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 radiation burns in a matter of seconds. These burns heal poorly, and on rare occasions have required amputation of fingers.

• Localized radiation burns produced by the high intensity primary x-ray beam is the principal hazard associated with the use of analytical x-ray equipment.

Scattered Radiation

A hazard may 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 a couple of orders of magnitude less than that of the primary beam. It is possible for these scattered radiation fields to result in exposures, which exceed regulatory limits, however.

• Scattered Radiation may exceed regulatory exposure limits.

Hazards Associated with X-Ray Exposure

The hazards most often associated with exposure to x-ray radiation include increased risk of cancer and increased risk of genetic effects in exposed populations. These effects are effectively discussed in a number of readily available publications and will not be elaborated upon in this document. NRC Regulatory Guides 8.29, entitled Instruction Concerning Risks from Occupational Radiation Exposure, and 3.13, entitled Instruction Concerning Prenatal Radiation Exposure published by the Nuclear Regulatory Commission have been included as Appendix B and C in this manual.

Skin Burns

As discussed in the introduction, the principal hazard associated with use of analytical x-ray equipment is localized skin burns following exposure to the primary beam.

• Experience with exposure of relatively large areas of skin to radiation has shown that it requires doses of approximately 300 rad (3 gray) to produce a visible reddening of the skin.
• Doses of approximately 1500 rad (15 gray) are required in order to produce serious burns with blistering.
• When doses reach 3000 rad (30 gray) very serious burns requiring skin grafts or amputation may result.

The bum symptoms may require from one to several weeks to develop, depending on the dose.

Target Size

Experiments have shown that when the irradiated area is very small, it takes higher doses to damage the skin.

• Decreasing the size of the irradiated area from 100 cm2 to 1 cm2 has been reported to require 10 times the dose to produce the same degree of damage.
• Further reduction of the irradiated area from 1 cm2 to 1 mm2 will again require 10 times the dose to produce the same damage.

Eye Damage

There have occasionally been reports of accidental exposure of the eye during use of analytical x-ray equipment. Doses capable of causing skin burns are capable of producing serious permanent damage to the eye.

• Studies have also shown that doses greater than 200 rad (2 gray) are capable of producing cataracts in the lens of the eye.

Intensity of the Primary X-Ray Beam

X-ray fields near a bare x-ray tube are very intense.

• For this reason, regulations do not allow the use of instruments without a protective tube housing or shield.

The x-ray tube housing contains one or more ports which provide a narrow beam of useful x-rays. The x-ray dose rate at the beam port may be several thousand rad per second (several tens of gray per second). Inadvertent placement of fingers at the beam port for even a second can result in serious burns.

As a further precaution, current regulations require a shutter for all beam ports on the tube housing. The shutters must automatically close unless a collimator, camera, or other equipment is attached to the beam port. Use of a beam collimator greatly increases safety of analytical x-ray equipment on two ways.

1. The dose rate at the hand of 10 cm collimator is reduced to several thousand rad per minute (several tens of gray per minute).
2. In addition, the dimensions of the collimated beam are usually on the order of 1 mm2..

The possibility of receiving a high dose to any portion of the skins is unlikely under these conditions. Natural movement of the hand will ensure that the same 1 mm² area of the skin is not irradiated for any significant amount of time.

The intensity of the x-ray beam decreases very rapidly as the distance from the tube increases. The dose rate as a function of the distance from the tube follows the well known inverse square relationship.

Possible Radiation Intensity Near Analytical X-Ray Equipment
Location	Dose Rate
Primary beam at tube port	several tens of gray per second
Primary beam at end of 10 cm collimator	several tens of gray per minute
Scattered radiation near sample	several milligray per hour
Scattered radiation near table edge	1 milligray per hour

Scattered Radiation

Radiation is scattered when the primary beam impinges on surfaces of collimators, samples, beam stops, or shielding. The intensity of the scattered radiation may be as high as several hundred millirad per hour (several milligray per hour) near the collimator, but rarely exceeds 100 millirad (1 milligray) per hour at the edge of the equipment table.

Additional Protective Devices on Analytical X-Ray Equipment

The information provided above on the x-ray fields produced during use of analytical x-ray equipment represents a worst case type of configuration, Most equipment is not used in an open beam configuration. Usually a combination of filters, cameras, beam enclosures and shielding are used and reduce the radiation fields around the equipment significantly.

X-rays produced in analytical x-ray equipment are usually filtered to modify the quality of the beam. These filters may be placed in front of the collimator, but are often placed in front of the sample or detectors. When the primary beam is filtered, the intensity of the beam is reduced to by a factor of from 2 to 6.

Often a camera or other equipment is used which encloses the beam. In these cases, the radiation hazard is limited to scattered radiation.

Fluorescence spectrometers utilize a special interlocked sample chamber, which encloses the beam. In this equipment the beam is more intense that that required for diffractometers. In addition, the sample must usually be closer to the beam port. In order to prevent access to the high radiation levels of the primary beam, fluorescence equipment must be equipped with an interlocked sample chamber. Access to the sample requires removal of an interlocked cover. Removal of the cover shuts off the power or blocks the beam thereby preventing injury to fingers, which are carelessly placed in the sample chamber.

In all but the oldest equipment, some type of enclosure is used which will prevent inadvertent insertion of hands and fingers into the path of the primary beam. These enclosures may be constructed of plastic or glass and are usually interlocked. When the enclosure is opened, the power is shut off, or the beam is blocked.

Shielding made of plastic, glass, or metal may also be used to reduce the level of scattered radiation in occupied areas. This type of shielding is not typically interlocked.