[vmelkon]

I was wondering if it is possible to concentrate potassium 40 just as a fun experiment.
Perhaps if there was a way to extract the potassium 40 and 41 at the same time which make up 0.012% and 6.73%.
Would dissolving a salt in water and then slowly drying it do it? Has this been done?

[AlbertoA]

no, potassium 40 and 41 are chemically identical, soy you can't separate them by evaporation

[Borek]

http://en.wikipedia.org/wiki/Isotope_separation

[vmelkon]

In the case of calcium, I have read that our bones tend to absorb Ca 40 and less of the heavier isotops like Ca 42 (2.086% in natural calcium). In osteoporosis cases, people who lose bone mass give off a lot of Ca 40 so they do urine test for the 40/42 ratio.
This seems to suggest that it should be possible to do it by some means with K as well.

[gippgig]

It could always be done by mass spec. Extremely effective & extremely slow...

[vmelkon]

Woops. I meant to say Ca 44, not Ca 42.
Ca 44 is 2.086% in natural calcium. They do Ca 42 / Ca 44 ratio test.

[ericsocialad]

concentrate potassium 40 lol, cool idea )))

[Fluoroantimonicacid]

You can separate ⁴⁰KF and ³⁹KF using diffusion,I think.

[johnmathew44]

if I require a macroscopic pile of Potassium-40 to do strange and wonderful beta-particle related shenanigans with. What exactly would I have to do to a banana(s) in order to retrieve this isotope?

[billnotgatez]

have lots of bananas ??

from the internet

Bananas are radioactive for a similar reason. The fruit contains high levels of potassium. Radioactive K-40 has an isotopic abundance of 0.01% and a half-life of 1.25 billion years. The average banana contains around 450 mg of potassium and will experience about 14 decays each second. It's no big deal. You already have potassium in your body, 0.01% as K-40.

[AlbertoA]

Another idea (but totally impractical) would be to heat pure K untill it boils (the pure metal, not an aqueous solution), so the heavier isotope has a tendency to stay in the liquid and the lighter isotopes would boil away

[Enthalpy]

People who measure isotope ratios have instruments that count individual atoms, hence show extremely small deviations in the composition.
So bone composition does not mean that the process is any practical for purification purpose. In fact, it's not.

Hydrogen is the sole atom whose isotopes can be separated chemically. All others need inefficient and expensive methods, the least bad presently being centrifuges (ask the Iranis, they made them of carbon fibres, better than the steel used elsewhere), and in the near future maybe lasers - little is known about this latter process.

⁴⁰K looks little interesting as a radioactive heat generator because it produces gammas and has a too long life, but if we could influence its decay rate... That's a puzzling challenge! Some people claimed to see slightly faster electron capture at the high pressure of sonoluminescence, but this claim is widely rejected. Neither do people from inertial confinement (laser, Z-machine) work on this subject to my knowledge - but I ignore a lot. The energy investment must be too big for a very brief pressure increase.