Nuclear History archive — page 20

A straight beam of light from a glowing sample in a lead block passes unbent between the poles of a horseshoe magnet onto a glass plate, while thinner beams beside it curve away

Villard Discovers Gamma Rays (1900)

Paul Villard's 1900 plates showed an undeflected beam from radium that passed 0.2 mm of lead; he called it X-rays from radium, Rutherford named it gamma rays in 1903, and in 1914 it was shown to be electromagnetic.

A glowing green lump of uranium ore sends beams of light into a row of upright aluminium foils; the orange beams stop at the first foil while the blue beams pass through all of them

Atoms & the Discovery of Radiation

Rutherford Splits Uranium's Rays into Alpha and Beta (1899)

Rutherford's foil-by-foil measurements, signed in Cambridge in September 1898 and published in January 1899, showed two components in uranium radiation; identifying them as electrons and helium nuclei took another decade.

A small corked glass vial holding a few softly glowing blue crystals, resting on a heap of black pitchblende ore

Atoms & the Discovery of Radiation

The Curies Discover Polonium and Radium (1898)

In 1898 the Curies announced polonium and radium by following radioactivity through pitchblende, and by 1902 several tons of mine residue had yielded 0.12 g of radium chloride.

A clear glass vacuum tube in which a glowing blue beam passes between two metal plates and curves down to a green spot at the wide end

Atoms & the Discovery of Radiation

J.J. Thomson Discovers the Electron (1897)

In 1897 J.J. Thomson measured the mass-to-charge ratio of cathode rays, found it over a thousand times smaller than a hydrogen ion's, and concluded that atoms contain far lighter charged particles.

A half-open wooden desk drawer lined with black paper, holding a glass plate with yellow-green uranium-salt crystals and a small metal cross whose shadow glows faintly beneath it, next to a window with a cloudy sky

Atoms & the Discovery of Radiation

Becquerel and the Uranium Rays (1896)

In 1896 photographic plates stored in a drawer during cloudy weather showed Henri Becquerel that uranium emits radiation without sunlight, a discovery that won him half of the 1903 Nobel Prize and gave its name to the unit of radioactivity.

A glowing vintage glass discharge tube next to a softly lit fluorescent screen on a bright background

Atoms & the Discovery of Radiation

Röntgen Discovers X-rays (1895)

In November 1895 Wilhelm Röntgen noticed a screen glowing beside a covered discharge tube, spent about seven weeks testing the invisible rays, and published the discovery of X-rays that swept the world in 1896.

A glowing glass Crookes tube with a violet beam leaving the cathode, a metal cross in the middle and the cross's dark shadow on the apple-green glowing far end

Atoms & the Discovery of Radiation

Particle or Wave? Cathode Rays from Faraday to the Crookes Tube

From Faraday's dark space in 1838 to Crookes's "radiant matter" lecture in 1879 and Perrin's negative-charge measurement in 1895, cathode rays split physicists into particle and wave camps and built the vacuum tools behind X-rays and the electron.

A grid of blue, teal and amber glass tiles with three glowing empty squares, one golden tile hovering above a gap

Atoms & the Discovery of Radiation

Mendeleev's Periodic Table and Its Blanks (1869)

Mendeleev's 1869 table ordered 63 elements by atomic weight and left gaps whose predicted occupants, gallium, scandium and germanium, were found by 1886.

A polished brass balance scale with a small pearly sphere on the raised pan and a larger sphere on the lower pan, against a bright pale-blue background

Atoms & the Discovery of Radiation

Weighing the Invisible — Dalton's Atomic Theory (1808)

Dalton's 1808 atomic theory gave every element an atom with a characteristic weight and explained the law of multiple proportions, even though his rule of greatest simplicity made water HO and oxygen 7 instead of 16.

A rough block of white marble on a sunlit surface, with clear glass beads breaking away from it and shrinking into fine sparkling grains against a bright blue sky

Atoms & the Discovery of Radiation

Ancient Atomism: Democritus, Epicurus and the Uncuttable Atom

Democritus and Epicurus imagined uncuttable atoms in a void; Lucretius's poem carried the idea, a 1417 rediscovery and Pierre Gassendi revived it, and modern physics kept the name while splitting the atom.