Underappreciated X-rays

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Roberto Ferrari
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Underappreciated X-rays

Post by Roberto Ferrari »

Fellows
Found this article about undesired x-ray production in a lab during high voltage and vacuum experiments.
Is an interesting exercise about characterizing, measuring and controlling stray radiation.
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Chris Giles
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Re: Underappreciated X-rays

Post by Chris Giles »

However, it appears typical that unconditioned electrodes can have can have vacuum emission currents
of 1 µA or more [15–18] and indeed, this is typical of the levels observed in the apparatus described here
Interesting paper. If I understand correctly they are describing all current flowing in vacuum between Anode & Cathode as "leakage" current so in practice that is all/most of the current from the HV line in a Fusor. They are looking at uA current levels. Admittedly they are measuring very close to the device and I presume the intensity drops off with an inverse-square law. I guess the radiation would be proportional to the leakage current (?) so almost 1,000x these levels? Any views or measurements anyone?
... we observed a dose rate as large as 2.5 mSv hr−1 immediately outside the apparatus when leakage currents of ∼1–10 µA were present at applied voltage in the ±20–±30 kV range. ...This level of radiation represents a substantial hazard under conditions frequently used in university physics laboratories.
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Richard Hull
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Re: Underappreciated X-rays

Post by Richard Hull »

100mrem = 1 mSv. All of this is known relative to fusor operation. At the glass view port window, pointing down at the absorbing concrete floor in my lab, at 35kv, 10ma I read about 300 mrem/h rate. This equals 3.5mSv. This is why I suggest never pointing a view window at anything other than an absorber and away from any nearby human activity. However, at my operating station, 7 feet from the fusor, I read no more than 1mrem/hr.

This is from a normal .0625-inch thick walled, 304 SS fusor operating at near 1,200,000 fusions per second. This is good but not great fusion display.
A 1 mrem per hour rate is nothing to fear. Plus the operational time at this level of fusion is normally well under 5 minutes.

This tends to indicate that with a fusor, you have to expend 350 watts of energy into a running fusor to receive a 1mrem/hr rate at 7 feet, providing one is not stupid enough to have a view window pointing at them.

A fusor loses in a dangerous radiation situation at voltages under 40kv due to all the radiation prevention issues. This is mostly due to a steel chamber absorbing all but the most potent x-rays which are out on the tail of the maxwellian, and the short exposure time, coupled with the inverse square law.

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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