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Re: mrad silicon
The confusion over the "rads (Si)" dosimetry is the result of frequent
use of "shorthand" for terms "everybody knows." To be complete, each
use of the term "rad" should have the material absorbing the radiation
included. Since most uses of the term (in the health physics arena) are
for protection of people from radiation, the "tissue" qualifier is
commonly dropped, or understood to be present unless some other qualifer
(like silicon in the original message) is used.
As noted previously, the energy absorption coefficients for various
materials tend to converge as the energy of the radiation increases, but
the difference in coefficients can be great at low energies.
Dosimetry of flash x-ray systems, with their extremely short
(nanosecond) pulse lengths can be tricky. Some also have very high
output per pulse. Because of these factors, the characterization of
flash x-ray systems using the terms commonly used in diagnostic
radiology does not work well. The instantaneous dose rates can exceed
the measurement capabilities of many dosimetry systems.
Send me a personal or call if you want to discuss further.
Ed Tupin
RSO, Center for Devices and Radiological Health
EAT@fdadr.cdrh.fda.gov
(301) 827-1230
Fax: (301) 594-4760