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Let’s say we have element X with half life of 100 years. Can chemical bonds like X−X or X−Cl increase/decrease half-life of X?

As a follow up question, can it increase/decrease radioactivity of X?

andselisk
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suyashsingh234
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    See https://physics.stackexchange.com/questions/713918/can-a-beryllium-7-nuclei-be-stable-if-it-has-lost-its-electrons/713923#713923 which has one answer (full disclosure - it is mine), and a link to another related post. A fully stripped $^{7}$Be ion can't decay by electron capture since there isn't an electron to capture. Further, electron density in compounds with $^{7}$Be$ do impact the measured half life. – Jon Custer Aug 16 '22 at 19:38
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    https://chemistry.stackexchange.com/a/62042/9961 – Mithoron Aug 16 '22 at 19:50
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    https://chemistry.stackexchange.com/a/85435/9961 – Mithoron Aug 16 '22 at 19:51

2 Answers2

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It might depend on the type of decay undergone by the element, but certainly for some decays it is possible. That being said, these are the exception rather than the rule. Typically, nuclear decay is controlled by the weak nuclear force, which is mediated by the W and Z bosons in the Standard Model of Particle Physics. This is in contrast to chemical bonds arising from interactions between electrons, resulting from the electromagnetic force which is mediated by photons in the Standard Model. Any impact is primarily going to relate to the interactions between the pertinent quantum fields. Electrons can undergo processes guided by the weak nuclear force, so implicitly any impact to the electron's wavefunction will subtly—and occasionally noticeably—affect its ability to interact with the nucleus.

Different chemical bonds perturb the electronic environment of the nucleus, and thus any decay processes that are in some way dependent on the local electronic environment will have a shift in decay-rate, and thus a shift in half-life. The easiest example is electron capture. Electron capture is a decay process where an electron is captured by a proton and converted into a neutron. If the electronic wavefunction doesn't sufficiently overlap with where it needs to be for the weak force to mediate electron capture, then the decay rate will change. Here is a paper where the authors lengthen the half-life of a beryllium-7 atom by encapsulation with palladium atoms.

While I didn't see any examples in my (admittedly surface-level) search just now, I would also put forth that this likely holds for some other decay processes, such as beta decays. Beta decay occurs when a quark in a nucleon decays into a quark of the opposite type (called "flavor") and emits a W boson that itself decays either to a positron or to an electron* depending on if it was a proton $\rightarrow$ neutron decay (positron emission) or a neutron $\rightarrow$ proton decay (electron emission). Both of these processes produce a charged particle, and thus I imagine that screening of the local electron environment affects their rates (similar to how a chemical reaction is less favorable if there is a high activation energy, etc). Brief aside, all of this isn't particularly relevant for alpha decays (emission of a helium-4 nucleus) due to the fact this decay is due to interactions with the strong nuclear force and thus the impact of nuclear binding energy is significantly greater in magnitude than impact from the Coulombic interactions.

*and the relevant antineutrino

In reference to your final question, radioactivity is determined explicitly by decay process and decay rate—just like half-life—and so a shift in half-life would imply a shift in radioactivity a priori. The magnitude of change likely isn't enough that it would practically impair or accelerate radioactivity though, especially for the heavier elements where chemical bonding would be less relevant due to the larger role of valence electrons in chemical bonding than core electrons.

thelocalsage
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  • I'm not convinced on beta decays, but have requests in for a few review papers from some time ago. In electron capture you need an electron to capture, and the electron density near the nucleus provides them. Considering it as an overlap integral between initial state and final state, you can impact the initial state. In beta decay, extant electrons around the nucleus really don't impact the decay channel (the final state), so might not impact the rate. – Jon Custer Aug 16 '22 at 21:50
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    And, the second comment by Mithrion pointing to https://chemistry.stackexchange.com/questions/85425/is-it-possible-to-speed-up-radioactive-decay/85435#85435 contradicts my assertion on not impacting the final state, so, yes, beta decay is another option. Good call! – Jon Custer Aug 16 '22 at 21:52
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    While the answer outlines some of the rare exceptions, it should also be worth emphasizing that these are very rare. Most radioactive nuclei will have the same rate of decay whatever chemical environment they are found in. – matt_black Aug 17 '22 at 13:36
  • @matt_black yeah I tried to mention it a bit, but you're right I should place more emphasis on it. I'll update it now! – thelocalsage Aug 17 '22 at 16:24
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    This makes me think of a hypothetical machine which can switch on/off radioactivity by making and breaking chemical bonds. – suyashsingh234 Aug 18 '22 at 19:32
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The half-life of a radioactive nucleus is not affected by the molecule or the ion containing this nucleus. It has been demonstrated plenty of times in the beginning of the 20th century.

Maurice
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    This is not true, see https://physics.stackexchange.com/questions/713918/can-a-beryllium-7-nuclei-be-stable-if-it-has-lost-its-electrons/713923#713923 - elements that decay by electron capture are sensitive to the electronic environment. Note the paper on experimental measurements of the half-life of $\ce{^7Be}$ in different chemical compounds, and the ability to see differences in the half-lifes. – Jon Custer Aug 16 '22 at 19:20
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    @Jon Custer. OK. I did not know about $\ce{^7Be}$. Is Beryllium-7 the only nuclid where half-life can be modified by change of electronic environment ? – Maurice Aug 16 '22 at 20:35
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    basically any electron capture lifetime can be changed. The extreme is still fully stripped ions leading to infinite lifetime (seen in cosmic rays). $^{7}Be$ has the nice properties of (1) being proposed as a target by Segre and Wiegand in 1949, and (2) having a tractable lifetime of a bit less than 2 months allowing fairly short experiments. Citations for Segre's paper indicate a variety of longer review articles over the decades, so it seems unlikely that $^{7}Be$ is the only one. – Jon Custer Aug 16 '22 at 21:42
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    @EdV - indeed, per ENSDF, normal $\beta^{-}$ decay is 4.33E10 years, but fully ionized is only 32.9 years, called bound state $\beta^{-}$ decay as referenced in https://chemistry.stackexchange.com/questions/85425/is-it-possible-to-speed-up-radioactive-decay/85435#85435 in a comment above. Still waiting on my library to get me a review article I've requested... – Jon Custer Aug 17 '22 at 16:51
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    @EdV - I'm learning a lot here too, so no harm done at all, in fact pushing to find more is turning out to be quite interesting... – Jon Custer Aug 17 '22 at 17:23
  • @EdV - Even more interesting, $^{163}$Dy is stable as a neutral atom, but has a half life as $^{163}$Dy$^{+66}$ of 48 days because of bound-state $\beta$ decay. – Jon Custer Aug 17 '22 at 19:39