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→The curious case of Beryllium-7
==The curious case of Beryllium-7==
==The curious case of Beryllium-7==
Radioactive decay rates are very stable and repeatable. In fact, this phenomenon was remarked upon by [[Henri Becquerel]] in 1896, almost immediately after discovering radioactivity. Prior to that time, all properties of elements (other than their atomic weight, which has to be constant due to conservation of mass) were dependent on the chemical state. An element's color, solid/liquid/gas state, oxidation/reduction state, and so on, all depended on what chemical compound it was in. But Becquerel noticed that the radioactivity of Uranium remained constant no matter what its chemical state.
The reason is that all those properties are properties of the electron cloud. Radioactivity comes from the nucleus, far from the electrons. Though of course Becquerel didn't know that. Radioactivity proceeds from the properties of the quantum mechanical wave function, which depends on the Schrödinger equation. The electron cloud has almost no effect on this.
Electron capture events are the exception to this. The probability of an electron capture depends on the availability of electrons in the vicinity of the nucleus. Things that change the location of electrons can change the radioactive decay rate.
In fact, if the atom is completely ionized, the electron-capture decay rate essentially goes to zero and the half-life essentially goes to infinity. Furthermore, the normal beta-plus decay rate can change because it becomes easier for ejected electrons to leave the vicinity of the nucleus. Ionizing Rhenium-187 has been observed to accelerate its decay by a factor of one billion.<ref>https://creation.com/billion-fold-acceleration-of-radioactivity-demonstrated-in-laboratory billion-fold acceleration of radioactivity demonstrated in laboratory (a creationist website)</ref>
Electron capture events generally involve the innermost electrons, in the "1s" orbital. Chemical properties (oxidation, reduction, etc.) involve the "valence" electrons in the outermost shell. So chemical effects on radioactivity are almost never observed.
But there is a well-known exception to this. Beryllium, with an atomic number of 4, has only two electrons in the "1s" orbital and two in the "2s" valence orbital. The latter electrons are so close to the nucleus that chemical changes can have a small but measurable effect on the decay rate. Beryllium-7 is an electron-capture nucleus, decaying into Lithium-7 with a half-life of 53 days. This half-life can vary by up to 1.5% due to the chemical state.<ref>https://creation.com/radioactive-decay-rate-depends-on-chemical-environment radioactive decay rate depends on chemical environment (a creationist website)</ref>
==References==
==References==