Recoil after alpha decay

Alpha decay leads to a decrease of the atomic number by two units, Z — Z — 2, and causes an expansion of the electron shell, as illustrated in Fig. 9.5 for the a decay of radioisotopes of Bi. EHffercnccs in the binding energies arc marked for electrons in the inner shells. Furthermore, there arc two surplus electrons after a decay. However, in the case of a decay the excitation effects due to the change of the atomic number are relatively small compared with the recoil effects that have been discussed in the previous section, with the result that the recoil effects dominate. 

Emanation is the process by which radon is transported from a solid to a gas or liquid medium. At the soil particle level, radon gas is transferred from soil particles into pore spaces (gas- or liquid-filled spaces between soil particles) primarily by alpha recoil. Alpha recoil occurs after radium decays by emitting an alpha particle. After the particle is ejected, the resulting radon atom actually recoils in the opposite direction. Alpha recoil results in breaking of chemical bonds in the solid. 

Fig. 22 Schematic illustration of the RDT technique. Prompt gamma rays are observed at the target position. The nucleus then recoils out of the target and flies through the separator where it is implanted in a Si detector. After a while the nucleus decays by a characteristic alpha decay in the same position, identifying the earlier implant. In the bottom panel a calcnimetric electron signal additionally indicates the decay of an isomeric state...

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