The number is the total atomic mass. Helium 2 is 2 protons. Helium 3 is 2 protons and a neutron.
Regular helium is Helium 4. By far the most abundant, over helium 3 (one proton).
That’s Helium 3, it’s rare but it exists.
A diproton is Helium 2. It’s extremely unstable and doesn’t hang around. (We assume it exists during fusion).
Relative to the amount of boring old He-4, rare.
He - 3 may be more common on the surface of the moon, due to deposition from the solar wind. People have speculated that He - 3 could be mined on the moon and used in fusion reactors. As of now it’s a rather far fetched idea, but it’s not totally absurd.
To add to @Chronos’s point: How strongly attracted single neutrons and/or protons are to one another depends on the quantum mechanical spin of the two particles. All three pairings (nn, pp, np) are unstable in the case that the nucleon spins are anti-parallel. So for the deuteron (np), the neutron and proton always have parallel spins.
So, why doesn’t this lead to comparable nn and pp bound states? The problem is that these involve identical particles and thus they run afoul of the Pauli exclusion principle. The nuclear force requires the spins to be parallel to have a potentially bound state, but the exclusion principle doesn’t allow identical particles to occupy the same state, which means that spatial overlap (which is part of the quantum state) is disfavored in the parallel-spin nn and pp cases.
So, the np case is the uniquely bound case because the neutron and proton can have the same spin without penalty.
Uranium is pretty cheap and accessible. Whether or not thorium can be used, uranium is very easy to get. They also make plutonium bombs and I once wondered why they didn’t use neptunium and other actinides. The answer is, for at least neptunium, it’s not easy to acquire. Thorium seems to be similar in that sense.
Previous thread on neptunium’s bomb-making capacity:
Here’s a resource that’s pretty good. AFAIK the physics is good, even if the articles themselves are a little long in the tooth, as that stuff doesn’t really change fast these days.
and a broader set of nuclear weapons topics.
I thought one of the advantages of thorium is that it is abundant. Waaaay more abundant than uranium. Very easy to access.
Thorium is a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. It is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium. Soil contains an average of around 6 parts per million (ppm) of thorium. Thorium is very insoluble, which is why it is plentiful in sands but not in seawater, in contrast to uranium. - SOURCE
Acquiring thorium for power production may be attractive if the price of uranium goes up. However, if you are trying to build a bomb, is a slight difference in the cost of ore your primary consideration?
For any sort of nuclear context, what’s relevant is never how easy it is to get the element. It’s how easy it is to get the appropriate isotope of the element.
You’re gonna mess up the world using heavy radioactive elements, explosive or not.
Creating fine-powder (i.e. “weapnised”) and mailing it, air dropping Anthrax (hard to make - how much you got?) from unmarled plames is the way to go.
ETA: last week the police or some LEO’s in NYC received envelopes filled with white powder. it was Boric Acid which is poisonous (to insects0
If it were high quality Anthrax powder even looking upon white powder may have led to their demise.
Oh, neat! I don’t see why it couldn’t be used, in that case. Despite any physical properties I don’t know about, I assume somewhere in the process of making it it costs more.
Not all radioactive isotopes are fissionable. Most aren’t, in fact.
It would take two steps for the thorium to turn into uranium. Thorium 233 decays into protactinium 233 with a half-life of 21.83 minutes. Then protactinium decays into uranium 233 with a half-life of 26.975 days. It works for a nuclear reactor, but not for a bomb.
https://www.nndc.bnl.gov/nudat3/
99.98% of naturally occurring Thorium is 232 Th, the one you want.