Module 101 Properties of Uranium
which can be helpful or harmful depending on how they are
All isotopes of uranium are fissionable, which means they
U, are fissile, which means they can also be fissioned by
slow (thermal) neutrons. A fissile material can be involved
in a criticality accident, resulting in the release of a lethal
amount of radiation. Criticality is discussed in more detail
in Module 105 - Criticality Sa fety.
The primary isotopes of uranium are all long-lived alpha
emitters. However, several other radionuclides can be
radiologically significant at uranium facilities, depending
on the history of the uranium materials and the processing.
These other radionuclides include the following beta
Th, 234mPa, 231Th, and 99Tc. The degree of
enrichment also affects the controls that are required for
external radiation exposure because of the increase in the
amount of gamma-emittin g 235U that is present. The
uranium daughter products may also include some low-
energy gamma and x-ray radiation. For example, the
daughter products of 232U represent a potential gamma-
Although there are several isotopes of uranium, only three
exist naturally, and all three are radioactive. See the table
below for half-lives and natural percent abundance for
important uranium isotopes in the nuclear fuel cycle.