Volume 1, Number 4 October 2002
TNT Inbox:
Q: I have been told that it is possible to enlarge images of components by moving them closer to the X-ray source and away from the detector. Won't this produce excessive unsharpness?
A: Using a source with an extremely small target will allow magnification of the component. Typical X-ray tubes have targets in the 1-3 mm range. Targets on specialized tubes are measured in microns, providing a near point source of radiation that allows the component to be some distance from a detector while maintaining acceptable unsharpness.Q: Your article on Ultraviolet Safety (Vol. 1, No. 1) states "If an inspector's hands are subject to 5000 µW/cm2, then the recommended daily ultraviolet-A exposure can be exceeded in 200s." What is the source of this information? What about exposure at less than 5000 µW/cm2? What are the symptoms of such exposure? What about using sunscreen?
A: The statements are based upon the threshold limit values (TLV's) for UV-A recommended by the American Conference of Governmental Industrial Hygienists (ACGIH) for chemical substances and physical agents. For UV-A radiation, ACGIH recommends that the total irradiance incident upon the unprotected skin or eye should not exceed 1.0 mW/cm2 (1,000 µW/cm2) for periods greater than 103 seconds (approximately 16 minutes).
- For exposures less than 5,000 µW/cm2, a linear interpolation is sufficient. To demonstrate, the time limit for 5000 µW/cm2 is (1000/5000) x 103 seconds = 200 seconds.
- Symptoms range from sunburn to suntan. Note that the limits are for people with "average" skin sensitivity and do not apply to photosensitive individuals.
- Sunscreen is very effective. When using sunscreen, all exposed skin should be treated including the face, neck, etc. Also wear long sleeved shirts and gloves, where necessary.
E-mail, fax or phone questions for the TNT Inbox to:
Editor, hhumphries@asnt.org
(614) 274-6899 fax
(800) 222-2768 X206
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