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

Abstract

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.

Fig. 1

The main decay chain and daughter products. The half-life of each isotope is indicated. Only the dominant decay pathways are shown and low-probability branches (e.g., to ) are omitted for clarity.

Fig. 2

(a) Difference between the true and calculated elapsed time since death using the two pairs of isotope number ratios. Note that no uncertainty was assumed for the input quantities to the model. The RTDC could calculate the accurate time of death to within seconds. (b) Distribution of errors in post-mortem interval estimation under constant radon exposure conditions, showing Gaussian distribution pattern of discrepancy between predicted and actual time since death.

Fig. 3

This figure demonstrates how minimization is used to estimate the time of death based on forward model data. A single postmortem measurement, which did not match accurately the true time of death, was also analyzed using double measurement approaches. Under lifetime-varying radon exposure, the minimization curve deviates from the forward model (true ratio curve) when using a single postmortem measurement. In contrast, the dashed line representing the double measurement approach closely matches the forward model. (a) shows the minimization result for isotope ratio and (b) the minimization result for isotope ratio .

Fig. 4

(a) Difference between the true and calculated elapsed time since death using two pairs of isotope ratios. The study employed a double measurement approach, where two pairs of isotopes were measured twice at separate time intervals. Note that no uncertainty was assumed for the input quantities to the model. The RTDC could calculate the accurate time of death to within 10 minutes. (b) Distribution of optimization errors in post-mortem interval estimation under varying radon exposure conditions, showing Gaussian distribution pattern of discrepancy between predicted and actual time since death.