Search

A systematic study of isotopic effects in the break-up of projectile spectators at relativistic energies has been performed with the ALADiN spectrometer at the GSI laboratory. Searching for signals of criticality in the fragment production we have applied the model independent universal fluctuations theory already proposed to track criticality signals in multifragmentation to our data. The fluctuation of the largest fragment charge and of the asymmetry of the two and three largest fragments and their bimodal distribution have also been analysed., Comment: 6 pages, 4 figures, IX International Conference on Nucleus-Nucleus Collisions, Rio de Janeiro, Brazil, August 28 - September 1, 2006

This talk will discuss the fragment yield measurements from the reaction of 58 Ni+ 9 Be and 58 Ni+ 181 Ta using the A1900 fragment separator at the National Superconducting Cyclotron Laboratory. In addition, the charge distributions for these two reactions as well as reactions using the 86 Kr beam will also be presented.

Summary form only given. It is well known that intense beams of energetic electrons are accelerated in z-pinches. Using magnetic deflection and Faraday cup detection we measured electron energies and the current of beams produced in conical wire array z-pinches and x-pinches. The variations in pointing and divergence of the beams reduced the accuracy of these measurements. However, the beam activity can be correlated with the x-ray emission of the z-pinches. We will present results of these measurements.

The ground state of Li-11 is the preeminent example of a two-neutron-halo nucleus and is part of an isobaric sextet. Another member of this sextet, the double isobaric analog of Li-11(g.s). in B-11, has been identified in the Be-12(p, 2n)B-11 reaction. The state was discovered through its two-proton decay branch. From detected 2p + Li-9 events, its excitation energy was determined to be 33.57(8) MeV using the invariant mass method. With the known masses of Li-11 and its isobaric analog state in Be-11, three members of the same sextet have measured masses for the first time, permitting the masses of the remaining members to be extrapolated using the isobaric multiplet mass equation. All members of this multiplet are expected to have a two-nucleon halo structure and this was found consistent with the evolution of the mass across the sextet. The momentum correlations of the detected protons were found to have both "diproton" and "cigar" components.

The angular dependence of proton-proton correlation functions is studied in central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ nuclear reactions at E=80 MeV/A. Measurements were performed with the HiRA detector complemented by the 4$\pi$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation functions for both systems that greatly exceeds the measured and expected isospin dependent difference between the neutron-rich and neutron-deficient systems. Sources measured at backward angles reflect the participant zone of the reaction, while much larger sources observed at forward angles reflect the expanding, fragmenting and evaporating projectile remnants. The decrease of the size of the source with increasing momentum is observed at backward angles while a weaker trend in the opposite direction is observed at forward angles. The results are compared to the theoretical calculations using the BUU transport model.

The N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios /Z and the isoscaling parameters of Z, 23 pages, 29 figures, published in Physical Review C

Resonance-decay spectroscopy is used to study particle-unbound excited states produced in interactions of E/A=50 MeV {sup 12}Be on polyethylene and carbon targets. The particle-unbound states are produced in a variety of reaction mechanisms, ranging from projectile fragmentation to proton pickup. New proton-decaying excited states are observed in {sup 9}Li(E*=14.1{+-}0.1 MeV, {gamma}=207{+-}49 keV) and {sup 10}Be(E*=20.4{+-}0.1 MeV, {gamma}=182{+-}74 keV). In addition a new {alpha}-decaying state is observed in {sup 13}B(E*=13.6{+-}0.1 MeV, {gamma}{ 2. A second T=2 state was confirmed in {sup 12}B at 14.82 MeV, which decays to the p+{sup 11}Be, {sup 3}H+{sup 9}Be, and {alpha}+{sup 8}Li channels. Its width was found to be {gamma}{

The breakup of $E/A=50$ MeV $^{12}\mathrm{Be}$ fragments following inelastic scattering off of hydrogen and carbon target nuclei has been studied. The breakup channels $\ensuremath{\alpha}+$$^{8}\mathrm{He}$, $^{6}\mathrm{He}$$+$$^{6}\mathrm{He}$, $t+$$^{9}\mathrm{Li}$, and $p+$$^{11}\mathrm{Li}$ were observed. Two doublets at excitation energies of 12.8 and 15.5 MeV were found for the $\ensuremath{\alpha}+$$^{8}\mathrm{He}$ channel. A low-energy shoulder in the excitation-energy spectra at 10.2 MeV indicates one or more additional states. This work could not confirm the presence of $^{6}\mathrm{He}$$\text{\ensuremath{-}}$$^{6}\mathrm{He}$ rotational structure reported by Freer et al. [Phys. Rev. C 63, 034301 (2001)], although possible peaks at excitation energies of 13.5 and 14.5 MeV were found for $^{6}\mathrm{He}$$+$$^{6}\mathrm{He}$ decay. Significant structure is observed in the excitation-energy spectrum for $p+$$^{11}\mathrm{Li}$ at 25--30 MeV which maybe associated with $T=3$ analog states.

An exponential dependence of the fragmentation cross-section on the average binding energy is observed and reproduced with a statistical model. The observed functional dependence is robust and allows the extraction of binding energies from measured cross-sections. From the systematics of 75,77,78,79Cu isotope cross-sections have been extracted. They are 636.94 +/- 0.40 MeV, 647.1 +/- 0.4 MeV, 651.6 +/- 0.4 MeV and 657.8 +/- 0.5 MeV, respectively. Specifically, the uncertainty of the binding energy of 75Cu is reduced from 980 keV (listed value in the 2003 mass table of Audi and Wapstra) to 400 keV. The predicted cross-sections of two near drip-line nuclei, 39Na and 40Mg, from the fragmentation of 48Ca are discussed., 12 pages, 3 figures

A new experimental approach was developed that can reduce the uncertainties in astrophysical rapid proton capture ($rp$) process calculations due to nuclear data. This approach utilizes neutron removal from a radioactive ion beam to populate the nuclear states of interest. Excited states were deduced by the $\ensuremath{\gamma}$-decay spectra measured in a semiconductor Ge-detector array. In the first case studied, $^{33}\mathrm{Ar}$, excited states were measured with uncertainties of several keV. The 2 orders of magnitude improvement in the uncertainty of the level energies resulted in a 3 orders of magnitude improvement in the uncertainty of the calculated $^{32}\mathrm{Cl}(p,\ensuremath{\gamma})^{33}\mathrm{Ar}$ rate that is critical to the modeling of the $rp$ process. This approach has the potential to measure key properties of almost all interesting nuclei on the $rp$-process path.

A search for $^{19}\mathrm{Mg}$ was performed using projectile fragmentation of a $150\phantom{\rule{0.3em}{0ex}}\text{MeV}∕\text{nucleon}$ $^{36}\mathrm{Ar}$ beam. No events of $^{19}\mathrm{Mg}$ were observed. From the time of flight through the fragment separator an upper limit of $22\phantom{\rule{0.3em}{0ex}}\text{ns}$ for the half-life of $^{19}\mathrm{Mg}$ was established.

The knockout of protons from ${}^{8}\mathrm{B}$ and ${}^{9}\mathrm{C}$ on a carbon target has been studied at average energies of 76 and 78 MeV/nucleon, respectively, with beams from the A1900 fragment separator incident on a stack of silicon detectors. The following cross sections were obtained: ${\ensuremath{\sigma}}_{\ensuremath{-}1\mathrm{p}}{(}^{8}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}}^{7}\mathrm{Be})=130(11)\mathrm{mb},$ ${\ensuremath{\sigma}}_{\ensuremath{-}1\mathrm{p}}{(}^{9}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{C}}}^{8}\mathrm{B})=54(4)\mathrm{mb},$ and ${\ensuremath{\sigma}}_{\ensuremath{-}2\mathrm{p}}{(}^{9}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{C}}}^{7}\mathrm{Be})=98(7)\mathrm{mb}.$ The results are discussed within the framework of an eikonal approach and compared with measurements performed at higher energies. From this analysis, a consistent picture emerges that gives evidence for the validity of the eikonal approach at energies below 100 MeV/nucleon. Knockout reactions at intermediate energy can thus be used to deduce absolute shell occupancies. We find the spectroscopic factors to be reduced by ${R}_{s}$ of 0.86(7) and 0.82(6) for ${}^{8}\mathrm{B}$ and ${}^{9}\mathrm{C},$ respectively, relative to shell-model predictions. The ${}^{9}\mathrm{C}$ result provides an accurate measurement of the asymptotic normalization coefficient of $1.27(10){\mathrm{fm}}^{\ensuremath{-}1}.$ A new technique is reported for determining separately the contributions from stripping and diffractive breakup.

A search for 19Mg was performed using projectile fragmentation of a 150 MeV/nucleon 36Ar beam. No events of 19Mg were observed. From the time-of-flight through the fragment separator an upper limit of 22 ns for the half-life of 19Mg was established.

Measuring magnetic field and current distribution in Z-pinch plasma systems is crucial to the validation of Z-pinch theory. In this letter, the demonstration of proton deflectometry to pulsed-power-driven loads at the mega-amp scale is presented, which is capable of making more detailed field maps in high-density regions of plasmas. In this method, a laser-driven, broad-spectrum, MeV-energy proton beam is directed through a pulsed-power-driven plasma system, and the resulting deflections are measured to examine configuration of magnetic fields and to infer the currents that support them. The technique was first demonstrated on simple short-circuit loads, and the results are in excellent agreement with numerical simulations providing reliable estimates of the field and current configurations. It was then applied to a more complex—radial foil—plasma load. The measurements show unexpected proton deflections that exhibit the complexity of the plasma load and that with further analysis will reveal details about the current and magnetic field topology in this complex configuration.

In hexagonal crystals such as quartz, an asymmetric Bragg reflection from two equivalent internal crystal planes can separate unpolarized x-rays into two linearly polarized components. The perfectly polarized and tunable x-rays from a synchrotron are ideal to evaluate polarization spitting in detail. One unanticipated feature is that additional reflections from the crystal affect the diffraction intensity of the two polarized components, an effect that is unlikely to matter in polarization spectroscopy of radiating plasmas for which the crystal is intended.

Two-proton decay is discussed in a number of light isobaric multiplets. For the lightest two-proton emitter, 6Be, the momentum correlations between the three decay products were measured and found to be consistent with quantum-mechanical three-cluster-model calculations. Two-proton decay was also found for two members of the A=8 and A=11 quintets. Finally, a third member of the A=11 sextet, the double isobaric analog of the halo nucleus 11Li in 11B was observed by its two-proton decay.