I would like to apologize to everyone for creating such a busy thread
(an what could perhaps be construed as an occasionally belligerent
tone), but I really do want to know the right answer to this! I am
trying to model radiation damage from first principles, and in such
models you cannot have arbitrary scale factors.
And I really do appreciate the effort Dale, Ian, Marc, and many others,
put into their posts. Taking bits from many of them, I think I can say
that:
The "unit of B factor" is: hemi-(cycle/Angstrom)^-2
and the dimensions of the B factor are length^2
Apparently, the B factor is derived from the square of a spatial
frequency, which has fundamental units "cycles per meter". However,
there is an extra factor of two that makes the B factor incompatible
with merely "spatial frequency squared" (with no scale prefix) as the
unit, so I think we have to include the prefix "hemi" before we can make
the 2*pi radians/cycle go away. Marc and Ian I imagine will tell me
that cycle = 1 and hemi = 1 and therefore we have Angstrom^2 and they
are more than welcome to do that in their papers, but I think it
important here to clarify exactly what "one B factor unit" means.
-James Holton
MAD Scientist
