Time Scale Problem: Solving Diffusion Time of Particles in 2D Space

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The discussion centers on deriving the diffusion time for particles in a two-dimensional space, focusing on parameters like particle speed, scatterer density, and linear cross-section for scattering. Participants express confusion about the definitions of density and cross-section, with density being clarified as the number of scatterers per square meter. The linear cross-section is explained as a measure of the likelihood of scattering events occurring. There is a request for further clarification on the normalization of these parameters. Overall, the thread highlights the need for foundational understanding in tackling the diffusion time problem.
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I am having a lot of trouble starting the following problem. Any ideas? Thanks a lot for helping!

Derive from first principles, the diffusion time for particles traveling at speed v in a two dimensional (x,y) space to reach a distance R from their release point if the scatterers have a density n(m^-2) and linear cross section for scatter \sigma(m) Let each particle scatter with equal probability into the +/- x, +/-y directions.

I don't know what some of these things mean and they aren't explained well in my book or anywhere i look. What is the density it is referring to? What is the linear cross section for scatter? Again, thanks for any help.
 
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Density n(m^-2) is number per square meter. The cross-section determines the probability of scatter - I am not sure how the normalization has been set up.
 

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