x-rays

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.
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Ryan Catalano
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Real name: Ryan Catalano

x-rays

Post by Ryan Catalano »

Yesterday, I conducted some tests at 18kv at around 8ma with my new xrt based power supply. I was about six feet away and at some points three feet away when I was operating it, And I was at an angle to the viewport. I decided to fire up my geiger counter and check for x-rays during the first test. The second I turned it on, the geiger counter began freaking out. I went back a couple of feet and it was at about 10 feet that the radiation would disappear. My neutron detector also began freaking out as well (going off scale at 1x), which was pressed right up against the ss of the chamber in a hdpe moderator. I was having a lot of issues with electrical noise. Was this actually x-rays and if it was, should I be concerned about being overexposed (exposure time of about 2 mins)? Any feedback is greatly appreciated!
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Rich Feldman
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Re: x-rays

Post by Rich Feldman »

Good point about electrical noise, Ryan. What happens if you cover the viewport with a metal pipe cap or a piece of sheet metal?

Assuming you _are_ detecting X-rays, please don't worry that you have already injured yourself or increased your lifetime risk of cancer. It takes a lot of X-ray photons to hurt you, and GC's can be very sensitive. Mine clicked away when I ran a real Coolidge tube on 11 kVp at 1 microampere, from rectified 15 kV NST. I helped a teenager make x-rays by unspooling Scotch tape in a vacuum, and correlate the Geiger count rate with voltage. That is, the DC voltage to tape winding motor. :-)

Better safe than sorry. The increase in Geiger count rate is an alert to think about your distance, exposure time, shielding, and dose measurement technology. It would help if you or a mentor can talk with someone trained in radiation safety.

Trouble is, you can't easily translate GC counts to roentgens (or grays or sieverts) because the tube's spectral response is far from flat. The units of measurement, and standard dosimetry, are based on ionization of plain air.

Now that the hysteria following Fukushima meltdowns has abated, it's once again easy to find sensitive quartz-fiber dosimeters on, say, ebay for around $10. CDV-138 has full scale range of 200 mR. I took one to my dentist, who x-rayed it, and the pointer moved about 10 mR. Tape one over your viewport and see if you can make its pointer move. You will need to buy or contrive a charger for the dosimeter.
All models are wrong; some models are useful. -- George Box
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Richard Hull
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Re: x-rays

Post by Richard Hull »

Many, many FAQs on this issue. None of them have been read, I bet.

You can never use a GM counter to tell you one iota of quantifiable information on x-rays other than, yes, they are there. No data available from a GM counter.

You need an ion chamber detector to quantify X-ray exposure. A 200mrem dosimeter will expose very slowly in a beam of x-rays at 18kv over the view port, but not at all at the metal fusor body.

There is zero to worry about at 18kv in a metal fusor body at all. Just stay clear of the view port. All this kind of info is in the FAQs. Read 'em!

If you have a neutron detector going nuts, you either don't have a real neutron counter, it is setup terribly or there is electrical noise and your neutron counter cable, detector housing or instrument is not RF "tight"

DecentGM counters are typically EM noise immune as they are rather "electronically clunky".

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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