Gamma and X-Ray External Dose

DOE-HDBK-1113-98

Module 103 External Dose Control

Lesson Plan

Instructor's Notes

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 -inch of plastic.

Gamma and X-Ray External Dose

Show OT-27

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