Calculating % of X-rays Penetrating Lead with Al Attenuation Coefficient

[MrKoffee]

Okay, the question I'm suppose to answer is:

If the attenuation coefficient of Al is 1.73/cm for soft-xrays, what percentage of X-rays penetrate a piece of lead 3.00mm in thickness
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What I seem to have is

I = Io*e^(-ux)

I believe u = 1.73/cm and x = 3.00mm.

My 3 questions are:

1) Am I going in the correct direction?
2) How do I determine what Io be? (soft x-rays?)
3) Can someone point me to the FAQ for the equation editor?

Thanks in advanced.

 

[lightgrav]

You're asked for a "percentage" ... that is, what fraction of those impinging ...
which is : I(at depth)/I(at zero depth) , so the Io cancels out.

ps. the format is [ tek ] ... and [ /tek ] , without the spaces .

 

[MrKoffee]

Well, now I feel really stupid...

Thanks :)