Re: [Phys-l] Gamma-Gamma Coincidence

[John Denker <jsd@av8n.com>]

On 03/28/2010 04:19 PM, Michael Edmiston wrote:
> John, before you said...
>
> > "From the nucleus" is not the only possible definition.
> > AFAICT it's not even the usual definition.
>
> ... did you do any serious checking?  

I did.

> The figure you linked to is really old.

But as I said, there were many others, and all I
could find were consistent.  I chose one that was 
scanned at a high resolution and had a variety of 
units: wavelength, frequency, and energy.

> You might check even Wikipedia under "gamma ray" 

I did.  Unless it has changed in the last few minutes,
the second sentence of that article says
  "They are produced by sub-atomic particle interactions 
   such as electron-positron annihilation, ...."

directly contradicting the "nucleus only" definition.

As I have previously pointed out in other contexts,
it is not unusual for wikipedia articles to be self-
contradictory (in addition to just plain wrong).

>  I carelessly let the wording 511-gammas slip into a draft of my 
> thesis (in just one place), and my whole committee noticed it, and I was 
> asked to change it to 511-keV (gamma)(+-) , which I did, with embarrassment.

<snip>

> I have a whole shelf of reference books and nuclear physics books that say 
> the same things, and this is the way all my "nuclear colleagues" talk and 
> write.  What more do you need?

I stand by my assertion that "nuclear only" is not the
only definition.  I checked earlier, and I checked again
just now, and there are many, many instances of annihilation
radiation being called gamma rays.

My one-time colleague recently wrote:
   A. P. Mills, Jr., D. B. Cassidy and R. G. Greaves
  "Prospects for making a Bose-Einstein-condensed Positronium
   Annihilation Gamma Ray Laser"

I very much doubt that his choice of words was sloppy,
ignorant, or out-of-date.

A search for
  http://www.google.com/search?q=gamma+annihilation
turns up millions of hits, and instances of "gamma ray"
vastly outnumber instances of "(gamma)(+-)".  I consider
this an unbiased sampling of recent usage.

A search of scientific papers via
  http://arxiv.org/find/all/1/ANDNOT+ti:+AND+gamma+annihilation+ti:+dark/0/1/0/all/0/1
produces the same overwhelming statistics in support
of what I said.  Again I consider this an unbiased 
sampling of recent usage.