4. Transmutation of the Elements

    • Observations of light emitted from an electrical discharge through a glass tube filled with air, called a cathode ray tube, led to the discovery of the electron.

    • Glowing gas tubes also emit invisible x-rays.

    • Radioactive elements such as uranium emit energetic charged particles.

    • Radioactive elements emit alpha rays, the nuclei of helium atoms, and beta rays, or energetic electrons.

    • The escape of an alpha particle from the nucleus of a radioactive element has a very small probability, governed by the tunneling effect, which explains how alpha particles get out of the nucleus and why there are still large amounts of radioactive uranium present on the Earth.

    • Radioactive dating determines the age of a radioactive rock by measuring the relative amounts of a radioactive element, like uranium, and its decay product, such as lead. Such dating indicates the Earth is about 4.6 billion years old.

    • The variable energies of the beta ray electrons emitted by radioactive elements implied the existence of an unseen, uncharged particle named the neutrino to carry energy away and conserve the overall energy of beta decay.

    • Evidence for the existence of the neutrino was determined from observations of a nuclear power generator.

    • High-energy charged particles known as cosmic rays are always entering the Earth’s atmosphere from all directions in outer space.

    • Many sub-atomic particles have been discovered as the byproducts of cosmic rays colliding with particles in the Earth’s atmosphere; these discoveries include the positron, which is the anti-matter particle of the electron.

    • When alpha particles, or helium nuclei, collide with nitrogen in our air, nuclear transformation can occur, producing oxygen nuclei from nitrogen nuclei.

    • When protons are accelerated to high energies in the terrestrial laboratory and directed at lithium nuclei, they split the nucleus apart and produce two alpha particles.

    • Particle accelerators have been built that can accelerate protons up to nearly the speed of light.

    • When uranium is bombarded with neutrons, the uranium is broken in two in a process known as nuclear fission, which produces enormous energy and led to the development of the first atomic bomb.

    • The CERN Large Hadron Collider has directed two beams of high-energy protons into collision with each other, producing evidence for an elementary particle named the Higgs boson that can explain why other elementary particles are massive.

Copyright 2010, Professor Kenneth R. Lang, Tufts University