Promethium riddle geometry

Pm 148 is an element called promethium. It is radioactive, but lighter than gold or mercury. The riddle is: Why does Pm decay in 12 years, but it is lighter than tungsten?

The core of Pm has a cube 4x4x4. That is unstable. Tungsten has a cube 3x3x3, so it is stable. The only elements with a cube-4 at the center are Tc, Pm, Pa, Og. The periodic table of nuclear structure is provided. That is based on iron. See the Journal of Nuclear Physics, March, 2019. My paper explains the ideas of me, Alan Folmsbee. Or see my you tube channel with 27 videos.

Charge distribution in each nucleus is using the rules given here:
https://impuremath.wordpress.com/charge/
In the cube, protons repel protons. Outside the cube, protons form lines of protons.

Profound importance was discovered as I took the learnings from iron and its cube-3, because when I made a cube-4 analog of the iron lattice, an element was found to be appropriate. That element was not predicted, as I started to put 3 layer pyr