Even Holt's tougher lads became somewhat affected by the gloomy prognostications of some of the amateurs who made such dire predictions. Well aware though they were of the more obvious dangers of the mission, and as intrepidly prepared as they might be to face them, the idea of possibly returning to their homes with manhood impaired by treacherous, invisible rays, or that their posterity might be endangered by mysterious "mutation changes," was depressing to even the least sensitive.
To lay the ghost of such fears and trepidations, Holt turned to the foremost radiation physicist, who was no other than Senator Perucci and to whose sympathetic understanding much of the money and facilities available to Operation Mars might be ascribed. Perucci found time to keep up with the study of cosmic radiation, despite his political activity, and was not long in responding favorably to Holt's request that he come to Kahului for a lecture on cosmic rays and their physiological effects, in order that the fears of the spacefarers might authoritatively be allayed.
"We refer," Perucci began his lecture, "to tiny particles, moving with enormous velocity from the depths of the cosmos into more proximate space, as cosmic rays. Most of these tiny particles are protons, that is, atomic nuclei of the hydrogen atom. About 0.4 % of them, however, represent atomic nuclei of heavier elements, of which the heaviest particles hitherto observed possessed a mass 96 times heavier than that of protons, thus corresponding to the weight of the nuclei of molybdenum.
"When such particles penetrate our atmosphere, they not infrequently collide with its atoms. Such collisions may occur after two fashions, according to whether the penetrating particle is decelerated only by the electrical field of the atomic nucleus, or collides headon with the latter. In the first case, only ionization takes place along the paths of the incident particles. Their energy loss by ionization is low. However, the probability is considerable for every oncoming particle to impinge directly upon an atomic nucleus within the uppermost layers of the atmosphere. In this case, a so-called 'explosion shower' is generated, in which protons, neutrons, mesons electrons, positrons, photons, as well as heavy atomic fragments consisting of nuclei of elements like carbon or nitrogen, are hurled out.
"The more energetic electrons and photons created in such an explosion shower are of particular interest. Electrons are rigorously slowed down by the fields of atomic nuclei, thereby generating additional radiation quanta or photons. These photons, while traversing the strong electric fields of other atoms, are able to materialize by forming pairs of electrons and positrons which then fly off. If these electrons and positrons enter the fields of further atoms, they are retarded and again create photons. Thus the so-called 'cascade showers' develop.
"Mesons, which have a mass some two hundred times greater than the electronic mass and have one positive or negative charge, are but slowly absorbed in the atmosphere and even in the solid crust of the Earth. They have been found thousands of feet under water and even at the bottom of deep mines. Nonetheless, their number decreases rapidly during their travel through the atmosphere due to their inherent instability: Mesons are subject to radioactive decay; after an average lifetime of one millionth of a second, they disintegrate into a common electron and a neutron. "Decay and transmutation products thus induced, together with fragments, now have the effect of secondary radiation. The secondary particles are subjected to further collisions which give rise to tertiary radiation, and the chain continues. Thus we, at the bottom of our sea of air, and anywhere within it, are constantly exposed to a continuous hail shower composed of an already much weakened primary radiation, largely very fast protons, plus a whole family of collision products. Among these collision products are secondary protons, electrons, positrons, neutrons, photons, mesons and heavy atomic fragments.
"Experience has shown that our human organism is very capable of long withstanding this shower of radiation, at any rate insofar as its strength and composition at ground level are concerned.
"Science is still largely in the dark as to the true origin of primary cosmic radiation.
The mean quantitative distribution of primary particles in protons and heavier nuclei seems to reflect quite accurately the quantitative distribution of the chemical elements in the cosmos, as derived from spectroscopic examinations of fixed stars. The latter show hydrogen to predominate to a marked extent. There is, therefore, a tendency to regard cosmic radiation as a product of atomic explosive catastrophes within the universe, although we unfortunately are as yet unable to conceive of the mechanism of such explosions. The energy of the fastest particles hitting the top of our atmosphere has been estimated to be as much as one thousand million million electron-volts. Most particles, however, have lower energies, their abundance being inversely proportional to about the square of their energy. The average energy of the incident particles amounts to ten thousand million electron-volts. If we consider that the famous splitting of the uranium atom produces only some 200 million electron-volts, and that this would be multiplied only by about one thousand were the mass of the uranium atom wholly to be converted into energy, the origin of the huge energy of some primary particles remains a moot question. It is thought at the present time that there are pulsating magnetic fields in the vastnesses of space, created by cosmic clouds, streams of ions or clusters of fixed stars.
The original, slow, energy-lacking protons fly through such fields and are accelerated.
They move from one field to another with increasing velocity, as in a betatron. But this theory is unable to explain many phenomena and certainly requires further perfecting.
"For our particular purposes, however, we may well omit further theorizing on the origins of cosmic radiation. Let it suffice that such rays exist and let us examine whether, and if so, how dangerous they may be to the human frame during extended space travel.
"We are justified in considering primary cosmic radiation particles, as well as their secondary and tertiary offspring resulting from collisions with atmospheric particles, as tiny projectiles constantly traversing our bodies. Since the human organism is also constructed of atoms and molecules, collisions occasionally take place between these projectiles and the building blocks of our bodies. Such collisions induce decay and transmutation products as well as fragments, just as did collisions in the atmosphere, representing a new family of secondary rays. There's no doubt that the body-molecules involved may be damaged in such collisions.
"On the other hand, the probability of one of these tiny projectiles contacting a body molecule during its passage is but small. The atomic nuclei with their circling electrons of which our body is composed, are separated by such wide spaces that most particles pass through without any contact or disturbance, as though through a coarse sieve. In order to visualize this we must remember that the size and interval relationships between the building blocks of our bodies have the same relationship to one another as size and interval relationships between the Sun and planets in our solar system. Thousands of such particles pass through us every minute and we can compute the probabilities of hits over any given period.