FAQ - X-ray radiation!!

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Richard Hull
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Re: FAQ - X-ray radiation!!

Post by Richard Hull »

I am surprised that Andrew asked this question. In two posts in this flow, I specifically recommended an ion survey meter if you are working over 40kev and mentioned that a GM counter was only to be used as an indicator of the presence of ionizing radiation.

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Re: FAQ - X-ray radiation!!

Post by Andrew Haynes »

Thanks Carl , I found this site http://www.chpconsultants.com/index.php ... ments.html which has the Eberline's ASP-1.
Richard just was shore if that was a good meter
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Re: FAQ - X-ray radiation!!

Post by ab0032 »

A long time ago I calculated the attenuation of wax for x-rays on some online calculator and got something like 15cm of wax would absorb 99% of the x-rays. I probably would never find this attenuation calculator again, but you could choose materials and thickness and perhaps also the x-ray energy, I cant remember.

Could this be true? A wax shield with some borax in it is easy to make.

Any comments?
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Richard Hull
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Re: FAQ - X-ray radiation!!

Post by Richard Hull »

I can't imagine 3" of wax stopping hard x-rays. (>40kev). Use lead for xrays first and then backed with borated paraffin if you also want to attenuate the neutrons, too.

Sheet lead in any useful thinckness and size can be readily purchased from Roto-metals ready to rock and roll and at a reasonable price. I now use them exclusively for all my specialty metals needs. (Cast my own bullets - Pb:Sn:Sb, make my own specialty low melting alloys - Pb:Sn:Cd:Bi:In and special solders Pb:Ag:Sn:Sb:Zn) Roto has it all in experimenter sized lots and shapes, except the Ag.

I have discussed making a small "shadow cone" shield for fusors in prior posts here.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: FAQ - X-ray radiation!!

Post by Rich Feldman »

Alexander Biersack wrote:
> A long time ago I calculated the attenuation of wax for x-rays on some online calculator and got something like 15cm of wax would absorb 99% of the x-rays. I probably would never find this attenuation calculator again, but you could choose materials and thickness and perhaps also the x-ray energy, I cant remember.

I agree with Richard. Low-Z materials like wax and boron will do even less than water for x-rays.

I've used this online calculator for x-rays, and corresponded with the author:
http://www.radprocalculator.com/XRay.aspx
It lets you choose x-ray tube voltage (thus an energy spectrum, I bet assuming a tungsten anode) and shielding materials.
The following NIST website has tables (and an online calculator somewhere) of x-ray attenuation coefficients for many materials. Wax isn't on the list, but polyethylene is also just C and H at about the same densities, so looks the same to x-rays. http://physics.nist.gov/PhysRefData/Xra ... /tab4.html

[edit] just used radprocalculator for the first time in a couple years.

For x-ray tube at 40 kV (and 10 mA, which shouldn't matter) the thickness for 99% attenuation is
0.33 mm of lead
1.9 mm of iron
42 mm of aluminum
70 mm of concrete
345 mm of water

At 25 kV, Alexander's 15 cm of wax would probably do what he said.
As would 0.09 mm of lead (0.0035"), or 0.42 mm of steel (0.0165", about 28 gauge).

What attenuation factor is needed for safety? Even at 25 kV, the x-ray flux inside the fusor is enough to kill cells rapidly. But an ordinary stainless steel fusor enclosure, as touted by Richard H. et al, allows less than one millionth to escape. If not for that inherent shielding, the dose rate 1 meter away could be thousands of R/h (tens of Sv/h). Look up what that would do to you.
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Re: FAQ - X-ray radiation!!

Post by Steven Sesselmann »

Alexander,

You can set up a really simple experiment to measure attenuation, with an Americium source and a geiger counter or scintillation detector. Use two lead bricks with a small hole in, to collimate the beam set up the source bricks and detector so the 59keV x ray beam traverses a gap of say 4" , take a steady reading of the counts over a set period of time.

Now try inserting various materials across the beam and see how it attenuates the 60keV x-rays.

You will see that a thin 1/16 piece of lead will almost fully stop the counts, but what about a block of wax, glass of water or a leg of pork?

Even if we think we know the answers, there is nothing like actually doing it, and it is a lot safer to do it on a leg of pork, than using your own body as an attenuator.


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Re: FAQ - X-ray radiation!!

Post by ab0032 »

Richard Hull wrote:
> I can't imagine 3" of wax stopping hard x-rays. (>40kev). Use lead for xrays first and then backed with borated paraffin if you also want to attenuate the neutrons, too.
>
You are probably right for hard x-rays. I was surprised myself. But 15cm is 6". Maybe this is an option for people who are building a borated paraffin block to attenuate the neutrons. If they use low energies they might only need to make the paraffin a little thicker to handle the x-rays with the same shield and save some hassle with the lead.

I would definitely recommend checking the attenuation by measurements as you turn up the voltage and not trust some online calculator.
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Re: FAQ - X-ray radiation!!

Post by ab0032 »

Thanks Rich Feldman for these extra words of warning and the online calculators.

These comparisons for materials and energies are quit interesting.

So one is stuck in a dilemma, from the radiation side you would like to stay at low energies around 25kV if possible and from the neutron count side, one would like to go to high voltages to get as many neutrons as possible.

Nobody should expose himself to Si/h, but as you show, this can easily happen with a fusor, this is an important warning that should be heeded.
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Re: FAQ - X-ray radiation!!

Post by ab0032 »

Steven Sesselmann wrote:
> You can set up a really simple experiment to measure attenuation, with an Americium source and a geiger counter or scintillation detector. Use two lead bricks with a small hole in, to collimate the beam set up the source bricks and detector so the 59keV x ray beam traverses a gap of say 4" , take a steady reading of the counts over a set period of time.
> Now try inserting various materials across the beam and see how it attenuates the 60keV x-rays.

This may be scientifically interesting, but in the case of a fusor you dont have a narrow beam.
The attenuation is affected not only by the thickness of the material, but also the width of the material and the spread of the x-rays.

Hence I would always recommend to turn up the voltage slowly on the fusor and check your radiation exposure behind your shield for the real dose you are getting to be on the safe side.
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Re: FAQ - X-ray radiation!!

Post by George Dowell »

Unfortunately the housing on pen dosimeters limit their low end response. Even the latest technology using conductive plastic instead of metal housings is pretty puny below 16 keV. Those low energy rays are the very ones absorbed by the skin.

Energy response chart encloed.

Geo
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Re: FAQ - X-ray radiation!!

Post by George Dowell »

RadPro Calculator- Fooling around with dose at 10 cm from a 30 kVp 10 Ma
X-Ray source, shielded by iron or lead.

Dose at 10 cm with 2mm Iron shielding (fusor chamber? = 5 R/H

Dose at 10 cm with 2mm Pb shielding = 1 10E-21

It takes little effort to shield 30 kV rays.

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Richard Hull
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Re: FAQ - X-ray radiation!!

Post by Richard Hull »

The assumption here in these calcs is that you are operating a formal, tungsten target "x-ray tube". All the energy is in a focused beam blasting "naked" into air. The fusor is never this kind of device, of course, so all the unshielded values given by this program are super wrong to start with, when referencing a fusor, as the levels will be 2-3 orders of magnitude lower due to the isotropic emission and SS lower Z target-shell shield.

A better test is to let the x-ray tube filter and target be 2mm of iron which is closer to the natural fusor. Unfortunately, we aren't allowed to choose the target, but can choose Cu for our filter. The program, though, forces a minimum of 85kv for that filter and will not accept lower KV numbers. Thus, it is valueless, on many levels, for use with a fusor.

We have actually, physically measured at the SS shell of a fusor working around 35kv @10ma. We record about 100 mr/hr at the shell ~3 - 5cm distant and at 1 meter, less than one mr/hr. This is not worth consideration as a rad hazard if your operating station is over a meter distant from such a fusor and operated for infrequent, short periods.

For the paranoid, hyper-ventilator's, a millimeter or two of lead will leave you in, hopefully, a "feel good" operational environment.

For me, 50-60 kv applied is when I might put up a thin Pb shield, assuming I am 1.5 meters from the fusor.... as it is in my case.

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Re: FAQ - X-ray radiation!!

Post by George Dowell »

Richard, may I ask what you measured the 100 mR/H with? A low energy intergrating ion chamber I assume? George Dowell
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Re: FAQ - X-ray radiation!!

Post by George Dowell »

By the way a tungsten target does not turn on until above 59 keV (tungsten K edge) . A real X-Ray tube designed to work at lower HV would have an MO or copper target. Or in the case of a fusor, a very large iron target. A peak of about 6 keV would result, with a background of Bremsstrahlung from 0-35 keV (average of around 1/3 that).

Geo
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Re: FAQ - X-ray radiation!!

Post by Chris Bradley »

George Dowell wrote:
> By the way a tungsten target does not turn on until above 59 keV (tungsten K edge) .
There is an X-ray continuum too, related directly to the electrons' energies. It is not just the atomic signature from which one gets X-rays.
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Re: FAQ - X-ray radiation!!

Post by George Dowell »

Correct Chris, that's caused by electron Bremsstrahlung.

It is not exactly an X-Ray by definition, it is Bremsstrahlung radiation, but ionizing photon radiation nonetheless. Photon's are often called by the manner of their origin, i.e. X-Rays, Gamma Rays, Annihilation Radiation,Bremsstrahlung etc.

At the receiving end, they are all the same thing and indistiguishable from one another.

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Re: FAQ - X-ray radiation!!

Post by Carl Willis »

Hi George,

Richard has mentioned at least three times toward the top of the thread that an ion chamber is preferred for dosimetric measurement of x-rays. The model I've seen him use is a Victoreen 471, and he has photos of it here: viewtopic.php?f=13&t=5972#p34416

I'd argue that the commonly-understood meaning of "x-ray" implicitly includes bremsstrahlung. There does not appear to be any confusion about what physical mechanism produces radiation in the amateur fusion environment, and no need for affecting a hyper-distinction in the nomenclature.

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Re: FAQ - X-ray radiation!!

Post by JohnCuthbert »

I'm fairly sure that most of what Dr Roentgen named X rays were what would later be classified as bremstralung, but that didn't stop them being X rays any more than light isn't light if it didn't come from the sun.
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Re: FAQ - X-ray radiation!!

Post by Richard Hull »

Yes, I use a large chambered victoreen ion chamber. Two other similar ion chamber instruments brought by others over the years have agreed to within 20%. 200mr pen dosimeters placed at varying ranges have also agreed to within a similar error range.

I have used as many as 20 pens in a single test before. My pocket dosimeter has never registered a readable amount in all the various runs where I have worn one.

The fusor, as such, is a pretty low emission x-ray device up to about 35kv due to the SS shell shielding. I rely heavily on distance and the inverse square law to operate with zero shielding up to about 40kv. at 1.5 meters there is no reading seen on the 3mr/hr lowest range with two Victoreens and one Eberline ion chamber detectors that I have.

Also about 1 run session of max output for a total of 30 minutes every three months or so (average) keeps the time averaged absorbed exposure to effectively nothing.

In short, no significant x-radiation from naked fusor IV operating between 20kv and 40kv, provided you are positioned a meter or more from it over much of its full power, operational time.

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Re: FAQ - X-ray radiation!!

Post by George Dowell »

John Cuthbert wrote:
> I'm fairly sure that most of what Dr Roentgen named X rays were what would later be classified as bremstralung, but that didn't stop them being X rays any more than light isn't light if it didn't come from the sun.

Yes actually it does John if we are to be anything like scientifically correct. We use terms like Radio, Laser Light, Arc Light, Lime Light, X-Rays etc for a reason even though they are all electromagnetic radiation.
For example in the case of a fusor or *any* vacuum chamber with two electrodes, electron flow and HV, there will be a number of sources of ionizing photon radiation. If the "target" i.e. anode is iron, the peak radiation will be at 6 keV, from the characteristic XRF of iron. Each anode element would have it's own energy of characteristic X-Ray emission, but the electron beam must be of sufficient energy to excite this emission. That's why X-Ray tubes have different target material for different usage. Ironically those very low energy X-Rays are specifically filtered in radiology because they don't penetrate tissue,rather absorbed, therefore don't add to an image, but cause the burns.

Understanding this allows the observer to select the correct instrument to monitor the dose. For example, many if not most instruments are blind to 6 keV due to self shielding.

The ion chamber I use for that is a Victoreen 440 RF/D which has a very thin magnesium window, specifically designed to allow low energy X-Rays in.

PS, to put it in perspective, my experiments with X-Rays use sources of 20 to 30 kV at up to 100 MICROAMPS only. Yes these are isotropic sources. A normal all metal fusor is a diffuse source. No one can say what Bell Jar fusors are.

George Dowell
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Re: FAQ - X-ray radiation!!

Post by Carl Willis »

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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Re: FAQ - X-ray radiation!!

Post by Rich Feldman »

> 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.

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Re: FAQ - X-ray radiation!!

Post by George Dowell »

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 »

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.

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

Post by George Dowell »

So the Deuterium ions are the canal rays?

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