Re: Tissue ionization by UV

[daleboyce@charter.net]

Hi all,



I'll reply to the list as I have received other similar replies directly.

Yes, most UV absorption does not involve ionization.  Tanning increases the

level of melanin.  Melanin has conjugated ring structure which greatly

enhances resonant absorption of UV and turns it into heat without producing

chemically reactive intermediaries.  This protects the skin from the harmful

effects of UV.



The question I am asking is what fraction of the UV absorption causes

chemical reactions in the skin.  The second question then is when you

multiply the UV energy flux by this fraction, do you get skin erythema at a

similar rate as with say x-rays?



In my first post I SWAGged a 1 mm depth, but with UV it is probably much

less than that.  So the discrepancy between energy flux of UV and X-ray to

cause erythema is probably much more than the factor of 100 I threw out.



Dale





----- Original Message ----- 

From: "Michael McNaughton" <mcnaught@lanl.gov>

To: <daleboyce@charter.net>; <radsafe@list.Vanderbilt.Edu>

Sent: Monday, June 21, 2004 8:59 AM

Subject: Re: Tissue ionization by UV





> At 03:37 PM 06/19/2004, daleboyce@charter.net wrote:

> >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.

>

> the best information I have found indicates that the chemistry of sun

> tanning mostly involves molecular excitation rather than ionization.

> However, I don't mind being contradicted, and anyway I would be interested

> in learning more.

>

> mike

> Mike McNaughton

> Los Alamos National Lab.

> email: mcnaught@LANL.gov or mcnaughton@LANL.gov

> phone: 505-667-6130

>

>





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