[1]Words appearing in SMALL CAPITAL LETTERS are defined in the Glossary
beginning on page 49.
[2]The process of natural radioactive decay is described in the Appendix
beginning on page 52.
[3]The U. S. War Department program during World War II that developed
the first nuclear weapons.
[4]Drawn to scale, the whole age of man is represented by less than the
width of the line.
[5]For more information on the structure of atoms, see _Our Atomic
World_, a companion booklet in this series.
[6]From the _Chart of the Nuclides_, prepared by David T. Goldman,
Knolls Atomic Power Laboratory, August 1964.
[7]This decay process proceeds in a series of steps, during which 6
alpha particles and 4 beta particles are emitted. (See Appendix.)
[8]Named after their creator, John Napier, a Scottish mathematician
(1550-1617), who also invented the decimal point.
[9]It is difficult to determine the half-life of ¹⁴C exactly. In the
early days of ¹⁴C dating, in order not to delay continued work, an
arbitrary value of 5568 years was chosen and this value is still
used in calculations.
[10]This means that uranium decays through successive steps in which the
entire series emits eight alpha particles. (See Appendix.)
[11]Remember, this enormous period of time is a measure of the _rate_ of
spontaneous fission, _not_ of the age of ²³⁸U.
[12]The rhenium-osmium scheme is shown below the dotted line because the
method is still in an early experimental stage and its general
utility is not yet established.
[13]For more on this family of elements, see _Rare Earths, The Fraternal
Fifteen_, a companion booklet in this series.
[14]For a fuller explanation of the fission process, see _Our Atomic
World_, another booklet in this series.
[15]Neutrons that have had their speed reduced by passing through a
moderator (graphite, for example) which is built into every reactor
to accomplish this very thing. For more about how this is done, see
_Nuclear Reactors_ and _Research Reactors_, companion booklets in
this series.
[16]Note that some radionuclides sometimes decay by one method,
sometimes by another. For example, 98.8% of the nuclei of
actinium-227 emit a beta particle to form thorium-227; the remaining
1.2% emit an alpha particle to form francium-223; both of these
daughter products decay to radium-223.
[17]Some of the protactinium (0.12%) changes by an intermediate step,
known as isomeric transition, in which its nucleus shifts to a lower
energy state. The process does not alter the remaining
parent-daughter progression in the series.
[18]Undergoes both alpha and beta decay, in definite proportion of decay
events, as shown.
This booklet is one of the “Understanding the Atom” Series. Comments are
invited on this booklet and others in the series; please send them to
the Division of Technical Information, U. S. Atomic Energy Commission,
Washington, D. C. 20545.
Published as part of the AEC’s educational assistance program, the
series includes these titles:
_Accelerators_
_Animals in Atomic Research_
_Atomic Fuel_
_Atomic Power Safety_
_Atoms at the Science Fair_
_Atoms in Agriculture_
_Atoms, Nature, and Man_
_Careers in Atomic Energy_
_Computers_
_Controlled Nuclear Fusion_
_Cryogenics, The Uncommon Cold_
_Direct Conversion of Energy_
_Fallout From Nuclear Tests_
_Food Preservation by Irradiation_
_Genetic Effects of Radiation_
_Index to the UAS Series_
_Lasers_
_Microstructure of Matter_
_Neutron Activation Analysis_
_Nondestructive Testing_
_Nuclear Clocks_
_Nuclear Energy for Desalting_
_Nuclear Power and Merchant Shipping_
_Nuclear Power Plants_
_Nuclear Propulsion for Space_
_Nuclear Reactors_
_Nuclear Terms, A Brief Glossary_
_Our Atomic World_
_Plowshare_
_Plutonium_
_Power from Radioisotopes_
_Power Reactors in Small Packages_
_Radioactive Wastes_
_Radioisotopes and Life Processes_
_Radioisotopes in Industry_
_Radioisotopes in Medicine_
_Rare Earths_
_Reading Resources in Atomic Energy_
_Research Reactors_
_SNAP, Nuclear Space Reactors_
_Sources of Nuclear Fuel_
_Space Radiation_
_Synthetic Transuranium Elements_
_The Atom and the Ocean_
_The Chemistry of the Noble Gases_
_The First Reactor_
_Whole Body Counters_
_Your Body and Radiation_
A single copy of any one booklet, or of no more than three different
booklets, may be obtained free by writing to: