Isovector soft dipole mode in 6Be

By using the 1H(6Li,6Be)n charge-exchange reaction, continuum states in 6Be were populated up to E_t=16 MeV, E_t being the 6Be energy above its three-body decay threshold. In kinematically complete measurements performed by detecting alpha+p+p coincidences, an E_t spectrum of high statistics was obtained, containing approximately ~5x10^6 events. The spectrum provides detailed correlation information about the well-known 0^+ ground state of 6Be at E_t=1.37 MeV and its 2^+ state at E_t=3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by Delta L=1 angular momentum transfer without other significant contributions. This structure can be interpreted as a novel phenomenon, i.e. the isovector soft dipole mode associated with the 6Li ground state. The population of this mode in the charge-exchange reaction is a dominant phenomenon for this reaction, being responsible for about 60% of the cross section obtained in the measured energy range.Comment: 8 pages, 7 figure

Unbound states studied by direct reactions

International audienceThe t(6He,8He)p t(8He,10He)p reactions were studied in experiments with 25A MeV 6He beam and 27.4A MeV 8He beams and an unique tritium gas target. Results on the 8He and 10He excitation energy spectra are presented. The 8He spectrum exhibits 3 states, apart of the ground state and known (2+) state at 3.6 MeV, the third state is seen at 5.4 MeV. A tentative assignment 1+ is proposed for this structure. The 10He spectrum shows no event at the excitation energy below 3 MeV what is in contradiction with the earlier reports on this nucleus. A high statistics of α-n coincidence events collected for the 8He beam run has been subjected to analysis in order search for the bound tetraneutron. The search produced a negative result

Study of the 6He structure in the reaction of quasifree scattering 4He(6He, 2α)

Expérience à Dubna (RU)In our experiment we studied three body momentum correlations of 6He breakup products emitted in the quasifree knockout reaction 4He(6He, 2α) at 6He beam energy 25A MeV. For the first time a detailed study of nuclear structure was done in the reaction of quasifree scattering with an unbound system as a spectator. In the experiment we used a detection system of large angular acceptance allowing us to investigate the process in a wide range of kinematical parameters. It was shown that the data obtained in the experiment are well consistent with the predictions obtained with the use of the Plane Wave Impulse Approximation allowing for the final state interaction between the two spectator neutrons

First Results of a 8^{8}He+d Experiment

International audienceSecondary 8He beam delivered by the fragment separator ACCULINNA was used in an experiment designed for the simultaneous study of the 7H and 9He exotic nuclei. Attempt to observe 7H produced in the reaction 2H(8He,3He)7H resulted only in setting a cross section limit, d$\$sigma/d$\Omega$−20 fm on the scattering length is obtained), and with a$5/2^+$ resonance located at ~4.2 MeV

First radioactive beams at ACCULINNA-2 facility and first proposed experiment

New fragment separator ACCULINNA-2 was installed at the primary beam line of the U-400M cyclotron in 2016. Recently, first radioactive ion beams were obtained. The design parameters of new facility were experimentally confirmed. Intensity, purity and transverse profile of several secondary beams at the final focal plane were studied. The intensities obtained for the secondary beams of 14B, 12Be, 9;11Li, 6;8He in the fragmentation reaction 15N (49.7 AMeV) + Be (2 mm) are in average 15 times higher in comparison to the ones produced at its forerunner ACCULINNA separator. The ACCULINNA-2 separator will become a backbone facility at the FLNR for the research in the field of light exotic nuclei in the vicinity of the nuclear drip lines. The planned first experiment, aimed for the observation of the 7H nucleus at ACCULINNA-2, is outlined