Analytical X-Ray

 

Overview

Radiation exposures from x-ray diffraction or fluorescence units can be extremely hazardous. Dose rates in the primary beam can exceed 100,000R/minute. Any part of the body momentarily placed in the beam would receive enough radiation to cause serious radiation burns. X-ray diffraction machines must be operated in accordance with the following basic requirements.

Radiation exposures to individuals must be so controlled that the shallow dose equivalent, eye dose equivalent, and deep dose equivalent limits are not exceeded. In particular, personnel must not expose any part of their bodies to the primary beam.

Operator Responsibilities

An individual will be permitted to operate an analytical x-ray unit if he/she has received radiation safety training, demonstrated competence in the safe operation of the machine and radiation survey instruments, and received the approval of the Radiation Safety Officer.

The operator is responsible for all operations including radiation safety. In particular, he/she should keep radiation exposures as low as practical, observe safety precautions and procedures as they apply to each machine operated, and notify the Radiation Safety Officer of any known or suspected abnormal radiation exposures.

Operating Procedures

Written operating procedures must be readily available to the operator. The operator should be in immediate attendance at all times when the machine is in operation. When not in operation, the machine must be secured in such a way as to be inoperable to unauthorized persons.

Maintenance

Only properly trained personnel are permitted to install, repair, or make other than routine modifications to the X-ray generating apparatus and tube housing.

Beam Alignment

Procedures and apparatus utilized in beam alignment should be designed to minimize radiation exposure to the operator. Particular attention should be given to viewing devices to assure that lenses and other transparent components attenuate the radiation beam to minimal levels. When alignment involves working near the open primary X-ray beam, the beam current should be reduced in order to lower exposure rates.

If a fluorescent alignment tool is used, dimming the room light will permit a significant reduction in beam current. The fluorescent alignment tool should be long enough to permit the operator's hand to be kept at a safe distance from the beam. The operator should be familiar with the manufacturer's recommended alignment procedures, and copies of these should be available for reference.

Altering Safety Devices

If it is necessary to alter any safety device, (bypass interlocks or remove shielding):

  • The actions must be authorized in advance by the Radiation Safety Officer.
  • The actions must be performed under the supervision of the registered user.
  • The actions must be terminated as soon as possible and safety devices reinstalled.

Any attempt to bypass or alter safety devices should only be undertaken as the last resort to proceed with the research. During the bypass period, a readily discernible sign bearing the words "Safety Device Inoperable" shall be placed on the radiation source housing.

Personnel Monitoring

X-ray diffraction machine operators will wear a monitoring device (a dosimeter or TLD finger ring) when:

  • They are operating; or
  • They are near an operating machine.

The dosimeter should be worn on the torso and the finger ring should be worn on the hand most likely to be exposed.

Area Monitoring

Users must monitor routinely for stray or scattered radiation in the immediate vicinity of the X-ray machine with an appropriate detector. Leakage radiation from the tube housing must be less than 2 millirems per hour at 5 cm and leakage from the generator cabinet must be less than 0.25 millirems per hour at 5 cm. All safety devices (interlocks, shields, shutters, shields, cabinets, etc.) must also be checked. In addition to routine surveys, a survey must be made after each repair or modification of the apparatus. If any modification is made to the machine, Radiation Safety Officer must be notified.

High Voltage Hazards

The high voltage power supply of X-ray machines can be particularly hazardous. Personnel must never tamper with high voltage equipment. Only properly trained personnel are permitted to install, repair, or modify high voltage equipment.

Safety Engineering

The equipment should incorporate engineered safety features of a fail-safe design to prevent possible exposures:

For open beam configurations, a safety device to prevent entry of hands and other body parts into the primary beam, or that will shut off the X-rays if the beam path is entered, must be provided.
Unused ports must be secured so that the shutters cannot be opened unless a collimator or coupling is connected.
Safety interlocks should be employed on tube head ports or shielding.
The coupling between the X-ray tube and the collimator of the diffractometer, camera, or other accessory must prevent stray X-rays from escaping the coupling.


Warnings

Visual warnings must be used to indicate the potential for radiation exposure on all devices of open beam configuration:

  • Easily visible flashing lights or equally conspicuous signals located near the tube housing that indicate when the X-ray tube is on or off must be provided if the primary beam is controlled in this manner.
  • If the beam is controlled by shutters, a readily discernible indication of shutter status (open or closed) must be located near each port on the radiation source housing.
  • The warning devices should be of a fail-safe design and must be labeled so that their purpose is easily identified.
  • A red warning light with the notation "X-RAY ON " or the equivalent, should be located on the control panel, and should light only when the X-ray tube is activated.
  • A sign or label bearing the words "Caution- RADIATION, THIS EQUIPMENT PRODUCES X-RADIATION WHEN ENERGIZED " or words having similar intent, must be placed near any switch which energizes an X-ray tube.
  • A label bearing the radiation symbol and the words "Caution - HIGH INTENSITY X-RAY BEAM " must be placed on or adjacent to each X-ray tube housing. It should be located so as to be clearly visible to any person who may be working near the primary radiation beam.
  • Each area or room containing analytical X-ray equipment must be posted with a sign bearing the radiation symbol and the words "Caution - X-RAY EQUIPMENT ".

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