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Radiation Safety Training Module
Radiation Safety Training
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 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

Time

Obviously, the less time a person spends in a radioation 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.
 
Distance 
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. 

The radiation dose rate from point sources can be calculated using the following formula:

                                                               Dose rate = Γ A/ (d2)           [R/h]

where:

- Γ is a constant that depends on the radionuclide [Rm2/Ci×h]
- A is the activity in (Ci)
- d is the distance from the source in (m)

 From the above formula for two distances d1 and d2 results that:

                                                                 E2= E1*(d1)2/(d2)2

where,            

E1= initial exposure rate at distance d1
E2= final exposure rate at distance d2

   
Methods to maximize distance
  • Be familiar with radiological conditions in the area.
  • During work delays, move to lower dose rate areas.
 
Shielding

Shielding places protective materials between the worker and the source; for example, walls, barriers, or protective clothing. 

 
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).

Finger rings are worn on the work hand and underneath a glove
so as not to contaminate the ring.

The
DRDs are worn adjacent to the whole body badge.








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.
 
 
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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.