Old TV x-ray exposure

[electroking]

Originally Posted by kx250rider

I don't think there's any risk from any X-rays from any TV. ...

Charles

What you think or do not think about any technical problem is irrelevant.
The actual physics is what matters. X-ray emission by electrons being
decelerated is a fact of life, and unless you can confirm what you claim
with reliable measurements, I consider it prudent to avoid spending too
much time near the high-voltage circuits of a large color CRT set.

[nasadowsk]

I've never heard of any cancer cases linked to TV x rays.

FWIW, RCA says anything above 16kv (absolute) is suspect, but even then, you're talking so far on the weak end of the spectrum, that it's doubtful the x rays even get anywhere.

25kv at 2 or 3 ma really isn't much in the realm of x-rays...

Keep the HV box closed and don't stare at that funky 6BK4 too long, and you'll be fine. You're more likely to get zapped than anything else...

[zenith2134]

Good point made here. Electrocution is probably a bigger risk than x-ray radiation. However, back to my point on yoke emf's...Since the CRT's tended to get bigger, and very few yokes are shielded in any way (copper windings all exposed) this could be an even bigger concern than x-rays. Think about it, all the cabinets were plastic after a certain point, removing any potential for shielding there. The sides of a set may be really 'hot' with low-frequency EM radiation. Whether or not this is irrelevant health-wise doesn't concern me much. Just curious about it all.

[stromberg6]

Last year sometime, a friend came over with a radiac meter, and we measured the x-ray output from the screen of my CTC-4 through the safety glass. On white screens, we measured a maximum of .4 millirems/hour. Strange that the max wasn't recorded on black screens when HV is at max 25KV.
We informed a member of our museum, who is an x-ray technician, and he said "that's pretty high". The three foot rule sounds prudent, but I wouldn't worry about it too much.
Kevin

[jeyurkon]

Originally Posted by stromberg6

Last year sometime, a friend came over with a radiac meter, and we measured the x-ray output from the screen of my CTC-4 through the safety glass. On white screens, we measured a maximum of .4 millirems/hour. Strange that the max wasn't recorded on black screens when HV is at max 25KV.
We informed a member of our museum, who is an x-ray technician, and he said "that's pretty high". The three foot rule sounds prudent, but I wouldn't worry about it too much.
Kevin

Actually that makes sense. The maximum x-ray energy will be related to the HV. But, the x-ray flux will be proportional to the current. You'll have a higher flux of x-rays on a white screen even though the maximum x-ray energy will be lower.

John

[Tubejunke]

I heard that IC's (integrated circuits) release a cancer causing frequency when paired with all forms of flat screen television, and even more particularly dangerous when mixed with digital broadcasting in color. Thus, a vintage, tube type, analog, black and white, television set is the ONLY healthy way to view the crap they call TV shows these days.

Spread the word before its too late!!

[kx250rider]

Originally Posted by electroking

What you think or do not think about any technical problem is irrelevant.
The actual physics is what matters. X-ray emission by electrons being
decelerated is a fact of life, and unless you can confirm what you claim
with reliable measurements, I consider it prudent to avoid spending too
much time near the high-voltage circuits of a large color CRT set.

That's my point... Nobody has quantified nor qualified/disqualified what strengths of X-rays may or may not be harmful... I'm speculating on the experts' speculation


In the meantime, I'll take my chances. I race motocross, and I drive on the Los Angeles freeways, so I don't think X-rays will get the better of me, myself. A friend died of lung cancer last year, and she never smoked, nor lived with a smoker, and she was a fitness nut in perfect physical shape. If your number is called, that's it.

Charles

[jeyurkon]

I assume the Radiac was a model 440 ionization meter. If so, you have to be careful interpreting results near the face of a CRT. The static charge on the surface can cause a false reading in the extremely sensitive electrometer.

I decided to try the same test. I used a Victoreen model 450B ionization counter. It is sensitive down to 0.01 mR/hr for x-rays above 7KeV.

I tried it on a 1949 Sylvania that has an anode voltage of 9.5KV. I measured nothing, but didn't expect to measure much. The end point energy would be close to 9.5KV but the yield above 7KeV would be low to start with and the glass attenuates most of it.

I tried a color CRT monitor with the same result. I thought my 42" rear projection might let me pick something up near the CRTs, but I didn't see anything there either.

At work I use an electron beam evaporator that runs at 10KV and has a maximum current of 1.5 amps. I was concerned that some damage I was seeing in foils that I was coating might be due to an x-ray dose. I put a personal dosimeter in the chamber. At 0.3 amps it maxed out the dosimeter. I had to do a very short run to even get the measurement on scale. This would have been a serious dose to a human.

I tried doing measurements outside of the chamber which is constructed of aluminum and has glass and acrylic windows. There was no detectable radiation outside of the chamber, even through the plastic window. x-rays of this energy are easily shielded. At 25KV the story would be a bit different. But I doubt that even the old roundies present much of a hazard. I think you would see more near the HV rectifier tube, but no one wants to get close to that anyhow.

John

[leadlike]

John, Maybe you could toss a dosimeter into a couple of hv cages , near the HOT, taped to the screen etc to determine some relative radiation levels in these old sets.

Kinda reminds me-does anyone know why every 1k3 hv recitifer I have ever come across has x-ray warnings screen printed on the tube, while the old stand by equivalent 1B3 doesn't boast any such warnings?

[nasadowsk]

Actually, I've seen it on 1B3s, too.

I think the 1K3 has a higher anode voltage rating, so it would have gone into higher voltage sets.

Though, just about everything used a 1B3, didn't it?

[wa2ise]

Originally Posted by leadlike

John, Maybe you could toss a dosimeter into a couple of hv cages , near the HOT, taped to the screen etc to determine some relative radiation levels in these old sets.

Another dosimeter taped to the face of the CRT (lower portion of the screen, so it doesn't much interfere with watching TV shows) would also be interesting. I assume that these things are cheap enough to expend casually.

[electronjohn]

All I know is that I sat waaaaay too close to the TV when I was a kid and that my third eye works just fine.

[jeyurkon]

I'll see what I can do. We always have extra film badges, but they may have to pay processing for each one turned in. If so, hopefully they'll consider this a part of "Outreach."

John

[jeyurkon]

Here's a table and graph of x-ray attenuation in pyrex glass.

http://physics.nist.gov/PhysRefData/...Tab/pyrex.html

If you take the attenuation coefficient and multiply it by the density of glass in g/cm**3, take the reciprocal, you get the thickness of glass required to attenuate the x-rays by a factor of 2.7

For 8KeV x-rays, this is 0.014cm or 0.0055". It doesn't take much to shield them.

For 20KeV x-rays it's 0195cm or 0.077". Quite a bit more and leaded glass is now needed to protect you.

John

[Tubejunke]

OK, so.....we're going to live watching our old TV's......
right?