X-Ray Problems.

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Alan Sailer
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X-Ray Problems.

Post by Alan Sailer » Sun Jan 05, 2020 2:22 am

'm finding myself puzzled with the radiation levels in my set-up.

I've been learning the set-up running deuterium and at some point during adjusting the voltage/pressure
on the system the counter goes through the roof. Much greater than 10mR/hour. Pegs the meter so I can't tell exactly.

After earlier tests on the system I was alarmed by the radiation levels and ordered a 12X36 inch sheet of 0.062 " (1.6 mm)
and constructed a radiation shadow. But the levels behind the screen are still alarming.

I don't have time to get good data on anything because my counter is just screaming. Voltage is in the low 20kV
range and pressure around 10mTorr. I'm using a sensitive Ludlum 44-3 scintillation counter that is
designed for 10-60KeV photons.

Unless I get some clarity on this issue I'm going to call it a day. Seeing neutrons is not worth hurting myself.

Are these kind of x-ray levels typical?

Cheers.

John Futter
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Re: X-Ray Problems.

Post by John Futter » Sun Jan 05, 2020 4:13 am

Alan
x-rays get absorbed and bounce off high density materials
I have had x-rays get around two right angle corners out of an E-Beam annealer.
Also my high voltage implanter at work shone back down on me
heavy concrete walls all around but open to above, --x-rays reflected down off the roof
suntan territory at 150 millisievert/ hr so shielding went above the implanter as well
http://www.coultersmithing.com/forums/v ... f=45&t=757.

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Richard Hull
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Re: X-Ray Problems.

Post by Richard Hull » Sun Jan 05, 2020 8:09 am

This not worth delving into in a post that will be lost a year from now, but the inverse square law will help more than any shielding. (Of course, 10mrem/hr is not so bad)
Regardless of shielding, how long will you be there working at full voltage?? Working a fusor is going to get you some rads to the nads.
Fusion should never be attempted by any living being who is afraid of a wee bit old good old fashion x-radiation and nuclear radiation. This is not a workplace where you are bathed in radiation 8 hours a day. Precautions taken in a workplace are ridiculous around a fusor.

Crosses are going to pump out more X-radiation than a spherical fusor. I have never used a shield of any sort around my 40+kev fusor. the x-ray producing window beams into the concrete floor. I use an ion chamber at my seat and it records about 1-2mrem/hr when running at full blast. Still here and healthy after 19 years at it.

My latest FAQ on this issue. In the FAQ I give a link to my original FAQ on X-rays.

viewtopic.php?f=31&t=12031

Richard Hull
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Alan Sailer
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Re: X-Ray Problems.

Post by Alan Sailer » Sun Jan 05, 2020 3:18 pm

Richard,

Thanks for the links. I have read through these and other threads and still have some confusion.

One that you may be able to clear up. I have read post where you talk about the idea of "breakthrough" (I may have the exact term wrong).
It is implied that at some certain voltage (depending on the type of fusor) the x-rays suddenly dramatically increase in intensity. This has me confused.

As far as I understand, x-ray penetration is a logarithmic effect. At no thickness of absorber can you stop all the x-rays. It's exponential with the tail decaying to
a (hopefully) insignificant level. The term breakthrough implies that at some voltage the transparency of the fusor walls suddenly changes,
emitting a radically higher flux of photons.

Obviously with the time you have spent working with fusor you are seeing some sort of effect. I just cannot understand what it is.

Am I misunderstanding your meaning?

Cheers.

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Richard Hull
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Re: X-Ray Problems.

Post by Richard Hull » Sun Jan 05, 2020 3:55 pm

The term is "shine through". The dangerous higher energy X-rays will at some point, be effectively seeing the shell of the fusor as being transparent, (virtually no attenuation). The flesh burning rays of up to 15kv or less are pretty much fully absorbed. I get zero reading touching the shell of my fusor at 20kv with my victoreen ion chamber. At about 25-30 KV the reading at the same point is about 5 mrem, this is zero worry at 6-7 feet distant and is unreadable at that point. At 40 kv applied very near the shell it reads 10-15 mrem. Again, no problem at range. In the region of the window near my camera I get over 250mrem/hr in a more or less beamed into the floor blast. At 3 feet from the window near the floor it is down to about 10-30 mrem.

The key is that at the seat for controlling the fusor 6-7 feet away I do read 1-2mrem/hour. A 0-200 mrem dosimeter worn by me has never registered visibly off the zero mark after a couple of hours at the fusor doing fusion. At this range I am bathed in the most penetrating of x-rays and the dosimeter reads zero.

You are right, the absorption is logarithmic but the thick steel shell absorbs a tremendous amount of the x-rays of lower intensity. As I plan to move to the cross, I am a little more concerned.

Maybe someone with a cross and working it hard, and who owns a Dosimeter and or an ion chamber might report to us. Jon are you out there?

Richard Hull
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Alan Sailer
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Re: X-Ray Problems.

Post by Alan Sailer » Sun Jan 05, 2020 8:01 pm

Richard,

Understood.

A friend of mine has loaned me an old survey meter that actually reads in mR/H. My present counters are mostly
CPM and I am beginning to suspect be way more sensitive than required. I'm hoping that I have been metaphorically
listening too hard for my own good. It's just hard to concentrate on operating a fusor when my radiation detectors
are screaming at me.

I'll play with the survey meter some time soon and see what it says. he also has some old ion chamber units that
he can get me at a later date.

Cheers.

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Richard Hull
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Re: X-Ray Problems.

Post by Richard Hull » Mon Jan 06, 2020 4:50 am

Just make sure the survey meter is an ion chamber type device. These used to be called "cutie pies" back in the day.

I attach a couple of images.

Richard Hull
Attachments
ion survey1.jpg
ion survey1.jpg (20.65 KiB) Viewed 140 times
ion survey2.jpg
ion survey2.jpg (9.09 KiB) Viewed 140 times
ion survey.jpg
ion survey.jpg (5.53 KiB) Viewed 140 times
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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Alan Sailer
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Real name: Alan Sailer

Re: X-Ray Problems.

Post by Alan Sailer » Mon Jan 06, 2020 1:58 pm

Richard,

Beggars can't be choosers. He gave me an old CB V-700.

I can't wait to find out why this meter is no good for this task.:-)

Cheers.

Alan Sailer
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Re: X-Ray Problems.

Post by Alan Sailer » Mon Jan 06, 2020 3:25 pm

Richard,

No need to tell me that the V-700 is a piece of crap and under-reports the x-ray dose. Mark Rowley told me.

So I ordered a Micron DMC 3000 dosimeter from Ebay. If this is not the right tool for radiation safety
measurements then I give up.

Cheers.

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Dennis P Brown
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Re: X-Ray Problems.

Post by Dennis P Brown » Mon Jan 06, 2020 3:39 pm

I simply had my Geiger counter and an exposure ion Pen (one that can be worn) calibrated by a company that does that for a modest price. Felt my health and safety was worth the cost. Both items on e-bay cost under $100 total so, even though cheap, they were proven and calibrated. So they provided exact values on the x-ray threat. For my system at 32 kV and 4 mm steel shell, nether device read anything but background levels.

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