Module 103 - External Dose Control

DOE-HDBK-1113-98

Radiological Safety Traning for Uranium Facilities

Module 103 - External Dose Control

III.

MODULE 103 - External Dose Control

Objectives

EO4

Identify t he radio logical concern s of exte rnal exp osure to uranium.

EO5

Describ e the meas ures tak en to con trol ext ernal ex posure t o uraniu m.

Alpha External Dose

Because of the relatively short range of alpha particles in dense matter, alpha radiation poses

little external dose hazard. The most energetic alphas produced by naturally occurring

radionuclides will barely penetrate the dead layer of skin on the human body. Little living tissue

will be affected when the alpha source is external to the skin.

Beta External Dose

Beta doses to the skin, extremities, and the lens of the eye can be limiting in facilities which

process unshielded depleted, natural, or low-enrichment uranium. Processes which separate and

sometimes concentrate beta-emitting uranium daughters are not uncommon in DOE uranium

facilities. Control of exposure is complicated by the fact that considerable contact work takes

place in facilities which process uranium metal.

Several uranium radioactive decay products are beta 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. Sign ifican t beta ra diatio n is also emitted f rom 234Th (also a daughter of 238U) and 231Th (a

daughter of 235U). Typically, these are shielded with -inch of plastic.