A Scientific Rationale For Pursuing New Immobilization Forms For So Called "Nuclear Waste."

[John ONeill]

2. Formation of heavy elements

'(Natural rubidium is, by the way, radioactive, because of the presence of the very long lived isotope Rb-87 which has survived since the supernova nuclear explosion that created the majority of the elements found on this planet.)'
You may have heard of the recent proposal that most of the elements heavier than iron were not formed in supernovas, but in 'kilonovas' - neutron star collisions. Supposedly, while much rarer events, these would jet out a far greater mass of trans-iron nuclei than the collapse of a red giant. This could mean that the concentrations of these elements in the universe are more patchy than thought - we might be lucky to have the actinides we do.
https://www.space.com/38493-gravitational-waves-neutron-star-gold.html
(Much of your chemistry is well above my head, but I always find something interesting to mull over.)
John O'Neill