Advantages of Tritium vs Radium in Lume paint (for non-scientists)

[pdxleaf]

Disclaimer: I fell into a rabbit hole about tritium lume. I don’t have a scientific background so it wasn’t a very deep hole and it didn’t take much for me to fall in. Still, this info about lume might be interesting to some others.

When talking about lume, we generally refer to lume that is made of radium, tritium or luminova. While only radium and tritium are radioactive, it’s easy to think of radioactive material as the source of the glow or illumination. But it is actually phosphor material that emits a glow, not the radioactive material. The radioactive material excites the phosphor, which then emits light. What makes the lume paint self-illuminating is the radioactive material that continuously emits energy.

As long as the material remains radioactive, the phosphor will continue to emit light. While the self-illuminating glow will be not as bright over time, it is because the radioactive material may be losing energy to excite the phosphor. But the paint will also glow less over time if the phosphor material deteriorates. If you shine a light on the lume and it glows, then it might not be glowing as brightly because the radioactive material has depleted. But if you shine a light on the lume and it doesn't glow, the radioactive material might still be just as radioactive but the phosphor material may have been destroyed.

Tritium is actually a gas, an isotope of hydrogen. Self-luminous paint production binds the tritium gas into a plastic binder, which is then combined with phosphor material and paint.

[Edit, per DanS below: "The polymer binder has hydrogen atoms in its molecular structure, and some of the naturally occurring isotopic hydrogen atoms are replaced with tritium in the molecular structure of the binder itself...Generally this "tritiation" is done to the precursor monomers prior to polymerization."]

There are many decisions to be made regarding the type of phosphor material that is used, as that will have a greater impact on how effective will be the paint.

The type of phosper is chosen based on how efficiently it converts beta-energy to light and the size of the phosphor particles. The size of the particles is important because it impacts how much radioactive material can be in the same material as well as how close the phosphor can be to the radioactive material, which can have a limited efficient range or distance.

In addition to the particle size of different phosphor, a silicate phosphor is preferred to a sulfide phosphor as the silicate based is more resistant to the harmful impacts of moisture and high energy radiation.

The choice of phosphor will determine the color of the paint:

Blue paint from calcium magnesium silicate, activated by titanium.

Green paint from zinc orthosilicate activated by manganese

Yellow paint from zinc cadmium sulfide activated by silver

Red paint from zinc phosphate activated by manganese

The differences we see in the color of aged lume, as well as how much it shrinks or how often certain references have moldy lume would seem to be the result of the type of phosphor used in the paint mixture as well as the plastic and solvent composition, more so than the radioactive material used.

Advantages of tritium over radium.

1. Tritium has low penetrating power and is thus safer for humans. Tritium is blocked by common materials like plastic and glass. Tritium is too weak to penetrate the skin. It must be inhaled or ingested to enter the body. Even then, huge quantities are needed to be extremely dangerous. Also, if tritium as a gas does enter the body, most of it will combine with oxygen to form water, which will exit the body in the urine, through moisture in the breath or as perspiration. If tritium gas is inhaled, much of it is immediately exhaled.

2. Radium is dangerous because if ingested in the body it lodges in bones and then radiates from there to cause damage to soft tissues. Radium emits gamma radiation, which continually radiates.

3. Radium also emits alpha particles, which destroy the phosphorescent crystals faster. Radium loses one-half of its original brightness each year following the production of the paint mixture. Tritium emits beta radiation, which does not destroy the phosphor. The rate of loss of brightness matches the rate of radioactive decay, about 6% per year.

4. Tritium has a half-life of 12 years whereas radium has a half-life of 1600 years. After 10 half-life periods, the material is considered not radioactive. This means tritium is radioactive for 120 years compared to radium, which lasts 16,000 years.

5. Tritium is a relatively lower cost to acquire (still not cheap);

6. Paint using tritium is safer for workers who apply the paint. Tritium is about 100,000 times less hazardous than radium if absorbed by the body and no expensive shielding is needed to prepare, handle and use tritium paint;

7. Tritium paints can also be made into various colors more effectively. Green is the conventional color because the human eye responds best to green. To change from the conventional green, more radioactive material is needed, which means phosphor is destroyed at a higher rate if using radium. But with tritium, when more tritium is used, the rate of loss does not change. Also, by using more tritium, the green painted lume can be made brighter than the green painted radium lume.

8. Because tritium is safer to use in larger quantities, it can be applied in larger amounts during manufacturing, lowering the cost of production by saving time.

If anyone knows of any inaccuracies, please comment and correct my error/s. Somewhat interesting to me, and it was more enjoyable than watching paint dry, which is what I would otherwise be doing as I am painting part of the house at the moment.

Edited: Sep 21, 2023

 

[krogerfoot]

I believe this is an area of @Dan S ’s expertise.

 

[pdxleaf]

krogerfoot

I believe this is an area of @Dan S ’s expertise.

And @Seaborg

 

[Dan S]

pdxleaf

Tritium is actually a gas, an isotope of hydrogen. Tritium will combine with oxygen to form water, just like hydrogen. Self-luminous paint production uses this feature to bind the tritium gas into a plastic binder

Not quite. The polymer binder has hydrogen atoms in its molecular structure, and some of the naturally occurring isotopic hydrogen atoms are replaced with tritium in the molecular structure of the binder itself. It's not specifically related to water. Generally this "tritiation" is done to the precursor monomers prior to polymerization.

Also, in some places you used the term "phosphorus" instead of "phosphor." Phosphorus is an element, phosphor is a compound that emits light after being excited, so you could just replace phosphorous with phosphor in a few places.

Luminous paint also generally contains pigment, and I think it's possible that degradation of the pigment over time could also contribute to color change.

Edited: Sep 21, 2023

 

[pdxleaf]

Dan S

Not quite. The polymer binder has hydrogen atoms in its molecular structure, and some of the naturally occurring isotopic hydrogen atoms are replaced with tritium in the molecular structure of the binder itself. It's not specifically related to water. Generally this "tritiation" is done to the precursor monomers prior to polymerization.

Also, in some places you used the term "phosphorus" instead of "phosphor." Phosphorus is an element, phosphor is a compound that emits light after being excited, so you could just replace phosphorous with phosphor in a few places.

Luminous paint also generally contains pigment, and I think it's possible that degradation of the pigment over time could also contribute to color change.

Thanks, Dan. I made edits based on your corrections.

 

[ErichPryde]

When tritium decays it emits a beta particle and as far as I am aware it essentially becomes a helium atom, since a beta particle is a high energy electron (-charge) emitted by a zero charge neutron, resulting in a proton.

If the hydrogen atoms are molecularly bonded within a polymer as hydrogens, this would be disruptive to the molecular formula of the polymer, yes? If so, another reason we see a change in the texture and color of the lume markers, since they're undergoing a chemical change, as CH groups lose some portion of their Hs. I doubt the chemistry is quite this simple but I don't think Helium is going to want to chemically cooperate like hydrogen in these bonds.

Tagging @Dan S for thoughts on this as I am an evolutionary biologist and not a chemist or particle physicist....

Edit: it looks to me as if Dan is suggesting this in his post here, perhaps I posted before reading thoroughly

Edited: Sep 21, 2023

 

[Dan S]

Correct. Tritium decay in polymers leads to changes in chemical bonding. Most likely the amount of tritium in the polymer isn’t enough to totally degrade it.

Edited: Sep 21, 2023

 

[pdxleaf]

Dan S

Correct. Tritium decay in polymers leads to changes in chemical bonding.

Could this tritium decay be a cause of lume shrinkage, or lume loss due to a break down in the polymer?

 

[padders]

I too have a background in Physics and have worked with emitters in lab conditions. One thing I would add is that the question of attenuation may not be as simple as stated above. Alpha particles are comparatively massive vs beta (electrons) as they are ionised atoms and are absorbed by even a very thin layer of material such as a sheet of paper. You can detect the beta from a tritium lumed watch dial through a crystal whereas you can’t read the alpha from radium as it is more or less fully absorbed.

You are correct to say that the main threat with Radium lume is ingestion or inhalation and what complicates things is that one of its decay products is gaseous. Radium’s decay does generate some gamma too but I wasn’t able to read this through a crystal so again it’s not perhaps the concern some think. I’m not saying that Radium is fully safe, it’s not, particularly if you disassemble the case and the lume is loose and dusty but perhaps it isn’t quite as scary as some think. If you were to follow the logic that any risk is too much then both types should be avoided, not just Radium as some have recently suggested on here. But then by that logic you should never go anywhere near cigarette smoke, fly, have X-rays or live anywhere with a high proportion of granite in the bedrock like Cornwall.

Edited: Sep 22, 2023

 

[Archer]

padders

If you were to follow the logic that any risk is too much then both types should be avoided, not just Radium as some have recently suggested on here. But then by that logic you should never go anywhere near cigarette smoke, fly, have X-rays or live anywhere with a high proportion of granite in the bedrock like Cornwall.

As much as I agree with you conclusion, the part I have quoted is somewhat faulty logic. Radiation exposure is cumulative, so when the either/or scenarios are presented as an argument against not being concerned about watches, it falls completely flat.

 

[padders]

Archer

As much as I agree with you conclusion, the part I have quoted is somewhat faulty logic. Radiation exposure is cumulative, so when the either/or scenarios are presented as an argument against not being concerned about watches, it falls completely flat.

I see your point, I wasn’t suggesting not considering the risks or brushing them asides, just trying to add context via comparison, in a badly framed way. Many things in life are risky, often a low risk though.

 

[pdxleaf]

padders

I see your point, I wasn’t suggesting not considering the risks or brushing them asides, just trying to add context via comparison, in a badly framed way. Many things in life are risky, often a low risk though.

That was my take away with the Tritium. It's not the same level of concern as radium.

 

[ErichPryde]

Anyway; it's not the Alpha particles that are a huge concern in either case (EDIT: edit: I worded this poorly. "If we aren't talking about inhalation" is kind of an important caveat). An alpha particle is essentially a Helium(4) nucleus with more energy, but it is both too large and (typically) doesn't have enough energy to penetrate human skin (as padders stated). The issue is the gamma ray energy (UNLESS we're talking inhalation), which is both highly energetic and highly penetrating. Just how much more energetic is a gamma ray photon than a beta ray electron?

Also; to add to this conversation about inhalation: my understanding is that inhaling an alpha particle itself is not particularly dangerous: it's inhaling the alpha particle emmiters that is dangerous. So radium lume that has broken down- you inhale some of that dust, you're getting an alpha and gamma source directly in the lungs. Alpha radiation occuring inside the body means you're being exposed to highly ionizing radiation in a way that it can cause damage. (Edit: more damaging than beta particles because an alpha particle has twice as much as energy, even if it can't penetrate as far).

And that's not to say that inhaling tritium lume would be good, as inhaling a beta particle source isn't probably good for you either. but less bad than inhaling an alpha source.

So in either case: the risk is inhalation- but there is some amount of greater risk from the radium lume on a general basis, even if the gamma emission is tiny.

Edited: Sep 22, 2023

 

[pdxleaf]

ErichPryde

Anyway; it's not the Alpha particles that are a huge concern in either case. An alpha particle is essentially a Helium(4) nucleus with more energy, but it is both too large and (typically) doesn't have enough energy to penetrate human skin (as padders stated). The issue is the gamma ray energy, which is both highly energetic and highly penetrating. Just how much more energetic is a gamma ray photon than a beta ray electron?

(For the TLDR group, the Radium emits gamma and alpha, while the tritium emits beta, which is one reason why tritium is a better source, correct?)

 

[ErichPryde]

pdxleaf

(For the TLDR group, the Radium emits gamma and alpha, while the tritium emits beta, which is one reason why tritium is a better source, correct?)

Yes. When tritium decays the energy is given off with an electron. My somewhat poor understanding here is that once inhaled, alpha particles are more dangerous because they have more ionizing power (in this case, their ability/"need" to strip electrons from what they impact) than does a beta particle, because it has less charge. But they have much less penetration power, so they're much more dangerous when inhaled and much less dangerous when not.

gamma rays don't care, they'll go right through you in either case, so the amount of gamma radiation produced by radium lume would be the factor here and padders could be totally right it's too small to matter.

 

[eugeneandresson]

Dan S

Luminous paint also generally contains pigment, and I think it's possible that degradation of the pigment over time could also contribute to color change.

Could this imply that modern lume could also change color over time? Lets talk in 60+ years i guess

 

[sxl2004]

Nice rabbit hole! Hopefully appropriately laminated.
I just want to add that
“ Beta particles from tritium can penetrate only about 6.0 millimetres (0.24 in) of air, and they are incapable of passing through the dead outermost layer of human skin.[8] Because of their low energy compared to other beta particles, the amount of bremsstrahlunggenerated is also lower. ”
Wikipedia

Good luck with measuring Tritium radiation from a watch. Just not happening.

Best

Edited: Sep 22, 2023

 

[ErichPryde]

eugeneandresson

Could this imply that modern lume could also change color over time? Lets talk in 60+ years i guess

Absolutely it could. the pigments in the paint could be effected by ultraviolet light, or oxidative reactions that break up the pigments themselves. I'd never thought about it but I'd be willing to bet that SOME of the yellowing we see in older watch markers is the result of photo-oxidation from sunlight exposure. I guess my next question is: how much ultraviolet wavelength do AR coatings and sapphire crystals stop vs. hesalite?

(unrelated: old glass often had manganese added to "neutralize" the color, since the iron would color the glass very lightly greenish or bluish, and adding manganese would result in clear glass. Ironically, if glass that contains manganese is exposed to enough ultraviolet light, the electrons can become excited enough that they exchange from the manganese to the iron, which, for whatever reason, results in the glass eventually turning a light shade of purple. You can speed this process up by directly irradiating old glass (OR any glass that contains manganese as some post WWI sources also contain it), but it typically comes out a much darker shade.)

Edited: Sep 22, 2023

 

[pdxleaf]

sxl2004

Nice rabbit hole! Hopefully appropriately laminated....

we're supposed to be painting right now...

 

[ErichPryde]

pdxleaf

we're supposed to be painting right now...

Lol. My wife saw this picture of your siding and without seeing your name said: "is that in Portland?"