isotopes

[devayaani]

Thank you for clarifying the doubts . I know chemical elements have naturally occurring isotopes. Is there any element (atomic number 1 to 92) that exists in nature but does not have any isotope ? (i.e. only one form?) can you give the name? If all elements (naturally occurring ones) possess isotopes, are all these elements having radio-active isotopes? Are there any elements having isotopes but none of these isotopes is radio-active? (name please.)
Thanking you.

[eltelioni]

Even hydrogen has multiple naturally occuring isotopes, therefore it is reasonable to assume that all naturally occuring elements have more than one naturally occuring isotope.

Every element has radioactive isotopes but many of these will have very short half lives.

[Clanad]

Some isotopes currently defined as stable, may not be due to extremely long half-lives...

[eltelioni]

Yes, "naturally occuring" and "radioactive" may not mean what you want them to mean. A highly unstable isotope of Helium may be produced on Earth by the decay of a naturally occuring radioactive element. Does that mean the Helium isotope is naturally occuring? And, as Clanad says, an isotope with a very long half life (say 1 miilion years) is radioactive.

[Teddio]

Surely radioactivity is a natural phenomenon? There are two isotopes of helium, neither of which are radioactive.

An isotope is radioactive if its nucleus is "unstable". A highly unstable nucleus, such as Polonium-210, which was used to murder Alexander Litvinenko, has a very high Decay Constant and, consequently, a very short Half Life (a few weeks)

A slightly radioactive active isotope, such as Uranium-238, has a very low Decay Constant and a very long Half Life (over 4000 million years).

What is the Half Life of an isotope such as Carbon-12? It seems stable and has never been observed to decay. Does it have zero Decay Constant and therefore an infinite Half Life?

[devayaani]

Thank you all for your prompt answers.
I very much appreciate your answers.