A novel method for assessing postmortem interval using radon radioisotopic decay - an internal radon 'time of death clock'.

Estimating the postmortem interval (PMI)-the time since death-remains a longstanding challenge in forensic and biological sciences due to the complex influence of environmental and physiological variables. Here, we present a novel computational framework that leverages the physical principles of radioactive decay to estimate PMI using the relative isotope abundances of radon progeny ([Formula: see text], [Formula: see text], and [Formula: see text]) in biological tissue. Our approach models the decay chain of inhaled [Formula: see text] and solves the associated system of differential equations to determine PMI based on isotope ratio dynamics. A key innovation is the use of paired measurements taken at two postmortem time points to capture the time-derivative of the decay curve, enhancing solution uniqueness, reducing dependence on prior exposure history, therefore minimizing error. Monte Carlo simulations were employed to assess model performance. If validated empirically, this approach lays the groundwork for a physics-based method for PMI estimation with potential applications in forensic science and radiation biology.