User:Awc/Changing decay rates
Changing decay rates
Wikipedia: Changing decay rates
The radioactive decay modes of  and  are known to be slightly sensitive to chemical and environmental effects which change the electronic structure of the atom, which in turn affects the presence of 1s and 2s electrons which participate in the decay process. A small number of mostly light nuclides are affected. For example  can affect the rate of electron capture to a small degree (generally less than 1%) depending on the proximity of electrons to the nucleus in beryllium. In 7Be, a difference of 0.9% has been observed between half-lives in metallic and insulating environments. This relatively large effect is because beryllium is a small atom whose valence electrons are in 2s s which have a large degree of penetration very close to the nucleus, and thus are subject to electron capture.
A number of experiments have found that decay rates of other modes of artificial and naturally-occurring radioisotopes are, to a high degree of precision, unaffected by external conditions such as temperature, pressure, the chemical environment and electric, magnetic or gravitational fields. Comparison of laboratory experiments over the last century, studies of the Oklo nuclear reactor, and astrophysical observations of the luminosity decays of distant supernovae (which occurred long ago so the light has taken a great deal of time to reach us), for example, strongly indicate that decay rates have been constant (at least to within the limitations of small experimental errors) as a function of time as well.
On the other hand, some recent results suggest the possibility that decay rates might have a weak dependence (0.5% or less) on environmental factors. It has been suggested that measurements of decay rates of],  and  exhibit small seasonal variations (in order 0.1%), proposed to be related to either solar flare activity or distance from the sun. However, such measurements are highly susceptible to systematic errors, and a subsequent paper  has found no evidence for such correlations in a half-dozen isotopes, and sets upper limits on the size of any such effects. However, research at  indicates that the rate of radioactive decay may not be truly constant, but slightly influenced by solar flares due to variations in  flux.
Chemical and environmental influence
Highly ionized heavy ions (Bound-state beta decay)
- Woodmorappe's Billion-fold Distortion of 187Re Radioactive Decay or How Young-Earth Creationists Misapply Conditions in the Cores of Hot Massive Stars to their 'Genesis Earth' - "Woodmorappe does not tell us the temperatures that are required to remove all of the electrons from a 187Re atom. However, he later admits that accelerating the lutetium-176 (176Lu) decay rate would require an environment with a MINIMUM temperature of 200 million degrees Kelvin (K). This is about 13 times hotter than the core of the Sun!!"
- Billion-fold acceleration of radioactivity demonstrated in laboratory, John Woodmorappe
- Direct observation of the bound-state beta-decay of fully-stripped 207Tl, Boutin (GSI) et al.] - "This process being weak in the terrestrial decays of neutral atoms, plays a significant role in stellar nucleosynthesis, where the extreme temperature and pressure lead to an intensive strippingo f the electrons. In the latter case drastic changes in nuclear decay rates can occur. This exotic decay mode was first observed in a pioneering expriment at the GSI facility with fully-stripped 163Dy . Subsequently also 187Re , 206Tl and 207Tl  were investigated experimentally. ... The calculated half-life T1/2 = 250 s, as well as the ratio λb/(λb + λc) = 0.146, are in good agreement with the experimental results presented above..."
- FIRST OBSERVATION OF BOUND-STATE BETA DECAY, 1992. AIP Physics News Update, ref. to PRL.
Influence of the Sun
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