PENETRATING RADIATIONS AND RADIOECOLOGY Contemporary biology has absorbed the rich inheritance of the evolu tional concepts concerning the live cover of the Earth's crust— the biosphere— in its closest dynamic reciprocal influences and interactions with the chemical and physical properties of the Earth and with the cosmic factors, and later in the interactions of individual organisms and between their groups. This subject has been designated in accordance with the needs and outlook of the different theoretical and applied disciplines, such as Vernadskii's biogeochemistry, Sukachev's geobiocenology, Tansley's ecosystem, Haeckel's ecology (1866).
The last term— ecology— proposed earlier than the others, was widely adopted and ultimately designated an independent branch of science. Al though its content has been repeatedly reinterpreted and distorted, it is a fairly comprehensive, expressive, concise, and convenient designation, provided it is reinvested with its original meaning. This term proved instrumental in the designation of the recently conceived /1-7/ synthetic trend in science— radioecology. This stemmed from the need for a correct understanding of the specific patterns involved in the interaction of the biosphere with the radioactive isotopes and their radiations (in creasingly invading the polluting the natural environments).
The theoretical aspects of radioecology display an even higher diversity /2/, as they overlap at the intersections of radiobiology with several other scientific disciplines, such as radiation genetics, paleonto logy and the theory of evolution, geology, geochemistry and biogeochemistry, and hygiene. Radioecology cannot ignore the penetrating radiations arriving on Earth from interplanetary space.
This space is permeated throughout by radiations of electromagnetic waves encompassing a wide spectrum (infrared, visible, ultraviolet, X rays, and gamma rays), and fluxes composed mainly of protons and alpha particles but also of heavy-element nuclei (primary cosmic rays).
Cosmic rays are a very important natural source of particles because of the extremely high energy of the particles despite the very low intensity of radiation. Therefore they interact with atomic nuclei and induce essential changes in the media (such as air, water, soil, or the living tissues of organisms) through which they pass and by which they are ab sorbed.
In the lower layers of the stratosphere, at a moderate distance from the Earth, the primary cosmic rays penetrating the atmosphere collide more frequently with the atomic nuclei of atmospheric elements, forming new particles by splitting the nuclei of both, and producing cascading showers, i, e., secondary cosmic radiation having soft and hard components. The soft radiation consisting of electrons, positrons, and photons is not highly penetrative, and is largely absorbed by the atmosphere, although some photons and electrons do reach the Earth's surface. The hard radiation consists of mu-mesons from which the radiation derives its extremely high penetrating power, against which neither the atmosphere, nor the hundreds of meters of the Earth's crust afford protection. Apart from these types of radiation, their transformations in the atmosphere create neutrons, protons and pi-mesons whose penetrating power is lower than that of the mu-mesons but higher than that of the photons and electrons.
Thus, all organisms inhabiting our planet throughout the innumerable generations have been and will continue to be affected by the penetrating cosmic radiations. The dose rate of this irradiation varies with the dif ferent sites on the globe and at different absolute elevations, and also depends upon the periodic and nonperiodic variations in space. Neverthe less, the average annual dose of cosmic radiation is about 0.03-0.3 rad,* according to geomagnetic latitude and absolute elevation.
Penetrating ionizing radiation of natural origin, which are independent of human activities, set up a so-called background radiation. Its yearly dose is larger than the afore-mentioned since it comprises, in addition to the ionizing activities of cosmic rays, radiations emitted through decay of a wide range of natural radioactive matter, ubiquitous in the Earth's crust (its soils, waters, atmosphere, and live and dead tissues of organisms). The main sources** of alpha, beta, and gamma rays causing air ionization are the result of radioactive decay, and produce doses ranging from approximately 45 mrad/year in sedimentary rocks to 110 mrad/year in granite.