Interactions of heavy nuclei, Kr, Xe and Ho, in light targets

Over the past few years, the HEAO-3 measurements of the abundances of ultra-heavy cosmic ray nuclei (Z 26) at earth have been analyzed. In order to interpret these abundances in terms of a source composition, allowance must be made for the propagation of the nuclei in the interstellar medium. Vital to any calculation of the propagation is a knowlege of the total and partial interaction cross sections for these heavy nuclei on hydrogen. Until recently, data on such reactions have been scarce. However, now that relativistic heavy ion beams are available at the LBL Bevalac, some of the cross sections of interest can be measured at energies close to those of the cosmic ray nuclei being observed. During a recent calibration at the Bevalac of an array similar to the HEAO-C3 UH-nuclei detector, targets of raphite (C), polyethylene (CH2), and aluminum were exposed to five heavy ion beams ranging in charge (Z) from 36 to 92. Total and partial charge changing cross sections for the various beam nuclei on hydrogen can be determined from the measured cross sections on C and CH2, and will be applied to the propagation problem. The cross sections on Al can be used to correct the abundances of UH cosmic rays observed in the HEAO C-3 detector for interactions in the detector itself

Fragmentation cross sections of relativistic ^(84)_(36)Kr and ^(109)_(47)Ag nuclei in targets from hydrogen to lead

With the addition of krypton and silver projectiles we have extended our previous studies of the fragmentation of heavy relativistic nuclei in targets ranging in mass from hydrogen to lead. These projectiles were studied at a number of discrete energies between 450 and 1500A MeV. The total and partial charge-changing cross sections were determined for each energy, target, and projectile, and the values compared with previous predictions. A new parametrization of the dependence of the total charge-changing cross sections on the target and projectile is introduced, based on nuclear charge radii derived from electron scattering. We have also parametrized the energy dependence of the total cross sections over the range of energies studied. New parameters were found for a previous representation of the partial charge-changing cross sections in hydrogen and a new parametrization has been introduced for the nonhydrogen targets. The evidence that limiting fragmentation has been attained for these relatively light projectile nuclei at Bevalac energies is shown to be inconclusive, and further measurements at higher energies will be needed to address this question

Response of Scintillators to UH Nuclei

In order to evaluate the performance of plastic scintillators for the detection of Ultra-Heavy cosmic ray nuclei, as envisaged in paper OG 10.1.14P, we have conducted experiments at the LBL Bevalac in which we exposed NE-114 and acrylic scintillators to beams of 47Ag ions and its interaction fragments. As a result we have calibrated these scintillators over the charge range 31 ≤ Z ≤ 47. Our results show that a combination of Cherenkov and scintillator detectors can resolve individual charges over this charge range. The resolution obtained in scintillator was 0.24 and 0.28 cu for NE-114 and acrylic scintillator respectively. In addition the light emission is shown to be linear to a good approximation with dE/dx over this charge range

Nuclear Interaction Cross Sections for UltraHeavy Nuclei

We summarize additions to our data base of charge-changing cross sections for relativistic ultraheavy nuclei interacting in targets ranging from H to Pb. We have improved parametric fits to those cross sections as functions of energy and of projectile, target, and fragment charge. At high energies, we have determined cross sections for Au projectiles at 10.6 GeV /nucleon in targets of H, CH_2, C, Al, Cu, Sn, and Pb. Compared with cross sections at 1 GeV /n, fragment production is substantially changed, especially for the H target. These changes have important implications for calculations of interstellar propagation of ultraheavy nuclei. At lower energies, we have added Kr and Ag to our list of projectiles. Analysis of these data has led to a better understanding of the systematics of these cross sections, hence more physically meaningful parameterizations for fragmentation at high energies and for charge pickup

Fragmentation of UH Nuclei

We have measured the total charge changing cross sections as a function of energy for projectile _(36)Kr nuclei in a wide range of targets ranging from polyethylene to lead. These cross sections are energy dependent and the dependence increases as the target mass increases

The Cosmic-Ray Abundances of the Platinum-Lead Elements as Measured on HEAO-3

The relative abundances of elements in the charge ranges of 75 ≤ Z ≤ 79 (platinum) and 80 ≤ Z ≤ 83 (lead) should be a sensitive indication of the contributions of the r- and s-processes in nucleosynthesis. Data from the HEAO 3 Heavy Nuclei Experiment are used to establish abundances, relative to iron, of these elements in the cosmic radiation, as well as the ratio of 'secondary' elements, in the 62 ≤ Z ≤ 74 range, to the primary lead-platinum elements. These results appear to suggest that either the source abundances are deficient in s-process elements or that they are not organized solely by first ionization potential. In addition, present propagation models can adequately represent the relative abundances of primary and secondary elements

Energy Dependence of the Fragmentation of UH-Nuclei

The fragmentation of 10.6 GeV/n Au in CH_2. C, Al, Cu, Sn, and Pb targets has been studied using an array of ion chambers, multi-wire proportional counters (MWPC), and Cherenkov counters. Total charge-changing cross sections were found to be monotonically increasing with target charge over cross sections measured and derived from lower energy data. Partial charge-changing cross sections yielding charge changes less than 1O were depressed from those measured at lower energy

The Response of Ionization Chambers to Relativistic Heavy Nuclei

As part of a recent calibration at the LBL Bevalac for the Heavy Nuclei Experiment on HEAO-3, we have compared the response of a set of laboratory ionization chambers to beams of _(26)Fe, _(36)Kr, _(54)Xe, _(67)Ho, and _(79)Au nuclei at maximum energies ranging from 1666 MeV/amu for Fe to 1049 MeV /amu for Au. The response of these chambers shows a significant deviation from the expected energy dependence, but only a slight deviation from Z^2 scaling

Galactic Cosmic Ray Origins and OB Associations: Evidence from SuperTIGER Observations of Elements 26_{26}Fe through 40_{40}Zr

We report abundances of elements from $_{26}$Fe to $_{40}$Zr in the cosmic radiation measured by the SuperTIGER (Trans-Iron Galactic Element Recorder) instrument during 55 days of exposure on a long-duration balloon flight over Antarctica. These observations resolve elemental abundances in this charge range with single-element resolution and good statistics. These results support a model of cosmic-ray origin in which the source material consists of a mixture of 19$^{+11}_{-6}$\% material from massive stars and $\sim$81\% normal interstellar medium (ISM) material with solar system abundances. The results also show a preferential acceleration of refractory elements (found in interstellar dust grains) by a factor of $\sim$4 over volatile elements (found in interstellar gas) ordered by atomic mass (A). Both the refractory and volatile elements show a mass-dependent enhancement with similar slopes.Comment: 9 pages, 12 figures, 2 tables, accepted by Ap