Nuclear Secrets

From Democritus the Greek (400 B. C.) to the late great Englishman John Dalton (1766-1844) scientists were blandly sure that the atom was the smallest thing in the world. Modern physicists know that this is not so, that the atom is composed of a nucleus and surrounding spheres of electrons, that these constituents are capable of being separated. Scientists probing into the infinitesimal atomic nucleus with various tools, last week published new data concerning the nature of the universe and the physical properties of drinking water.

The Nucleus, The late great Dmitri Ivanovitch Mendeleeff arranged the 92 elements in a periodic table according to weight. The late Henry Gwyn-Jeffreys Moseley found that each atomic number corresponded to the number of negatively charged electrons outside the nucleus. Element No. 1, hydrogen, has one such electron; No. 2, helium, has two; lithium, No. 3, three. . . . For each negative electron the nucleus of an atom must contain a positively charged proton. And, except in hydrogen, all nuclei were found to contain more protons than were electrons around them. The additional necessary electrons were found in the nucleus. Lithium, with three electrons outside the nucleus, must have a nucleus with a positive charge of three, and this positive charge may be made up in either of two ways: by six protons and three electrons, or by seven protons and four electrons. Thus lithium appears in two forms, and each form is called an isotope. Since the protons give an element nearly all its weight, the weights of isotopes differ.

H^2. Most elements have two or more isotopes. Tin has eleven. Several scientists have predicted that hydrogen, too, simplest of the elements, would be found to have two isotopes. Professor Harold Clayton Urey of Columbia University said last May that he was searching for a hydrogen isotope of weight two. Last week he found it. Co-discoverers were Dr George M. Murphy of Columbia and Dr. Ferdinand G. Brickwedde of the U. S. Bureau of Standards in Washington. Under low pressure Dr. Brickwedde liquefied hydrogen by reducing the temperature. Then he allowed the temperature to rise.' At 437-o below zero F. the liquid began to evaporate. Ordinary hydrogen atoms, being lighter, had risen to the top, evaporated first, leaving the heavier isotope in a richer mixture. At Columbia Professor Urey examined the hydrogen with a spectroscope, found lines only faintly visible in ordinary hydrogen, concluded they were caused by the isotope H^2. He estimated the proportion of H^2 to plain H was one to 800. In ordinary hydrogen gas it would be one to 4,000.

Scientists Urey, Murphy and Brick-wedde hoped eventually to get H^2 in a pure form. Having two protons and one electron in its nucleus, it is twice as heavy as the previously known hydrogen, whose nucleus has one proton. The discoverers thought H^2 would be of no commercial use. It would give water different spectral color, new physical properties, but would not affect the taste. But since its nucleus is the simplest yet found consisting of more than one particle it would be a great aid in the study of nuclei, might add to data on the cosmic ray which Dr. Robert Andrews Millikan thinks is the energy re-leased by the building up of elements in the universe.

Ray Bombardment Cosmic rays, which Dr. Millikan believes are superpowerful gamma rays released when protons & electrons combine to form elements are everywhere on earth. They are invisible, powerful, penetrate almost anything. By utilizing their ubiquity Dr. Carl D. Anderson, Dr. Millikan's assistant at the California Institute of Technology, made them disrupt an atom's nucleus, took photo-graphs of the process. Between the poles of an electromagnet he placed a Wilson cloud-chamber apparatus--a cylinder with a piston, filled with moisture-laden air. When the piston is suddenly withdrawn the air expands, forms fog. If electric particles are moving in the cylinder the fog forms first on them, making their path visible. Dr. Anderson put nitrogen into his cylinder, exposed a bit of radium, withdrew the piston, flashed a light. He saw lines of tiny water droplets curving away from a common point. In one direction moved protons, showing a clear path. In the other direction went the electrons, their paths much fainter. From the curvature he calculated their speeds--93,000 mi. per second for the protons, 186,000 mi. per second for the electrons. To produce such speeds 50,000,000 volts energy is needed, so Dr. Anderson concluded that alpha particles from the radium (5,000,000 volts) could not have done it, that it must have been done by the cosmic ray. Electrons released by the alpha particles moved much more slowly, left a track almost straight. Dr. Anderson took 1,100 photographs, got eleven good ones. These Dr. Millikan proudly showed to scientists at Columbia University last fortnight.

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