M. Milin

6He + α clustering in 10Be

In a kinematically complete measurement of the 7Li(7Li,α6He)4He reaction at Ei = 8 MeV it was observed that the 10Be excited states at 9.6 and 10.2 MeV decay by 6He emission. The state at 10.2 MeV may be a member of a rotational band based on the 6.18 MeV 0+ state.

First Measurement of the 19F(α, p)22Ne Reaction at Energies of Astrophysical Relevance

The observational 19F abundance in stellar environments systematically exceeds the predicted one, thus representing one of the unsolved challenges for stellar modeling. It is therefore clear that further investigation is needed in this field. In this work, we focus our attention on the measurement of the 19F(α, p) 22Ne reaction in the astrophysical energy range, between 0.2 and 0.8 MeV (far below the Coulomb barrier, 3.8 MeV), as it represents the main destruction channel in He-rich environments. The lowest energy at which this reaction has been studied with direct measurements is ∼0.66 MeV, covering only the upper tail of the Gamow window, causing the reaction-rate evaluation to be based on extrapolation. To investigate lower energies, the 19F(α, p) 22Ne reaction has been studied by means of the Trojan horse method, applied to the quasi-free 6Li (19F, p22Ne)2H reaction at Ebeam = 6 MeV. The indirect cross section of the 19F(α, p) 22Ne reaction at energies ≲1 MeV was extracted, fully covering the astrophysical region of interest and overlapping existing direct data for normalization. Several resonances have been detected for the first time inside the Gamow window. The reaction rate has been calculated, showing an increase up to a factor of 4 with respect to the literature at astrophysical temperatures. This might lead to potential major astrophysical implications.

Structure of neutron-rich Be and C isotopes

The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2−, and 3/2−, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C.

4He1H2+ and 4He2H+, exotic impurities in 6He+ beam

(HeH2+)-He-4-H-1 ions were observed as an impurity in a 17.0 MeV He-6(+) beam produced by CYCLONE, with the ratio of Intensities being 1:5400. A (HeH+)-He-4-H-2 beam was also observed, having 60 times weaker intensity and slightly lower magnetic rigidity than original He-6(+) beam

Transfer, sequential decay, and quasi-free reactions induced by 18-MeV 6He beam on 6Li, 7Li, and 12C

The 6He + 6,7Li and 6He + 12C scattering and reactions have been studied using an 18-MeV 6He beam. Experimental results for the elastic scattering on all three targets are in fair agreement with optical model predictions, using the potentials found in the analysis of the 6Li scattering on the same targets and at close beam energies. Several two-body exit channels show clear signatures of a direct reaction mechanism allowing extraction of spectroscopic information. The measured angular distribution for the 6He + 6Li → α + 8Li reaction indicated close similarity between the α + 2n configuration in 6He and the α + d configuration in 6Li. The obtained results for α-particle pickup from both 6Li and 7Li give large values of α spectroscopic factors for some 10Be states, indicating their well-developed α + 6He cluster structure. The exotic two-proton pickup reaction (6He, 8Be) was studied, as well as two-neutron and triton transfer reactions. Quasi-free scattering of 6He on deuteron and α particle in 6Li was also observed. The sequential decay reactions 6He + 6Li → 6He + α + d, 6He + 6Li → 2α + t + n, 6He + 7Li → 6He + α + t, and 6He + 12C → 10Be + 2α were clearly seen, and α clustering of some states in 6,7Li, 8–10Be, and 14C was thus studied. Several new spectroscopic results obtained for some 10Be states support the existence of a molecule-like rotational band in 10Be with a very large moment of inertia.

7Li quasi-free scattering off the α-cluster in 9Be nucleus

Abstract. Spectra of coincident charged particles from the reactions induced by a 52 MeV 7Li beam incident on a beryllium target were measured. Strong contributions of the 7Li quasi-free scattering off the α-cluster in 9Be nucleus were observed. This observation supports the conclusions from the study of complete fusion of weakly bound light nuclei at low energies that the “fragility” of the nuclei makes their fusion less probable.

BAND STRUCTURES IN 12Be: EXPERIMENTAL RESULTS

The structure of the neutron-rich isotope 12Be has been studied using different transfer reactions, which populate distinct structures in 12Be. This concerns two-neutron and three-neutron stripping reactions and two-proton pick-up reactions at incident energies of 15–20 MeV/u. Band structures of positive and negative parity are discussed.

Covalent Binding on the Femtometer Scale: Nuclear Molecules

Nuclear molecules are objects having two or more individual clusters as centres with extra nucleons (usually neutrons) binding them. The clusters have to be strongly bound themselves, while they get bound into molecules due to the specific properties of the nucleus-nucleus potentials and exchange of nucleons. The molecular, quantum mechanical covalent binding effect via the exchange of neutrons is the dominant source of binding in many light nuclei, overcoming the Coulomb repulsion in such structures. This results in states having valence neutrons in the π and σ orbitals, known from molecules in atomic physics; in this paper we discuss the structural properties of such states in light nuclei. The interaction between clusters resulting in nuclear molecules should show a repulsive interaction at smaller distances. This is generally the case for strongly bound clusters, like α-particles (but also for the 12C and 16O nuclei)—due to the Pauli principle, nucleons penetrating the second cluster show then a strong repulsion effect. The particular properties of nuclear clusters needed for the formation of bound molecules is their intrinsic stiffness (a large gap to the first excited states), which inhibits their excitation and allows their survival in a two-centre configuration. A large number of strongly deformed nuclear states in light nuclei with neutron excess have been experimentally identified in the last decades, and some of them have been associated with covalent structures, mainly via their grouping into rotational bands. These results have been confirmed in many theoretical studies with nuclear cluster models, but also in model independent calculations, e.g. in the Antisymmetrized Molecular Dynamics approach, where no a priori cluster structure is assumed.

Reactions induced by {sup 7}Li beam and optimization of silicon detector telescope

Focus of this article is put on a method of compensating for non-uniformity of 50μm thin silicon detectors, rather than measurement results. The same high sensitivity of particle identification on thin-detector thickness enables to accurately model thickness variation using the measurement data, rather than measuring the thickness separately.

Halo effects on fusion cross section in 4,6He+64Zn collision around and below the coulomb barrier

The structure of the halo nuclei is expected to influence the fusion mechanism at energies around and below the Coulomb barrier. Here new data of 4He+64Zn at sub-barrier energies are presented which cover the same energy region of previous measurements of 6He+64Zn. The fusion cross section was measured by using an activation technique where the radioactive evaporation residues produced in the reaction were identified by the X-ray emission which follows their electron capture decay. By comparing the two system, we observe an enhancement on the fusion cross section in the reaction induced by 6He, at energy below the Coulomb barrier. It is shown that this enhancement seems to be due to static properties of halo 2n 6He nucleus.