The Original Schrödinger's Cat Revisited: The First Decay

Schrödinger's original Cat explicitly refers to both “one of the atoms decays” and “the first atomic decay.” This paper examines the first decay occurrence of a finite radioactive sample. Let t₁ denote the time of the first atomic decay. Existing quantities such as half-life, decay constant, mean lifetime, and activity describe radioactive decay collectively, whereas t₁ identifies the first actual decay occurrence of a particular sample. Probability theory contains well-developed treatments of first occurrences, including waiting times, first-arrival times, first-passage times, hitting times, and related stochastic processes. Such treatments require information about the underlying process. This raises two distinct questions for radioactive decay: what information determines the probability distribution of t₁, and what information, if any, determines the actual t₁ of a particular finite sample of a given radioactive isotope before the first decay occurs?