From key@physics.utoronto.ca Fri Mar 21 21:41:19 2008
Date: Fri, 21 Mar 2008 21:41:17 -0400
From: Tony Key <key@physics.utoronto.ca>
To: jere.chan@utoronto.ca
Subject: Re: Small error in journal tablet 8

Hi Jeremy - thanks for your note.  Indeed there is a slight error, but I
don't think it is the one you point out!

6.95x10^(-5)/0.068 = 1.02x10^(-3).
The units are (J/kg)/(cm^2/g) = (J x g)/(kg x cm^2) = (J x g)/(10^3 g x
cm^2) = 10^(-3) J/cm^2.
So the final answer is 1.02x10^(-3)x10^(-3)/cm^2 = 1,02 x 10^(-6) J/cm^2.

I think you have done the units OK, but you have a simple arithmetic error
in your calculation,
You write - ""( 6.95 x 10^-5 x 10^-3 ) / 0.068 = 1.02 x 10^-9  J/cm^2 ""
Should be - ( 6.95 x 10^-5 x 10^-3 ) / 0.068 = 1.02 x 10^2 x 10^-8  J/cm^2 =
1.02 x 10^(-6) J/cm^2
(6.95/0.068 =102 = 1.02 x 10^2 !!)

The units in the journal notes for the fluence should be J.g/(kg.cm^2) NOT
J/cm^2. The units in the following line are OK, however, as the 10^(-3)
factor has been taken into account.

Let me know if you agree! .. and thanks for checking!

TonyK
>
>
>
> jere.chan@utoronto.ca wrote:
> > Dear Prof. Key,
> >
> > There is a small calculation error in the Lecture 8 the journal (tablet)
> > notes
> >
> > 1. Exposure = exposure rate x time = ( 800 x 10^-3 ) x (10^-2 )  R
> > 2. Dose in air = Dair  = 8.69 x 10^-3  X   = 6.95 x 10^-5   Gy
> > 3. Energy fluence in air =  Dair / (? /?)air
> > Here Dair is in Gy = Joule /Kg   and   (? /?)air is in cm^2/g
> > Dair / (? /?)air  should be  ( 6.95 x 10^-5 x 10^-3 ) / 0.068 = 1.02 x
> > 10^-9  J/cm^2
> > ?
> > ?
> > ? ( a factor of 10^-3 is missing)
> > ?
> >
> > 8 The final answer in body should be D = E /M = 53 x 10^-9 J /Kg = 53
> > nGY.
> >
> >
> > Jeremy
> >
> >
>