Slashdot Mirror
Bismuth No Longer the Heaviest Stable Element
forii writes "Bismuth-209 was commonly thought to be the heaviest stable element. But now Physicists have discovered that Bi-209 actually is unstable and decays with a halflife of 2*10^19 years. This means that the average 8oz (237ml) bottle of Pepto-Bismol contains one decay event every 36 hours or so."
Incidentally, all elements have unstable isotopes. Bismuth's are pretty rare, but they do exist!
Bismuth obsessive will rejoice in the web site of the Bismuth Producers Association.
I prefer Tums, myself.
Bismuth-209 is the most common isotope of bismuth (with its mean atomic mass being 208.98038), so it would be acceptable to say ' Bismuth No Longer the Heaviest Stable Element', according to webelements and The Jefferson Lab.
If you look at the periodic table, the answer is obviously the next smaller element, lead, which is what most of the heavier elements eventually decay to.
You are in a maze of twisty little passages, all alike.
In the article, it mentions that people actually have predicted this decay using theory. The nucleus is not completely understood, but the theory of basic decay phenomena is pretty complete.
Any time you talk about the quanta of physics, you need to use quantum mechanics. The quanta are of course the so-called fundamental particles, including the proton, neutron and electron.
The nucleus is held together by the strong force. This force must be very strong to keep the protons, whose like charge repels one another, very close together. The strong force only pulls over very short distances: if some nucleons get far enough, their electromagnetic repulsion will continue to push each other apart and they will be separated permanently.
However, the particles in the nucleus don't have enough energy to get over the hump, so nuclei are stable. This is where quantum mechanics applies. Even if the hump is very tall, the nonlocality of quantum mechanics means that some particles can escape if the hump isn't very wide. Because they have a probabilistic spread in space, some of them can creep to the other side. When they get lucky like this, a nuclear decay occurs. The details of the nucleus determine how high the barrier and how wide the hump, both of which affect the probability of tunneling.
In stable nuclei, particles are prohibited from escaping. In this case, it's not that the hump is too high, but that it's asymmetrical. If the nuclear force is strong enough compared to the energy of the nucleons, it can dig a deep well for the particles. In this case, having some possibility of getting past the hump doesn't really help: the area on the other side of the hump is prohibited regardless.
One way to think of this process is to say that quantum mechanics would allow you to borrow the energy you need to jump over a fence as long as you fell back down on the other side, no matter how tall the fence.
But you can't keep the borrowed energy, so you could never jump to the top of a roof, even if it were no taller than the wall you just jumped over.
How about "Bismuth not stable; Lead now heaviest stable element". (Polonium has no stable isotopes).
Since nobody knows how long even simple elements will last, it is all a matter of degree. Some things decay fast, and some really really really slow, beyond our level of detection. If there is any element that is stable forever, we probably cannot test that since the Universe likely won't last forever according to current theories.
Thus, "stable" is probably not really a Boolean thing.
Table-ized A.I.
Deuterium has different hydrogen bonding properties from H-1. This is a problem because a lot of biology (DNA, for instance) relies on hydrogen bonding to hold things together correctly. If you started drinking a lot of D2O, the differently shaped molecules wouldn't fit together correctly and you would begin breaking down at the cellular level. If I recall correctly the effects are a lot like radiation poisoning.
Another way that D2O differs from regular H2O.
Heavy water poisoning of animals is caused by the D2O (heavy water) inhibiting cell division (mitosis). Bacteria growth rates are reduced, leading to problems in the GI tract, and bone marrow activity is reduced. So GI infections and enemia are symptoms. You would need to approach about from about a quarter to about a third of your body weight in D2O to achieve toxic levels. It would cost in the vicinity of $10,000 dollars and you would weight several pounds more when you died.
---- ---- --- -- --- ------ Keep Cool But Do Not Freeze
No! Deuterium behaves chemically exactly like hydrogen-1 (protium) in the compounds that it forms. The physical properties are slightly different (heavy water--deuterium oxide--is denser, and has higher freezing and boiling points. Heavy water ice cubes will sink in a glass of regular water.) Problems arise simply because of its added mass. It's chemical kinetics are different--reactions involving deuterium run more slowly than reactions involving protium.
In the delicately balanced biochemical environment of the body, this slight slowing of reactions by the involvement of a heavier isotope would likely cause unpleasant symptoms. This has never been tested (to my knowledge) in any system larger than a cell culture. In those cases, replacement of roughly half the light water with heavy water prevented the formation of microtubules, blocking cell division.
Heavy water costs about three hundred U.S. dollars per liter--so poisoning a human being by this technique would be extremely costly. Not only that, the effect would be reversible with consumption of regular water. The effects would be like radiation poisoning or chemo, because rapidly dividing cells (in hair follicles, digestive tract, bone marrow) would be affected first.
~Idarubicin
You are right about the role of the weak force. The process you are thinking of is beta decay. In this process a neutron is converted into a proton, an electron and an antineutrino.
Beta decay is detected by looking for beta particles, also known as electrons. This is another interesting process, but the article mentions that they looked for and found alpha particles.
I hope this makes things clearer. Incidentally, we've talked about two of the three kinds of radiation here:
My dad had a copy of Lange's Handbook of Chemistry that was published back in the sixties. I distinctly remember seeing that it listed the half life of Bi-209 as 2x10^23 years. That was only four orders of magnitude too long.
In principle there are no stable nuclei heavier than iron 56. If you have a nucleus with atomic number A and atomic weight X, and you add up the binding energy of that nucleus, and compare it to the sum of the binding energies of an alpha particle and of a daughter nucleus with atomic number A-2 and atomic weight X-4, you will find that alpha decay is at least a little energetically favorable for many nuclei heavier than iron.
If alpha decay is energetically favorable for a nucleus, then that nucleus is not stable. Alpha decay is a barrier tunneling process. If there's a potential energy drop on the other side of the barrier, the barrier will get tunneled through by an enterprising alpha particle eventually. It's just a matter of how long it will take- which is determined by the barrier width and the magnitude of the potential energy difference. The only reason many elements (iodine, gold, mercury, lead, etc.) are considered stable by human beings is that their decays have never been observed- because they are difficult to observe within human time scales. You might have to set up your experiment and wait for years, maybe centuries, before you see a decay. A bottle of mercury might contain two alpha decays per century. Is mercury stable? Not really, but for all practical purposes it is. It's all in the eye of the beholder.
So it seems someone has caught bismuth in the act. Does this mean lead is now the heaviest stable nucleus? No, absolutely not. Lead has some advantages over bismuth- even numbers of neutrons and protons, etc. Pb-208 will definitely have a longer half life than Bi-209. Determining the half life of Pb 208 is going to be hard. But quantitative differences aside, the only real difference between lead and bismuth is that bismuth got caught!