Abstract

The nondecay probability of an unstable particle at a definite moment of time is investigated provided this particle existed at all earlier observation moments separated with the time interval Δ. Using the usual postulates for quantum measurements it is proved that this probability is described by the exponential function of Δ>0, and it tends to 1 as Δ → 0. An approximate formula is found for the effective decay width Γ(Δ) appearing in the case of multiple measurements. It is shown that Γ(Δ) → 0 as Δ → 0. For Δ → ∞, the width Γ(Δ) → Γ0, with Γ0 being the standard decay with in Weisskopf-Wigner theory. At finite δ's Γ(Δ) may be smaller or greater than Γ0 depending on the parameters of the theory.