
 Cross section (Site not responding. Last check: 20071020) 
  In geometry, a cross section is the intersection of a body in 3dimensional space with aplane, or of a body in 2dimensional space with a line, etc. More plainly, when cutting an object into slices one gets manyparallel cross sections. 
  In nuclear physics, it is found convenient to express probabilityof a particular event by a cross section. 
  Thus for slow neutrons absorbed by the (n,gamma) reaction the cross section in some cases is as much as 1,000 barns, while the cross sections for transmutations bygammaray absorption are in the neighborhood of 0.001 barns. 
 www.therfcc.org /crosssection30089.html (436 words) 
