Metastable Isotope?

[gwiyomi17]

Can someone explain to me, what does Metastable isotope means?

I already read the definitions on the internet but I really don't understand it.

 

Thanks in advance.

[Jargon]

If you look at the definition of metastable, what a metastable isotope is becomes obvious. It is an isotope, an element that has a variance in its number of neutrons, that happens to be stable, meaning it could last for many years, but less stable than its normal counterparts.

[swansont]

Metastable means that it's an excited state that lasts longer than one would naively expect. Usually this is because the primary channel for decay is forbidden for some reason.

[gwiyomi17]

If you look at the definition of metastable, what a metastable isotope is becomes obvious. It is an isotope, an element that has a variance in its number of neutrons, that happens to be stable, meaning it could last for many years, but less stable than its normal counterparts.

what do you mean??

can you give me an example?

 

Metastable means that it's an excited state that lasts longer than one would naively expect. Usually this is because the primary channel for decay is forbidden for some reason.

how about Technitium-99m? it is a metastable isotope, but its half life is 6hrs, which is less than its half life in its stable state.

[swansont]

how about Technitium-99m? it is a metastable isotope, but its half life is 6hrs, which is less than its half life in its stable state.

 

The "long" comparison is with other excited states. Most of them last no more than a picosecond, and are considered metastable if their half-life is more than ~1 nanosecond.

 

BTW, "half-life" and "stable state" really don't go together. If it's stable it doesn't decay. When a system is not excited, it is in its ground state (which may or may not be stable)

[gwiyomi17]

The "long" comparison is with other excited states. Most of them last no more than a picosecond, and are considered metastable if their half-life is more than ~1 nanosecond.

 

BTW, "half-life" and "stable state" really don't go together. If it's stable it doesn't decay. When a system is not excited, it is in its ground state (which may or may not be stable)

tc 99's half life is 212,000 years, while tc99m is 6hours. If the half life is shorter that means that tc will live longer. Since tc99m's half life is 6hours that means that it will live shorter. This is opposite of the meaning of a metastable isotope. Why is it like that?

[swansont]

tc 99's half life is 212,000 years, while tc99m is 6hours. If the half life is shorter that means that tc will live longer. Since tc99m's half life is 6hours that means that it will live shorter. This is opposite of the meaning of a metastable isotope. Why is it like that?

 

The metastable state usually decays to the ground state via photon emission, so in that case it's not one or the other. Occasionally the metastable state undergoes beta decay, but as it has more energy than the ground state, this may influence the lifetime.

 

However, as I said, the 212,000 year half-life is the ground state. The decision to name it metastable depends on the excited state lifetime being longer than typical excited state lifetimes. 6 hours is much, much, much longer than a picosecond, hence, it is metastable.

[gwiyomi17]

The metastable state usually decays to the ground state via photon emission, so in that case it's not one or the other. Occasionally the metastable state undergoes beta decay, but as it has more energy than the ground state, this may influence the lifetime.

 

However, as I said, the 212,000 year half-life is the ground state. The decision to name it metastable depends on the excited state lifetime being longer than typical excited state lifetimes. 6 hours is much, much, much longer than a picosecond, hence, it is metastable.

oh ok. thanks!