Gamma and X-Ray External Dose - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Module 103 External Dose Control

Lesson Plan

Instructor's Notes

Discuss all other beta

emitters of importance at

Several uranium radioactive decay products are beta

your facility.

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. Significant beta

radiation is also 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 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 material.