I Al26 Meta Stable State: Forbidden Xray Transition?

[x_engineer]

TL;DR Summary

Can one get to Al26m from Al26?

When looking at the energy level diagram of Al26, I see a meta stable state 2.836keV higher that has a half life measured in seconds compared to the half life of the ground state measured in megayears.

Would it be possible to push a sample of Al26 to the Al26m state by irradiating it with the appropriate Xrays? Is that transition forbidden, and what would be needed to make it happen?

 

[Steve4Physics]

Would it be possible to push a sample of Al26 to the Al26m state by irradiating it with the appropriate Xrays? Is that transition forbidden, and what would be needed to make it happen?

EDIT.
I wasn't aware of the critical role of angular omentum for metastable transitions until I read @Vanadium 50's Post #3. So please don't give any weight to my original reply (below).
_________

Hi @x_engineer. I’m definitely no expert but it sounds like the process you are asking about is equivalent [or closely related] to the Mössbauer effect.

If you are not familiar with the Mössbauer effect there's plenty of information available online.

The Mössbauer effect has been observed in a number of elements – but not aluminium. E.g. see here: Link Removed

I’d guess one problem is that the lifetime of Al-26ᵐ is too long (half-life around 6.3s). The relatively long half-life results in a very narrow line-width for the emitted photons. This makes resonant absorption of photons very difficult to achieve.

Edit: And trying to produce useful amounts of Al-26ᵐ this way would be infeasible.

 

[Vanadium 50]

If the transition A → B + C is possible but slow (what the "m" means), C + B →A will be possible but rare.
Because you need to gain (if I recall correctly) 5 units of angular momentum, it's a magnetic duotrigonopole transition (I just made that word up) and as such will be very, very, very rare indeed.

 

[x_engineer]

EDIT.
I wasn't aware of the critical role of angular omentum for metastable transitions until I read @Vanadium 50's Post #3. So please don't give any weight to my original reply (below).
_________

Hi @x_engineer. I’m definitely no expert but it sounds like the process you are asking about is equivalent [or closely related] to the Mössbauer effect.

If you are not familiar with the Mössbauer effect there's plenty of information available online.

The Mössbauer effect has been observed in a number of elements – but not aluminium. E.g. see here: Link Removed

I’d guess one problem is that the lifetime of Al-26ᵐ is too long (half-life around 6.3s). The relatively long half-life results in a very narrow line-width for the emitted photons. This makes resonant absorption of photons very difficult to achieve.

Edit: And trying to produce useful amounts of Al-26ᵐ this way would be infeasible.

Actually, this is useful information. I am looking for a metastable state that is reachable from a nearly stable isotope with a small amount of energy, that then decays with the release of a large amount of energy. So, what you are telling me is that I would do better looking for short-lived m states with a small spin difference from the nearly stable state.

 

[Vanadium 50]

This isn't going to work. You can't pump a state up because the probability is low (hence the "metastable") and the requirement for a narrowly tuned gamma source. (Mossbauer does this, but is not exactly efficient)

Your best bet is to get your metastable isotope by radioactive decay of the parent. For example, if you wanted Hf-174m(2), with a 30 year half life, you would get some W-178 which then cascades down.

 

[x_engineer]

I am not looking to create a sample of the metastable isotope. I just want to push a stable isotope into a metastable state, and the faster it decays to the final state (which should have a much lower energy than the initial state) the better.

The problem (as I understand it) is that one has no control over radioactive decay, i.e. there is no way to speed it up or slow it down.

Niket Patwardhan

 

[Vanadium 50]

I just want to push a stable isotope into a metastable state

You can't. No matter how you rephrase it. Oh, sure you can maybe get an atom or two up, but the probability is very, very low. For the reasons discussed.

People have tried this with Th-229m, which is unique in that its transition energy is in the VUV, most likely 8 eV - hundreds or thousands of times easier than what you propose. This is hard.

 

[x_engineer]

You can't. No matter how you rephrase it. Oh, sure you can maybe get an atom or two up, but the probability is very, very low. For the reasons discussed.

People have tried this with Th-229m, which is unique in that its transition energy is in the VUV, most likely 8 eV - hundreds or thousands of times easier than what you propose. This is hard.

Thanks. I will look at Th229m.
Also for more ways to effectively broaden the m line.

 

[Vanadium 50]

Also for more ways to effectively broaden the m line.

If the line is magically broadened, then it won't be metastable any more.