Tissue ionization by UV

[daleboyce@charter.net]

Howdy all,



I am trying to find data on the ionization of tissue by UV light i.e. what

fraction of the energy of UV incident on tissue goes into ionization.  In

doing training I find that I frequently gets asked about the equivalence of

radiation to radiation from the sun.  I always go off on the difference

between cosmic rays and the low energy radiation from the sun that doesn't

make it to earth, and wind up ignoring UV.



I have found sources of information that indicate that 1 unit of UV Index is

25 mW/m^2 in the 280-320 nm band, and that a dose to a non-tanning

individual to cause the onset of erythema is 210 J/m^2 (a little under 15

minutes on a Texas summer day where a clear day has an index of 10 and even

cloudy days are 8 or so).  If you assume a mean absorption depth of 1 mm

then you come up with something like 2100 Gy of UV to produce erythema.

Since this is the order of 100 times the erythema dose for ionizing

radiation, I'd like to find something that tells me if the ionization vs.

non-ionizing absorption is say 1%, and therefore ties in with skin dose to

ionizing radiation.



I don't expect an exact correlation since water is fairly transparent in

this band (otherwise it wouldn't get through the atmossphere. So biological

effects will be due to direct interaction with organics.  Still it would be

interesting for training to be able to make a fair comparison of sunlight to

ionizing radiation in the same units.



Thanks!



Dale

daleboyce@charter.net





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