Atom
Inti atom terdiri atas proton dan neutron yang terikat bersama pada pusat atom. Secara kolektif, proton dan neutron tersebut disebut sebagai nukleon (partikel penyusun inti). Diameter inti atom berkisar antara 10 hingga 10m. Jari-jari inti diperkirakan sama dengan
formula_1  fm, dengan "A" adalah jumlah nukleon. Hal ini sangatlah kecil dibandingkan dengan jari-jari atom. Nukleon-nukleon tersebut terikat bersama oleh gaya tarik-menarik potensial yang disebut gaya kuat residual. Pada jarak lebih kecil daripada 2,5 fm, gaya ini lebih kuat daripada gaya elektrostatik yang menyebabkan proton saling tolak menolak.
Neutrino elektron
Dear radioactive ladies and gentlemen,
As the bearer of these lines [...] will explain more exactly, considering the 'false' statistics of N-14 and Li-6 nuclei, as well as the continuous "β"-spectrum, I have hit upon a desperate remedy to save the "exchange theorem" of statistics and the energy theorem. Namely [there is] the possibility that there could exist in the nuclei electrically neutral particles that I wish to call neutrons, which have spin 1/2 and obey the exclusion principle, and additionally differ from light quanta in that they do not travel with the velocity of light: The mass of the neutron must be of the same order of magnitude as the electron mass and, in any case, not larger than 0.01 proton mass. The continuous "β"-spectrum would then become understandable by the assumption that in "β" decay a neutron is emitted together with the electron, in such a way that the sum of the energies of neutron and electron is constant.[...]But I don't feel secure enough to publish anything about this idea, so I first turn confidently to you, dear radioactives, with a question as to the situation concerning experimental proof of such a neutron, if it has something like about 10 times the penetrating capacity of a "γ" ray.I admit that my remedy may appear to have a small "a priori" probability because neutrons, if they exist, would probably have long ago been seen. However, only those who wager can win, and the seriousness of the situation of the continuous "β"-spectrum can be made clear by the saying of my honored predecessor in office, Mr. Debye, [...] "One does best not to think about that at all, like the new taxes." [...] So, dear radioactives, put it to test and set it right. [...]With many greetings to you, also to Mr. Back, your devoted servant,