Re: [Phys-l] Gamma-Gamma Coincidence

[John Denker <jsd@av8n.com>]

On 03/28/2010 11:40 AM, Michael Edmiston wrote:

> The 511-keV 
> photons from B+ annihilation are not gamma rays.  Gamma rays come from the 
> nucleus and these definitely are not coming from the nucleus. 

"From the nucleus" is not the only possible definition.  
AFAICT it's not even the usual definition.

The usual definitions revolve around energy aka frequency
aka wavelength;  anything below 100 keV is an X-ray
while anything above 100 keV is a gamma:
  http://img20.imageshack.us/img20/9160/1260675741893.jpg
  and many others.

The energy-based definition makes sense to me.  In
particular, if I'm building a gamma detector, I don't 
care whether it was produced by a nucleus, by a 
positron, by a pulsar, or whatever.  The gamma is
a gamma, even after it is long separated from its
original source.

511 keV is not even close to the "soft" end of the
"soft" gamma rays.