Coulomb dissociation of N 20,21

Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at

Coulomb Excitation of Proton Rich Nuclei 32Ar and 34Ar

In the present thesis an investigation of the low-lying strength in the proton-rich nuclei32Ar and 34Ar is reported. The earlier observation of low-lying dipole strengthin neutron-rich nuclei and its interpretation with respect to basic nuclear properties(symmetry energy, skin thickness) initiated the investigation of this phenomenon inproton-rich nuclei. Macroscopically this so-called Pygmy strength could be interpretedwith the resonant dipole oscillation of a proton-skin against an isospin-symmetric core.For nuclei like 32Ar the occurrence of pronounced dipole strength is predicted in the lowenergyregion between 8-10 MeV excitation energy. For the 34Ar the pygmy strengthis expected to drop sharply and vanish entirely for the N=Z nucleus 36Ar. Using theCoulomb excitation method in inverse and complete kinematics at the LAND/R3Bsetup at GSI Helmholtzzentrum f¨ur Schwerionenforschung GmbH in Darmstadt, Germany,an experiment using radioactive 32Ar and 34Ar beams has been performed. Theisotopes were obtained via fragmentation of a 825 AMeV primary 36Ar beam on a6.347g/cm2 Be target. The produced proton-rich projectiles with a similar mass-tochargeratio were separated from the primary beam and from other reaction productsin flight using the Fragment Separator FRS. The selected and identified proton richisotopes with a remaining energy of 650 AMeV were subsequently directed to a leadtarget of the LAND/R3B setup placed in Cave C. In order to determine the excitationenergy after projectile excitation on the Pb target, all the products of the decay fromthe resonance are detected and identified (fragments, protons and gammas). The reconstructionof the excitation energy for one- and two-proton emission channels for 32Arand 34Ar were derived from the particles momenta using the invariant mass techniquein an event-by-event mode, allowing for an investigation of dipole strength appearance.After the experiment, all the detectors have been calibrated and the Coulombdissociation cross section for one and two proton emission were determined with twodifferent techniques, which are in good agreement. The data provide first evidencefor the existence of low-lying dipole strength in 32Ar, while no low-lying strength isobserved in 34Ar. However, further analysis is necessary in order to define the detailsand interpretation of the appearance of the low-lying strength dipole in 32Ar

The \u3csup\u3e33\u3c/sup\u3eS(p,γ)\u3csup\u3e34\u3c/sup\u3eCl reaction in classical nova explosions

The analysis of microscopic grains within primitive meteorites has revealed isotopic ratios largely characteristic of the conditions thought to prevail in various astrophysical environments. Recently, several grains have been identified with isotopic signatures similar to those predicted within the ejecta of nova explosions on oxygen-neon white dwarfs. A possible smoking gun for a grain of nova origin is a large 33S abundance: nucleosynthesis calculations predict as much as 150 times the solar abundance of 33S in the ejecta of oxygen-neon novae. This overproduction factor may, however, vary by factors of at least 0.01 - 3 because of uncertainties in the 33S(p,γ)34Cl reaction rate over nova temperatures. In addition, better knowledge of this rate would help with the interpretation of nova observations over the S-Ca mass region, and contribute towards the firm establishment of a nucleosynthetic endpoint in these phenomena. Finally, constraining this rate may help to finally confirm or rule out the decay of an isomeric state of 34Cl (Ex = 146 keV, t1/2 =32 min) as a source for observable gamma-rays from novae. Direct examinations of the 33S(p,γ)34Cl reaction in the past have only identified resonances down to Er = 434 keV. At nova temperatures, lower-lying resonances could certainly play a dominant role. Several recent, complementary studies dedicated to improving our knowledge of the 33S(p,γ)34Cl rate, using both indirect methods (measurement of the 34S( 3He,t)34Cl and 33S(3He,d) 34Cl reactions with the Munich Q3D spectrograph) and direct methods (in normal kinematics at CENPA, University of Washington, and in inverse kinematics with the DRAGON recoil mass separator at TRIUMF) are presented here. Our results affect predictions of sulphur isotopic ratios in nova ejecta (e.g. 32S/33S) that may be used as diagnostic tools for the nova paternity of grains. © ?Copyright owned by the author(s)