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APPENDIX I:Hazards of Analytical
X-Ray Equipment
Sources of Radiation
Typical Exposure Rates
Sources of Radiation (top)
The National Bureau of Standards Handbook III provides the following
information on the sources of radiation hazards from analytical x-ray
equipment.
Hazardous radiation may come from the following sources:
The primary beam:
The primary beam is most hazardous because of the extremely high
exposure rates. Exposure rates of 4 x 105 R/min at the port have been
reported for ordinary diffraction tubes.
- Leakage or scatter of the primary beam through cracks in ill fitting
or defective equipment:
- The leakage or scatter of the primary beam through apertures in
ill fitting or defective equipment can produce very high intensity
beams of possibly small and irregular cross section.
- Penetration of the primary beam through the tube housing, shutters
or diffraction apparatus:
- The hazard resulting from penetration of the useful beam through
shutters or the x-ray tube housing is slight in well designed equipment.
Adequate shielding is easily attained at the energies commonly used
for diffraction and florescence analysis.
- Secondary emission from the sample or other material exposed to
the primary beam.
Diffracted rays:
Diffracted beams also tend to be small and irregular in shape. They
may be directed at almost any angle with respect to the main beam,
and occasionally involve exposure rates of the order of 80 R/h for
short periods.
Radiation generated by rectifiers in the high voltage power supply:
Radiation from the high voltage power supply may result from gassy
rectifiers. The effective potential is twice the potential applied
to the x-ray tube. This condition can arise at any time and the only
effective countermeasure is to shield the assembly that contains the
rectifiers.
Typical Exposure Rates (top)
The following table provides information on typical exposure rates
measured in and near diffractometers and spectrometers.
Point of Measurement |
Approximate exposure rate(a) (mR/second) |
Inside specimen chamber of spectrometer |
10,000 |
Inside crystal chamber of spectrometer |
5 |
Outside exit window of spectrometer |
0.0005 |
At open port of diffraction tube tower |
2,000 |
At sample position of diffractometer |
5 |
At receiving slit of diffactometer |
0.5 |
At exit collimator of Debye-Scherrer Camera
(with no exit collimator) |
100 |
(a)Assuming maximum tube operation
Adapted from "Incidence, Detection and Monitoring of Radiation
from X-Ray Instrumentation" by R. Jenkins and D. Haas in X-Ray
Spectrometry, 4 (33), 1975.
The following table provides information on typical exposure rates
measured under various conditions, using a copper target:
KvP |
mA |
R/min* |
Filter |
35 |
18 |
2,000 |
none |
35 |
15 |
360 |
Nickel |
35 |
30 |
600 |
Nickel |
35 |
19 |
2,900 |
Nickel |
50 |
40 |
620 |
Vanadium |
* Measured at 6 inches from tube port
Taken from "X-Ray Diffraction and Other Analytical X-Ray Hazards:
A Continuing Problem" by J. Lubenau et al. (1967), a paper
presented at the 1967 Health Physics Society Annual Meeting.
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