Radiation producing machines are regulated by Federal and State agencies. The Food and Drug Administration (FDA) regulates manufacturers of electronic systems capable of producing X-rays. Wisconsin regulates and licenses those who use X-ray machines within the state. Wisconsin Administrative Code, Radiation Protection Chapter 157, describes regulations for machines used in the State of Wisconsin.
It is important to know that radiation-producing machines must not be used on humans except for healing arts. Exceptions to this must be secured in writing from the Department of Health Services (DHS).
All radiation-producing machines have to be registered with DHS. All machines used at the University of Wisconsin–Madison, including the Medical School, are registered by the UW–Madison Office of Radiation Safety (RSO). When you purchase a machine capable of producing X-rays or, the unit is replaced or broken, please have the person responsible for the system notify the Radiation Safety at 608-265-5000 so the necessary changes in registration can be accomplished.
Since electron microscopes are designed to exclude people, they are exempt from many of the regulations that apply to other X-ray devices. However, these devices must be registered with the UW–Madison Office of Radiation Safety and DHS and have written operation and emergency procedures. These devices must follow the guidance listed in “Electron Microscope General Safety Protocol.”
If you have any questions regarding regulations of radiation producing machines call the UW–Madison Department of Environment, Health & Safety at 608-265-5000.
Cabinet and Analytical X-ray Devices
The predominant X-ray-producing equipment used in research is analytical X-ray. It produces intense beams of low-energy X-rays. Exposure to the direct beam can cause severe injury. To prevent exposures, newer instruments are designed with hood enclosures, interlocks, and beam shielding to minimize the risk of inadvertent exposures. It is possible that the radiation exposure rate from the primary beam can be up to 40,000 Roentgen per minute. With this high exposure rate, the hazard is not limited to the primary beam, but can also be related to leakage or scatter radiation. As result, these X-ray machines shall not be modified without the authorization of the RSO.
A radiation survey shall be done whenever a new sample is placed in the beam, the beam is diffracted, experimental setup changed, or equipment is replaced. The analytical X-ray machines usually have a low energy that can be readily shielded with about one millimeter (1 mm) of lead. Due to the intensity of the primary beam, leakage and scatter may create a significant source of unwanted radiation. Use shutters and collimators, secure unused ports, reduce the beam cross-section by collimation, and whenever appropriate enclose the entire beam path or use a sufficient beam stop. Consider additional sources of X-rays from miscellaneous support equipment such as high-voltage supplies. Investigations of accidents have identified four main causes:
- Poor equipment configuration (e.g., unused beam ports not covered)
- Manipulation of equipment when energized (e.g., adjustment of samples or alignment of cameras when X-ray is energized)
- Equipment failure (e.g., shutter failure, warning light failure)
- Inadequate training or violation of procedure (e.g., incorrect use of equipment, overriding interlocks)
X-rays are produced in the electron microscope whenever the primary electron beam or back scattered electrons strike metal parts with sufficient energy to excite continuous and/or characteristic X-radiation. In terms of X-ray hazards, two aspects are important: the composition of the parts which are struck and their efficiency as X-ray sources and the effectiveness/integrity of the shielding provided by the metal casing of the microscope around these.
The higher the voltage and atomic number of the “parts”, the greater the efficiency of X-ray production.
The degree of X-ray “leakage” also depends on the shielding provided by the metal casing. A poorly designed microscope may have weak points where X-rays can escape, for example, between the gasket sealed junctions of two sections of the column.
An electron microscope system is an X-ray system where the X-ray tube is enclosed in a structure that contains the irradiated material, provides radiation shielding, and excludes people.
In most cases dosimeters are not required otherwise it will be provided by the Office of Radiation Safety.
All users must be provided specific written instructions by the Permit Holder before using the equipment. These instructions include notice of radiation hazards; machine specific safe work practices; proper operating procedure; symptoms of acute exposure; procedure for reporting an emergency situation.
The following document should be placed near the controls of each analytical X-ray unit and readily accessible to the operator:
- “Notice to Employees”
- Certificate of registration
- Specific written instructions
- Analytical X-ray Emergency Procedure
- Symptoms of Injury from Acute Local Exposure to Radiation
- Radiation Hazards from Analytical X-ray Units
- Safe Working Practices for Analytical X-ray
Analytical X-ray equipment will be posted and labeled with:
- Label bearing the words “Caution Radiation This Equipment Produces Radiation When Energized” near the tube activation switch.
- Sign “Caution High-Intensity X-ray Beam,” next to each tube-head. The sign must be clearly visible to any person operating, aligning, or adjusting the unit or handling or changing a sample.
- Posting on the exterior side of the room’s doors indicating the presence of X-ray producing equipment such that visitors to the lab will see the sign.
All X-ray machines will contain an operational and clearly visible indicator of an active X-ray beam near the X-ray tube. In addition, there must be a shutter status indicator that unambiguously reports if the shutter is open or closed.
Interlocks and Safety Devices
Operational interlocks and safety devices will be provided to ensure that the primary X-ray beam cannot be interrupted by any portion of an individual’s body or extremities or by machine equipment under any operating condition. If the beam is interrupted, this interlock will shut off the primary beam. Interlocks and safety devices may not be altered without the written authorization of the RSO. Approved temporary modifications must be terminated as soon as possible, specified in writing and posted near the X-ray machine tube and operators console. Securely close any unused tube ports to prevent accidental opening.
Analytical X-ray Emergency Procedure
If there is a suspected or actual case of accidental radiation exposure, turn off the system power and notify the RSO immediately. If required, exposed individuals should go to the UW Health Urgent Care Clinic to seek medical attention.
Biological Effects of Acute Radiation Exposures
With a properly functioning machine, there is little risk of radiation exposure. However, one should know the signs of an acute exposure to a localized area of the human body. These symptoms are shown in Table 1. Be aware that these effects can be caused by contact with the beam for only a fraction of a second. Typical primary beam exposures are 100,000 to 400,000 rad per minute. The most common effects from a large radiation exposure from an X-ray device are reddening of the skin (erythema). With a dose of a few hundred rem, the superficial layers of the skin are damaged and the skin will redden in a fashion similar but more complex than a sunburn. The erythema effect will most often reverse itself within a few weeks. It is also possible that doses on this level could damage cell division and temporarily stops hair growth and possibly causes the hair to fall out. With a low enough dose, hair growth should return. There could also be damage to the sebaceous glands that produce the skin oil, which could cause a temporary decrease in the amount of oil produced. There is other less common and less transitory responses. If a large area is exposure to a large amount of radiation, there could be changes in the skin pigmentation. This effect may not be reversible and could result in permanent skin changes. If the exposure is large, the transitory damage to the skin, skin hair, or sebaceous glands could cause skin scarring or lead to Radiation Dermatitis, Chronic Radiation Dermatitis, or radiation induced skin cancer. To protect yourself from the radiation consider the following potential sources of radiation exposure:
- The primary beam.
- Primary beam leakage from poor shielding or guide tube replacement.
- Beam penetration through stops and shutters.
- Secondary radiations from beam interaction of the primary beam with the sample or shielding.
- Radiation released from the diffraction of the beam.
- Radiation produced from support equipment such as power supplies.
|200 – 300 rad to the skin||Erythema (redness of the skin). The area may turn red within two to three weeks after the exposure depending upon dose. Epilation (hair loss) is possible within two to three weeks.|
|1000 – 5000 rad to the skin||Wet or dry blisters within one to two weeks of exposure that usually break open and are subject to infection. Epilation may be permanent.|
|Over 5000 rad to the skin||Severe trans epidermal injury that resembles intense scalding or chemical burn with the immediate onset of pain. Epilation is permanent.|
|Above 200 rad to the eye||There may be conjunctivitis (inflammation of the eye). It is possible that chronic exposures may lead to cataract formation.|
- A trained and qualified user should only do an alignment, if applicable.
- If safety locks must be bypassed, first gain RSO approval and then post a sign indicating the safety switch status. Reinstate the safety switch as soon as possible.
- Wear a finger dosimeter (ring badge).
- Whenever available, use electronic alignment.
- Use the lowest power settings possible for beam alignment procedures.
- Use long handles on the fluorescent alignment screens.
- Ensure the X-ray beam is inactive by using a radiation detector.
- Use the shutter to stop X-rays. Verify shutter activation that the shutter indicator is properly reporting shutter status.