From key@physics.utoronto.ca Wed Mar 26 12:56:42 2008
Date: Wed, 26 Mar 2008 12:56:41 -0400
From: Tony Key <key@physics.utoronto.ca>
To: xiao.ou@utoronto.ca
Bcc: Tony Key <key@physics.utoronto.ca>
Subject: Re: Photon fluence rate

Again, Xiao, it comes down to precise definitions.

Photon Fluence rate is the no. of photons per square metre per second - you
have that correct.

The energy striking an area A per second is the photon fluence rate
multiplied by the area A.  The photon fluence rate however is normalized to
one square metre.

In your example, the box would have more energy per second impinging on it -
but the "density" of the energy - i.e. the fluence rate - is the same for
box and book.

Memorize your definitions!

TonyK



xiao.ou@utoronto.ca wrote:
> Sir I have a quick question about the photon fluence rate question in
> class. I thought fluence rate was number of photons/area of matter  struck
> * time.
> 
> So that means that the A would be the area of a person that is exposed  to
> the beam. So why, in the clicker question, does it suggest that the
> photon fluence rate is the same regardless of the size of the object
> being exposed? For instance,  we used the surface area of a sphere  over
> the activity, I see how we got that. But if we were to place a  large
> cardboard box next to a small book, why is the photon fluence  rate for
> both the same?
> 
> 
> Wouldn't the box have a higher fluence rate since it's exposed surface
> area is larger?
> 
> Thanks.
> 
> 
> Xiao
> 

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