Gamma Radiography

Gamma radiography is a technique which using radioisotopes to check cracks and other faults in aircraft welding, as well as gas and oil pipelines.

Gamma radiography involves placing a radiation source(iridium 192 ) on one side of the gas pipeline, and
a photographic plate on the other. The radiation that can pass through cracks will show up on the photographic plate. This checking process could have been done using X-rays like in the hospital, except there is a lot of equipment required for X-rays, whereas using gamma radiography requires only a radiation source which can simply be a small pellet of radioactive material. X-rays also require electricity, whereas radioisotopes do not.

The exact process is done by taping a special photographic film over the weld or suspected crack of a pipeline. A pipe crawler carrying the sealed radiation source is then dispatched down the pipe to the weld position. The field technician performing the check then sends a remote control message to the crawler to tell it to expose the radiation. When this happens, the radiation passes through any cracks that may exist, onto the photographic film taped on the outside. This film is then developed and checked for cracks or welding deterioration.

Gamma radiography is used frequently at airports in order to screen luggage. This type of radiation offers a clear picture of what is in luggage, so that airport security screeners can identify flight hazards such as bombs or weapons. Airport security checkpoints may use gamma radiation or x-rays in order to form a picture of a passenger. This allows security personal to check passengers for weapons before they get on the plane. Gamma radiation devices are usually smaller than x-ray machines, but the high frequency wavelengths of this type of radiation can cause negative health effects in even small doses. It is important that radio-active isotopes should be handled in such a way that radiation received by operators is kept to a minimum. A check should be kept on the amount ofradiation received by carrying film badges or ionisation chambers. The maximum permissible dose from iridium 192 for continuous working is 0.3 rontgens per week. The radiation from an unshielded source is 0.5 milli-rontgens,/hour/milli-curie. A 2-curie radiographic source would therefore give a week’s radiation in 20 minutes at a distance of one metre.