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As far as I understand, there are forces in opposition within a nucleus: the protons are pushed apart by their positive charge, but held together (along with neutrons) by the strong force. For a nuclide to be stable, the forces must be balanced.

In this chart, it appears that the type of radioactive decay that occurs in an atom is determined by its composition; eg, those that undergo beta minus decay have excess neutrons (compared to stable isotopes) and those that undergo beta plus decay have excess protons.

Suppose you had a sample with a mix of radioisotopes representing various types of decay. If you could wave a magic wand and weaken or strengthen one of the atomic forces throughout that sample, would some of the radioisotopes decay faster than usual and others slower?

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  • $\begingroup$ Note that some unstable nuclei (eg, potassium-40) can do both types of beta decay. That is, they become more stable by converting a neutron to a proton, or by converting a proton to a neutron. $\endgroup$
    – PM 2Ring
    Jun 25, 2020 at 13:32

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In addition to overlap integrals, decay rates depend on the energy gaps between the initial state and the final state, with high-energy decays proceeding more rapidly than low-energy decays with the same quantum numbers. The spectrum of nuclear excited states is quite complex and depends on many factors, and a change to one of the couplings that defines the strong force would cause some states' energies to increase and some to decrease. So a small tweak to the strength of the strong force would cause some decay transitions to go faster and others to go slower, depending on the effects of the tweak on the energies of the initial and final states in the decay.

This argument was used a few years ago to make a controversial claim that the electromagnetic fine structure constant, $\alpha$, may have a value which differs by a few parts per million over the volume of the visible universe. In that case the observable was the (relative) wavelengths of light in the (redshifted) spectra of heavy atoms in distant galaxies. A small change in $\alpha$ would increase the energy of some transitions and decrease the energy of others, in a way that is both predictable and observable.

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  • $\begingroup$ "This argument was used a few years ago to make a controversial claim that the electromagnetic fine structure constant, α, may have a value which differs by a few parts per million over the volume of the visible universe." Do you mind if you include a reference to this, please? Thank you. $\endgroup$
    – Stratiev
    Jun 25, 2020 at 15:42
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    $\begingroup$ @Stratiev Here's a recent paper on the subject, whose bibliography would probably lead you to a literature review. If you find an overview reference that satisfies you, please consider editing a better link into my answer. $\endgroup$
    – rob
    Jun 25, 2020 at 17:18
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Using Fermi's golden rule one can express the decay rate of elementary particles (and, by extension, of composite isotopes). One can see that this rate is proportional to the transition amplitude, which is computed through Feynman diagrams in Quantum Field Theory. These diagrams tend to be proportional to the coupling constants, which control the strength of the interactions.

So in principle changing the values of these constants would change the amplitudes, which in turn change the decay rates. Due to interactions (or equivalently due to virtual particle production), however, several different coupling constants (EM force, weak force, strong force) can play a role in the calculation of the amplitude and they might have both a positive and a negative contribution (or in general complex) to the amplitude so it is not easy to see precisely which atoms will decay faster and which ones slower.

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