FAQ - X-ray radiation!!

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Carl Willis
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Re: FAQ - X-ray radiation!!

Post by Carl Willis » Thu Feb 07, 2013 7:30 pm

There's no misunderstanding, George.

The argument over terminology is unnecessary. For what it's worth, the current Oxford English Dictionary discussion of the term "x-ray" includes the following:

X-rays are produced by the deceleration of charged particles, esp. electrons, or by electron transitions in atoms [...]

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Rich Feldman
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Re: FAQ - X-ray radiation!!

Post by Rich Feldman » Thu Feb 07, 2013 7:58 pm

> For what it's worth, the current Oxford English Dictionary discussion of the term "x-ray" includes the following:
> X-rays are produced by the deceleration of charged particles, esp. electrons, or by electron transitions in atoms [...]

Interpreted broadly, that includes synchrotron radiation -- the brightest practical source of continuous x-rays?

My non-professional understanding is that gamma rays are distinguished from x-rays by their source (nuclear processes) rather than by their energy.

As usual, talking comes easier than looking something up on the Internet.

-Rich
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Re: FAQ - X-ray radiation!!

Post by George Dowell » Thu Feb 07, 2013 8:36 pm

Yes there are still texts that try to distinguish X-Rays from Gamma rays by their position on the spectrum chart, not by their origin. If you talk to Dr. Gordon Gilmore, you better call say annihilation radiation by its real name not X-Rays!

In the case of X-Ray generators, in my humble opinion, the difference between Bremsstrahung continuum and Characteristic X-Rays peaks are quite important and relevant to the discussion.

Then again I'm no expert, just a hobbyist.

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Re: FAQ - X-ray radiation!!

Post by Carl Willis » Thu Feb 07, 2013 9:35 pm

The x-ray/gamma ray terminology predates scientific understanding that came with the "modern physics" revolution. When Roentgen gave "X-strahlen" their name, the word simply meant the penetrating radiation emitted from a cathode-ray tube--which we now know is photons produced via two entirely-different processes. When Rutherford named "gamma rays", all he knew what that their origin was in radioactive decay and that they were more penetrating than x-rays using the sources he had. The terms remain in use today, having undergone no formal refinement or redefinition even as the underlying processes have come to be understood in detail. Their domains of common meaning have not really changed. When someone talks about x-rays, the assumption is that they are talking about penetrating radiation emitted from a cathode ray tube.

Synchrotron radiation was identified and understood later, after the modern physics revolution. Calling it x-radiation wouldn't be decisively wrong, but it would be odd.

The current Pope's Latinist, Reginald Foster, often has to translate concepts postdating the fall of Rome and its language into Latin (he's borrowed "breviloqui" from Cicero, repurposing it to mean "to Tweet"). Although it's brief speech, there's no doubt a lot is lost in the translation, such as the whole essence of Twitter being a massively-networked electronic communication medium. Cicero would be clueless. The first synchrotron radiation observed and understood correctly was in fact visible light. Roentgen would be confounded if he found his old term being used to describe it. However, he would be right at home with the penetrating radiation coming out of fusors, and could adeptly make a nice photo of his hand bones with it.

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Re: FAQ - X-ray radiation!!

Post by George Dowell » Fri Feb 08, 2013 12:16 am

So the Deuterium ions are the canal rays?

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Re: FAQ - X-ray radiation!!

Post by Rich Feldman » Fri Feb 08, 2013 12:57 am

George wrote:
>So the Deuterium ions are the canal rays?

I like it!

Carl, thanks for your historical perspective. I like to use words in their most general sense, especially since English so often has separate words for specific subcategories.

It's always been a delight to learn things about the history of science. People working with synchrotrons seem to generally use "x-ray" for the photon spectrum of higher energy than ultraviolet. Here's a nice historical summary, found on the Lawrence Berkeley website: http://xdb.lbl.gov/Section2/Sec_2-2.html

Which leads us to the classification (as x- or γ-ray) of 511-keV annihilation radiation.
It seems to traditionally be called gamma, although neither atomic nuclei nor radioactive decay are directly involved. Sounds right to me. There are subatomic particles reacting with each other in ways other than electron binding and electromagnetic forces.

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Re: FAQ - X-ray radiation!!

Post by George Dowell » Fri Feb 08, 2013 1:25 am

To quote Dr. Gordon Gilmore from another forum:

The point about nomenclature is that it does give information about origin
and mechanism of production. You could suggest that we call any
electromagnetic radiations as photons - and scrap all that nonsense about
radio waves, light etc.

Gamma-rays are photons emitted as a consequence of de-excitation of an
excited nucleus. That nucleus could be excited because it is the product of
a nuclear decay, or it could be product of a nuclear reaction or simply
excited by being clouted by some other particle.

X-rays, at least as far as gamma-spectrometry is concerned, are photons
emitted as a consequence of de-excitation of the electron shells of an
atom. That could be a consequence of photoelectric absorption or internal
conversion etc.

Incidentally, it is incorrect - repeat incorrect - to refer to the 511
photon emitted during annihilation as the 511 gamma-ray. IT IS NOT A GAMMA
RAY. (sorry to shout!) It is not generated by de-excitation of a nucleus.
It is a photon or annihilation radiation. You can refer to the peak in a
spectrum as the 511 peak though. That's what it is.
When John Hemingway and I received the proofs of the first edition of 'The
Book' we found we had fallen into the trap ourselves and had to go through
the proofs very carefully to correct all the '511 gamma-rays'.

I could go on...
Precision in nomenclature helps understanding. Sloppy use of nomenclature
may well cause confusion and misunderstanding.

You could also ask if beta particles are simple electrons, why don't we
call them that? Because the nomenclature helps.
Beta- particles are electrons emitted during a nuclear decay.
Beta+ particles are positrons emitted during a nuclear decay.
That reminds us that those particles do not have a defined energy - any
individual will have an energy between zero and the decay energy.

In gamma spectrometry we refer to internal conversion electrons and Auger
electrons as such because they have defined energies determined by the
electron shell energy they have been expelled from.

I mentioned in an earlier post about nomenclature confusing matters in
relation to the term Branching Ratio. I won't go on again.

And of course there is isotope and nuclide. They are all *nuclides* unless
you are discussing nuclides of the same element - then you can discuss
isotopes. To say 'the isotopes Co-60 and Co-57' is correct use of the word
'isotope'. To say 'the isotopes Co-60 and Cs-137' IS NOT correct.
When you see the word isotope used incorrectly it says 'non-professional'.
Even the nuclear equipment manufacturers are getting it right these days -
not so journalists and broadcasters.

Regards,
Gordon Gilmore
--

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Re: FAQ - X-ray radiation!!

Post by Carl Willis » Fri Feb 08, 2013 1:38 am

Yes, deuterium ions in a fusor would fit the definition of canal rays.

It's common in didactic materials to find a distinction between x- and gamma rays based solely on energy, but this just reflects the historical origin of those names and is not a general guide. The common radioactive sources at the dawn of the 20th century were uranium and thorium and their daughters, which emit rather high-energy photons. The x-ray tubes of the period operated from <100 kV Ruhmkorff coils, producing mean energies in the tens of keV. It's not common to hear of 6-MeV radiotherapy photons called "gamma rays" or of americium's 59-keV photons called "x-rays", and people would indeed complain that such usages are out of line with the precedent.

Electron annihilation radiation is probably commonly labelled as gamma rays because of its close association with radioactive decay (namely, positron emission, and other decays that produce energetic gamma rays leading to pair production and thus have annihilation radiation in the downscattered spectra).

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Re: FAQ - X-ray radiation!!

Post by Daniel Firth » Fri Feb 08, 2013 3:07 am

I noticed a lot of replies to this FAQ in the last couple days, and wondered if there was interest in an idea I had.

I've recently received a CD V-700 from eBay. After testing all of my ore samples, I did an air plasma fusor run. It seemed to be pretty quiet up until about 17kV. 18kV started to make some good counts, 19kV was roughly middle of the X100 scale, and 20kV maxed out the instrument.

I noticed that this roughly corresponds to my neutron counts. That is, no detectable fusion under 18kV (with my instruments, anyway), very low between 18-19kV, and a sharp increase over 19 to 20kV (my power supply's max output).

Anyway, if there is interest I will do a simultaneous neutron/x-ray run, and get a bunch of photos & measurements.

The point being, it could be a simple test to see if someone's fusor is "in the ballpark" for fusion capability, without having deuterium or neutron detection equipment.

I could also get some photos & readings of the X-ray cone emission pattern from a viewport, and show how the stainless steel blocks x-rays. I would probably do this around Feb. 16th.

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Re: FAQ - X-ray radiation!!

Post by George Dowell » Fri Feb 08, 2013 3:35 am

While interesting, such a test is not really quantitative, because you are experiencing the low energy cut off of the GM tube walls. In other words, does the X-Ray flux really increase, or does the raised energy just allow more to get inside the tube?

This is the big stumbling block when working with XRF- some the energies are so low, most probes can't detect them no matter how much flux there is.

20 keV seems to be near the limit for metal enclosed probes of any kind. To get below 10 we need beryllium windows, then they still cut off at 4 or 5. The thin mica windowed pancake probe is one of the best *DETECTORS* at really low energies, but
what you want to *MEASURE* X-Rays.

George Dowell

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