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*To*: radsafe@romulus.ehs.uiuc.edu*Subject*: Re: Scattering cross sections*From*: photcoef <photcoef@tiac.net>*Date*: Wed, 15 Apr 1998 21:20:43 -0400 (EDT)

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? > > > > >

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