Radiation Safety Office
Low Energy & Portable Hand Held
State regulations require that all x-ray machines that are to be operated on the Oklahoma State University campus and used for research purposes be registered with the state and included on the campus inventory of radiation producing machines. This requirement covers both “true” x-ray machines (e.g. XRDs, XRFs, DEXA units, Micro CTs) and what some are sometimes referred to as “low energy” x-ray machines (e.g. XRDs and XRFs that are filtered to produce only “soft” x-rays). These latter types of machines can lead to some of the most potentially dangerous exposures because rather than pass through the body and associated soft tissue these lower energy rays are absorbed in the skin leading to high skin doses and associated skin damage. In fact, most recorded human radiation overexposures from analytical x-ray equipment are from damaging low energy x-ray effects in live layers of skin and shallow tissues.
For obvious reasons, most tissue damage caused by x-ray exposure is to the hands. For x-ray photons ranging from 5-30 KeV, irradiation of the fingers or hands deposits most of the damaging energy in shallow tissues from the epidermis to the outer layer of the bones of the fingers. Due to the photoelectric effect, the x-ray photons entering the skin are essentially converted to electrons with approximately the same kinetic energy as the initial x-ray photons. These photoelectrons can further travel and transport into live soft tissues. Thus, the majority of the energy of low energy x-rays is deposited in live soft tissues of the fingers and hands.
Typical visual effects such as erythema (sunburn-like reddening of the skin) are manifest at as little as 50-100 rem of dose equivalent low energy x-ray delivered to the skin almost immediately after the exposure. At high intensity exposures of low energy x-rays, acute skin damage similar to thermal burns occurs. Very high exposures may necessitate skin grafts and/or amputation of fingers and possibly portions of the hands.
To illustrate the table below provides typical beam Dose Rates in machines operating at 15 kVp vs. 50 kVp tube voltage for hand held units
|Quantity (United States||Dose Rate 15/kVp max setting (rem/hr)||Dose Rate 50 kVp max setting (rem/hr)|
|Deep Dose Equivalent||14||110|
|Shallow Dose Equivalent (US NRC Definition)||251||40|
Note that at 15 kVp maximum as quoted by the manufacturer’s representative results in the majority of the dose (251 rem/hr) being deposited in the live layers of skin. The higher energy of 50 kVp is actually less damaging to the skin than the 15 kVp setting since only 40 rem/hr of the 50 kVp energy is deposited in the live layers of the skin.
In addition, sales representatives and manufacturer’s tend to obscure the fact that the 15 kVp instrument above is not a regulatory “exempt” x-ray device and so it must be registered with state regulators and attached to the OSU permit just as any other device designed to emit x-rays is, even if it is delivered on loan or donated as a demonstration model. Finally note that there are documented cases of persons having lost fingers and significant portions of hands by placing their hands directly in a “low-energy” X-ray diffraction machine beam for less than one second.
Thus, in order to maintain compliance with state regulations, the Radiation Safety Office must be made aware of any radiation producing equipment that comes to this campus for any length of time prior to its operation.
If you have any questions or intend to acquire or use a low energy or portable hand held x-ray device, including demonstration models of a hand held analytical x-ray unit(s), please call the Radiation Safety Officer at 405-744-7890 in order to gain the required authorization and training prior to ordering or acquiring a permanent or demonstration unit.
Finally, please notify the RSO if you plan to hold a demonstration of a low energy or portable hand held x-ray device on campus, even if the demonstration will be provided by a licensed representative or other person(s).