Random Wilson cloud-chamber photographs of cadmium and molybdenum foils show that the double negatron half-life is greater than or equal to 1×{}10¹⁷ years in Cd¹¹⁶ and 3×{}10¹⁷ years in Mo¹⁰⁰, and that the double positron half-life is greater than or equal to 6×{}10¹⁶ years in Cd¹⁰⁶ and 4×{}10¹⁸ years in Mo⁹². The background appears to be primarily caused by Compton electrons and photoelectrons ejecting other electrons on their way out of the foil and by photons that suffer two Compton scatterings while traversing the foil.
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R. G. Winter (1955) studied this question.
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