The data on isotopic ratios of elements in Galactic Cosmic Rays (GCR) is steadily improving and has recently reached the point where some information can be extracted, which has bearing on the problem of the origin of the cosmic rays. By and large, these data have generally confirmed the similarity between solar-type matter and GCR source, when spallation effects and selective acceleration are taken into account. The silicon and iron isotopic ratios, for instance, are consistent with meteoritic ratios. For iron, this is particularly important since two or perhaps even three different nucleosynthesis mechanisms are required to account for the species 54Fe, 56Fe, 58Fe. For carbon, nitrogen and oxygen the problem is that the spallation corrections are large compared to the solar system ratios but nevertheless the present upper limits are not in contradiction with the solar system ratios.

Interstellar fragmentation provides the greatest contribution to the abundance of cosmic ray nuclei with Z = 17–25 observed at earth. The usual procedure to estimate the source abundance of these nuclei is to correct for this interstellar fragmentation using a propagation model and a set of fragmentation parameters for Fe nuclei and its products. Only a fraction of these fragmentation parameters have actually been measured and the accuracy of these as well as the semi empirical parameters used for the unmeasured cross sections is no better than ± 10–15%. As a result the actual source abundances of these nuclei can only be deduced to an accuracy of ± 2–3% of the Fe abundance.

We are reporting here on the results obtained from a balloon exposure of a cosmic ray detector flown in 1977. This detector, described elsewhere, Gilman and Waddington (1975), Young (1979), measures elemental charge from scintillation and Cherenkov signals and mass from Cherenkov and total energy determined from a measure of residual range in nuclear emulsion. The charge resolution obtained ranged from 0.19 to 0.21 charge units between neon and nickel. This resolution was sufficient to ensure that all but a few percent of the nuclei were correctly identified, even for those elements of low abundance that have neighbors with high abundances, such as Cl or Al. The mass resolution obtained for those nuclei that stopped in the emulsions ranged from 0.40 to 0.70 amu for A between 20 and 60 amu. This was not adequate to uniquely resolve neighboring mass peaks in many cases, but was adequate to draw a number of conclusions regarding many of the more abundant elements.

First order Fermi acceleration at the boundary between supersonic stellar winds from OB and Wolf-Rayet stars and the surrounding interstellar medium could be influential in the bulk energization of the local cosmic radiation. Since wind acceleration is not supposed to accelerate thermal particles, a continuous injection of low energy particles (E ~ 1 to 10 MeV/n) is required. We keep open the possibility that these particles may be injected from the interior of the stellar cavity, i.e. by the mass-losing star itself via a flare-like surface activity for instance. Observations of flare activity on hot and massive stars are mandatory to settle this idea. In this context, we expect that the CR reservoir is the surface of young and active stars and that the difference between the CR source (CRS) composition (i.e. corrected for propagation effects in the interstellar medium, ISM) and the surface composition of young stars (reflecting for most of them the present local ISM) is principally due to selective effects at injection depending on the atomic properties of the elements. This idea is supported by 3 arguments (Cassé and Goret, 1978, Meyer et al., 1979) i) the general resemblance between solar CR elemental abundances and elemental CRS abundances (see e.g. Mewalt, 1980) ii) the correlation between the (CRS/local galactic) abundance ratio and the first ionization potential and iii) the fact that dust grains must have been thoroughly destroyed in the medium from which CR are extracted. In the interstellar gas in which dust grains are present, Ni, Fe, Mg and especially Ca and Al are highly depleted whereas they are normally abundant in CR.

A study of the relative abundances and energy spectra of heavy cosmic rays and isotopic composition in the region of Fe peak can yield significant information concerning their origin, acceleration and interstellar propagation. In recent years solid state nuclear track detectors have been employed extensively to study heavy primary cosmic rays. Plastic track detectors necessarily have large geometric factors for heavy primaries, and a continuous sensitivity for the duration of an extended exposure. A balloon-borne experiment consisting of 1 m2 passive detector array has been designed in order to obtain charge and energy spectra of primary cosmic rays in the region of Fe peak. Included in the array is a new type of nuclear-track-recording plastic, a polymer made from the monomer allyl diglycol carbonate (commercially known as CR-39). The stack was built as a set of nine modules. Three types of stack assembly was adopted for these modules: one consisting of ‘pure’ CR-39 plastic track detector: the next one, a composite assembly of CR-39 with three layers of 600 micron thick nuclear emulsions: and the last one with CR-39 and Lexan Polycarbonate. The payload was flown successfully in June 1979 from Eielson Air Force Base, Alaska. The flight was aloft for 3 hours 30 min at an average ceiling of 3 gm/cm2 of residual atmosphere. An attempt to stabilize and orient the payload utilizing a biaxial magnetometer combined with and electrical rotator was unsuccessful. The failure to orient the payload in a stable position would prevent us from determining the true direction of each cosmic ray particle and trace it backwards through the earth's magnetic field using a computer tracing program. Recovery of the payload was routine and all materials were in perfect condition.

The Supernova (SN) is one of the most important and most complex phenomena in astrophysics. Detailed observations of SN require advanced techniques of astronomy and high energy astrophysics, but the theoretical explanation of SN involves virtually every branch of physics. Supernovae, however, offer more than a challenging physics problem because SN are involved in the origin of most of the heavy elements, are the birthplaces of neutron stars, pulsars and probably black holes, control the structure of the interstellar medium, may be responsible for the birth of new stars (and possibly our own solar system), and, of greatest concern in this paper, are involved either directly or indirectly in the origin of the galactic cosmic rays.

Theories on the Origin of Cosmic Rays almost invariably invoke the Supernova (SN) phenomenon in its early phases as the cause for production and acceleration of high energy particles. So far only optical information about SNe has been available and from it there is no direct evidence of Cosmic Rays. It is not surprising then that models of Cosmic Ray production are still rich in free parameters. On April 19th 1979 a very bright (~12 mag) SN, labelled 1979c, was detected in the relatively nearby galaxy (~16 Mpc) M 100 (≡NGC 4321). This galaxy, incidentally has produced 4 SNe in 78 years. Event 1979c was followed quite intensively in the optical and UV (with IUE) regions of the spectrum as well as observed at radio and X-ray frequencies. A detailed account of these observations is in press (Panagia et al. 1980). Here we summarize only very briefly the results relevant to the present discussion.

Results from ground level and underground experiments on cosmic rays with energy 1012 to 1020eV are reviewed. They show that the energy spectrum has two significant features, a ‘knee’ and an ‘ankle’. The arrival directions of these cosmic rays at the solar system are anisotropic, features of the anisotropy appearing to be correlated with features of the spectrum. Detailed interpretation of this information awaits conclusive evidence regarding the composition of these cosmic rays. New results and prospective new results on the composition are described and discussed.

The origin of the highest energy cosmic rays is unclear but the observation that many are seen to arrive from high Galactic latitudes supports the idea of Extragalactic sources. The characteristic features to be explained by any origin model are: the flattening of the energy spectrum above 1019eV and the apparent presence of a directional anisotropy which increases systematically with energy.

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.

The present evidence about the origin of high-energy cosmic rays is that two ranges exist: one below 1018 eV related with galactic sources, and one up to 1020 eV, corresponding to extragalactic processes (Kiràly et al. 1979). However the continuity of the spectrum indicates that the physical mechanisms must be correlated. In the global energetics the spectral range above 1012 eV is irrelevant and the bulk of CR energy is actually provided by supernovae, pulsars, X-ray binaries, etc. in the Galaxy. Nevertheless none of these objects seems capable of producing CR above 1015 eV/nucleon. We have investigated the possibility that the acceleration at higher energies is statistical, taking place over a hierarchy of scales. A model has been developed in terms of the quasi-linear theory of particle acceleration by MHD turbulence. Cosmic rays with ≲1015 eV/nucleon injected by single sources into interstellar space undergo momentum diffusion by stockastic interaction with long wavelength MHD perturbations; small wavelength modes provide pitchangle scatterings. These MHD perturbations, Alfvèn and last magnetosonic waves, are generated by the dynamic interaction of supernova remnants with the interstellar medium. From observations (Jokipii 1977), the range of possible wavelengths extends from the proton gyroradius to the size of the so-called “superbubbles”, up to 100 pc, with a power-law spectrum. Correspondingly acceleration is efficient up to 1018 eV/nucleon; in fact for B 10−3 + 10−5 G, n = 0.01 ÷ 1 cm−3 and L = 0.1 ÷ 100 pc, we find that the acceleration timescale (ε = eBL is the maximum allowed energy) is always shorter than the time scales of losses and turbulent structure lifetimes; α = 3.5 ÷ 4 is the speciral index of turbulent modes. Contrary to the original Ferm i mechanism, in this theory the time scale for acceleration up to any energy ε is fixed by the final phase, previous steps being negligible.

Recent studies of the spectrum of high energy primary electrons using emulsion chambers have been made with an exposure factor some 10 to 100 times larger than those obtained by other experimental devices. The total exposure is now almost 6 m2-day-str., including the recent exposure at Palestine, Texas in May 1980, and it is now quite possible to extend observations of the electron spectrum into the TeV region with reliable accuracy in the next few years.

The existence in the cosmic rays of ultra-heavy (UH) nuclei with Z ≥ 30 was established by two separate experiments in 1966. Fleischer et al. first demonstrated the fossil tracks of such nuclei in certain meteoritic crystals and shortly afterwards Fowler established their existence in present-day cosmic rays with the detection of their tracks in photographic emulsion which had been exposed during a high altitude balloon flight. The fluxes of such nuclei are very low, only ~ 10−4 of that of iron, and the most suitable method of detection to date has been the analysis of the tracks formed by these particles in very large(several m2) arrays of plastic detector material, notably Lexan polycarbonate. Such exposures on balloons and on Skylab have provided practically all present knowledge of the UH cosmic rays. Unfortunately, the charge resolution obtained was disappointing, even though scrupulous care was taken in the handling and etching of the material, and the charge scale itself of necessity had to be based on a considerable extrapolation from the iron peak and could not be used with great confidence. The situation now, however, is in the process of being transformed. We have two satellite experiments devoted to the study of UH cosmic rays and in operation at the moment. These are the Bristol University experiment on Ariel 6 launched on 3rd June 1979 and the joint group under Israel, Waddington and Stone on HEAO-C launched in September 1979. It is therefore appropriate, I believe, if I devote this review to the new preliminary results and a comparison of this material with the published data.

The third High Energy Astronomical Observatory, HEAO-3 was launched on the 20th Sept., 1979 into a 496 km, 43.6° orbit, and has since been successfully returning data from all three experiments on board. One of these experiments, that intended to study the heavy and ultra heavy nuclei in the cosmic radiation, is described here.

Propagation of cosmic rays is discussed with the intent of deriving results relevent to the origin of cosmic rays. Starting from a brief description of the methods for demodulating the effects of the solar wind on the spectra of particles, we describe an accurate method for correcting for spallation effects on the cosmic-ray nuclei during their transport from the sources subsequent to their acceleration. We present the composition of cosmic rays at the sources and discuss its implications to their origin. We discuss briefly the effects of stochastic acceleration in the interstellar medium on the relative spectra of primaries and secondaries in cosmic rays and show that the observation of decreasing relative abundance of secondaries with increasing energy rules out such phenomena for galactic cosmic rays. The spectrum of cosmic-ray electrons is discussed in terms of contributions from a discrete set of sources situated at various distances from the solar system on the galactic plane. We show that unless there are at least 3.104 sources actively accelerating cosmis rays in the Galaxy the spectrum of electrons would have a premature cut-off at high energies. Finally we point out some important questions that need to be clearly resolved for making further progress in the field.

The chemical composition of cosmic ray nuclei with 3≤Z≤28 between ~100 MeV/nuc and a few hundred GeV/nuc are compared with a consistent set of propagation calculations. These include the effects of spallation (energy-dependent cross sections are used), escape and ionization loss in the interstellar medium and deceleration in the solar cavity. This has enabled a consistent study of the cosmic ray pathlength distribution to be made over this entire energy range. Details of the propagation calculation are left to a forthcoming paper.

It has been suggested that the Galactic cosmic rays may be accelerated by a two stage process in which one process, such as stellar flares, inject non-relativistic, super-thermal particles which are subsequently boosted to cosmic ray energies by some other mechanism, perhaps related to supernovae (eg. Cassé and Goret, 1978). Two-stage models in which the injection and re-acceleration processes are uncorrelated are apparently untenable because they cannot fit the observed energy dependence of the LiBeBN/CNO ratio. Here it is shown that additional contraints derived by considering the energy losses and nuclear reactions suffered by the super-thermal particles prior to their re-acceleration severely restrict other types of two-stage models.

The understanding of the nature of strong radio emission associated with galaxies and quasars has significantly increased in the last five years. A large contribution to this increase has been obtained from the arcsec and milli-arcsec mapping of radio sources which show remarkable features. Because of the recent, extremely good review articles concerning extended extragalactic radio sources (Miley 1980 and Willis 1978), I shall emphasize some new, mostly unpublished works, stemming from VLA observations. This is not to slight European experimental and theoretical work which have led in the formulation of our current thinking, but to try to bridge the inevitable communication gap caused by the Atlantic Ocean and ever higher airfares.