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Could atoms be encouraged to decay?

If radioactive material is made of atoms that have too much energy to be stable long term, could they be encouraged to decay in a process akin to the stimulated emission of light?
John Birkett from Edinburgh (age 25-34)

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2 Responses

  1. For alpha decay there is an energy barrier to overcome before the nucleus can eject an alpha particle – in essence the alpha particle quantum-mechanically “tunnels” out. For beta(minus)-decay the weak interaction changes one of the quarks inside neutron, turning it into a proton end ejecting an electron. Both of these are quantum mechanical events and are random so it is hard to see how they can be affected externally (although that doesn’t mean to say that it isn’t entirely possible). We can slow down decay by moving the particles near the speed of light but that would have the opposite effect to the one desired! For gamma decay of nuclei, which usually happens when a nucleus is in a “meta-stable” state we can stimulate emission. A prime example is the meta-stable state of Hafnium-178; Hf178m, which normally has a half-life of 31 years. If this nucleus is bombarded with x-rays of the right energy it can be stimulated to decay. This material has been suggested as a nuclear power source that can be turned on or off by turning on or off an X-ray source. In fact it was suggested as a possible power source for nuclear aeroplanes. It has similarly been suggested as a mini nuclear explosive as 1kg decaying simultaneously would release as much energy as about 10 tonnes of TNT.

  2. There are a number of circumstance in which we can already alter the rates of decay of nuclear states. In some forms of beta decay the process proceeds by the capture of an atomic electron by a proton with the emission of a neutron and a neutrino. If we remove all of the electrons from the atom so that we have the bare nuclei then this process is no longer possible. This has been done at the GSI laboratory in Darmstadt, Germany, one of Europe’s most important nuclear physics laboratories. The radioactive nuclei are produced in high energy collisions between stable nuclei from a synchrotron and light nuclei in a thick target. The unstable nuclei produced are separated and identified in flight and injected into a high-vacuum storage ring. They lose all of their electrons in the initial violent collisions. They then circulate in the storage ring until they decay. Without their electrons they decay at a different rate from the same “fully clothed” nuclei stopped in material. This situation mimics what happens in stars, where the nuclei are part of plasma and the nuclei are stripped of electrons.
    A similar process has been observed in the decay of certain excited states of nuclei, where the main decay process involves the atomic electrons – so-called electric monopole transitions. We have studied such decays for nuclei stripped of electrons and their lifetimes are greatly lengthened by the removal of this decay mode.
    Finally as mentioned in other answers so-called nuclear isomers, states with very long half-lives could be made to decay more rapidly if the emission was stimulated. This has applications both benign or malevolent. so far there has been no case where we have found an isomeric state that can be conveniently stimulated to decay, despite claims to the contrary from the U.S.A.

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