X-ray Diffraction

Safety

There are a number of safety guidelines and factors to consider when using the equipment for X-ray diffraction.

X-ray equipment and radiation hazards

X-rays are highly energetic ionizing radiation and as such are hazardous to human health. They can trigger a lot of chemical reactions in the human body that ultimately lead to cancer and death. Precautions to prevent exposure to X-rays are therefore essential for any XRD laboratory. These include sufficient shielding of all X-ray equipment, limited access to the laboratory, measuring and recording of all radiation exposure of staff and students with dosimeters. Under normal circumstances direct exposure to X-rays in a laboratory is very unlikely. However, users need to be aware of the risks associated with the equipment since all precautions, in principle, can fail.

Radiation hazards

Analytical X-ray equipment makes use of very narrow collimated X-ray beams of high intensity. Exposure of the eyes or the skin of the body to the primary X-ray beam may result in severe localised radiation burns in a matter of seconds. These burns heal poorly, and on rare occasions have required amputation of fingers.

Hazards also exist from exposure to scattered radiation. Scattered radiation is produced when the primary beam strikes collimators, samples, beam stops or shielding. The intensity of the scattered radiation is several orders of magnitude less than that of the primary beam. However, these scattered radiation fields may still result in exposures, which exceed regulatory limits.

Preventative measures

All the instruments are inside radiation housings, which reduce radiation leakage below detection limit. Whenever a door of the enclosure is opened, lead shutters cut off the X-ray beam and interrupt the measurement. With some equipment, even the generator may be shut down and you will have to ask an operator for assistance.

To prevent exposures: to record possible malfunctioning of equipment you are compelled to carry dosimeters whilst working with the X-ray equipment. This will not prevent radiation damage from occurring, but it does enable immediate medical action to minimise damage and to replace faulty equipment. The physical measure for radiation is the energy dose. It is equal to the energy deposited per unit mass of medium and therefore has the SI unit J/kg = Gy, Gray in honour of the English physicist L. H. Gray (1905-1965). This, however, is only of limited use to determine the actual hazard associated with the radiation. A lot depends on the kind of radiation. The notion that the harder (the shorter the wavelength) the radiation, the greater the hazard is a myth. Actually, copper radiation (λ=1.54187 A) used in powder diffraction is ten times as dangerous as the much harder silver radiation (λ=0.56087 A) used in medical equipment. The reason lies in the different absorption coefficient. While the harder X-rays can potentially cause more damage, they are very much less likely to interact with body tissue and therefore actually cause less damage. To correct for these effects, the so-called equivalent dose is used which multiplies the energy dose with a dimensionless factor Q that depends on the nature of the radiation used. This unit is named Sv or Sievert in honour of the Swedish medical physicist Rolf Maximilian Sievert (1896-1966). This unit is used in our personal dosimeters. The X-ray intensity rapidly decreases with the distance from the X-ray tube. The following table should give you a rough idea about the hazards.

Estimated radiation doses at analytical X-ray equipment: