Answer to Question #11377 Submitted to "Ask the Experts"

Category: Radiation Basics — Radiation Shielding

The following question was answered by an expert in the appropriate field:

Q

If a person's gloved hands are in the primary beam during an x-ray exposure, does the interaction of the primary beam x rays with the gloves result in the production of characteristic x rays from the lead inside the gloves?

A

It is certainly true that in many instances attenuation of primary x rays in the lead of leaded gloves will result in characteristic x-ray emission from the lead. This is a simple consequence of a photoelectric effect, or in some instances a Compton scatter event, which removes an electron from the lead. When the vacancy produced by such an event is filled by an outer-shell electron dropping into it, the associated energy release occurs in the form of an emitted photon of characteristic energy—a characteristic x ray if the energy transition that has occurred is sufficiently high to yield a photon in the x ray energy range.

For such an event to occur the energy of the incident x ray must be greater than the binding energy of the involved electron. For example, the binding energy of the K-shell electrons in lead is about 88 kiloelectronvolts (keV). An x-ray machine operating at 100 peak kilovolts (kVp) would produce a few x rays energetic enough to induce some K characteristic x rays, ranging in energy from about 73 to 85 keV. Lower-energy emissions may also be expected when electron vacancies in the L-shell of lead are filled, yielding characteristic x-ray energies from about 10 to 15 keV.

The characteristic x rays produced may be given off in all directions. Many of them may be attenuated further in the lead of the glove. Some may reach the skin of the glove wearer. Others may be emitted in directions away from the body. The characteristic x rays produced by the gloves will likely contribute just a small fraction of the dose that accrues to the hands of an individual whose gloved hands are placed in the beam, with most of the dose coming from the primary and scattered x rays from the primary beam.

One should keep in mind that modern fluoroscopic machines used in interventional procedures may often increase the voltage in response to the attenuation provided by lead gloves, and this, in turn, may increase the energy and intensity of x-ray beam radiation reaching the skin. It is most appropriate to attempt to minimize any placement of the hands in the direct beam and not to rely on gloves to minimize dose.

George Chabot, PhD

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