C. Mazzocchi

Neutron-induced background by an α-beam incident on a deuterium gas target and its implications for the study of the 2H(α, γ)6Li reaction at LUNA

Abstract.The production of the stable isotope 6Li in standard Big Bang nucleosynthesis has recently attracted much interest. Recent observations in metal-poor stars suggest that a cosmological 6Li plateau may exist. If true, this plateau would come in addition to the well-known Spite plateau of 7Li abundances and would point to a predominantly primordial origin of 6Li , contrary to the results of standard Big Bang nucleosynthesis calculations. Therefore, the nuclear physics underlying Big Bang 6Li production must be revisited. The main production channel for 6Li in the Big Bang is the 2H(α,γ)6Li reaction. The present work reports on neutron-induced effects in a high-purity germanium detector that were encountered in a new study of this reaction. In the experiment, an α-beam from the underground accelerator LUNA in Gran Sasso, Italy, and a windowless deuterium gas target are used. A low neutron flux is induced by energetic deuterons from elastic scattering and, subsequently, the 2H(d,n)3He reaction. Due to the ultra-low laboratory neutron background at LUNA, the effect of this weak flux of 2-3MeV neutrons on well-shielded high-purity germanium detectors has been studied in detail. Data have been taken at 280 and 400keV α-beam energy and for comparison also using an americium-beryllium neutron source.

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.

Proton spectroscopy of Ni 48, Fe 46, and Cr 44

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

β decay of 71 , 73 Co: Probing single-particle states approaching doubly magic 78 Ni

Low-energy excited states in 71,73Ni populated via the decay of 71,73Co were investigated in an experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). Detailed analysis led to the construction of level schemes of 71,73Ni, which are interpreted using systematics and analyzed using shell-model calculations. The 5/2 states attributed to the the f5/2 orbital and positive-parity 5/2+ and 7/2+ states from the g9/2 orbital have been identified in both 71,73Ni. In 71Ni the location of a 1/2 -decaying isomer is proposed, and limits are suggested as to the location of the isomer in 73Ni. The location of positive-parity cluster states are also identified in 71,73Ni. Beta-delayed neutron branching ratios obtained from this data are given for both 71,73Co. DOI: 10.1103/PhysRevC.85.034326 PACS number(s): 23.40. s, 21.10.Pc, 21.60.Cs, 27.50.+

Nuclear Astrophysics At LUNA: Status And Perspectives

The talk will be mainly devoted to the measurement of the cross section of the 3He(α,γ)7Be reaction which belongs to the p‐p chain. Actually, solar neutrino fluxes depend both on astrophysical and on nuclear physics inputs, namely on the cross sections of the reactions responsible for neutrino production inside the Solar core. While the flux of solar 8B neutrinos has been recently measured at Superkamiokande with a 3.5% uncertainty and a precise measurement of 7Be neutrino flux is foreseen in the next future, the predicted fluxes are still affected by larger errors. The largest nuclear physics uncertainty to determine the fluxes of 8B and 7Be neutrinos comes from the 3He(α,γ)7Be reaction. The uncertainty on its S‐factor is due to an average discrepancy in results obtained using two different experimental approaches: the detection of the delayed γ rays from 7Be decay and the measurement of the prompt γ emission. The LUNA Collaboration has performed a new high precision experiment with both techniques at th...

Beta‐delayed proton decay of a high‐spin isomer of 94Ag

We have observed the high‐spin states in 93Rh populated by delayed‐proton emission following the β decay of 94Ag. The existence of a second isomer in 94Ag with I⩾17, T1/2=0.42(5) s, whose β‐decay energy is at least 15.5 MeV, has been established. This state features most likely the highest spin ever observed for β‐decaying nuclei.

Recent developments at the GSI Online Mass Separator

Abstract The research programme at the GSI Online Mass Separator focuses on the study of exotic nuclei far from the valley of stability. Special emphasis is placed on the investigation of decay properties of isotopes along the N = Z line between the double shell closures at 56 Ni and 100 Sn. In this contribution, the major recent achievements along with the corresponding experimental methods are reviewed.

Proton spectroscopy of 48Ni, 46Fe, and 44Cr

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

Proton spectroscopy of Ni48,Fe46 , and Cr44

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

Pre-equilibrium GDR in a heavy composite system

The excitation of the Dynamical Dipole mode along the fusion path was investigated for the first time in the formation of a heavy composite system in the A~190 mass region, in fusion-evaporation and fission events. The composite system was formed at identical conditions of excitation energy and spin from two reactions with different charge asymmetry: the charge asymmetric 40Ca + 152Sm and the nearly charge symmetric 48Ca + 144Sm at E lab =11 and 10.1 MeV/nucleon, respectively. In this paper, we report the results on fusion evaporation events and the preliminary analysis on fission channel.