Why there is a general lack of neutrons in the Earth?

[Javier Lopez]

I where looking for elements that can absorpt neutrons without generating radioactive materials, and I found that most of them in Earth are suitable. I found that could work:
C, O, Si, S, N, H
The most common isotopes can receive one or two neutrons being stable, but if a neutron would be subtracted it would convert to an unstable isotope.

 

[Orodruin]

There are not many neutrons around to be absorbed. The neutron life-time is just below 900 s.

 

[mfb]

Carbon, oxygen, silicon and sulfur are produced from the fusion of several alpha particles, they start with an equal number of protons and neutrons but a neutron more gives them a more favorable neutron to proton ratio, so they are still stable with it (sometimes even with more than one).

Nitrogen is created as part of fusion reactions linked to carbon and oxygen (CNO cycle) so you get a similar relation there.

Most hydrogen is from the big bang where the heavier isotopes of hydrogen quickly combined to helium and only H-1 and He-4 were left in relevant amounts after fusion stopped.

Helium is an example where you can remove one neutron and still get a stable nucleus, but if you add one neutron it is emitted again within 10^-21 s.