Ralph Segel

The 23Na(p, γ)24Mg reaction and the giant dipole resonance in 24Mg☆

Abstract The 23 Na(p, γ) 24 Mg reaction has been studied over the region of excitation corresponding to the giant dipole resonance. Gamma rays to the ground state and to the first and to the second plus third excited states have been observed. The (p, γ 0 ) cross section is on the average smaller than it is in other doubly even nuclei in this region. The (p, γ 1 ) cross section is considerably larger than the (p, γ 0 ) and clearly follows a giant-resonance shape. A part of the giant resonance built upon the second and/or third excited states is also observed. A fluctuation analysis finds the coherence width to be about 75 keV. The angular distributions of both γ 0 and γ 1 show the usual small energy variation that has come to be associated with the giant resonance.

Measurement of kaonic X-rays from Al, Si, Ni and Cu

Abstract We have identified X-rays associated with stopped negative kaons in Al, Si, Ni and Cu. We report relative intensities, strong interaction energy shifts and strong interaction line broadenings. The measurements are found to be in good agreement with those predicted on the basis of a simple phenomenological potential except for the Ni (5 → 4) transition width.

Experiments with a radioactive 56Ni beam

Abstract A technique for producing a high-quality radioactive 56 Ni (T 1/2 =6.1 d ) beam via the two-accelerator method has been developed. Beam intensities of 2×10 7 56 Ni/s were extracted from the ion source and 2×10 4 56 Ni/s were delivered to the target. For a study of neutron transfer reactions in inverse kinematics, a high-efficiency detection system was built consisting of a large solid angle (2.8 sr), high-granularity Si detector array for measuring the outgoing protons in coincidence with the heavy reaction products identified with respect to mass A and nuclear charge Z in the focal plane of a recoil mass separator.

Study of radiative capture reactions with radioactive ion beams

A technique for separating and identifying reaction products from radiative capture reactions induced by radioactive ion beams has been developed. The {sup 18}F(p,{gamma}){sup 19}Ne and {sup 18}O(p,{gamma}){sup 19}F reactions have been measured in inverse kinematics by identifying the {sup 19}F and {sup 19}Ne reaction products with respect to mass and charge at forward angles in the Fragment Mass Analyzer. A total detection efficiency of 30% and a suppression factor for the incident beam relative to the (p,{gamma}) reaction products of better than 10{sup 12}:1 was achieved. Details of the detection technique, the beam monitoring procedure as well as experience in the use of polypropylene targets in experiments with radioactive beams are discussed.

The Use of a Gas-Filled-Magnet in Experiments with Radioactive Ion Beams

Abstract A detection system has been developed for experiments with radioactive beams which have considerable contamination from a stable isobar. The system uses the gas-filled magnet technique and identifies reaction products according to nuclear charge and mass with good resolution even at energies below 1 MeV/u. In a first experiment the device has been used to measure cross sections for the 18F(p, α)15O reaction in the energy range between 650 and 840 keV/u.

Quasi-free proton-scattering at 164 MeV☆

Abstract Inclusive proton spectra have been measured over the angular range 25° – 150° for 164 MeV protons on 27 Al, 58 Ni, 62 Ni and 208 Pb. At 25° and 30° a peak attributable to quasi-free scattering, accounting for ≈20% of the total number of fast protons at these angles, is present. No quasi-free peak is evident in the spectra at larger angles. These results are in disagreement with previously published work at this energy but in line with results reported at other energies.

10+ Resonance at Ec.m. = 19.0 MeV in 12C(12C, α)20Ne☆

Abstract The resonance previously observed in 12 C( 12 C, α) 20 Ne at E c.m. = 19.0 MeV is assigned J π = 10 + from the shape of the ground-state angular-distribution measured at resonance.

4+ and 6+ core-excited states in 20Ne

Abstract Selective population of the 4 + and 6 + states at E x = 9.04 and 12.16 MeV, respectively, in the 12 C( 12 C,α 20 Ne reaction identifies those states as the 4 + and 6 + members of the first K π = 0 + core-excited band, whose lower members are the 0 + state at 7.20 MeV and the 2 + state at 7.83 MeV.

Nuclear Reactions Studies with Radioactive 18F Beams at ATLAS

Abstract The contribution of the 18 F(p,γ) reaction to the production of 19 Ne which is the crucial isotope for the breakout from the hot CNO cycle into the rp process, has been investigated in experiments with 18 F beams. Measurements of the cross sections for the 18 F(p,α) 15 O and the 18 F(p,γ) 19 Ne reactions indicate that the contribution from the (p,γ) route to the formation of 19 Ne is small.

Precision Mass Measurements of Heavy 252Cf Fission Fragments Near the r-process Path

The path of the astrophysical r process and the resulting elemental distribution are dependent on the neutron-separation energies of species far from stability. The mass models used to extrapolate these energies have increasing uncertainties with neutron number. Therefore, precision mass measurements of species near the r-process path are vital to generate more precise predictions of elemental abundances produced by this explosive nucleosynthetic process. As part of an ongoing program, the Canadian Penning Trap mass spectrometer at Argonne National Laboratory is measuring the masses of fission products from a 150-µCi 252 Cf source placed inside a new large-volume He gas catcher. Within the region investigated, new precision mass measurements have been made closer to the r-process path than have previously been published, with precisions near 15 keV/c 2. our results differ from the AME03 [1] by up to 325 keV/c 2. Work will continue with the current fission source until 2009, when measurements of many more neutron-rich isotopes will be made at the CARIBU upgrade to the ATLAS accelerator at ANL. c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.