Phyllis S. Freier

Radiation Hazard in Space from Solar Particles.

There were about six solar flare events during the last solar cycle which would have exposed a space traveler to serious radiation from solar particles. The radiation from two of these events was intense enough to necessitate extra precautions being taken to protect space travelers.

Transverse Momentum Spectrum of Mesons Produced in High-energy Nucleus-nucleus Collisions

Abstract The momentum of all charged mesons produced in 19 high energy, high multiplicity nucleus-nucleus collisions of cosmic rays in emulsion have been measured. The transverse momentum distribution differs qualitatively from proton-proton collisions at comparable energies. One possible interpretation is in terms of a transverse explosion with effective temperature T =78 MeV and transverse flow velocity υ =0.61 c .

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.

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.

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.

Nucleus‐nucleus collisions at a mean E=20 GeV/nucleon

Four hundred interactions of cosmic ray nuclei of Z?8 in nuclear emulsion have been studied. The nuclei have E≳7.5 Gev/n and a mean energy of 21 GeV/nucleon. The mean meson multiplicity is 11.9 for these nucleus‐emulsion collisions compared to 6.0 for proton‐emulsion interactions at 22.5 GeV. The angular distributions of emitted particles show some interesting effects. There is a statistically significant excess of mesons emitted in close pairs and groups with separation angles <5 °. One to two percent of the interactions also show meson emission in ’’fans’’ or ’’jets.’’

Exposure of CR-39 plastic to the bevalac Mn beam

CR-39 plastic nuclear track detector has been exposed to a fragmented beam of 25Mn nuclei in order to calibrate plastics used in a recent ballon flight. Response to the 1.75 GeV/amu Mn beam and the fragments produced in a polyethylene target was determined as reduced etch rate S = 0.0746 (Zs)0.95 for s = 0.93 and 18 ⩽ Z ⩽ 25. Charge resolution in the plastic at the Mn peak was found to be 0.14 charge units. A measurement of partial inelastic cross-sections for 18 ⩽ Z ⩽ 25 yielded qualitative agreement with other measurements.

Phase space dependence of the correlations among particles produced in high energy nuclear collisions

The fluctuations of produced particles are investigated in central collisions of proton, oxygen and sulphur projectiles with (Ag,Br) target nuclei at 200 GeV per nucleon. The analysis is carried out in terms of factorial moments and correlation integrals in different pseudorapidity regions. Evidence is found for nonstatistical fluctuations. These fluctuations depend weakly on the phase space, although a slightly stronger effect is seen in the forward pseudorapidity region. The dependence of the observed effect on the mass of the projectile particle disagrees with the expectations of superposition models. The results of this analysis indicate that a self-similar cascade process is the origin of the fluctuations, even though the association of the observed effect with the occurence of a second order phase transition cannot be definitely ruled out.

On the Detection of Heavy Primaries Above 1014 eV

Knowledge of the chemical composition is fundamental to understanding the origin, acceleration and propagation of cosmic rays. At energies much above 1014 eV, however, the detection of single primary cosmic rays is at present impossible because of their low flux, and the only source of information is from the cascades initiated by energetic primary particles in the atmosphere--the extensive air showers (EAS). A similar situation exists for the study of hadronic interactions above 1015 eV. A recent EAS experiment (Goodman et al., 1979) suggests the possibility that the spectrum becomes increasingly rich in heavy nuclei as the total energy per nucleus approaches 1015 eV. Above that energy the overall spectrum steepens and the question of composition is almost completely open.