Note that lead-208 is at a “double magic number”, with a complete shell of neutrons and also of protons. Beyond that you don’t get the extra stability from completing a shell
Yeah, but it’s surprising that it doesn’t begin until after Bismuth, given that. It seems like it skips one on the neutron side as well.
Does the shell theory explain why it becomes unusually unstable once there’s two neutrons past the shell (and not when there’s two protons past the shell)?
And also, why does the decay mode suddenly change to alpha particles? I guess the alpha particle decay becoming favorable explains why it “skips one” on each side, and perhaps since He_4 is also doubly magic, maybe that’s why it prefers to do alpha decay in this region.
Does the shell theory explain why it becomes unusually unstable once there’s two neutrons past the shell (and not when there’s two protons past the shell)?
For alpha decay, a bunch of two protons and two neutrons need to detach. Two protons will have a greater intrinsic chance of breaking away, because of charge repulsion from other protons. So it’s detaching the neutrons which is hardest.
So, if you are considering various nuclei with two nucleons outside the filled shells, and asking when alpha emission faces the lowest energy barrier, it might be the case in which the two protons come from a filled shell (and can use charge repulsion to escape), and the neutrons are the two loose nucleons.
And also, why does the decay mode suddenly change to alpha particles?
The proton shell after Z=82 seems to be the threshold at which electrostatic repulsion between protons, wins out over strong-force cohesion among nucleons. Although it can take a while… the half-life of bismuth-209 is 10^19 years!
Do we know what’s up with the yellow square starting at Polonium where the half-lives suddenly get short?
Note that lead-208 is at a “double magic number”, with a complete shell of neutrons and also of protons. Beyond that you don’t get the extra stability from completing a shell
Yeah, but it’s surprising that it doesn’t begin until after Bismuth, given that. It seems like it skips one on the neutron side as well.
Does the shell theory explain why it becomes unusually unstable once there’s two neutrons past the shell (and not when there’s two protons past the shell)?
And also, why does the decay mode suddenly change to alpha particles? I guess the alpha particle decay becoming favorable explains why it “skips one” on each side, and perhaps since He_4 is also doubly magic, maybe that’s why it prefers to do alpha decay in this region.
For alpha decay, a bunch of two protons and two neutrons need to detach. Two protons will have a greater intrinsic chance of breaking away, because of charge repulsion from other protons. So it’s detaching the neutrons which is hardest.
So, if you are considering various nuclei with two nucleons outside the filled shells, and asking when alpha emission faces the lowest energy barrier, it might be the case in which the two protons come from a filled shell (and can use charge repulsion to escape), and the neutrons are the two loose nucleons.
The proton shell after Z=82 seems to be the threshold at which electrostatic repulsion between protons, wins out over strong-force cohesion among nucleons. Although it can take a while… the half-life of bismuth-209 is 10^19 years!