Why are Some Neutron-rich Isotopes Unstable?

Most recent answer: 01/30/2018

I wanna to know, why very neutron-rich isotopes are unstable nuclei? Please answer me.
- MaungMaungchit (age 33)
Mandalay, Myanmar

Consider the lowest neutron-rich isotope, a single neutron.  It is unstable and will decay into a proton, an electron, and an anti-neutrino.   The answer is that the neutron's mass is larger than that of the sum of the masses of the proton, the electron and the anti-neutrino.  

The same argument holds for more complicated nuclei.  Additional effects are caused by the shell structure of nuclei.  If an extra neutron in a nucleus is in a high energy shell and there is a lower energy shell that a proton would fit into, it will cheerfully relinquish its position to that of a proton, an electron and an anti-neutrino. 

It's all about energy.



(published on 01/30/2018)