C. J. Waddington

The cascading of cosmic-ray nuclei in various media

More than a thousand interactions of primary heavy nuclei of the cosmic radiation with charge ≥10 and energy >1 GeV nucleon−1 in nuclear emulsion have been studied with emphasis on how the primary nucleus fragments. It has been determined that the cases of multiple successive fragmentations that have been observed do not occur more frequently than expected. The fragmentation ofZ>20 nuclei does depend on the target nucleus to some extent so it is important to try to separate the interactions in emulsion by theirNh (number of evaporation prongs). The fragmentation of816O at 2.1 GeV nucleon−1 measured at the Bevalac shows a similar dependence on target nucleus. By using data from these new interactions combined with published data we have simulated on a computer nuclear cascades in both emulsion and air. Results on these cascades are given for both primary silicon and primary iron nuclei. These results are used to discuss the fluctuations expected in extensive air showers produced by heavy primary nuclei.

Large-area scintillating-fiber time-of-flight/hodoscope detectors for particle astrophysics experiments

Abstract A new generation of detectors of ultra-heavy (UH) cosmic rays is being built which require the use of large-area, light-weight detector elements. In this paper, we present the design and operation of a new type of scintillating optical fiber detector, which can serve as both a time-of-flight (TOF) detector and coded hodoscope (i.e. trajectory detector). We demonstrate that this type of detector can make TOF measurements with a time resolution of 48xa0ps. We also present results of position measurements from a large area TOF/hodoscope that was flown on a high-altitude balloon flight in August, 1995. Finally, we discuss areas of modification and improvements that can be made to these detectors to enable them to be more useful for making UH cosmic ray measurements.

The fragmentation of cosmic-ray nuclei in interstellar hydrogen

In order to calculate the effects of traversal of interstellar matter on the charge spectrum of the cosmic radiation it is necessary to have values for the fragmentation parameters of nuclei of each element into all lighter elements. Most of these values have not been experimentally determined. As a consequence, they have been calculated from a semi-empirical mass spallation relation designed to fit the available partial cross-sections obtained from radio chemical determinations. This calculation has attempted to take into account the conditions that are peculiar to the cosmic ray problem. Values of the parameters are given for three characteristic energies and a comparison is made with the sparce experimental data. The effects of using these parameters in a calculation of the extrapolation of the charge spectrum through interstellar space are shown for some representative cases.

The charge and energy spectra of heavy cosmic ray nuclei

A charged particle detector array flown on a high altitude balloon has detected and measured some 3×104 cosmic-ray nuclei withZ≥12. The charge spectrum at the top of the atmosphere for nuclei withE>650 MeV·n−1 and the energy spectrum for 650≤E<1800 MeV·n−1 are reported and compared with previously published results. The charge spectrum at the ‘source’ of cosmic rays is deduced from these data and compared with a recent compilation of ‘galactic’ abundances.

On the Modulation and Energy Spectrum of Highly Charged Cosmic Ray Nuclei.

The intensity and energy spectrum of cosmic ray VH-nuclei (20≤Z≤30) has been measured in a stack of nuclear emulsions exposed over Fort Churchill in 1968. The integral intensity above 300 MeV/nucleon was 1.04±0.04 nuclei m−2 sr−1 s−1 and three differential intensities were measured below 750 MeV/nucleon. Because of the current controversy regarding the true intensities of helium nuclei at this phase of the solar cycle we have also measured these nuclei, obtaining results intermediate between those quoted by other workers. Comparison of these results on the VH-and helium nuclei with those obtained in previous observations made at times of low solar modulation leads to the conclusion that there is no significant charge dependence in the modulation process. This conclusion is in conflict with an earlier analysis but depends on results of improved statistical weight and greater reliability for the VH nuclei and on our measurement of the helium nuclei in the same detector.

Interactions of 10.6 GeV/n Gold Nuclei in Targets from _1H to _(82)Pb

The 10.6 GeV/n gold beam from the AGS has been allowed to interact in a wide range nof targets. The emerging fragments with charges between _(80)Hg and _(57)La have been identified. nPreliminary values have been determined for tile total cross sections for charge changing ninteractions, for the partial cross sections for the production of heavy fragments, and for the npartial cross sections for charge pickup.

Interactions of 10.6 GeV/nucleon gold nuclei in nuclear emulsion

Stacks of nuclear emulsion were exposed at the Brookhaven AGS to a 10.6 GeV/n beam of gold nuclei in the BNL 868 experiment. A preliminary analysis of the main features of the interactions of these nuclei is reported here and compared with those observed previously at lower energies,E<1 GeV/n. The multiplicity and pseudo-rapidity distributions of the singly charged particles emitted both in central and in minimum bias samples of interactions have been analyzed in order to look for any non random effects indicative of the nuclear state during the interactions. The fragmentation characteristics of the gold projectiles appear to be different at 10.6 GeV/n from those at ≦1 GeV/n incident energy. Fission of the gold projectiles, which was relatively frequent at low energy, is almost entirely suppressed. Some of alpha particles from the projectile are emitted with very large transverse momenta. In gold-emulsion interactions the residual target nuclei are significantly smaller than in oxygen and sulfur interactions in emulsion.

Measurement of charge of heavy ions in emulsion using a CCD camera

Abstract A system has been developed for semi-automated determination of the charges of heavy ions recorded in nuclear emulsions. The profiles of various heavy ion tracks in emulsion, both accelerator beam ions and fragments of heavy projectiles, were obtained with a CCD camera mounted on a microscope. The dependence of track profiles on illumination, emulsion grain size and density, background in emulsion, and track geometry was analyzed. Charges of the fragments of heavy projectiles were estimated independently by the delta ray counting method. A calibration of both width and height of track profiles against ion charges was made with ions of known charges ranging from helium to gold nuclei.

Comparison of particle production in Pb(158 GeV/nucleon)-AgBr collisions with the VENUS and FRITIOF models

Abstract Data on multiparticle production in interactions of 158 GeV/nucleon lead ions with the heavy nuclei in emulsions (Ag,Br) are compared with the predictions of the VENUS and FRITIOF models. It is found that total multiplicities of produced charged particles are reasonably well reproduced by both models. On the other hand, discrepancies between the data and the predictions are observed for the forward charge and pseudorapidity distributions. Furthermore, dynamical fluctuations, revealed in the data by application of the method of factorial moments, are absent from the model simulations. The dynamical fluctuations observed in the data can be at least partly due to Bose-Einstein correlations.

Evidence for a nuclear phase transition in target nuclei after relativistic nuclear interactions

The degree of excitation of the emulsion target nuclei due to nuclear interactions of oxygen and sulfur projectiles at 200 GeV/nucleon incident energy has been investigated. Using the plausible assumption that the numberNb of slow particles emitted from the struck target nucleus can be interpreted as a measure of the temperatureT of the residual nucleus, we have found that there exists a critical temperatureTc of the excited target nucleus. For Ag and Br target nuclei this temperature corresponds to ≌12 and it is attained when the impact parameters are less than about 4 fm.