Ultra Heavy Cosmic Ray Nuclei Research Articles

Charge fragmentation in cosmic radiation – and the question of physical anomalons

Abstract Data analysis is carried out for four detector stacks composed of passive Lexan polycarbonate detectors exposed in space by the Ultra Heavy Cosmic Ray Experiment on board NASA’s Long Duration Exposure Facility. Scanning and analysis of the 0.21 m2 detector area resulted in the finding of 72 ultra heavy (68 ≤ Z ≤ 96) cosmic ray nuclei. About 15% of the cosmic ray nuclei show charge fragmentation within the detector stack of 5.6 g × cm–2. A detailed analysis of these fragmented cosmic ray nuclei is presented, including a discussion within the context of “physical anomalons”. This last term, describing a sub-set of all anomalon phenomena, is defined in the text.

Fragmentation of Relativistic Gold Nuclei with Energies between 0.92 and 4.0AGeV in Hydrogen

Modeling the propagation of ultraheavy (UH) cosmic-ray nuclei through the interstellar medium requires a knowledge of the fragmentation cross sections. The cross sections for the production of fragments from the interactions of relativistic gold nuclei in hydrogen have been measured from 0.56 to 10.6 A GeV, using the Lawrence Berkeley Laboratory (LBL) Bevalac and the Brookhaven alternating gradient synchrotron (AGS). The total charge-changing cross sections are found to be essentially independent of energy. The partial elemental cross sections vary significantly with energy but show a transition to energy independence at the highest energies. These cross sections can be scaled to apply to neighboring elements, corrected for the effects of radio active decay, and applied to propagation models to deduce source abundances of the heaviest UH elements from those observed near Earth. There are serious uncertainties involved in deducing the cross sections applicable in space from those measured on Earth. Hence calculations of propagation must be regarded with caution.

Propagation of UH cosmic ray nuclei in a leaky box

A weighted slab approximation to a leaky box model has been developed to study the influence of various parameters and cross sections on the propagation of Z > 28 ultraheavy (UH) cosmic ray nuclei from the source to earth. This model starts with nuclei of a given charge and energy and then follows them as they lose energy, fragment and escape. It is possible to vary the path length distribution, the escape length and the energy dependent cross sections of all the nuclei generated during the propagation. By combining the results for different nuclei and energies it is possible to compare any assumed source abundance distribution with that predicted at earth. This paper specifically considers the effects introduced when the cross sections are adjusted to take account of radioactive decays in flight, and shows that they are generally rather minor. Some predictions are made as to which elements will provide the best discriminators between various assumed sources.

Some comments on the investigation of nuclear and electromagnetic interactions of relativistic ultra heavy cosmic ray nuclei in the Dublin-ESTEC experiment

Recent results on the fragmentation of Z>70 nuclei with energies up to 10 GeV/nucleon have given new information on the energy dependence of nuclear and electromagnetic cross sections relevant to the study of high energy ultra heavy cosmic ray nuclei. The impact this new information could have on the Dublin-ESTEC Ultra Heavy Cosmic Ray Experiment, (UHCRE), is discussed and measurements being undertaken as part of the programme to provide a charge spectrum for nuclei with Z>70 are described. Preliminary results will be presented.

Nucleosynthetic clues to sources of ultra heavy cosmic ray nuclei

As a result of recent successful International Collaboration Experiments, a statistically significant sample of reasonably well resolved charge composition of Ultra Heavy(UH) Cosmic Rays near Earth, will be available in the very near future. Though propagation calculations are riddled with considerable uncertainties, due mainly to the lack of experimentally measured relevant cross-sections, some broad trend of source characteristics can neverthless be inferred from the available bulk composition ratios, as was done earlier with a much smaller sample from Ariel-VI and HEAO-3 results. With the very large expansion of the database, it is hoped to make this inference about the sources of cosmic rays more quantitative. This hope is strengthened in view of new experiments planned in the near future, to remove major uncertainties in the propagation calculations. However, comparison of detailed relative abundances of individual elements has to still contend with considerable ambiguities in the calculation of source abundances, arising due to lack of full understanding of several quantitative details of the site as well as the involved nuclear physics of the τ- process of building nuclei heavier than Fe. These are brought to light here.

Ultra heavy cosmic rays — Preliminary results from the Dublin-ESTEC experiment on LDEF

Acquisition of data on the charge spectrum of ultra heavy cosmic ray nuclei in the region Z≥65 is made difficult by the extremely small abundances of these nuclei in our Galaxy. Several experiments carried out on balloons and spacecraft in the nineteen seventies resulted in the collection of a sample totalling no more than several hundred events. Here we report on some initial results from an experiment with a very large area-time factor which was designed specifically for the study of ultra heavy nuclei and which was flown in earth orbit aboard the Long Duration Exposure Facility (LDEF) for 69 months. Current scanning estimates indicate that approximately 3000 nuclei with Z>65 have been recorded. Details of the preliminary analysis of a sample are presented, future plans and prospects are discussed and the impact of the expected results on cosmic ray astrophysics is addressed.

Dependence of the interstellar propagation of ultraheavy cosmic-ray nuclei on various parameters

A stepwise program of interstellar-cosmic-ray propagation suitable for implementation on a small work-station has been used to study the sensitivity of propagation models of ultraheavy cosmic-ray nuclei (UH nuclei) on the input parameters. In this program an initial set of relevant parameters describing the astrophysics of the propagations process and the nuclear physics representing the interactions was assumed. These parameters were then varied within the estimated uncertainties in order to evaluate the sensitivity of the predictions on the assumed values. It is shown that current uncertainties in the estimates of the UH nuclei nuclear cross sections for the production of lighter fragments present the most significant sources of error and are sufficient to preclude reaching detailed conclusions about the source composition. Other uncertainties, such as those in the escape probabilities, or the mean interstellar density, while still significant, are less serious.

The Bulge of the Milky Way and cosmic rays

The propagation of cosmic ray protons and anti–protons from the inner Galaxy via the galactic halo to the Sun supplies a good agreement with the observed cosmic ray gradient and is in the order of the measured anti-proton flux. Ultra heavy cosmic ray nuclei may have the same origin.

Hypervelocity impact simulation experiments on LDEF°-foils

A variety of space environmental effects can be studied on many experiments having been exposed on the LDEF-satellite. Among others the thermal blankets of the Ultra-Heavy Cosmic Ray Nuclei Experiment (“UHCRE”, Exp. A0178) displayed many micrometeoroid / space debris impact features. In an effort to understand their nature and characteristics, an experimental impact simulation program has been carried out. UHCRE-spare foils have been impacted by glass, aluminium, and iron projectiles with masses ranging from about 30 nanograms up to several milligrams. Impact velocities range between about 3 km/s and 13 km/s. Characteristic impact craters and perforation holes have been produced. Their sizes and morphologies have been related with respective projectile impact parameters. “Halo zones” around perforation holes, as they had been observed in the exposed LDEF-foils, have also been obtained experimentally. They were found to be delamination effects within the foil layers caused by the propagation of impact shock waves.

The outlook for ultra heavy cosmic ray studies with plastic track detectors

Abstract Recent investigations of environmental and ageing effects on the latent signal of highly ionising particles in solid state nuclear track detectors provide improved information on the charge resolution obtainable with solid state nuclear track detectors used in the study of ultra heavy cosmic ray nuclei. The impact of recent findings on the analysis of data from long term experiments in space such as the ultra heavy cosmic ray experiment (UHCRE) on LDEF, the proposed Heavy Nucleus Collector and similar studies which will be made possible during the Space Station era, is assessed.

On the Identification of Tracks of Ultraheavy Cosmic Ray Nuclei in Extraterrestrial Olivines

The results of an investigation of tracks of ultraheavy galactic cosmic ray nuclei (Z ≥ 50) in extraterrestrial olivines are presented. The etching of volume tracks in olivine crystals in described together with a detailed description of the method of partial annealing, which is essential for a reliable measurement of the nuclear charge number distributions of these cosmic ray nuclei and for erasing the background of tracks from lighter nuclei. Special emphasis is placed upon the identification of Z ≥ 50 nuclei in olivine crystals. Possible methods to identify the origin of anomalously long tracks observed in the JINR Dubna are discussed.

The propagation of ultraheavy cosmic-ray nuclei revisited

The propagation of ultraheavy (Z = 30 or more) cosmic-ray nuclei is investigated theoretically in the leaky-box model, expanding the analysis of Brewster et al. (1983) to include more individual nuclides and account for recent findings with respect to source compositions, cross sections, and the dependence of escape length and spectral characteristics on rigidity. The results of numerical computations are presented in tables and graphs and compared with observational data (from HEAO-3) and other theoretical predictions. Good agreement is obtained for Z = 32-42 and 50-58 using a solar-system source with a first-ionization-potential correlation factor and the solar-system abundances given by Anders and Ebihara (1982).

An extensive solid state nuclear track detector array for the study of ultra heavy cosmic ray nuclei aboard the NASA long duration exposure facility (LDEF)

The Long Duration Exposure Facility (LDEF), which is scheduled to be placed in Earth orbit during 1984 by the NASA Space Transportation System (flight STS-13), will carry a large array (≌ 20 m 2sr) of solid state nuclear track detector stacks. This array has been designed to study the charge spectrum of ultra heavy (Z > 30) cosmic ray nuclei, in particular those with Z > 70, by collecting a larger sample of events than that obtained in any previous exposure. Pre-flight calibration with high energy ultra heavy ions has been employed for the first time. An update on the implementation and astrophysical significance of the experiment is presented together with related detector development results.

The propagation of ultraheavy cosmic ray nuclei

The propagation of ultraheavy cosmic ray nuclei (Z greater than 30) has been studied using a model based on the leaky-box formalism. This model has been used to examine the possible composition of the source, the path length distribution, and the mean escape length of the confinement region. Various abundance ratios have been found that have a sensitive dependence on one or more of these factors. Comparison of the theoretical values of these ratios with published data suggests that the source composition is similar to that of solar system matter, but that in the Pt-Pb region, enrichment in material produced by the r-process cannot be ruled out. Data for the secondary-to-primary ratio (Ru-44 - Cd-48)/(Sn-50 - Ba-56) show the presence of significantly more secondaries than are predicted, even when a truncated path length distribution is used in the model.

Ultra heavy cosmic ray nuclei - analysis and results

Ultra heavy cosmic ray nuclei - analysis and results

Abundance of nuclei with Z greater than 52 in galactic cosmic rays - Long-term averages based on studies of pallasites

About 1200 fossil tracks due to ultraheavy (Z>50) cosmic-ray nuclei have been studied in olivine crystals from two meteorites, Marjalahti (cosmic-ray exposure age approx.175 x 10/sup 6/ yr) and Eagle Station (50 x 10/sup 6/ yr). The track length data are analyzed in terms of relative abundances in the flux in space of Z+52 elements of kinetic energy greater than 1--1.5 GeV per amu, taking into account all uncertainties due to effects such as annealing, space erosion, and nuclear fragmentation within the meteorites. The longest tracks in Marjalahti are of maximum recordable length approx.900 ..mu... If these tracks are assumed to be due to elements of 90 or =4. (AIP)