Charge Creation and Reset Mechanisms in an Ion Guide Isotope Separator (IGIS)

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Abstract
An ion guide permits direct mass separation of primary recoil ions created in radioactive α-decay. About 2% of the decay products are neutral and more than 99% of the rest are in a charge state + 1 when leaving the guide. The atomic processes which produce a wide charge-state distribution of the recoil ions from + 1 up to + 40 and finally reset them to the state + 1 are described as they appear from a survey of literature. Three processes which may create charged recoils in the ion guide are suggested: Auger cascade following a nuclear internal conversion, internal ionization during alpha decay and stripping in collisions with helium atoms. Charge reset may take place via several electron-capture processes mainly between the recoil ions and helium atoms down to the charge state + 2. The step from + 2 to + 1 can be understood in terms of charge-transfer reactions between the ions and impurity molecules within helium. Such reactions are unable to neutralize the remaining charge state + 1.