. Coincidence spectra were measured in kinematic conditions favoring the quasifree $^{3}\mathrm{He}+^{2}\mathrm{H}$ process. The bare astrophysical factor ${S}_{b}(E)$ for the $^{3}\mathrm{He}$($d,p$)$^{4}\mathrm{He}$ reaction was extracted from the three-body cross section in the modified plane-wave Born approximation. Comparison with the ${S}_{b}$ extrapolation from the free two-body data is presented. The independent estimate of the screening potential as obtained with the present work seems to confirm the theoretical adiabatic limit.

For improved cross section measurements of the reaction 12 C ( α , γ ) 16 O in inverted kinematics, a recoil separator ERNA is developed at the 4 MV Dynamitron tandem accelerator in Bochum to detect directly the 16O recoils with high efficiency. The 16O recoils are produced by the 12C projectiles in a windowless 4He gas target. We report on the charge state distribution of the 16O recoils, the gas target density, the beam heating of the gas target, and the acceptance of the separator along the extended gas target.

For the beta(+)-decay of Na-22 in the metallic environment Pd cooled to T = 12 K the Na-22 half-life was observed to be shorter by 1.2 +/- 0.2%. The result is consistent with-but lower than-the prediction of the Debye plasma model.

6Li+-ions accelerated electrostatically to energies of 200–390 keV are electronically excited by the beam-foil technique. The emitted light is analyzed with a Seya-Namioka VUV monochromator in the wavelength range 400–1900 a. All Li II and Li III lines known from theory — in one case emitted by an=9 level — are detected, several of them for the first time. Lifetimes of 20 Li II levels, some not measured previously, are determined after correction for cascades. The accuracy of the experimental values for several lifetimes is better than that of theoretical predictions.

H 2 + ions or protons, accelerated to energies between 80 and 300 keV, are sent through a thin carbon target. Light emitted by the excited atoms moving out of the foil with a definite velocity is analyzed using interference filters and a cooled photomultiplier. Intensities of theH α,H β, andH γ lines are measured as functions of the distance from the foil. The data is analyzed with a computer program, which yields (in agreement with theory) mean lives of the hydrogen atom excited states involved, and the relative initial state populations of states belonging to the same principal quantum number. There is no indication of cascading.