Code of practice for the protection of persons exposed to ionizing radiations / [prepared by the Standing Advisory Committee].

  • Great Britain. Radioactive Substances Advisory Committee.
Date:
1957
Catalogue details

Licence: Public Domain Mark

Credit: Code of practice for the protection of persons exposed to ionizing radiations / [prepared by the Standing Advisory Committee]. Source: Wellcome Collection.

    79/92 (page 73)
    Ionizing radiation: electromagnetic radiation (X-ray or -ray photons or quanta), or corpuscular radiation («-particles, ®8-particles, electrons, protons, neutrons, and heavy particles) capable of producing ions. X-rays: electromagnetic ionizing radiation which originates from the field outside the nucleus of the atom, and resulting from loss of energy of charged particles, e.g., electrons. Of shorter wavelength than ultra- violet radiation. ‘-rays: electromagnetic ionizing radiation which originates within the nuc- leus of the atom. (Often the terms “X-rays” and “‘y-rays” are used indiscriminately in radiology. Scientifically, there is no distinction be- tween X-ray photons and gamma-ray photons of the same energy.) a-particle (a-ray): corpuscle consisting of the nucleus of a helium atom and emitted by radioactive atomic nuclei. Usually travelling at high speed. electron (or positron): high-speed sub-atomic particle or corpuscle which is negatively (or positively) charged and which originates from extra nuclear sites. @-particle (8-ray): a high-speed corpuscle having the same mass and charge as the electron (or positron) and originating from nuclear processes. proton: a nuclear particle of unit mass number having a charge equal and opposite to that of an electron. The nucleus of the hydrogen atom (not of the isotopes deuterium and tritium) is a proton. neutron: radioactive corpuscle which has no electric charge and has a mass slightly greater than that of the proton. It decays, when in the free state, with a half-life of 10 to 20 minutes to a proton and an electron. The type of interaction which occurs between neutrons and atoms depends upon the kinetic energy of the former. If the kinetic energy of the neutrons lies between about 20 keV and 10 MeV (so-called “fast neutrons’’) or between 10 MeV and 500 MeV (so-called “high energy neutrons’’), they can set in motion the nuclei of atoms with which they collide with sufficient velocity to ionize matter. “‘Slow neutrons’, which are usually classed as having energies up to 0-1 eV, and include “‘thermal neutrons” which have energies (about 0-025 eV) associated with room temperatures, enter into nuclear reactions with atoms they meet, resulting in the emission of ionizing radiations. Between slow and fast neutrons is a group known as “epithermal neutrons” (or “intermediate neutrons’’). Isotopes: nuclides having the same atomic number but different mass numbers.