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Radiation Safety Training Module
Radiographic Sciences and Analytical X-ray Machines
Study Guide
ISU Technical Safety Office, Campus Box 8106
Pocatello, ID 83209
(208) 282-2311/2310

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External Exposure

Careful planning of work, good handling techniques and thorough monitoring are all necessary to minimize the external exposure. Adequate shielding and distance from sources are also important factors in reducing exposure.
Workers can apply three principles to protect themselves from ionizing radiation exposure:
  • Time
  • Distance
  • Shielding


Obviously, the less time a person spends in a radiation field, the less exposure he/she will receive.  Keep in mind that exposures to radiation are additive in their effect.
Methods to minimize time of exposure to a radiation field
  • Preplan the task thoroughly prior to entering the area.  Use only the number of people required for the job.
  • Have all the necessary tools prior to entering the area.
  •  Work efficiently but swiftly.
  •  Do the job right the first time
  • Perform as much work outside the area as possible.
The greater the distance you are from a source the smaller the exposure.  Staying away from a radiation source, even a few feet, will greatly reduce worker exposure. 
Methods to maximize distance
  • Be familiar with radiological conditions in the area.
  • During work delays, move to lower dose rate areas.
  • DO NOT hold patients.

Shielding places protective materials between the worker and the source; for example, walls, barriers, or protective clothing (i.e., lead aprons).

Proper uses of shielding
  • Take advantage of permanent shielding.
  • Erect temporary shielding as necessary.

Monitoring of External exposure 

personal dosimeters

External exposures are monitored by using individual monitoring devices.  These devices are required to be used if the worker is likely to receive an external exposure that will exceed 10 percent of your allowed annual dose.  The most commonly used monitoring devices are:
  • Thermo-Luminescent Dosimeter (TLD)- (modern technology often uses Optically Stimulated Luminescence (OSL) Dosimeters)
    • Whole body badge
    • Finger ring
  • Direct Reading Dosimeter (DRD)
    • Pocket dosimeter
    • Electronic dosimeter
The whole body badge is worn to measure the exposure to the whole body (i.e., between the neck and the waist).

The DRDs are worn adjacent to the whole body badge.

If lead apron is used, the whole body badge needs to be worn on the collar outside of the lead apron.

Dosimeter use and storage

Dosimetry devices issued from ISU's Radiation Safety Office are used to monitor the exposure that you receive while performing work at ISU only, and cannot be used at any other facility.  It is important that they are returned to their proper storage location when they are not in use.  This ensures that the badges are only recording your exposure from work performed at ISU, and also minimizes the chance of the badges being misplaced or lost.
If you are personally receiving radiation exposure for diagnostic or therapeutic purposes, DO NOT wear your dosimeter. Contact the RSO to discuss this situation. Be certain to contact RSO/TSO if you are exposed to radiation at other institutions.

The dosimeters will be picked up and replaced every three months for processing.  Personnel that fail to return dosimeters, or return them to their proper storage locations, will be restricted from continued radiological work at ISU.
Temporary Dosimeters
Temporary dosimeters will be issued on a case by case basis only.  The professor in charge of the lab or facility will be responsible for the radiological actions of the potentially exposed individual. Temporary badges will not be issued as a vehicle to circumvent training requirements.

survey instruments

The responsible user shall ensure that instruments used
for determining exposure rates are calibrated biannually and capable of responding appropriately to the types of radiation anticipated.

Lantern Mantle Check Sources
We have recently provided laminated lantern mantle check sources to verify that your survey instrument is in proper working order.  Contact TSO if you do not know how to use these.
Records and Reports

All the records of surveys, measurements and individual monitoring are maintained at the TSO. Records of the doses to individuals are reported, at least annually to the workers in a format required by the NRC       (10 CFR 20.2106). If a dose received by a worker exceeds any of the annual dose limits, any occupational exposure will be prohibited for the overexposed individual for the rest of that year (Reg. Guide 8.29).

Upon the request of a former ISU worker, the dose report for the period of time that the individual was engaged in ISU activities will be furnished to the worker (10 CFR 19.13).

If the workers are concerned about safety issues in their workplace, they may request that the NRC conduct safety inspections.

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This web based training was developed for use within Idaho State University.  It is intended for use by, and applies to ISU employees, staff, visitors, and students.  If this web site or any part of it is used elsewhere, neither its authors nor the University accept responsibility for its contents.  This information may NOT be used for commercial development or profit.