3 ms·

Thorium-229 has two energy states. A ground state, and an excited isometric state. The laser is used to transition the nucleus from the ground state to the exc

Thorium-229 has two energy states. A ground state, and an excited isometric state. The laser is used to transition the nucleus from the ground state to the excited isometric state.

bboygravity 2y ago
And then?
- topspin 2y ago
  And then the nuclei return to the ground state. That process is probabilistic and measured in half-lives. The key point is that the decay back to ground state happens at a very precise rate that is not influenced by effectively anything, and can be measured accurately. Thus, a clock.
  - dtx1 2y ago
    > That process is probabilistic and measured in half-lives > The decay back to ground state happens at a very precise rate that is not influenced by effectively anything That sounds contradictory to me.
    - topspin 2y ago
      I suppose it could: the term "probabilistic" applies to the quantum probability of any one metastable isomer (excited nucleus) decaying to ground state. In application you measure large numbers of decays, and in great numbers the decay curve is extremely precise.
phendrenad2 2y ago
Isometric? Like, is the nucleus gaining a virtual proton or something?
- nullc 2y ago
  Nucleons occupy orbital energy states like electrons. The application of energy can shift the state of the nucleus, and some of these alternative states are relatively stable. https://en.wikipedia.org/wiki/Nuclear_shell_model https://en.wikipedia.org/wiki/Nuclear_shell_model
- pfdietz 2y ago
  The correct word is "isomeric", as in the state of a nuclear isomer.
tinco 2y ago
Not a physicist, so this comment is more of a guess with the intention of someone correcting me, but I think the thing all the physicists leave out because it's probably very obvious is that when an excited nucleus returns to its ground state, it will emit radiation. So they hit their thorium with a laser, and then instead of the laser passing through, it gets absorbed, and then they get a flash of radiation back, letting them know the thorium was excited. The delay between the laser pulse and the flash of radiation is a property of the particular thorium nucleus, and is not affected by environmental circumstances like temperature or electric/magnetic fields, so can be relied on as a very precise measurement of time.
zackmorris 2y ago
25 years ago, there were experiments to move element 72 hafnium (Hf) between its low and excited isomer states, which would allow for the creation of a nuclear battery that could store 100,000 times more energy than a chemical battery, with a 31 year half life, but without neutron release: https://en.wikipedia.org/wiki/Hafnium_controversy https://en.wikipedia.org/wiki/Hafnium_controversy This would be Iron Man and Star Wars tech if it worked. Unfortunately experiments went dark after 2009, probably because it worked haha, but maybe because Hf is too rare to make a practical battery. So it looks like they tried spalling element 73 Tantalum (Ta), 74 Tungsten (W) and 75 Rhenium (Re) with protons at 90-650 MeV to create 72 Hf with atomic masses 178, 179 and high spin 178m2, 179m2 isomers if I read this right: https://publications.jinr.ru/record/151982/files/071%28E6-2008-71%29.pdf https://publications.jinr.ru/record/151982/files/071%28E6-20... https://apps.dtic.mil/sti/tr/pdf/ADA525435.pdf https://apps.dtic.mil/sti/tr/pdf/ADA525435.pdf There's a lot here though, so I can't really get a clear picture of what the yields are, or simply how many joules it takes to store one joule in an excited isomer. Which is of course all that matters, but papers often leave off the one part we're curious about, forcing us to learn nearly the entirety of the subject matter to derive it ourselves. Although on the bright side, maybe that protects us from nuclear armageddon and stuff. Maybe someone can fill us in? Edit: dangit _Microft beat me by 17 minutes, please answer there :-)
- _Microft 2y ago
  Oh, by all means discuss this here please - your comment is a lot more substantial than my lonely link to Wikipedia.

Thorium-229 has two energy states. A ground state, and an excited isometric state. The laser is used to transition the nucleus from the ground state to the excited isometric state.

bboygravity 2y ago

And then?

topspin 2y ago
And then the nuclei return to the ground state. That process is probabilistic and measured in half-lives. The key point is that the decay back to ground state happens at a very precise rate that is not influenced by effectively anything, and can be measured accurately. Thus, a clock.
- dtx1 2y ago
  > That process is probabilistic and measured in half-lives > The decay back to ground state happens at a very precise rate that is not influenced by effectively anything That sounds contradictory to me.
  - topspin 2y ago
    I suppose it could: the term "probabilistic" applies to the quantum probability of any one metastable isomer (excited nucleus) decaying to ground state. In application you measure large numbers of decays, and in great numbers the decay curve is extremely precise.

phendrenad2 2y ago

Isometric? Like, is the nucleus gaining a virtual proton or something?

nullc 2y ago
Nucleons occupy orbital energy states like electrons. The application of energy can shift the state of the nucleus, and some of these alternative states are relatively stable. https://en.wikipedia.org/wiki/Nuclear_shell_model https://en.wikipedia.org/wiki/Nuclear_shell_model
pfdietz 2y ago
The correct word is "isomeric", as in the state of a nuclear isomer.

tinco 2y ago

Not a physicist, so this comment is more of a guess with the intention of someone correcting me, but I think the thing all the physicists leave out because it's probably very obvious is that when an excited nucleus returns to its ground state, it will emit radiation. So they hit their thorium with a laser, and then instead of the laser passing through, it gets absorbed, and then they get a flash of radiation back, letting them know the thorium was excited. The delay between the laser pulse and the flash of radiation is a property of the particular thorium nucleus, and is not affected by environmental circumstances like temperature or electric/magnetic fields, so can be relied on as a very precise measurement of time.

zackmorris 2y ago

25 years ago, there were experiments to move element 72 hafnium (Hf) between its low and excited isomer states, which would allow for the creation of a nuclear battery that could store 100,000 times more energy than a chemical battery, with a 31 year half life, but without neutron release: https://en.wikipedia.org/wiki/Hafnium_controversy https://en.wikipedia.org/wiki/Hafnium_controversy This would be Iron Man and Star Wars tech if it worked. Unfortunately experiments went dark after 2009, probably because it worked haha, but maybe because Hf is too rare to make a practical battery. So it looks like they tried spalling element 73 Tantalum (Ta), 74 Tungsten (W) and 75 Rhenium (Re) with protons at 90-650 MeV to create 72 Hf with atomic masses 178, 179 and high spin 178m2, 179m2 isomers if I read this right: https://publications.jinr.ru/record/151982/files/071%28E6-2008-71%29.pdf https://publications.jinr.ru/record/151982/files/071%28E6-20... https://apps.dtic.mil/sti/tr/pdf/ADA525435.pdf https://apps.dtic.mil/sti/tr/pdf/ADA525435.pdf There's a lot here though, so I can't really get a clear picture of what the yields are, or simply how many joules it takes to store one joule in an excited isomer. Which is of course all that matters, but papers often leave off the one part we're curious about, forcing us to learn nearly the entirety of the subject matter to derive it ourselves. Although on the bright side, maybe that protects us from nuclear armageddon and stuff. Maybe someone can fill us in? Edit: dangit _Microft beat me by 17 minutes, please answer there :-)

_Microft 2y ago
Oh, by all means discuss this here please - your comment is a lot more substantial than my lonely link to Wikipedia.