Radiation Hazards of Analytical X-Ray Equipment
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.
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
- 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
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.
Burns Produced by X-Rays
|Description of Tissue Damage
||Approximate Dose Required (gray) |
|Perceptible reddening of skin
|Dry desquamation of skin
|Wet desquamation and blistering
|Ulceration and necrosis of skin
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.
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
- The dose rate at the hand of 10 cm collimator is reduced to
several thousand rad per minute (several tens of gray per
- 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
Possible Radiation Intensity Near Analytical X-Ray
||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
milligray per hour |
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
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
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
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.