Do old CRT and O-scopes degrade to emit harmful X Rays?

[Albertgauss]

Hi all,

Presently I use an old oscilloscope and old cathode-ray-tube computer monitor as a demo/lab where students can bring a magnet near either device. In the case of the old oscilloscope, the magnet they bring near deflects the beam; in the case of the old computer monitor, colored circles appear. And there is a lot of educational value to these demos we discuss.

But I worry that as these devices age--and I thought i'd maybe get 2nd-hand-used stuff like this off ebay for my department--if they start to leak X Rays in any harmful manner. I am under the impression that for all televisions and CRT computer monitors made until the 1990s as consumer goods, these devices did produce X rays but the X rays were kept inside the tubes by a thin layer of lead that shielded the consumer while they watched tv. If that is true, would that shielding weaken over time and allow X rays out of the monitor or scope?

I attach a couple photos of the old machines in question.

 

[.Scott]

Don't use any color CRT's before the FDA 1968 Radiation Control Act.
Before that time, unintentional and excessive X-ray radiation was emitted by many color TV sets.
The remedy included putting lead in the glass formula. Physical attacks notwithstanding, that type of shielding is not goes to degrade over mere centuries.

I believe that even specialty color TV CRTs max out at about 50Kv. Shielding for 50Kv x-rays is not challenging.

 

[Hornbein]

Glass can contain up to 40% lead and still be transparent. I was amazed when I learned this.

Benjamin Franklin invented a musical instrument called the glass harmonica. It gave the players lead poisoning.

 

[Albertgauss]

Hi all, I'm watching the responses as they come in.

Does Hornbein's percentage mean that old consumer CRT devices pass lead or absorb it? Is 40% lead in glass a number typical of old computer monitors and O scopes and therefore remdering these devices unsafe to use? Thats what I want to know here.

Please no fun facts. I dont want to digress on a tangent off topic.

 

[sysprog1]

Hi all, I'm watching the responses as they come in.

Does Hornbein's percentage mean that old consumer CRT devices pass lead or absorb it?

No, It means that they're made with enough lead in the glass to ensure that instead of passing x-rays, they block them.

Is 40% lead in glass a number typical of old computer monitors and O scopes

Yes, 40% is not atypical, although closer to 30% would be closer to average, but higher than 40% would be common in the parts of the tube near the element.

and therefore remdering these devices unsafe to use? Thats what I want to know here.

The lead is bound into the glass in a lead silicate crystal lattice structure, and therefore not much of an exposure or ingestion hazard.

Please no fun facts. I dont want to digress on a tangent off topic.

Now that you have countenanced extending the topicality from the potential X-ray hazard, so as to now have allowed it to include discussion of a possible lead hazard, I think it's not too much further a digression to point out that the main hazard from old CRTs is the implosion hazard $-$ the usual way 'back in the day' of addressing that hazard when throwing away a dead tv was to break the 'nipple' off the back of the tube, to let the air hiss in to restore ambient pressure, with little risk of shattering the tube.

 

[Nik_2213]

Please DO NOT dispose of that lead-doped glass such that recycling *might* mix it with food-grade feedstock.
Yes, yes, considerable dilution should occur, but the popularity of 'flat screens' means fragmented 'legacy' lead-fronted 'Bottles' may be over-looked...

 

[sysprog1]

Please DO NOT dispose of that lead-doped glass such that recycling *might* mix it with food-grade feedstock.Yes, yes, considerable dilution should occur, but the popularity of 'flat screens' means fragmented 'legacy' lead-fronted 'Bottles' may be over-looked...

Yes, it should be circumspectly recycled. There is usually over a kilogram of lead, phosphors, and other non-silicon content in a 15.6" CRT monitor or a 19" TV $-$ the lead oxide is in higher concentration in the funnel near the element, and the front/screen part typically uses more barium and strontium than lead.

 

[Albertgauss]

Sounds good, all. I did not realize the subject of lead in glass was pertinent to the blocking power of Xrays in monitors. So, yes, if you have ideas about that, let me know.

The only thing I worry about is, with the neodyn magnets, they really hit hard with a force into the Oscope when they get too close. I don't see any obvious damage to the old Oscope I was using but maybe its a good time to quit using it. I don't know if Xrays could get through microcracks from this.

 

[hutchphd]

Glass can contain up to 40% lead and still be transparent. I was amazed when I learned this.

Benjamin Franklin invented a musical instrument called the glass harmonica. It gave the players lead poisoning.

Benjamin Franklin invented a musical instrument called the glass harmonica. It gave the players lead poisoning.

Have you a reference for this? It seems unlikely to me, but data might be convincing. Also a red herring in this context.

 

[Hornbein]

Have you a reference for this? It seems unlikely to me, but data might be convincing. Also a red herring in this context.

https://en.wikipedia.org/wiki/Glass_harmonica

 

[hutchphd]

https://en.wikipedia.org/wiki/Glass_harmonica

To my reading this article saye that claims of lead poisoning were made but seem very unlikely. Pleae represent claims more carefully....or am I missing something?

 

[tech99]

Don't use any color CRT's before the FDA 1968 Radiation Control Act.
Before that time, unintentional and excessive X-ray radiation was emitted by many color TV sets.
The remedy included putting lead in the glass formula. Physical attacks notwithstanding, that type of shielding is not goes to degrade over mere centuries.

I believe that even specialty color TV CRTs max out at about 50Kv. Shielding for 50Kv x-rays is not challenging.

X-rays are not emitted below 20kV accelerating voltage so far as I know, so it was only when colour TV started that it became an issue. A CRO uses much lower voltages. We normally use a traditional CRO in our science classes. It is better as a teaching aid than a computer one because (a) you can show actual electrons being deflected with a magnet and (b) it is not so mundane - kids have seen a computer before.

 

[256bits]

X-rays are not emitted below 20kV accelerating voltage so far as I know, so it was only when colour TV started that it became an issue. A CRO uses much lower voltages. We normally use a traditional CRO in our science classes. It is better as a teaching aid than a computer one because (a) you can show actual electrons being deflected with a magnet and (b) it is not so mundane - kids have seen a computer before.

Physics department in high school used a Crookes tube for the electron beam deflection demonstration. Very anti-climatic anyways, even if one could see the electron beam along its length.

The older TV's had tubes, not much silicon in most of the circuitry.
The HV circuit had tubes and some of these acted as x-ray sources in which case the tube was enclosed within a metal shroud and or with inner glass coatings of the tube. The amount of ionizing radiation was ( most likely ) comparable to a degree to that of the background, which let ( and still does ) people live to a ripe old age. Still, precaution was the best policy to follow.

 

[256bits]

Sounds good, all. I did not realize the subject of lead in glass was pertinent to the blocking power of Xrays in monitors. So, yes, if you have ideas about that, let me know.

The only thing I worry about is, with the neodyn magnets, they really hit hard with a force into the Oscope when they get too close. I don't see any obvious damage to the old Oscope I was using but maybe its a good time to quit using it. I don't know if Xrays could get through microcracks from this.

huh?
Microcracks??
Wrap your strong magnet is a sock so as to avoid scratching the surface, or put a sheet of plexiglass in front of the CRT viewing surface.
And use a lessor-strong ferrite magnet that you, or a student, can control by hand as it is swept across the viewing surface.
Better still as a possibility, an low voltage electromagnet with varying magnetic field intensity might show much more to the students than a permanent magnet with fixed field intensity.

If you must use a supermagnet, YOU will use it, and not the students, as YOU will know how NOT to scratch the viewing surface, as the magnet is uncontrollably attracted to the metal mask behind the glass of the viewing surface of the color monitor or TV. If an implosion does occur ( even in all likely hood never ), wouldn't it feel better that it happened to not one of the students.


AND - write down the procedures to follow as the experiment is performed, in terms of safety, and as a means to come back to the experiment the next year ( ad hoc each time from memory suggests that accidents can and will happen ). Actually, you can do this every year for each class to come up with the procedures ( with you as a guide since you will know what is safe and necessary ) as a teaching tool on how develop an experiment from a concept to reality ).

I don't think the real problem with implosion is realized here. It's not that the failure will rip your hand or arm off - there may be some obvious cuts with imbedded glass fragments. It is the many tiny shards of glass that get flung out as the air rushes into the vacuum, and then rebounds as a secondary effect, flinging the shards up to many feet away. Tiny shards ( mm size ) mean an impossible clean up problem, and you will never know you have gotten them all, until some student(s) days later start complaining about getting cuts on their fingers from rubbing a surface, or worse eye problems ( from transferring a tiny shard somehow to the eye as people love to rub their eyes ).