WHO WANTS TO BELIEVE IN MAGIC!
Potassium 40 is a radioisotope that can be found in trace amounts in natural potassium, and is at the origin of more than half of the human body activity: undergoing between 4 and 5,000 decays every second for an 80kg man. Along with uranium and thorium, potassium contributes to the natural radioactivity of rocks and hence to the Earth's heat.
This isotope makes up ten thousandths of the potassium found naturally. In terms of atomic weight, it is located between two more stable and far more abundant isotopes (potassium 39 and potassium 41) that make up 93.25% and 6.73% of the Earth's total potassium supply respectively. With a half-life of 1,251 billion years, potassium 40 existed in the remnants of dead stars whose agglomeration has led to the Solar System with its planets. Potassium 40 has the unusual property of decaying into two different nuclei: in 89% of cases, beta-negative decay will lead to calcium 40, while 11% of the time argon 40 will be formed by electron capture followed by gamma emission at an energy of 1.46 MeV.
This 1.46 MeV gamma ray is important, as it allows us to identify when potassium 40 decays. The beta electrons leading to calcium, however, are not accompanied by gamma rays, have no characteristic energies, and rarely make it out of the rocks or bodies that contain potassium 40.
Beta-minus decay indicates a nucleus with too many neutrons, and electron capture a nucleus with too many protons. How can potassium 40 simultaneously have too many of both? The answer reveals one of the peculiarities of nuclear forces.
Everyone has roughly 140g of potassium = 0.016 grams of Potassium 40 = 5.643ounces
The charge radius is a fundamental property of the atomic nucleus. Although it globally scales with the nuclear mass as A1/3, the nuclear charge radius also exhibits appreciable isotopic variations that are the result of complex interactions between protons and neutrons. Indeed, charge radii reflect various nuclear structure phenomena such as halo structures6, shape staggering7, shape coexistence8, pairing correlations9,10, neutron skins11, and the occurrence of nuclear magic numbers5,12,13. The term โmagic numberโ refers to the number of protons or neutrons corresponding to completely filled shells. In charge radii, a shell closure is observed as a sudden increase in the charge radius of the isotope just beyond magic shell closure, as seen, for example, at the well-known magic numbers N = 28, 50, 82, and 126 (refs. 5,12โ14). In the nuclear mass region near potassium, the isotopes with proton number Z โ 20 and neutron number N = 32 are proposed to be magic on the basis of an observed sudden decrease in their binding energy beyond N = 32 (refs. 2,3) and the high excitation energy of the first excited state in 52Ca (ref. 1). Therefore, the experimentally observed a strong increase in the charge radii of calcium4 and potassium5 isotopes between N = 28 and N = 32, and in particular the large radius of 51K and 52Ca (both having 32 neutrons), have attracted substantial attention