External Dose Measurements - hdbk1113cn10135

DOE-HDBK-1113-98

Radiological Safety Traning for Uranium Facilities

Module 103 - External Dose Control

External Dose Measurements

The radiation from uranium that affects external dose includes beta, gamma, X-ray and neutron

irradiation. An effective external exposure control program for uranium requires a variety of

radiation d etection in struments tha t are respons ive to these fo rms of radiati on. Radiation surveys

should be performed on a routine basis and during events, tasks, procedures, or situations that are

likely to cause radiological conditions to change. There are two general categories of

measurement used for external exposure associateed with uranium, portable survey instruments

and personnel dosimeters.

Gamma radiation from uranium is normally not the controlling problem. For example, the

contact beta radiation field from depleted uranium is approximately 240 millirem per hour, while

the cont act gamma ra diatio n field i s less th an 10 mill irem per h our. Howe ver, sign ifican t gamma

fields can exist in areas where large quantities of uranium are stored, such as a storage area for

uranium contaminated soil. The accuracy and precision of survey instruments used for

measurement of beta radiation fields depend on many factors which must be addressed, such as

energy response and geometry factors. Accordingly, these surveys are typically conducted by

Radiological Control personnel. Neutron fields from enriched uranium fluoride compounds can

also add to this area of concern. Depending on the magnitude of neutron fields generated,

periodic neutron dose rate measurements are made, typically by Radiological Control personnel.

Personnel dosimeters produce the data which becomes the formal or "legal" record of personnel

exposure, thermoluminescent dosimeters, used in most DOE uranium facilities, provides the most

accurate and precise means of measuring doses received by workers.

External Dose Reduction and Control Techniques

External Dose Control Program

The primary purpose of an external dose control program is to control dose to the

individual radiation worker to below regulatory limits and administrative levels and

ensuring that doses are As Low As Reasonably Achievable (ALARA). In all cases at