Scattering cross sections

["Hartley, Lyn" <Lyn.Hartley@health.wa.gov.au>]

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?