• Choose a category
• All
• Classic-Fiction

By Root 1101 0

projected the bones of his hand. Rontgen called the phenomenon ‘X-rays’. (A startled and righteous assemblyman in New Jersey, apprised of the discovery, introduced legislation ‘prohibiting the use of X-rays in opera glasses’.) In 1896, the French physicist Henri Becquerel, inspired by Rontgen’s finding, decided to look for X-rays in materials that fluoresced—that is, absorbed light from one part of the spectrum and emitted light from another part. He wrapped a photographic plate in black paper, dusted it with a uranium compound, then left the plate in the sun. After a few hours, he wrote: ‘I saw the silhouette of the phosphorescent substance in black on the negative.’ Becquerel tried the experiment again, but, discouraged by a succession of cloudy days in Paris, and assuming the sun had caused the tracing on the negative, he closed the plate in a drawer. He was surprised, several days later, when he looked at the plate, to find that the silhouette effect had occurred even in the dark. It was not the sun, but something in the uranium, that had penetrated the black paper and left its ghostly image. Two years later, the French wife-husband team Marie and Pierre Curie discovered two new elements, polonium and radium, that gave off Becquerel’s mysterious discharge. They dubbed it ‘radioactivity’.2

Something was coming off, or out of, atoms. They were not themselves the smallest things, nor were they as solid and ‘massy’ as billiard balls. Thomson’s tiny electrons and the presence of radioactive emission demonstrated that. (Scientists would ultimately identify three types of radiations— alpha, beta, and gamma rays—with the betas being streams of electrons.) Over the first two decades of the twentieth century, Rutherford, who moved from Montreal to Manchester in 1910, ‘systematically dissected the atom’, as Richard Rhodes has written. He found that atoms, far from stable, might change themselves into another form of the same element they comprised (called an isotope) or another element altogether. He calculated that an enormous amount of energy came with radiation; if things went badly wrong, he said, ‘some fool in a laboratory might blow up the universe unawares’. And, on 7 March 1911, speaking before a general audience in Manchester, Rutherford announced that he had revised his notion of the atom’s structure: it had a central mass, or nucleus, around which spun electrons. Since electrons carried negative electric charges, the atomic nucleus must be charged positive. The force exerted by the electrons must be equal to that of the nucleus for the atom to remain stable.3

Rutherford did not work alone. At McGill he had teamed with Frederick Soddy, a chemist who, like Rutherford, would win a Nobel Prize, and also with the German Otto Hahn, who conjured with isotopes and would go on to do revolutionary experiments with the nucleus during the 1930s. In Manchester there was another German, Hans Geiger, builder of an electrical machine that detected radiation and clicked in its presence. He helped train James Chadwick, the Australian Marcus Oliphant, the Russian Peter Kapitsa, and the Japanese Yoshio Nishina—the latter two of whom would play leading roles in their nations’ nuclear-weapons programs. The great Danish physicist Niels Bohr considered himself Rutherford’s student, though he was Rutherford’s equal at refining ideas about the structure of the atom. (Curiously, a Japanese scientist named Hantaro Nagaoka suggested in 1903 that an atom resembled the planet Saturn, with the planet itself as a nucleus and the rings representing electrons orbiting it. Rutherford seems not to have known of Nagaoka’s vision, despite the two men having met in Manchester.)4

Rutherford concluded in 1919 that the nucleus of hydrogen, the first element in the periodic table, was a single, positively charged particle he called a proton. More complicated elements had more protons, and every nucleus of a single element had the same number of protons, which figure gives the element its atomic number. Rutherford and others, however, suspected that there was