What the purpose of putting radio active metals in tubes or electronics? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: August 27, 2019, 10:09:29 pm
content: I have heard of thoriated tungsten or cobal60(Scarry!) in some Russian parts. Does this act like the thermal photons that interact some how to lower a certain property to make an emission start sooner/ lower voltage potential of something? They seem like they use the alpha particles. Would a beta emitter in a vacuum tube have some effect since vacuum tubes essentially make beta radiation?

author: james_s
author_rank: Super Contributor
timestamp: August 27, 2019, 10:37:41 pm
content: In most cases it's to help ionize a gas, reducing the required striking voltage. For example a lot of NE-2 style glow lamps reach a state when they age where they will not reliably start unless exposed to light, a little radioactivity would greatly improve the situation however it's not really necessary for that particular application. It's fairly common in ceramic metal halide lamps to have a bit of radioactive Krypton for that same reason, to help them reliably strike without requiring an excessively high ignition voltage.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 27, 2019, 11:38:42 pm
content: A lot of neon bulbs actually do have a trace amount of radioactive material to ease starting.http://www.techlib.com/science/ion.html#Neon%20as%20Resistor

author: xmetal
author_rank: Contributor
timestamp: August 28, 2019, 08:42:23 am
content: Some smoke detectors use a small amount of radioactive material to ionise the air.

author: borjam
author_rank: Unknown
timestamp: August 28, 2019, 01:11:02 pm
content: Thoriated tungsten is still used as a welding electrode. I purchased some a couple of years ago at a nearby mall to check a Geiger counterAnd indeed the counts per minute increased!

author: Gyro
author_rank: Super Contributor
timestamp: August 28, 2019, 07:10:06 pm
content: Thorated Tungsten is used in many directly heated tube filaments (ie. cathode) because it has a higher work function than pure tungsten (nothing to do with radioactivity).Unfortunately Thorated Tungsten filaments also undergo a physical change at a critical transition temperature during heating and cooling which causes embrittlement and necking, leading to eventual failure depending on the number of power cycles.As others have said, radioactive material in either solid (painted on to glass or electrode) or gas (Tritium) is used to create a constant low level of isolation to speed up initiation of discharge. These range from Neon lamps to GDT protectors.It's certainly not specific to Russian parts, it's universal.I have my doubts about any use of Cobalt-60 though. Radiotherapy machines, sure (there have been several accounts of multiple deaths due to ignorant opening of scrap machines around the world).... I think you're going to have to provide a citation for its use in tubes or other electronic components though!

author: Beamin
author_rank: Super Contributor
timestamp: August 29, 2019, 07:52:25 am
content: Quote from: Gyro on August 28, 2019, 07:10:06 pmAs far as the cobalt60 goes I think it was in some Russian tubes that normally would have had an incandescent light inside the piece of equipment to "activate" the desired effect in the tube. The amount was absolutely minuscule, but still not a good idea if you ask me.I always wondered what they did with all the krypton from nuclear reactors as most fissions of U235 > krypton and barium but sometimes iodine and another element. The products it splits into follow a bell curve with heavier and lighter Z "pairs" of fission products. Chemistry must be a nightmare, or just use nitric acid and mix it all together. Anyways they wouldn't still use that in HIDs as it would be considered a hazardous material like tritium?On a unrelated question what acts as the electron generator if the cathode of the filament is not connected as the cathode on indirectly heated tubes? It seems like this would be trying to hook up a battery by putting the connecting wire next to but not touching the negative terminal.

author: vk6zgo
author_rank: Super Contributor
timestamp: August 29, 2019, 10:32:56 am
content: Quote from: Beamin on August 29, 2019, 07:52:25 amThe cathode emits electrons when it gets hot.If we could heat it by some other method, it would still emit them.--- for the desired operation, the filamentsupply is only incidental.In an indirectly heated tube, the cathode is in very intimate contact with the heater as far as heat transfer is concerned, but is electrically insulated from it.There is a major advantage in insulating the heat source from the emission source, in that the former (the heater), may be operated from ac, without that source modulating the electron emission.Indirectly heated cathodes become very difficult to produce for very high powered tubes, which are almost universally directly heated, using either DC supplies, or ac with various hum cancellation circuits, such as centre tapped transformers, etc.

author: Canis Dirus Leidy
author_rank: Regular Contributor
timestamp: August 29, 2019, 11:26:27 am
content: Quote from: Beamin on August 29, 2019, 07:52:25 amWell, cobalt is used to makekovar- an alloy with the same coefficient of thermal expansion as borosilicate glass. But it's "just" cobalt, not Co60, which is gamma-ray source, so it's worst choice for any "activation" or "ionization".

author: coppercone2
author_rank: Super Contributor
timestamp: August 31, 2019, 08:35:06 am
content: work function of emission of surface is changed by thermionic dopingas for radiationhttps://www.orau.org/ptp/collection/consumer%20products/electrontubes.htmI only heard about this being used in plasma tubes, not vacuum tubesi wonder if there is a good naming convention, like plasma tube vs vacuum tube

author: GlennSprigg
author_rank: Super Contributor
timestamp: August 31, 2019, 12:55:48 pm
content: Basically, 'Thoriated' Tungsten vastly improved the Electron Emissions from Cathodes. (A given).However, for the supporters of Conventional Current flow, I guess it vastly improved the ABSORPTIONof electrons, or did something 'magical' to the Positrons that REALLY flowed from the Anode...

author: coppercone2
author_rank: Super Contributor
timestamp: August 31, 2019, 01:01:56 pm
content: Quote from: GlennSprigg on August 31, 2019, 12:55:48 pmI thought this was due to properties of thorium which do not rely on radioactivity and more with emissivity, so a unhappy match by physics to a nasty metal (obviously you are in deep shit with mother nature if you need to use radioactive materials in a god damn radio amplifier)https://en.wikipedia.org/wiki/Hot_cathode#Thoriated_filamentsthey are also used in old coleman lanterns (but I think now they use some kind of cerium ). It seems to require a plasma to function in a lantern, you will not get the brightness from electrically heating it, as I learned from this forum to my displeasure (complicated physics). It is not just a heat to light converter that functions in the presence of a plasma either, I think it needs to have 'flow' and some how depletes it.https://en.wikipedia.org/wiki/CandoluminescenceIt's probably some how related to the electrical effect? (maybe why they thought to try to use it)

author: vk6zgo
author_rank: Super Contributor
timestamp: September 01, 2019, 05:04:09 am
content: Quote from: coppercone2 on August 31, 2019, 01:01:56 pmThe characteristics of thorium that are used in these applications are not primarily to do with their radioactivity, as there are other materials which have similar properties, but have little or no radioactive content.Thorium was used, because it works better-- that's all.Indirectly heated tubes may or may not use thorium oxide in their "oxide coated cathodes" (most likely, not!).In any case, the quantity is miniscule---- the probability of damage from the radiation from such cathodes is vanishingly small from listening to a tube radio.Large transmitting tubes use "thoriated tungsten", where the filament material is an alloy of thorium & tungsten.By a mechanism described in the Wiki you linked previously, the thorium component becomes concentrated at the surface, improving the ability of the filiament to emit electrons.Obviously, these are larger elements, so there would be more possibility of radiation.Most high powered Transmitting tubes have an external anode, which makes up most of the structure of the tube.Any radiation has to make its way through these massive structures, then through the metal of the transmitter cabinet & so on.We need a "reality check" when we start worrying about peripheral radiation sources like this.People work daily with such delights as Cyanide, which has a "half life of infinity"-------it will always be just as poisonous as it is now!Another thing is Phosphoric Acid --- a lot will burn you alive, a little bit is great for killing rust.We used to make teeth fillings with Mercury amalgam ----How many people died from that?People used coal fires to get warm for many years---burning coal releases radioactve products, to say nothing of the several kW of Electromagnetic radiation in the form of heat!