X-Ray Laboratory Precautions
Surveys are performed to monitor for the failures in shielding (leaks) and activated areas. Minimum survey frequencies are specified on the Radiation Permit. Surveys results must be documented.
A portable thin crystal NaI scintillation survey meter should be used to conduct surveys around low-energy X-ray sources such as X-ray diffractometers and electron microscopes. A NaI survey meter usually displays readings in counts per minute (cpm). This type of instrument is primarily used for detecting leaks but not for quantification of radiation present.
Geiger counters may be used for detecting X-ray or gamma radiation but their detection efficiency for this purpose is low.
Ion chambers should be used to determine dose rates from X-ray or gamma radiation.
How to Perform a Meter Survey
Perform an instrument check. To check the operation of a survey instrument, perform the following:
- Calibration check:
a. Check the calibration label on the instrument and ensure the instrument is within the calibration period. If the ‘calibration due date’ has passed, contact Radiation Safety to have the instrument re-calibrated and find another instrument to use.
- Battery check:
a. Turn the switch on the survey meter to "BATTERY" or flip the battery switch to "ON." The needle on the meter face should move to a position within or beyond the indicated area on the meter face scale. Replace batteries if needed before using the survey meter.
- Speaker check:
a. If there is an audio switch on the survey meter, turn it to "ON." Set the survey meter to the lowest scale. The survey meter should "chirp" or "click." If the speaker does not function, the survey meter can be used, but the surveyor will need to check the reading on the survey meter face frequently.
- Background check:
a. Go to an area with an expected low background rate. Note the response when the survey meter is switched to the lowest scale. The background rates should be: <400 counts per minute for a NaI meter, <100 cpm for a Geiger counter, and <0.05 mrem/hour for an ion chamber. If background readings exceed these levels, investigate the area for unknown sources of radiation or detector contamination.
- Instrument response check:
a. Expose the survey instrument to an appropriate check source (often a thorium lantern mantle). The survey meter should respond to the check source thus providing positive indication that the instrument is functioning properly.
Check the most likely sites for radiation such as seams in shielding, areas that could become activated, and areas that occupied by personnel.
Record survey results, survey locations, date of survey, and the person performing the survey in a retrievable log. Obtain a copy of the Survey Log from Appendix E of the X-Ray Safety Manual.
The use and type of personnel dosimetry is determined by the activities and functions the individual performs. By regulation, any person who receives or is likely to receive more than 10 percent of the maximum permissible dose or who enters a "High Radiation Area" must be provided with and must wear personnel monitoring devices.
To obtain dosimetry, complete a Dosimetry Request Form and return it to the Division of Research Safety (DRS). Upon receipt, DRS personnel initiate the request process with the dosimetry vendor. The turn-around time is typically one week for a “rush” order. Therefore, ensure dosimetry requests are made in advance of the need to perform radiation related work. Obtain a copy of the Dosimetry Request Form from Appendix E of the X-Ray Safety Manual.
Whole body dosimeters, or badges, monitor exposure to the whole body and should be worn between the neck and the waist, usually on the front of the body.
Finger ring dosimeters monitor radiation exposure to the hands and fingers. These dosimeters may be worn on any finger and should normally face the palm-side of the hand.
Each person with assigned dosimetry must wear the dosimetry when working with sources of ionizing radiation.
The dosimeter reading is the legal record of an individual’s occupational radiation exposure. Therefore, dosimetry shall be worn only by the individual to whom it is assigned, shall not be tampered with or experimentally irradiated, and shall not be used to measure radiation exposure received as a medical patient.
When not being worn, dosimeters must be stored in a location where they will not be exposed to radiation.
Dosimeters are collected on a monthly or quarterly frequency by DRS personnel and sent to a vendor for processing. Dosimeters must be made available for this exchange to occur.
If a dosimeter is lost, discontinue radiation-related activities and contact DRS. Individuals who have lost their dosimetry must provide information to DRS personnel so that an assessment of their radiation exposure can be performed. DRS will order a replacement dosimeter, as necessary.
Declaration of Pregnancy
The increased sensitivity of rapidly dividing cells makes the human embryo and fetus more susceptible to injury from exposure to ionizing radiation. For this reason, regulations require that exposure to the fetus during the gestation period not exceed 500 millirem. Recommended reading for pregnant female radiation workers is provided in Appendix E of the X-Ray Safety Manual.
Any radiation worker who is pregnant or believes that she may be pregnant should contact DRS and review the recommended reading. All inquiries will be kept in confidence. The individual must complete a Declaration of Pregnancy Form. If a written declaration of pregnancy is not submitted, then the worker’s dose continues to be controlled under the normal dose limits for radiation workers.
For the type of radiation work performed at the University of Illinois, it is rarely necessary to recommend reassignment or changes to job duties to reduce exposure.
Last Update: 2/11/2016