External Dose Measurements - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Radiological Safety Training for Uranium Facilities

Module 103 External Dose Control

The probability of spontaneous fission is small; therefore exposure is not expected.

However, if fission does occur, such as in a reactor or from experiments, the

neutron radiation is typically contained. Neutron radiation that is not contained is

usually the result of a criticality accident which generates potentially fatal doses of

gamma radiation.

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 detection instruments that are responsive to these

forms of radiation. 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 associated 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 contact gamma radiation field is less than 10

millirem per hour. However, significant 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.