Invariant mass spectrum and α-n correlation function studied in the fragmentation of 6He on a carbon target

13 pags, 5 figures.-- PACS nrs.: 24.60.−t; 25.70.Ef; 27.20.+n.

Measurements of the dipole response with radioactive beams

The temperature dependence of photoabsorption of V13+

Photoabsorption cross sections of trapped V 13 + clusters were measured for energies between 1.4 eV and 6.1 eV by use of a two-photon fragmentation technique. Using two laser pulses separated by a 100-ns delay period the cross sections of hot clusters (up to 1800 K) could be compared to the values at room temperature. Whereas sodium clusters are known to exhibit pronounced temperature dependence below 300 K, no continuation of these effects to higher temperatures was found for V 13 + .

A large-area scintillating fibre detector for relativistic heavy ions

Abstract A scintillating fibre detector for relativistic heavy ions with an active area of 50 × 50 cm 2 has been developed and was tested with various ion beams (1 ≤ Z ≤ 92). At count rates of up to 10 5 particles/s, the position resolution was found to be determined by the fibre width of 1 mm; depending on the nuclear charge of the beam, efficiencies between 89% and 100% and time resolutions between 800 and 200 ps (FWHM) were obtained.

Continuum excitations in6He

T. Aumann et al. ; 11 pags.; 6 figs.; 2 tabs. ; PACS number(s): 27.20.1n, 25.60.Gc, 25.70.De, 29.30.Hs

Giant resonances in unstable oxygen isotopes

Abstract Electromagnetic and nuclear breakup of the neutron-rich Oxygen isotopes ranging from A = 17 to A = 22 is studied experimentally in reactions at energies around 600 MeV/u. The beams were produced in fragmentation reactions and separated by the GSI Fragment Separator FRS. By measuring the four-momenta of all decay products after inelastic scattering and neutron decay of the projectile, the excitation energy is determined. From the differential cross sections dσ dE ∗ for electromagnetic excitation, the E1-strength distributions can be deduced. For 18,20,22O, low-lying dipole strength is observed, exhausting about 5% of the Thomas Reiche Kuhn sumrule for energies up to 5 MeV above the …

Photoneutron cross sections for unstable neutron-rich oxygen isotopes.

The dipole response of stable and unstable neutron-rich oxygen nuclei of masses A = 17 to A = 22 has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about 600 MeV/nucleon. A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections d sigma/dE were derived up to 30 MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength.

Radiative Cooling of a Small Metal Cluster: The Case ofV13+

Size-selected stored metal cluster ions, ${\mathrm{V}}_{13}^{+}$, have been heated by photoexcitation ( $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}730$ to 229 nm) to well-defined excitation energies corresponding to temperatures between 1000 and 2100 K. A millisecond pump-probe photodissociation technique was applied to measure the time-resolved radiative cooling. The observed decay rates are directly related to the radiative energy loss and are explained quantitatively by the competing processes of photoemission and atom evaporation.

Halo excitations in fragmentation of He at 240 MeV/u on carbon and lead targets

Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while …

8He-6He: a comparative study of nuclear fragmentation reactions

19 pages, 3 tables, 6 figures.-- PACS nrs.: 27.20.+n; 24.70.+s; 25.06.-t.-- Available online Dec 4, 2000.