I looked at a bunch of the examples you gave, and just like I said should be done, those examples used gamma-ray *with further clarification*.
I would prefer "annihilation photons" but I don't really have a problem with "annihilation gamma-rays" or using the gamma(+-) notation. This makes it clear that these photons, or gammas, or whatever, were produced from an annihilation process.
Likewise, if the radiation is bremsstrahlung, we should say so. And likewise for other examples.
In my opinion, and based upon considerable research experience with good colleagues, if a person says gamma-ray without further clarification, the implication is a photon from a nuclear-level-transition. If a person says x-ray without further clarification, the implication is a photon from an atomic-electron-level-transition.
I believe you and I both agree that a person should communicate clearly. If we know the source of a photon, why wouldn't we want to refer to it in an unambiguous manner. I can't remember hearing colleagues refer to "x-rays" or "gamma-rays" when they were speaking of bremsstrahlung radiation. I only remember them calling it "bremsstrahlung radiation."
Furthermore, I agree with you that a NaI or GeLi detector doesn't care whether the photon it detected came from a nuclear transition, or an annihilation, or an electronic transition, or whatever. But the scientist cares, and often the experiment is either designed to observe a particular type of event, or the experiment is designed to determine what type of event produced the photons being detected. The detector can't tell the difference, but analysis of the data from that detector often can indeed tell the difference.
For example, as Bill Nettles pointed out, even though the GeLi detector doesn't care whether the 511-keV photon came from positron annihilation or from a nuclear transition, the difference is clearly obvious in the spectrum. The 511-keV annihilation photons produce a wide peak, and 511-keV photons from a nuclear transition produce a very narrow peak. The difference is striking; you can't miss it.
When nuclear spectroscopists observe fairly low-energy photons in a spectrum (say 70-keV) one of the early determinations that must be made is whether it is an x-ray or a gamma-ray. You don't want to add a level in your nuclear decay scheme to accommodate what you think is a 70-keV gamma-ray if it is really an x-ray. Or conversely, you don't want to miss adding a nuclear level to your decay scheme because what you treated as a 70-keV x-ray is really a gamma-ray.
I have indeed spent a portion of my research life designing detectors and the electronics that go with them. When I am in this phase of my life, I don't really care where the photons came from, I just want to detect them. I have indeed spent a portion of my research life doing experiments with my detectors with the goal of solving some sort of nuclear-physics puzzle. When I am in that portion of my life I most certainly care to determine the process that produced the radiation.
Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
Sent: Tuesday, March 30, 2010 2:34 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Gamma-Gamma Coincidence
On 03/29/2010 01:59 PM, Bill Nettles wrote in part:
If you know the source, use the correct name.
1) I am all in favor of using the "correct name".
2) But what is the correct name?
There is a divergence of opinion as to the correct name.
When I say "there is a divergence of opinion" the quoted
clause is *not* an opinion; there is overwhelming
objective evidence of the divergence.
People who prefer one name should not be too quick to
correct people who prefer another name, especially when
both names are in widespread, longstanding, and current
use by thoughtful experts who work in the field.
Defining gamma rays so that the only allowable source
is the nucleus is not the only definition. It is not
true that all references say the same thing. It is
not true that all journal editors will insist on this
one source-based definition. There is overwhelming
objective evidence of what I am saying.
You shouldn't think that annihilation radiation is a
special case because it is "almost" a nuclear process.
The term "gamma ray" is commonly applied to synchrotron
radiation, which does not involve anything resembling
a nuclear process: http://www.google.com/search?q=wiggler+%22gamma+rays%22
As another example, the term "gamma ray" is commonly
applied to high-energy bremsstrahlung http://www.google.com/search?q=bremsstrahlung+%22gamma+rays%22
even though the same physical process at lower energy
would produce what we usually call X-rays. This is an
instructive example because it shows the overlap between
the two terms.
3) Ideas are primary. Terminology is at best secondary.
Terminology is important only insofar is it helps us
formulate and communicate the ideas.
Loosely-defined terminology is sometimes a source of
confusion, but sometimes not. Sometimes the meaning
is obvious in context. For example, when somebody is
talking about "511 keV gamma rays" there is AFAICT no
possible confusion.
Arguing about terminology is usually a waste of time.
I recommend tolerance. You can use whatever terminology
you like. It's your choice. However, keep in mind that
other people may choose differently.