In the first half of the 20th century there was a fad for uranium glass, which is kind of like lead crystal, but with uranium in place of lead. Most uranium glass has about 2% uranium by weight, and that's the kind I'm talking about here. Some can have ten times that much, which seems a bit excessive.
The cool thing about uranium glass, as seen in the image, is that it glows bright green under black light.
Pretty.
Also radioactive.
Most heavy metals dissolve well in glass, and are very stable, chemically, once they have done so. This is why vitrification and burial is a proven engineering solution to radioactive waste disposal, although a lot of people have worked very hard to remain unaware of this so they can shriek, "But what about the waste???!!!" as if it was still an unsolved problem whenever the question of using nuclear power as one useful tool to fight climate change comes up.
I assume they get paid some kind of stipend from the coal industry every time they do this, as it's otherwise difficult to understand why people who claim to be deeply interested in the health of the planet haven’t kept up on the extensive progress made on this important topic since the nineteen seventies. I mean, wouldn't that be weird: to care deeply about something, but know nothing about what has been done in terms of technological improvement in the past forty or fifty years?
The thing about vitrification and burial is that it involves burial. Dissolving the waste into melted glass, cooling it down, and burying it in deep, stable, geological structures like the billion-year-old cratons of the Canadian shield is a nice thing to do to the small amount of actinide waste produced by modern molten-salt reactor designs, which have the potential to cut waste by almost a factor of a hundred compared to old-style PWRs and CANDUs.
Uranium glass, on the other hand, is intended to sit in people's homes, gently bathing them in radioactive goodness. Or badness, as the case may be. As with many things, what's most plausible can't be reduced to a simple slogan, and can't be discovered using the awesome power of paranoid ideology.
To understand radiation safety, we first have to know a bit about radiation. As it happens, I do, although I've not worked actively on any radiation transport problems for something like 20 years, and haven't been involved in radiation safety for even longer. So this is some information and some opinion. It's not advice. I can't say anything about the safety of any particular piece of uranium glass. But I can talk about radiation safety in general terms, and explain a bit about the nature of the radiation we get from uranium glass.
"Radiation" is kind of a stupid term, because we use it to describe completely different things. At root, "to radiate" means "to spread out from a central point": that is, to engage in radial motion. "Radiation" is then just "stuff that radiates", but that could be anything that moves in a more-or-less straight line out from a central source. We even use it metaphorically, talking about "adaptive radiation" in evolutionary biology to describe the process of a characteristic developing in different directions as speciation occurs.
In physics there are at least three meaningfully distinct things we refer to as "radiation":
1) Electromagnetic (EM) waves generally, which includes sunlight and cell phone radiation;
2) EM waves that have a high enough energy to knock electrons out of atoms, sometimes this is called "ionizing radiation";
3) A variety of massive particles that may or may not carry an electric charge and whose physics in interaction with matter is governed by different fundamental forces, as well as having radically different behaviour even when the fundamental force in question is the same.
All of this is "radiation".
Non-ionizing EM radiation is mostly boring, and the people who get all up about it seem mostly scared by the word "radiation", which again: just means something propagating outward from a central source.
Lighthouse beams are radiation. Vital, but not very interesting as physics, at least to me.
In terms of radiation that can actually do bad things to living tissue, we're mostly concerned with a handful of things:
1) Electrons, also known as beta particles
2) Positrons: like electrons, but positively charged. The most common form of anti-matter. And also known as beta particles, even though in certain respects they behave quite differently, like undergoing mutual annihilation when they run into an electron.
3) Gamma rays and x-rays: these are high energy, ionizing, EM radiation. For historical reasons, if something is created by a nuclear decay it's usually called a gamma ray, and usually has higher energy, and if something is caused by a beam of electrons interacting with matter it is called an x-ray, and usually has lower energy. "Usually" is doing a lot of work here: naturally occurring gamma rays run up to a few million electron-volts in energy, but if you've ever had radiation treatment for cancer you were probably exposed to x-rays at five to ten million electron-volts, well above the ordinary gamma range.
4) Alpha particles: thanks to the weirdness of the strong nuclear force, heavy nuclei tend to decay via throwing out a helium nucleus consisting of two protons and two neutrons, which is almost the most tightly bound form of nuclear matter. These are called alpha particles, until they stop, at which point they are just helium nuclei. Same thing, different state of motion, different name. I swear it's like physicists have never heard of relativity.
5) Neutrons: the bane of any particle astrophysicist's existence. While about half of ordinary matter is made up of neutrons, free neutrons are both relatively rare and extremely nasty. They aren't directly produced by any ordinary radioactive decay, but can exist in the environment due to cosmic ray interactions. They have a lifetime of about fifteen minutes, decaying into a proton and a beta particle. Only inside of a nucleus are they stable.
6) Protons: like neutrons, they aren't generally produced by the decay of any nucleus you're likely to find in your living room, but are well-represented in cosmic rays.
7) Muons: these are "heavy electrons" that are produced in cosmic ray showers, mostly from pion decay.
8) Etc: cosmic rays contain every kind of particle we can imagine and probably a number that we can't. They run up to stupidly high energies and are mostly harmless. There are also what are called "fission fragments", which are the leftovers from nuclear fission and typically consist of heavy ions plowing their way through matter to somewhat deleterious effect.
When someone talks about "radiation" they could be talking any or all of that, and if they're an expert they should be able to talk meaningfully and coherently about the differences between the various particles and processes involved.
Processes are important: how a given particle in a given energy range interacts with matter determines how it behaves and what its effects are. Low-energy x-rays interact with matter via a process called Rayleigh scattering, amongst other things. High energy x-rays (and gamma rays) interact primarily by something called Compton scattering, which has quite different characteristics.
X-rays are also subject to photoelectric absorption by atoms, and the photoelectric absorption cross-section--which is the "effective area" of a particle, and gives the probability that radiation passing by an atom will undergo a particular type of scattering--is strongly dependent on how tightly bound an electron is to its atom. As the x-ray energy increases over the binding energy of the most-bound electrons, the photo-electric absorption cross-section goes through the roof. The most deeply bound electrons in calcium, which is one of the most important elements in bone, is around four thousand electron-volts, and x-rays with energies higher than this will be copiously absorbed by calcium in bones. This provides good contrast with the surrounding soft tissue, which has a much lower absorbtion cross-section by virtue of having more weakly bound inner electrons. This is one of the natural paradoxes of radiation physics: more tightly bound electrons are more likely to absorb x-rays, so long as they have high enough energy.
And so on: every one of the particles listed above has a wealth of unique and complex interactions with matter.
So when we ask, "Is uranium glass safe?" the answer is, necessarily: "It's complicated."
Natural uranium consists of two isotopes. It's 0.7% U-235 and 99.3% U-238. Both of these decay almost entirely by alpha-emission, with about one in a million decays coming from spontaneous fission.
When a nucleus undergoes alpha decay, it converts some mass to energy and spits out an energetic alpha particle, which plows its way through the surrounding material as it comes to a stop, which it does in very short order: the 4.2 MeV alpha particles from U-238 decay have a range of less than a hundred microns in any reasonably dense substance, like glass or human tissue, and a few centimeters in air.
So the alphas are no big deal, although I wouldn't personally handle the stuff in a more than casual way: I don't like alphas, and I like to keep them outside of my body. But even thin rubber gloves would stop the alphas from uranium decay.
What happens next is the complicated bit: when uranium emits an alpha particle, what's left behind is a thorium nucleus: Th-231 in the case of U-235 and Th-234 in the case of U-238. A nuclear decay is, from the point of view of the nucleus involved, a violent event, and the daughter nucleus typically ends up in an excited state. Individual protons and neutrons in the nucleus have discrete energy levels, the same way electrons do in atoms, and there's only one arrangement of the protons and neutrons that has the lowest energy, which is called the ground state.
This is not generally the arrangement they are in after spitting out an alpha particle, and they reach the ground state by emitting a gamma ray. In the case of the thorium isotopes that come out of uranium decays, this gamma has an energy of 50-100 keV, which puts it in the same range or a bit higher than you would get from a diagnostic X-ray machine, although there are many fewer of them: the total dose is lower, even though the energy of the individual quanta is in the same ballpark.
Most uranium glass objects I've seen are running in the few thousand counts per minute range on a hand-held detector, which puts them--generously--in the range of maybe a few tens of thousands decays per second overall, assuming the kind of junky hand-held counter people are mostly using is missing a lot of the good stuff, in part because these counters have small areas and in part because they have low quantum efficiency. Call it a 37,000 decays per second, which is in old-style units 1 micro-curie: a trivial amount of radiation. Micro-curie calibration sources are handled routinely: they're about the size of a quarter and some decades ago, before lab safety had been invented, I had a student wander off with one and almost put it in a vending machine. But when not in use they’re kept in a lead safe.
So the total dose from the average bit of uranium glass seems low, based on what I've seen online: I've never measured one myself. Individual pieces may be much hotter, though: don't assume anything. If you can afford uranium glass you can afford a meter to measure it.
The gamma rays that uranium emits have a range of meters in air, and due to the way they interact with matter--which is a topic way beyond the scope of this post--they don't lose energy continuously, but rather in a series of discrete interactions, like a bouncing ball that loses energy each time it hits the floor, but keeps pretty much all of its energy between bounces. This means that as you stand farther away from a uranium source you'll get hit by fewer gammas and lower-energy gammas--because most of the ones that reach you will have hit a few things and lost energy--but you'll still be exposed to a few full-energy gammas even at quite a distance.
Which means if I you're concerned about very low levels of radiation, and want to display uranium glass in your home, putting it in a cabinet with lead-glass windows might be an idea.
But wait, there's more! We already have alphas (mostly harmless so long as they stay on the outside of your body) and gammas (not really a big deal if you're not near by, and low enough energy to be defeated by some lead glass shielding). What's left? Beta particles. And a few more gammas.
Excited nuclei typically decay by gamma emission in microseconds or less. But isotopes like Th-231 and Th-234 are unstable against beta decay. This can be thought of as a neutron in the nucleus decaying into a proton and spitting out an electron. The electron--or beta particle--carries off most of the energy, thanks to the magic of Newtonian physics, which still applies even in these exotic circumstances.
Th-234 beta-decays to protactinium 234 with a life time against beta decay of about 24 days. Th-231 beta-decays to Pa-231 with a lifetime of about 24 hours. Beta decay is a complicated subject in its own right, as it involves the weak nuclear force and the emission of an almost-massless particle called a neutrino, which means the beta particles come out with a range of energies, as the neutrino carries off some. Since neutrinos only interact with matter via the weak force, which is... well... weak, they are very difficult to detect.
In the case of these thorium isotopes, the full energy of the beta particles is between 100 and 200 keV, depending on which excited state of the daughter isotopes the decay feeds into. And because they feed excited states of their daughter isotopes, these beta decays also produce some gamma rays, generally in the same range of energy as the ones that follow the initial alpha decay.
Betas with energy of a hundred-odd keV will travel some tens of centimeters in air: unlike gamma rays they lose energy more-or-less continuously as they travel through matter, so they have a quite definite range beyond with they aren't reaching you, and as you move further away the ones that do reach you are always of lower energy.
But like gammas, they can be stopped by a pane of leaded glass, and a little distance, if you're that-way minded.
All of which suggests that there is no problem in having uranium glass in your home, if you take a little bit of care. Displaying it in a leaded glass cabinet is probably overkill, but if you're at all concerned, it's not a bad thing to do. Drinking out of a uranium-glass vessel does create a risk of ingesting a small amount of an alpha-emitting isotope, and while it's not a big risk compared to crossing the street or driving a car, it's one that is easily avoided, so why not?
But that said: drinking out of a uranium glass vessel is not remotely similar to the kind of massive ingestion of radio-isotopes that the famous "radium girls" suffered from, and anyone who compares the two is just declaring their ignorance of radiation safety. Which is nice of them, in a way: it lets you know who to ignore.
And finally: I'll mention in passing that higher-than-normal levels of background radiation may not be not particularly bad for you, and there is some evidence they are actually good for you. The phenomenon of radiation hormesis is the observable reality that people who live in high-background areas--like Denver, say, which by dint of its altitude gets significantly more cosmic rays than Seattle or Vancouver--have lower rates of cancer and some other health issues. The reason for this may be that being exposed to a bit of extra background keeps the body's DNA repair mechanisms running all the time, whereas for those of us who live on sandstone at sea level they tend to be a lot less active, in keeping with the biological principle that everything gets hyper-optimized in the struggle for reproductive success.
Although my training in radiation transport and radiation safety is entirely North American, I tend side with the French Academy of Sciences on the question of the "linear no threshold model" of radiation risk: the French think it is not supported by the data, and they are right. North American radiation safety organizations--including the US EPA--hold the opposite view.
So the bottom line is that having a bit of uranium glass around is probably not bad for you, and there are those who would argue that it might actually be to your benefit, even beyond the fact that it's very pretty.
None of this is advice: it is information. Do not rely on this for any decisions regarding any specific piece of uranium glass. As I said: if you can afford to buy it, you can afford to invest a bit in radiation measurement kit to see how hot it actually is.
This was wonderful! Ive always been fascinated by Uranium glass and I've always had the dream of scoring a sweet piece at the local Thrift shop. Bravo! Thank you.