In comments, crosspatch was checking out the isotope list wondering where the gamma radiation was coming from. He was putting them in wolframalpha and it was returning “mode of decay: beta” for every one.
Let me spend a minute on decay. Nuclei are “unstable”, meaning radioactive, when they don’t have a stable balance between the number of protons and neutrons. All known elements with more protons than lead are unstable in every isotope.
(There are heavier stable elements theorized, but we can’t make them yet.)
Every form of decay is the universe’s way of seeking a stable nuclear configuration.
In general, as protons increase, neutrons must increase even more to have a stable isotope. The very first radioactive isotope makes me seem a liar. Tritium, Hydrogen-3, has one proton and two neutrons. It’s unstable. It decays by pure beta emission and becomes Helium-3, which has two protons and one neutron.
Which naturally is stable. The universe is full of stuff like this.
But, in general, the more protons, the more neutrons needed.
Uranium is element #92. U-235 has a total of 235 protons and neutrons, so it has 92 protons and 143 neutrons. In fission, when one splits apart it usually splits into two smaller nuclei and, let’s say, releases three neutrons in the process. (These can go on to split more U-235 apart.)
So we have two fission fragments that total 92 protons and (now) 140 neutrons. You might expect an even split, which would give you 2 Palladium-116’s.
Almost never happens. Thus the twin-peak fission curve, aka the “Dolly Parton”:
But say you do get identical Pd-116 twins. You’ve now got two radioactive atoms, beta emitters, with a half-life of 11.8 seconds. Almost all fission fragments emit beta. Why?
The new nuclei have too many neutrons for the number of protons. Somewhere between “one too many neutrons” and “wah-hey! too many neutrons”.
Okay, beta particles are electrons to all extents and purposes. So in beta decay a neutron throws out the beta and turns into a proton. This brings things in balance, or closer to balance.
As a rule, the more unbalanced they are the shorter their half-life. Lots of fission products are never a problem because they don’t last long enough to trouble us. But their “daughter products”–the nuclei they turn into–are often radioactive as well.
Okay, this is getting lengthy. Didn’t get past one mode of decay, much less into gammas. Will resume later.
Any questions are of course welcome.