@Background Pony #8FB9  
Comments like yours are why I love Derpibooru so much.

@Dirty Bit  
+1

@Registered Anon
 
It’s very quantum-mechanicy (read: weird). I’m just a bio/chem guy, but I’ll try.
 
The nuclei of atoms have spin, which can be either 0 or multiples of 1/2. For a given number and configuration of protons and neutrons, only certain spin states are possible. When a nucleus is unstable, it wants to find a lower energy state (which causes a release of energy). Lower energy states are preferable, so the atom tends to find them. Higher spins have additional energy, which generally makes them unstable.
 
However, the transition to a lower energy state can only be done in certain ways. An atom can release gamma rays, which changes spin by 1 unit. A neutron can also capture an electron (electron capture), or a proton can split into a neutron and an electron (beta decay), or an entire helium nucleus can be shot out (alpha decay). These also alter spin, but it depends on the conditions.
 
The trick to Ta-180m is that is has a spin of 9 (very high!), and the only two other allowable states for it is a spin of 1 (due to quantum mechanics stuff). So at minimum it has to jump by at least 8 spin units all at once, which would mean emitting 8 gamma rays all at once. Every event that has to occur simultaneously makes it exponentially less likely.
 
So when the spin is very high in an isomer and it’s trying to transition to a much lower spin isomer, that spin itself can prevent the transition. There are nuclides with much higher spins than 9, but because the gap to the next nearest allowable spin is lower they aren’t as stable as the exceptional Ta-180m.
 
That’s all I can translate tonight… if it’s correct. There are more fun facts (like that nobody is sure how Ta-180m was generated naturally; nothing decays into the -m version. Supernova fun times likely.), but I guess those can wait until joycall’s periodic table reaches tantalum.

@Background Pony #766B  
Sounds cool. How exactly does spin suppression work?

If selenium stinks a lot, tellurium is worse. There are many stories of chemists who handled tellurium and its compounds - especially organotellurides - and found many disgusted faces for a month afterwards.

@Registered Anon
 
There are quite a few, but Ta-180m is by far the most extreme example (and I’m pretty sure it’s the only observationally stable one). A lot of heavier atoms have a few different metastable isomers, but they have much shorter half lives.
 
I just remembered that one example specifically, but the internet at large has some interesting stuff about nuclear isomers and spin-suppression of decay. It turns out you can shoot x-rays at it and force it to decay, so some people are investigating using that principle for power storage…

@Background Pony #766B  
That’s pretty cool. Any other isomers like that?

Tellirum-128 might have the longest confirmed half-life of radioactive nuclides, but my favorite isotope is Tantalum-180m. Ta-180 normally has a half-life of about 8 hours, but this nuclear isomer (that’s the m part) has a half life of at least 10^15 years (it’s hard to measure). They have the exact same number of protons and neutrons, so what’s the difference?
 
The secret is that the Ta-180m nucleus has so much spin (9!) that, due to quirks of energy conservation and quantum mechanics, it can’t release its energy. The massive spin prevents it from throwing off photons or particles (or capturing an electron) because they would have to cause massive changes in angular momentum, which makes such events very unlikely to happen.
 
It has never been observed to decay despite wanting to very badly.
 
Yay physics!

Tellurium-128 has the longest half life of all known radioactive nuclides, with a half life of 2.2 septillion years. Tellurium-130 has a half life of 790 quintillion years, which is still pretty long.

@Dirty Bit  
My car still has a CD player, so I still do. It also doesn’t hurt to have yet another physical back up of my music files.

Remember when we used to burn stuff on these? :U

You spin me right round