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Unformatted text preview: Then, d3p = p2 dp d = c13 E 2dE d : So, for photons in a xed energy interval dE around E , d3p is proportional to
the solid angle element d that encompasses their directions and to E 2dE .
We should here say a word about the notation d for solid angle; it is
measured in steradians, a unit such that the full 2sphere is 4 steradians,
i.e.
d = 4 :
sphere
Z In spherical polar coordinates, d decomposes into the two orthogonal directions,
d = sin dd' = d(cos )d' :
dθ
sin θ d ϕ If we consider photons moving in one direction and normally incident on
a detector, then d3x is related to their ux: 27 ...
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This note was uploaded on 12/29/2011 for the course AST 350 taught by Professor Dion during the Fall '09 term at SUNY Stony Brook.
 Fall '09
 dion

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