For all ionizing radiations operations, a radiation exposure assessment must be conducted during initial performance of the operation and re-validated annually.
This survey is usually conducted by the base Radiation Security Officer (RSO), bioenvironmental engineer, or bioenvironmental engineering technician. It involves a detailed review of the operation and a review of the established or proposed safety measures.
Surveys are conducted using instruments such as an ionization chamber. Ion chambers are enclosed volumes of air or some other gas with electrodes placed inside to collect ions produced by radiation. By measuring the current you can measure the relative radiation rate. Geiger-Müller or GM tubes like those commonly found in the ADM 300A Radiac Set can also be used for radiation detection.
Radiation measurements are actually energy rates and are usually displayed in micro- or milli-roentgens per hour. Measurements are taken where all potential exposures may occur. Including any possible public areas. The RSO or qualified technician then uses the measured radiation rates and reported usage rates to determine the maximum worst case exposure a worker, or a member of the public, could be exposed to.
In strict accordance with Title 10, Code of Federal Regulations Part 20, "Standards of Protection Against Radiation", workers may not be exposed to more than five REMs, or roentgens equivalent man, in a calendar year. Pregnant workers, more than 0.5 rem during their pregnancy, and the public may not be exposed to more than 0.1 rem per year.
If the RSO determines that excessive exposure exists, engineering controls, personal protective equipment, and administrative controls to reduce the exposure potential may be recommended. Based on the exposure potential, the RSO may decide to place personnel on a monthly or quarterly dosimetry program.
Certain jobs require personnel to be automatically placed in a dosimetry program. Pregnant radiation workers are required to be entered into monthly dosimetry. For these personnel, the base bioenvironmental engineering office will assign thermoluminescent dosimeters or TLDs to each individual and collect them on a monthly or a quarterly basis.
TLDs operate very simply by absorbing the radiation that they're exposed to and later releasing that information when heated in a TLD reading instrument. By measuring the amount of energy released, comparing it to the amount released by the control badge, and running the information through a computer program, the lab can determine an individual's exposure.
The results are sent out either monthly or quarterly on computer generated reports that detail the individual's exposure for the last monitoring period and the for the year-to-date. The report also breaks down the exposures to the extremities and specific target organs. At the end of each year a form is sent to document the individual's exposure. After the form is signed by the RSO, it is sent to the individual to review.