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 Forum index » Off-Topic Area » Security
CRT monitors emit radiation
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Lobster
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Joined: 04 May 2005
Posts: 15117
Location: Paradox Realm

PostPosted: Sat 19 Dec 2009, 20:33    Post subject:  CRT monitors emit radiation
Subject description: how to detect
 

As some of you know CRT monitors emit radiation
which can be detected from a distance - with specialized equipment Shocked

This Linux will allow an ordinary radio to play Beethoven's Fuer Elise from your monitor
http://www.dirk-loss.de/tempest-showroom.htm

I eh . . . Embarassed . . . where is the tin hat for my monitor . . .
[I am allowing my monitor to phone up for a white van - now]

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bugman


Joined: 20 Dec 2005
Posts: 2131
Location: buffalo commons

PostPosted: Sat 19 Dec 2009, 21:12    Post subject:  

i like my radiation

a little bit is good for you, like those people who go into radium mines

but cheaper

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Flash
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Joined: 04 May 2005
Posts: 11034
Location: Arizona USA

PostPosted: Sat 19 Dec 2009, 22:51    Post subject:  

X-rays are emitted when high-energy electrons ("cathode rays") strike pretty much anything. In the case of a CRT, the "phosphor" coating on the backside of the screen emits x-rays where the electron beam strikes it. If you've ever seen a broken CRT you probably noticed that the faceplate was quite thick glass. It is composed of leaded glass, and, being so thick, absorbs virtually all of the x-rays emitted by the phosphor layer. I'm pretty sure you get far more radiation damage from standing in the summer sun for an hour than from sitting in front of a CRT all day. On the other hand, your skin creates vitamin D from the sun. I doubt there is any health benefit to be got from sitting in front of a CRT all day, but I don't think the radiation emitted by a CRT is anything to worry about.

What Lobster refers to is radio-frequency radiation (Tempest) emitted by a CRT, which is not, as far as anyone has shown, a health hazard. It could be a hazard to keeping your job, if it were used to figure out what you were doing on the computer.
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mcewanw

Joined: 16 Aug 2007
Posts: 2338
Location: New Zealand

PostPosted: Sun 20 Dec 2009, 02:10    Post subject:  

As far as I recall, it is primarily beta radiation (high energy electrons?) that emits from the front of the CRT. However, Xrays are emitted from the Line Flyback Transformer (old TV sets, particularly the first colour ones [because higher extra high tension voltages involved than in Black&White sets], apparently emitted a fair whack of Xrays from that source). More modern CRT TVs shielded that EHT circuitry to a much larger extent.
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Lobster
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Joined: 04 May 2005
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Location: Paradox Realm

PostPosted: Sun 20 Dec 2009, 02:34    Post subject:  

Quote:
i like my radiation


Cool Thanks bugman.

Here is a Christmas message from the singer Bjork about CRT TV
influenced by the radiation of poets
http://www.youtube.com/watch?v=4d4rdat3HdA

I feel sane again
[cancel the white van] Smile

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davesurrey

Joined: 05 Aug 2008
Posts: 1201
Location: UK

PostPosted: Sun 20 Dec 2009, 21:11    Post subject:  

I agree with Flash in that the EHT accelerated electrons (the cathode rays) hit the tube and produce (relatively low energy) x-rays which are almost entirely absorbed by the glass and coatings of the tube. No need to worry there.

Years ago, when colour TV started, some tube (valve) based EHT regulators were found to be able to emit x-rays under fault conditions.
That's the only chance of x-rays in the flyback or line output stages.

But even if you can find a new CRT based monitor now it'll be all solid-sate and have good voltage regulation so no worry there.

The strongest radiation is usually the RF radiation mostly coming from the line output stage (multiples of 15.625kHz in Europe) which I believe is how TV detector vans search out the bad guys who don't pay their TV license fee. In which case that could be very harmful, to your pocket.

Personally, I believe the most dangerous stuff coming from a monitor is the guff often found on the net and the junk programs on TV. Very much detrimental to one's (mental) health.

Cheers
Dave

EDIT:
if anyone is still worried about x-rays then beware that scientists have found that peeling scotch tape off a roll emits x-rays. But you need to do it in a vacuum, so probably still okay to use it to wrap up your xmas presents.
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lwill


Joined: 13 Jun 2008
Posts: 173
Location: City Of Lights

PostPosted: Tue 22 Dec 2009, 00:38    Post subject:  

I once built an oscilloscope from plans in a magazine (Popular Electronics Sept. 1982 - I still have it!) that used a similar effect described in the link. It would pickup the HV signal from the fly-back and produce a signal picked up by the TV to put a bar on the screen like the distortion caused by a vacuum cleaner. The two signals were mixed with the voltage you were trying to measure and would produce a good representation on the screen (going up and down instead of left to right) and the frequency response was controlled with the vertical hold. It worked well from DC though audio range and was pretty accurate at measuring voltage, but there was no way to measure frequency. It cost less than $25 to build, was the first scope I owned, and I fixed a lot of amps and learned basic logic and timing circuits with it. In fact I still have it strapped to a 5" portable TV mounted to a board. I guess on one will be able to build them any more with the demise of analog TV.

Lyle
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mcewanw

Joined: 16 Aug 2007
Posts: 2338
Location: New Zealand

PostPosted: Tue 22 Dec 2009, 01:33    Post subject:  

http://www.hps.org/publicinformation/ate/q498.html:

Quote:
X rays can be produced in vacuum tubes when the electrons are accelerated and strike the anode. In the vast majority of situations, the intensity and energy of such x rays are so low that any radiation is effectively nonexistent. However, when very high voltages and currents are employed, the x-ray production can become significant. The prime example of such a situation was the generation of x rays in early color television sets (ca. 1965-1970). The three major sources of x rays from these sets were the picture tube, the vacuum tube rectifier, and the shunt regulator tube. The latter (designations 6EF4 and 6LC6) were a particular problem. Over a third of the 6EF4 tubes tested produced exposure rates above 50 mR/hr at a distance of nine inches, and exposure rates up to 8 R/hr were observed at seven inches with one defective tube! Modern television sets have essentially eliminated the problem of x-ray production however.


Mind you, there are "people" claiming today that the GHz band cellphone signals aren't dangerous because they are non-ionising. Time will tell. Luckily, for those of us who spent part of our lives in the period of the above mentioned old colour television sets, we didn't tend to sit right in front of them very often - so it is re-assuring(?) to believe the "experts" who tell us that modern CRT monitors no longer radiate sufficient radiation to do us any harm. Too late for me anyway... the old colour sets got me and the (amazing 50's vintage black and white projector TV unit my father brought one day - talk about a high intensity crt), as did the high-powered ham radio transmitters my father used to operate - not to mention the radar systems I used to test on the bench next to me when I was a technician working for "Ferranti's" in my student holiday days...

Make your own X rays (not for children):

http://www.kronjaeger.com/hv-old/xray/intro/index.html
http://www.dangerouslaboratories.org/xray1.html

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Dewbie

Joined: 15 Apr 2010
Posts: 1783

PostPosted: Wed 29 May 2013, 23:11    Post subject:  

The U.S. Food and Drug Administration wrote:
Quote:
TV receivers and computer monitors containing CRTs no longer pose a risk of emitting excessive x-radiation. Since the creation of the federal performance standard, the FDA has tested hundreds of TV receivers and computer monitors and rarely encountered any that were unsafe.

More here.
(Note that the federal performance standard was established in the 1960s, back when government was more functional and less influenced by industry lobbyists. That has to count for something. Smile )
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rjbrewer


Joined: 22 Jan 2008
Posts: 4422
Location: merriam, kansas

PostPosted: Sat 01 Jun 2013, 01:40    Post subject:  

bugman wrote:
i like my radiation

a little bit is good for you, like those people who go into radium mines

but cheaper


Back in the 50's, it was common for shoe stores to have xray
machines for the amusement of their customers.
Kids like me loved looking at our foot bones.
Little did we know that our future offspring would often be
born with two left elbows! Shocked

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