Radiation Safety
UIUC X-ray Safety Information
Electron Microscopes & Radiation Safety
X-rays are produced by electron microscopes when the primary electron beam or back scattered electrons strike metal parts of the microscope. The shielding provided by the metal casing of the microscope and leaded glass on the viewing ports is usually adequate to ensure that radiation exposure to personnel is kept to a minimum. However, there are some general principles of radiation safety that you should know about when working with or around electron microscopes.
General Recommendations:
- New users should be trained in the potential radiation hazards of electron microscopes
- Ensure that pre-1956 units have leaded glass windows and shielded intermediate viewing ports
- A radiation survey for x-ray leakage should be
performed:
- at time of installation
- any time the microscope is moved, modified, or attachments/accessories are added/removed
- when any part of the metal casing or viewing windows are removed
- if the current level is set higher than normal
- When surveying, pay particular attention to the
following parts of the microscope:
- gun
- camera / viewing chamber
- specimen changer
- junctions between column sections
- attachment joints
- If possible, radiation surveys should be carried out
under "worst case" conditions, such as:
- highest acceleration voltage
- highest beam current
- beam at crossover on specimen
- low magnification
- all apertures removed
A scintillation counter can be used to detect x-ray leakage. However, the energy dependent response of a scintillation counter makes it inappropriate for measuring x-ray leakage. When measurement of x-ray leakage is desired, an appropriately calibrated air ionization chamber should be used. It is recommended that the x-ray exposure rates do not exceed 0.5 milliRoentgen per hour at 5 centimeters from the surface of the unit.
The Radiation Safety Section of the Division of Research Safety can aid in the selection of appropriate radiation survey equipment or perform radiation surveys of electron microscopes on request.
For more information, contact:
Radiation Safety Section
Division of Research Safety
(217) 333-2755 or (217) 244-7605
