From key@physics.utoronto.ca Mon Mar 10 09:27:20 2008
Date: Mon, 10 Mar 2008 09:27:20 -0400
From: Tony Key <key@physics.utoronto.ca>
To: stuart.wiber@utoronto.ca
Subject: X-ray Intensity

Hi Stuart - as I explained the definition of Intensity in the X-ray field
depends somewhat on the reference.  Sometimes it is equivalent to photon
fluence rate, sometimes to energy fluence rate, occasionally just as 'photon
flux'.  Often, since it is a word in common use (intensity of emotion, of
light, magnetic intensity, etc.) it is not precisely defined.  If you need
to know exactly what it is, you have to read the reference you are using.
(The use of the word 'Flux' suffers from some of the similar problems).

I decided therefore not to use it in the course, but to stick to the precise
and unambiguous definitions of photon or energy fluence and fluence rate.

Of course in many cases, all it needs is some common sense - e.g. in PS#2,
3rd question about X-ray Film contrast) it could refer to any of the four
quantities I've defined above.  Whatever is meant in that question it is
obvious that it has to do with contrast between X-rays emerging from two
different paths - one through bone and tissue, the other through tissue
alone.  All that you usually need to remember is that fluence, fluence rate
(photon or energy!) decrease exponentially as the X-rays proceed through
matter.

Thanks for an excellent question.  I'm glad the importance of definitions is
at the heart of it!

TonyK

stuart.wiber@utoronto.ca wrote:
> Hi Professor Key,
> 
> 
> "Intensity" is a term used in the X-ray Gamma-Ray absorption lab. I am
> confused about its units. Is intensity equivalent to energy fluence  rate
> or simply fluence rate?
> 
> Thanks Professor,
> See you Monday :)
> Stuart
> 

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