Evaluating the effectiveness of bomb-pulse dating in the investigation of forensic anthropological human remains.
Miss Eden Johnstone-Belford1, Professor Soren Blau, Professor Stewart Fallon
1Monash University, Southbank, Australia
When human remains are discovered, the identification of the decedent is the initial aspect of the forensic medical investigation. The determination of year of death can provide vital information in the identification of the decedent, by either including or excluding missing persons to whom the remains may belong. In cases of skeletonised, or badly decomposed remains, estimating the year of death can be difficult, due to high rates of variation in decomposition due to taphonomic factors. Bomb pulse dating, a technique which is unaffected by external factors, directly compares levels of 14C within human tissues to atmospheric levels, and can provide an estimate of the year of death.
This study measured the 14C content in samples of hair, nail and puparia collected from donors at the Australian Facility for Taphonomic Experimental Research (AFTER). A total of 14 hair, 11 nail and 13 puparia samples were collected from 18 donors whose bodies were placed outdoors on the ground surface between 2016-2018. All donors were born between 1924-1957, and died between 2016-2018, with a mean age at death of 76.
Sample analysis was undertaken at the Radiocarbon Dating Laboratory at the Australian National University (ANU). Hair and nails were de-fatted using a mixture of dichloromethane and methanol (2:1), before undergoing an ABA pre-treatment involving 0.1 M HCL (30 mins), 0.1 M NaOH (1 hour), and 0.1 M HCL (30 mins). The nail samples required a second defatting treatment before drying could occur. Puparia were physically cleaned to remove dirt and debris, before a 30-minute 0.1 M HCL soak.
Pre-treated samples were placed into quartz tubes containing an oxidation agent (CuO) and silver, and torch sealed under vacuum, before being combusted for 6 hours at 900C. Graphitisation was then carried out, followed by measurement by the accelerator mass spectrometer at the ANU radiocarbon dating laboratory (followed published standard procedures). All data is background subtracted using 14C free coal, corrected for 13C and reported as F14C.
Results and Conclusion:
All samples were found to contain 14C levels consistent with modern post 1950 levels. Of all the samples, 71% produced a calibrated YOD range which encompassed the actual YOD, and all samples contained 14C concentrations that were within 4 years of the atmospheric concentrations at the known year of death.
The nail samples provided the most accurate year of death estimations, with 91% correctly predicting YOD. Hair samples were also highly accurate, with a 79% correct prediction rate. Both hair and nails were found to have a lag time of 0-1 years.
Puparia was found to have the highest levels of 14C, and as such, were the least consistent with the actual YOD. However, while only 46% contained 14C levels consistent with atmospheric levels at the time of death, all puparia samples provided YOD estimates which were within 4 years of the actual year of death.
Based on the results of this study, hair, nail and puparia should be considered as useful samples to obtain accurate estimates for YOD using bomb pulse dating.
Biography to come