Calculation of neutron transport cross section

[Kritmiss]

I have a book on nuclear reactions which details the mean free paths for thermal neutron scattering as:
0.37cm for water and
2.2cm for heavy water

The transport cross sections are listed as 0.45cm for water and 2.6cm for heavy water. Does anyone know how to calculate these from the thermal scattering cross sections?

Thanks!

 

[Stephan_doc]

macroscopic transport cross section=macroscopic scattering cross section *(1-cos(theta))
or generally
macroscopic cross section=1/mean free path

for water 1-cos(theta)=0.324 and 0.116 for heavy water

 

[Kritmiss]

Where do these values of 1-cos(theta) come from?

If I use them, I obtain very different values of transport cross section than those in my book. These values of 1-cos(theta) give 1.14cm for water and 19.16cm for heavy water?

 

[Stephan_doc]

Take a look here, maybe you understand better
http://mragheb.com/NPRE 402 ME 405 Nuclear Power Engineering/Neutron Diffusion Theory.pdf

 

[Kritmiss]

Thanks for the text, it was useful.

However, I am still unable to arrive at the values for the transport mean free paths which were stated in my book on nuclear reactions, and I do not understand where your values come from.

Thanks again for trying to help

 

[wannahead]

macroscopic transport cross section=macroscopic scattering cross section *(1-cos(theta))
or generally
macroscopic cross section=1/mean free path

for water 1-cos(theta)=0.324 and 0.116 for heavy water

Its not right to use theta in thermal energy because in thermal area of energy scattering is isotropic!