AW:

[Navert Stephan <Stephan.Navert@hsk.psi.ch>]

> -----Ursprüngliche Nachricht-----
> Von:	Mike Dupray [SMTP:dupray@gat.com]
> Gesendet am:	Donnerstag, 28. Januar 1999 18:03
> An:	Multiple recipients of list
> Betreff:	
> 
> Does anybody know what a 4pi steridian cross section looks like?
> Michael R. Dupray
> Senior Staff Health Physics Technician
> General Atomics
> 619-455-3561
> FAX 619-455-3465
	[Navert Stephan]   What do you mean with this question?

	Let's try to figure out: The differential cross section is
defined (in terms of basic particle physics) as the number of particles
scattered into one definded direction (seen from the scatterer) and a
certain (sufficient small) solid angle around that direction; divided by
the total number of incoming particles. It is clear that the
differential cross section is a function of at least the scattering
angle.
	Now,  if you do an integral of the differential cross sections
over the whole sphere around the target (ie. solid angle 4 pi!), you end
up with the total cross section of a scattering process. This number is
the total number of scattered particles divided by the number of
incoming particles, or in other words it is the something like "the
magnitude of the plane area covered by the target as seen by the
incoming particle". This is intuitively clear when looking to the
dimension of a total cross section: it is [m^2].

	Hope this helps!

	Stephan Navert

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