Cosmic Rays Trapped in Mountain-Top Laboratory (Nov, 1936)
Cosmic Rays Trapped in Mountain-Top Laboratory
The Story of a Strange Outpost of Science, Nearly Three Miles Above Sea Level, Where Man Seeks the Answer to a Riddle of Nature
By John E. Lodge
ON A lonely 14,000-foot mountain peak, fifty miles west of Denver, Colo., two scientists have just moved into the only house of its kind on earth. Shaped like a wedge tent and completely sheathed with copper, it stands among bare, wind-bitten bowlders, far above the timber line. It is the world’s first permanent cosmic-ray laboratory.
Here, Dr. Joyce B. Stearns and Dr. Fred D’Amour, of the University of Denver, are studying the mystery bullets which bombard the earth from outer space. With clicking, chattering instruments, they will seek answers to such teasing problems as the exact nature of the rays, where they are born, and how they affect human life.
Few riddles have aroused greater scientific curiosity than these. Believed to originate in the empty spaces of the skyâ€”the dark areas between the galaxiesâ€”cosmic rays are the largest “packets” of energy known. They can penetrate lead 100 times as far as X rays. Recent tests indicate that they are in part electrically charged particles and in part radiant energy similar to light and heat. They are unlike anything else we know, and they are engaging the attention of scientists around the world.
The two-room, mountain-top laboratory where the Colorado experimenters will work was especially designed to withstand everything from wild animals to February blizzards. It was constructed in Denver, knocked down, and then hauled by a caravan of eight motor trucks to the top of Mt. Evans, almost three miles above sea level. The twisting trail the cars followed was constructed especially for the purpose. Only one other road in the world goes so high.
At some points on this perilous trip, the laboring machines hugged the inside of the trail until their fenders brushed along the rock walls to keep from slipping over precipices. Inching around hairpin turns, they moved at a snail’s pace up the steep incline until all were safely at the top. There, skilled workmen quickly assembled the structure and roofers covered it with paper-thin sheets of copper.
This material protects the interior of the building from electrical disturbances, offers the least resistance to cosmic rays, and at the same time provides sufficient strength to withstand the gales and blizzards of the mountain top. As a further protection against electrical interference, all windows are screened with copper, and heavy cables of the same material run from the roof deep into the granite to which the structure is anchored, ending in moist earth surmounted by a layer of charcoal.
Within the copper shell of this lonely outpost of science, a battery of ray counters, gas-filled Geiger tubes, will record the shifting pulsations of cosmic energy. Seldom more than a foot in length, each of these glass tubes contains a copper cylinder and a rod of the same metal. One terminal of an electric generator is connected with the rod, the other terminal with the cylinder. Ordinarily, the current is unable to bridge the gap between the two. When a cosmic ray enters the tube, however, it ionizes the gas, or fills it with electrified particles which act as “ferry boats,” carrying the current across the opening.
These midget flashes of laboratory lightning are far too small to see. But the sound is amplified into a metallic click. At sea level, the clicks that record the passage of cosmic rays occur about one every four seconds. In the thin air of the mountain top, they are many times as numerous, the amplifier clattering continually like chickens pecking on a tin pan.
While Dr. Stearns is busy with his Geiger tubes and other apparatus, Dr. D’ Amour will concentrate upon the fascinating problem of what these potent rays do to living things. Generation after generation of white rats will live in the mountain-peak laboratory under the constant bombardment of the rays. The effect upon their evolution will offer valuable data for science to study. At present, there is no evidence that cosmic rays are injurious , to humans.
A thousand miles away from the Colorado outpost, on the shores of Lake Michigan, two other experimentersâ€”the famous Nobel Prize winner, Dr. Arthur H. Compton, and his research assistant, Haydon Jonesâ€”are tuning up a twelve-ton, electromagnetic “speed trap” for the study of cosmic rays.
Five miles of copper wire, three quarters of an inch thick, are wound around the two poles of the giant magnet. To carry off the intense heat generated by the current, the wire is enclosed in oil which, in turn, is cooled by a stream of running water.
Connected with the magnet will be a Wilson “cloud chamber,” a glass box filled with gas saturated to the point where an electric charge passing through it leaves a trail of minute water droplets which can be photographed by an automatic camera. Thus, the path of an invisible ray can be recorded on film. If he can bend the cosmic rays that enter the electromagnetic field of the new apparatus, and then photograph their trails, Dr. Compton will have a key to measuring their energy. For, it is known that the higher the energy of the particles, the less they are deflected by such a pull.
In 1929, a Russian scientist succeeded in photographing the “ghost trails” of cosmic rays in a “cloud chamber.” But, even though the chamber was in a magnetic field, the paths were straight. The velocity of the particles was so great they were unaffected by the magnet.
In the past, apparatus available for such work could measure no more than 20,000,000,000 volts. The Compton device is expected to lift the limit to 40,000,000,000 volts. In the 7-1/2-inch space between the poles, the magnet can exert a pull of six tons. One out of every fifteen cosmic rays entering the magnetic field, it is estimated, will be traveling in the right direction to be photographed.
A large collection of these ghost trails will give science a clearer insight into the nature of the visitors from outer space. In addition to providing a yardstick for measuring energy, the experiments are expected to settle the question of whether the particles are positively or negatively charged.
A few years ago, extensive experiments at Mexico City with a cosmic-ray “telescope” indicated that the former is true. Dr. Thomas H. Johnson, of the Bartol Research Foundation of the Franklin Institute, Philadelphia, made the tests. His instrument consisted of three ray counters placed in line so only the cosmic rays traveling directly toward the tube would be recorded by all three. Pointing this curious piece of apparatus at different parts of the sky, he found that the major ray stream travels from west to east. As the magnetism of the earth would naturally deflect positive electrical particles toward the east, it is assumed that cosmic rays are composed, at least partially, of positive electricity.
During the thirty-five years which have elapsed since the first hint of their existence, the story of cosmic rays has been one long succession of riddles. It was, in fact, a riddle which led to their discovery.
Back in 1901, workers in an English laboratory noticed a puzzling thing. They were testing the strength of radium with a small gold-leaf electroscope. In this instrument, a tiny electrical charge holds strips of gold leaf apart. When radium rays enter it, they ionize the air and permit the charge to escape, the rate of this leakage indicating the strength of the radium bombardment. But, the English scientists found, the charge leaks away gradually even when the electroscope is put away in its container. Various explanations were offered. One was that there might be radium in the earth nearby; another, that the atmosphere might contain some radioactive element. For nearly a decade scientists here and abroad puzzled over the mystery.
Then, in 1910, came the balloon flight of A. Gockel. This young Swiss physicist sailed high over Germany, carrying a small electroscope in the open basket of his balloon. If the leakage observed by the English workers were due to radium in the earth or to a radioactive element in the atmosphere, the effect would be less at higher altitudes, for there the instrument would be farther from the ground and in thinner air. Instead, a topsy-turvy thing occurred. The higher the balloon went, the faster the charge was dissipated. Other ascensions verified his observation. Science was left facing a blank wall.
So matters stood until after the World War. Two Americans whose names bulk large in cosmic-ray research, Dr. Robert A. Millikan and Dr. Arthur H. Compton, had become interested in the mystery and after hostilities ended they took up the trail. Dr. Millikan was the first to prove the puzzling effect was actually the work of rays bombarding the earth from cosmic depths.
The story of his search is one of the epics of science. Climbing mountain peaks in the Andes, sending aloft sounding balloons on the (Continued on page 115) Texas plains, making tests in a raging blizzard among the Rockies, lowering lead-lined boxes of instruments into the water of snow-fed lakes in the Sierras, he followed one clew after another. The mystery rays, he found, could penetrate the equivalent of seventy-three feet of water. Using this as the basis of computations, he calculated the wave length of a cosmic ray is approximately 10,-000,000 times shorter than that of light. It would take a billion such wave lengths to equal the thickness of one cigarette paper!
Four years ago, Dr. Compton organized an international survey in which coordinated expeditions made studies in all parts of the world. Later, automatic instruments circled the globe on steamers, recording cosmic radiation. And, recently, gigantic balloons, here and abroad, have carried scientists to the roof of our atmosphere where their instruments obtained additional data.
AN INNOVATION in high-altitude research started a few weeks ago in Texas. Dr. Millikan, still plumbing the upper sky with sounding balloons, began releasing tandem gas bags. Four or more of these strung together carry self-recording instruments to a height of from seventeen to twenty miles. Designed by Dr. Victor Neher, one of Dr. Millikan’s assistants at the California Institute of Technicology in Pasadena, the compact instruments include a clock, a camera, a cosmic-ray electroscope, a thermometer, and a barometer. Their total weight is only two pounds. In the thin air at the top of the ascent, the balloons burst and the instruments float to earth by parachute.
To get above the lower layers of the atmosphere, an expedition recently carried tons of equipment across deserts and rivers and mountains from Pasadena to Pike’s Peak in the Rockies. Heading this scientific trek was .Dr. Carl D. Anderson, noted for his discovery of the positrons, one of the invisible “building bricks” of which all matter is composed. At the top of the Colorado mountain, Dr. Anderson assembled his apparatus and snapped some of the most amazing pictures ever taken. They showed the flying fragments of an atom shattered by cosmic rays!
At the California Institute of Technicology laboratory, this research worker took eleven other pictures showing the same thing. The dream of the Dark Agesâ€”the transmutation of metalsâ€”was actually taking place before the lens of his camera.
As everyone knows, particles of the different elements are composed of billions of molecules which are, in turn, composed of atoms, or groups of electrons clustered about a positive core, or nucleus. In any one element, such as lead, every atom has a certain number of electrons. If it loses or gains a single one, the atom is so modified that it is no longer lead but becomes some other element. So, when the cosmic ray blasts electrons from the atoms of one element, it changes these atoms into another element.
AS EFFECTED at present, this change is – only temporary since the lead immediately begins to expel other electrons and to rearrange those left behind, so that each atom again contains just the right number. At some future day, however, science may learn how to make the transformation permanent and so harness cosmic rays to the work of producing elements at will.
Just as sensational is another discovery made at the California laboratoryâ€”the creation of tangible matter out of light and cosmic rays!
Some years ago, two scientists in the Cavendish Laboratory, at Cambridge University, England, proposed (Continued on page 116) the theory that matter might be produced from radiation in the distant parts of the sky. Now, Dr. Anderson and his associates have proved that short-lived positrons appear here on earth as the result of cosmic-ray activity. Many of the mysteries of astronomy, such as the interstellar gas clouds, the outer atmospheres of giant stars, the faint glow of the sky on clear, moonless nights, may be traceable to cosmic rays. At least, that is the opinion of Dr. Fritz Zwicky, of the Pasadena institution. He points out that the terrestrial aspects of cosmic rays have been studied on many fronts, but that the astronomical effects of the endless bombardment is a field virtually untouched.
ACCORDING to the famous Abbe G. Lemaitre, Belgian mathematician, cosmic rays may be part of the odds and ends left over when our solar system was created. His startling theory is that a certain amount of matter and energy failed to condense with the stars and planets and was left speeding through space. The matter is occasionally visible to us in comets and meteors which flame through our upper atmosphere. The energy is what we call cosmic rays.
Today, after intensive research by hundreds of scientists, we are just beginning to understand this strange, enormous flow of energy coming to us from the immeasurable depths of space. We know less about it than we did about electricity in the days when Benjamin Franklin flew his kite into the thunderclouds.
What discoveries lie ahead? The research man, groping about in so strange a realm, hardly dares hazard a guess. In the copper-covered, mountain-top laboratory of Dr. Stearns and Dr. D’Amour, as well as in other research centers throughout the world, scientists are on the threshhold of amazing possibilities. What they will find when they cross that threshold, is one of the alluring uncertainties of modern science.