The three-body breakup 6 He→ 4 Heϩnϩn is studied experimentally, using a secondary 6 He ion beam of 240 MeV/nucleon incident on carbon and lead targets. Integrated cross sections for one-and two-neutron knockout and differential cross sections d/dE* and d/d for inelastic nuclear or electromagnetic excitations into the 6 He continuum are presented. The E1-strength distribution is deduced from electromagnetic cross sections and is found to exhaust (10Ϯ2)% of the energy-weighted Thomas-Reiche-Kuhn sum rule or (40Ϯ8)% of the cluster sum rule for excitation energies below 5 MeV. Both the energy-weighted and non-energy-weighted dipole cluster sum rules are almost exhausted integrating the strength up to 10 MeV, a fact from which the root-mean-square distance between the ␣ core and the two valence neutrons of r ␣Ϫ2n ϭ(3.36Ϯ0.39) fm is derived. The known I ϭ2 ϩ ͑1.80 MeV͒ resonance in 6 He is observed in nuclear inelastic scattering; model-dependent values of the quadrupole deformation parameter ␦ 2 ϭ(1.7Ϯ0.3) fm or B(E2,0 ϩ →2 ϩ )ϭ(3.2Ϯ0.6)e 2 fm 4 are derived. No clear signature could be obtained for predicted higherlying 2 ϩ resonances, but low-lying continuum strength of multipolarity other than dipole, likely of monopole and quadrupole multipolarity, is indicated by the data. Two-body correlations in the decaying 4 Heϩnϩn system are investigated. The astrophysical relevance of the data with regard to the two-neutron capture process 4 He(2n,␥) 6 He is briefly discussed.

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Control over the motional degrees of freedom of atoms, ions, and molecules in a field-free environment enables unrivalled measurement accuracies but has yet to be applied to highly charged ions (HCIs), which are of particular interest to future atomic clock designs and searches for physics beyond the Standard Model. Here, we report on the Coulomb crystallization of HCIs (specifically (40)Ar(13+)) produced in an electron beam ion trap and retrapped in a cryogenic linear radiofrequency trap by means of sympathetic motional cooling through Coulomb interaction with a directly laser-cooled ensemble of Be(+) ions. We also demonstrate cooling of a single Ar(13+) ion by a single Be(+) ion-the prerequisite for quantum logic spectroscopy with a potential 10(-19) accuracy level. Achieving a seven-orders-of-magnitude decrease in HCI temperature starting at megakelvin down to the millikelvin range removes the major obstacle for HCI investigation with high-precision laser spectroscopy.

We have measured the Coulomb dissociation of 8 B into 7 Be and proton at 254 MeV/nucleon using a large-acceptance focusing spectrometer. The astrophysical S17 factor for the 7 Be (p,γ) 8 B reaction at Ec.m. = 0.25 − 2.78 MeV is deduced yielding S17(0) = 20.6±1.2 (exp.) ± 1.0 (theo.) eV-b. This result agrees with the presently adopted zero-energy S17 factor obtained in direct-reaction measurements and with the results of other Coulomb-dissociation studies performed at 46.5 and 51.2 MeV/nucleon. PACs: 25.40.Lw, 25.70.De, 26.65.+t The precise knowledge of the solar thermonuclear fusion of 8 B (from 7 Be plus proton) is crucial for estimating the 8 B solar neutrino flux and the predicted neutrino rates in terrestrial neutrino measurements. The relevant 7 Be(p,γ) 8 B cross section σ(E) is parameterized in terms of the astrophysical factor S 17 (E) which is defined by2 /hv is the Sommerfeld parameter. The flux of 8 B solar neutrinos is particularly important for the results of the Homestake, Super Kamiokande, and SNO experiments [1] which measure high-energy solar neutrinos mainly or solely from the 8 B decay. Unfortunately, this cross section has not been known with sufficient accuracy for a long time, despite the fact that several comprehensive direct measurements were reported for the 7 Be(p,γ) 8 B reaction [2][3][4][5][6]. The main difficulty in such experiments is the determination of the effective target thickness of the radioactive 7 Be target. This difficulty is reflected in the fact that the results of these measurements can be grouped into two distinct data sets which agree in their energy dependence but disagree in their absolute normalization by about 30%. In view of this discrepancy, experimental studies with different methods are highly desirable.As an alternative approach one can measure the inverse process, the Coulomb dissociation (CD) of 8 B into 7 Be and proton [7]. The CD yields are enhanced because thicker targets can be used and a larger phase space is available for CD. This method uses stable targets and thus is free from the difficulty of determining the effective target thickness. On the other hand, direct (p,γ) and Coulomb dissociation measurements have different sensitivities to the multipole composition of the photon fields. The E2 amplitude is enhanced in CD due to the large flux of E2 virtual photons, whereas it can be neglected in the (p,γ) reaction.Recently, Motobayashi et al. have performed a CD experiment at E( 8 B) = 46.5 MeV/nucleon, yielding values for S 17 in the energy range 0.6−1.7 MeV [8]. The extracted (p,γ) cross section is consistent with the results from the lower group of direct-reaction data points [4][5][6]. Another measurement at 51.9 MeV/nucleon by the same group with improved accuracy led essentially to the same conclusion [9].In this article, we report on an experiment of the CD of 8 B at a higher energy of 254 MeV/nucleon performed at the SIS facility at GSI, Darmstadt, Germany. The present incident energy has several advantages compared to those used in Refs. ...