Radiological Safety Training for Uranium Facilities
Module 103 External Dose Control
and 231Th (a daughter of 235U). Typically, these are shielded with ½-inch of
Gamma and X-Ray External Dose
Although beta dose from unshielded uranium presents the most common radiation
problem, storage of large quantities of uranium can create low-level gamma
radiation fields (less than 5 mrem/hr). Such fields can create external exposure
problems, particularly when significant numbers of people are working in adjacent
In addition to gamma emissions from the uranium decay chains (238U and 235U),
recycled fuel materials introduced back into the enrichment process will result in
higher gamma radiation fields because of 228Th, a gamma-emitting daughter of
232U with a relatively short half-life (1.9 yr).
Larger sources of gamma radiation may exist from specific uranium processes,
including unflushed UF6 cylinders. Gamma radiation emitted from residual
materials can result in gamma radiation fields of several hundred millirem per hour.
This problem can be controlled by flushing empty cylinders to remove residual
Neutron External Dose
As uranium is processed in the fuel cycle, it is often chemically bonded to fluorine
to create compounds such as UF4 and UF6. When uranium atoms in these
compounds decay, they emit alpha particles that are sometimes captured by the
between 0.5 and 4 mrem/h.