Al-20, a new three-proton-emitting isotope

[Astronuc]

In a study published in Physical Review Letters on July 10, physicists from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) and their collaborators have reported the first observation and spectroscopy of aluminum-20, a previously unknown and unstable isotope that decays via the rare process of three-proton emission.

"Aluminum-20 is the lightest aluminum isotope that has been discovered so far. Located beyond the proton drip line, it has seven fewer neutrons than the stable aluminum isotope," said Associate Prof. Xu Xiaodong from IMP, first author of the study.

Using an in-flight decay technique at the Fragment Separator of the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, the researchers measured angular correlations of aluminum-20's decay products and discovered the previously unknown nucleus aluminum-20.

https://phys.org/news/2025-07-physicists-aluminum-proton-emitting-isotope.html

https://journals.aps.org/prl/abstract/10.1103/hkmy-yfdk

The discovery is so new that the radionuclide is not yet in the Chart of Nuclides. I expect there needs to be independent confirmation.

 

[.Scott]

And their article says they estimated the Al20 half-life. But what's that estimate?

 

[fresh_42]

And their article says they estimated the Al20 half-life. But what's that estimate?

My book says that half-time is connected to decay energy by Heisenberg. And the authors give the energies they measured.

 

[.Scott]

My book says that half-time is connected to decay energy by Heisenberg. And the authors give the energies they measured.

Cool. So, what is your estimate?

 

[fresh_42]

$\tau \gtrsim \dfrac{\hbar}{400\,\mathrm{keV}}$ due to the experimental resolution. They assume it's bigger $\left(\tau \gtrsim \dfrac{\hbar}{30\,\mathrm{keV}}\right)$ by comparison with a comparable result from another experiment.

 

[.Scott]

$\tau \gtrsim \dfrac{\hbar}{400\,\mathrm{keV}}$ due to the experimental resolution. They assume it's bigger $\left(\tau \gtrsim \dfrac{\hbar}{30\,\mathrm{keV}}\right)$ by comparison with a comparable result from another experiment.

I understand. This is how Physicists talk with each other. "I'll be right with you, this will only take a $\dfrac{\hbar}{\mathrm{\mu eV}}$"

 

[fresh_42]

I understand. This is how Physicists talk with each other. "I'll be right with you, this will only take a $\dfrac{\hbar}{\mathrm{\mu eV}}$"

I haven't done the division since I don't really care. But I looked up whether Wikipedia already lists the isotope. No, but I found $\tau\left({}^{21}\mathrm{Al}\right) \sim 100\,\mathrm{ps}$ with $2.3\,\mathrm{MeV}.$ That is short. I don't know the scientists, but Darmstadt isn't the worst address in nuclear physics.

 

[.Scott]

I haven't done the division since I don't really care. But I looked up whether Wikipedia already lists the isotope. No, but I found $\tau\left({}^{21}\mathrm{Al}\right) \sim 100\,\mathrm{ps}$ with $2.3\,\mathrm{MeV}.$ That is short. I don't know the scientists, but Darmstadt isn't the worst address in nuclear physics.

So, it should be multiple nanoseconds.

 

[fresh_42]

So, it should be multiple nanoseconds.

Something like that. I always wondered how they can measure such short time spans in radioactive decays in general; certainly not by counting. I mean, there is a Uranium-236 isomer with a half-life of 115 ns. Now I got an impression, and the certainty that this strange physics book among my math books wasn't a complete loss, so thanks for asking.

 

[mfb]

Something like that. I always wondered how they can measure such short time spans in radioactive decays in general; certainly not by counting. I mean, there is a Uranium-236 isomer with a half-life of 115 ns.

At 10% the speed of light that's 3 meters, measuring the decay length is trivial.
If the decay length is too short to measure (<10 micrometer =~ 30 fs), you try to measure the decay width. In between these two methods there is a gap where you don't have a good direct way to measure the lifetime.

No, but I found $\tau\left({}^{21}\mathrm{Al}\right) \sim 100\,\mathrm{ps}$ with $2.3\,\mathrm{MeV}.$

2.3 MeV is the decay energy, not the decay width.
hbar/(400 keV) = 1.6*10^-21 seconds.

I don't know the scientists, but Darmstadt isn't the worst address in nuclear physics.

Well, it's Darmstadt-Wixhausen...

 

[fresh_42]

Well, it's Darmstadt-Wixhausen...

I know, I passed it more than once (B3, before you ask how close). But c'mon, that's a difference of less than 10km. We should be thankful that it doesn't count as Frankfurt/M.

As long as you do not try to translate either of these ...