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comment Why does the metastable form of Technetium-95 have a longer half-life than its most stable state?
@ManishEarth, BenNorris - I respectfully submit that nuclear isomerism is far more nuclear physics than chemistry, taking place on energy and length scales orders of magnitude removed from chemical processes and not involving electronic structure. I've only ever seen it discussed in chemistry in the context of understanding Mössbauer spectroscopy. Whilst I apologise for being a bit presumptuous, I do think this question would attract a greater breadth and depth of answers on the physics site.
Apr
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comment Why does the metastable form of Technetium-95 have a longer half-life than its most stable state?
Hopefully a moderator can shift this to phys.SE. Just surfing around tables of isotopes does however reveal that isomers that are longer-lived than their ground states are not uncommon (102mTc, 116mCs, etc.). Anyhow, this looks like another application of the difference between thermodynamic and kinetic stability. Intuitively, the decay pathways that lead to rapid decay of a ground-state isotope are less probable (maybe totally impossible) in an isomer. The isomer, whilst less thermodynamically stable, is stuck in a potential energy rut that it can only escape through slow processes.
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comment Have we managed to make a perfect vacuum?
@Hurricane - Antimatter can be stored in a Penning trap.
Jan
18
comment Do the energy levels of electron orbitals change relativistically?
Broadening of spectral lines occurs due to the Doppler effect (as well as a number of other effects) even in non-relativistic regimes. Otherwise emission and absorption spectra would be infinitely sharp. As a side note, you may be interested to know that relativistic mass increase becomes significant for bound electrons around about the second row of transition metals and quantum chemical calculations need to take it into account for accurate energy calculations.
Jan
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answered Explanation of the Graetz circuit
Jan
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comment How can two seas not mix?
@EmilioPisanty - It seems that Wikipedia has a page dedicated to the topic. Also, Atkins Physical Chemistry 3e pp. 632-634 talks about colloid stability.
Jan
16
answered How can two seas not mix?