Module 103 External Dose Control
Discuss all other beta emitters of
Several uranium radioactive decay products are beta
importance at your facilit y.
emitters. Normally, most of these betas are shielded by the
surrounding material or material worn as personal
protective clothing (such as Tyvek). A primary
radionuclide of concern is protactinium-234 in its
metastable state (234mPa), a daughter of 238U which produces
a very high energy beta particle that can travel up to 20 feet
in air. S ignific ant beta radiati on is als o emitted from 234Th
(also a daughter of 238U) and 231Th (a daughter of 235U).
Typically, these are shielded with ½-inch of plastic.
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 areas.
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 unflushe d UF6 cylinders.
Gamma radiation emitted from residual materials can result
in gamma radiation fields of several hundred millirem per