I know that certain elements like plutonium and certain isotopes of caesium are radioactive but what gives them this ability? If it's their electron/proton/neutron arrangement, what makes that arrangement give radioactive properties and how?

  • 3
    $\begingroup$ Temperature has no effect on the radio activeness of a species. $\endgroup$
    – Jori
    Commented Nov 30, 2014 at 16:06
  • $\begingroup$ You'd likely find the answer in the Physics section. $\endgroup$
    – gsurfer04
    Commented Nov 30, 2014 at 22:54

1 Answer 1


Radioactivity is not at all dependent on the atomic or molecular structure: it a purely nuclear phenomenon. The only thing that is relevant is the structure of the nucleus.

The nucleus contains only protons and neutrons and the distinguishing feature that makes nuclei radioactive is, crudely, the ratio of the two. Some arrangements are unstable for a variety of reasons a full understanding of which requires fairly advanced quantum theory. What you need to remember is that some ratios or arrangements of protons and neutrons are inherently unstable and spontaneously decay in a variety of ways to more stable nuclei. For example, 39K (which contains 19 protons and 20 neutrons) is stable but adding a neutron makes 40K which is slightly unstable and spontaneously decays in several possible ways. You can tell this isn't a simple phenomenon, though, as 41K, with two extra neutrons is stable again.

It is also important to note that radioactive decay is essentially uninfluenced by anything outside the nucleus. For any given nucleus there is a probability that it will decay but that event occurs randomly and we can't tell when it will happen (but the rate of decay is stable and not influenced by temperature, pressure or the chemical compounds the nuclei are present in).

  • 1
    $\begingroup$ It's not correct that "Radioactivity is not at all dependent on the atomic or molecular structure". Variations in half life have been observed as a function of chemical state, see math.ucr.edu/home/baez/physics/ParticleAndNuclear/… for examples. $\endgroup$
    – Ian Bush
    Commented May 16, 2018 at 18:53
  • 1
    $\begingroup$ @IanBush To be fair, I did qualify that in the final paragraph "essentially uninfluenced" which I think is a fair summary of an effect that is both rare and almost always small. $\endgroup$
    – matt_black
    Commented May 16, 2018 at 19:51

Not the answer you're looking for? Browse other questions tagged or ask your own question.