Answer to Question #3868 Submitted to "Ask the Experts"

I work in an x-ray crystallography laboratory. I just found out that I am pregnant and I want to know what are the best precautions for me to take. I've heard that women who work in x-ray laboratories use lead aprons to provide protection. Is this suitable? I should state that the x-ray diffraction equipment is housed in an enclosure. Stepping into the enclosure is required to mount a crystal and during this time the shutter is closed, although the generator remains running.

The regulatory radiation dose limit for an embryo/fetus of an occupationally exposed worker is 500 millirem during gestation (millirem is a unit of radiation dose commonly abbreviated mrem). The most likely radiation dose to you (and therefore your child) from operating an enclosed diffraction x-ray unit under normal circumstances is well below the 500 mrem limit. Therefore, the use of additional shielding (for example, a lead apron) beyond safety features already incorporated into the system enclosure and the tube housing should not be necessary.

There are two potential sources of radiation exposure: radiation leakage through the system enclosure and radiation leakage through the tube housing. The typical radiation level at the surface of a modern enclosed analytical x-ray system is very low if any; however, your description does not provide enough detail for me to be certain of your equipment set-up. The American National Standards Institute, in its standard ANSI/HPS N43.2-2001 Radiation Safety for X-ray Diffraction and Fluorescence Analysis Equipment¹, and many state regulations specify a limit of 0.25 mrem/h at 5 centimeters from the enclosure's outer surface during normal operation. At an operating position a foot or two from the enclosure, the radiation level would be even less.

Similarly, the typical radiation level external to a modern analytical x-ray tube housing with all shutters closed is low if even measurable. The Standard and many state regulations specify a limit of 2.5 mrem/h at 5 centimeters from the tube housing during normal operation. Once again, the increased distance from the radiation source (for example, tube housing) to your abdomen during sample mounting would significantly reduce any radiation level. A radiation safety survey of the equipment is probably performed annually and you should be able to get the actual radiation level values from your institution's radiation safety officer (RSO).

The standard radiation safety precautions of time, distance, and shielding are always useful when working with radiation sources. In this case, the application of shielding has likely reduced the radiation exposure to very low levels. In the case where there might be some radiation leakage from the enclosure or tube housing, you would want to maximize your distance from the source and minimize your time in the adjacent area.

Although there does not appear to be a significant risk of radiation exposure in this case, I suggest that you contact your RSO. The RSO will be able to do a complete radiation dose assessment based on actual survey results and better address your concerns based on the specifics of your equipment and procedures.

Glenn Sturchio
Certified Health Physicist

¹This standard can be ordered by visiting the Health Physics Society Website.