Re: Scattering cross sections

[photcoef <photcoef@tiac.net>]

One measure for the scattered component of radiation
that passed through an absorber is the Buildup Factor B.

A definition of B can be found at
www.photcoef.com/213.html

The Buildup Factor for lead shields of different
thicknesses can be derived by taking the ratio of the
Shielding Functions of Lead,
www.photcoef.com/2381.html
to the Transmission Functions of Lead,
www.photcoef.com/2392.html

Finally, most of the scattering at common energies is
caused by the Compton Effect. Graphs and Tables of
Compton Scattering  (and other) coefficients can be
found at
www.photcoef.com/2121.html 



Paul Kehler
AIC SOFTWARE, Inc.
photcoef@aol.com


At 01:42 AM 4/14/98 -0500, you wrote:
>I am posting this message for a friend who does not have an email account.
>Please respond to me personally.  She writes ....
>
>I completing a physics Masters by research. (I  absolutely have to be
>finished by the end of June)
>
>The project is looking at contrast modelling of photon imaging of dense
>objects with particular emphasis on computed tomography (x- and gamma-ray)
>of industrial objects such as rock cores. It is a simplistic model comparing
>the intensity transmission through two areas of an object, one an
>homogeneous area and the other with a small inclusion (for example quartz
>with an air inclusion). The aim of the modelling is to predict the
>theoretical minimum visible inclusion size given sufficient spatial
>resolution of the detectors. There are four scenarios: monochromatic narrow
>and broad beams and polychromatic narrow and broad beams.
>
>I've completed the first three of the scenarios and m now faced with
>polychromatic broad beam.
>
>I have divided each beam into ten energies (so I have a setting of 100keV
>and according to Kramers Law have a particular spectrum over the energy
>range of 0-100keV). The amount of scatter will vary for each of those 10
>energy ranges. Where I am stuck is trying to calculate the amount of scatter
>for each of the energy ranges. I am led to believe that the mass attenuation
>coefficient is related to the scattering cross sections and that somehow
>this will enable me to calculate the scatter factor for each of the energy
>ranges.
>
>For a start is it the mass attenuation or absorption coefficient?
>
>What exactly is a scattering cross section?
>
>How does all of this enable me to calculate the scatter factor?
>
>And finally (and prosaically), why does scattered radiation decrease
>contrast?
>
>
>
>
>