BETA Analytic Final Report

BETA Analytic’s final report includes the individual analysis method, the delivery basis, the material type, and the individual pretreatments applied. The final report will be sent by email and uploaded in the client’s secure online results portal.

 

Archaeology | Groundwater

Results Online Archive

All Beta Analytic clients have 24/7 access to results via their secure online archive.

Pretreatment Methods

Beta Analytic’s pretreatment methods are reported along with each radiocarbon dating result. All necessary chemical and mechanical pretreatments of the submitted material are applied at the laboratory to isolate carbon 14, which may best represent the time event of interest.

When interpreting the radiocarbon dating results, it is important to consider the pretreatments. Some samples cannot be fully pretreated, making their carbon 14 ages more subjective than samples that can be fully pretreated. Some materials receive no pretreatments.

AMS Dating Procedure

AMS carbon dating starts with the reduction of the sample carbon to graphite (100% C) along with preparation of standards and backgrounds. The graphite is then analyzed for carbon 14 content in an accelerator mass spectrometer. The final result is corrected for isotopic fractionation then converted into a calendar-calibrated date.

Radiocarbon Age and Calendar Calibration

The “Conventional Carbon 14 Age” is the result after applying carbon 13-carbon12 corrections to the measured age and is the most appropriate radiocarbon age. Applicable calendar calibrations are included for organic materials and freshwater carbonates between 0 and 42,000 BP. If certain calibrations are not included with a report, the results were either too young, too old, or inappropriate for calibration.

Beta Analytic started using the INTCAL13 database in February 2014 to calibrate radiocarbon age to calendar years. In previous years, the laboratory has been using the INTCAL09 database. If you need to have your results recalibrated, please email us at lab@radiocarbon.com.

Beta Analytic’s calibration program takes into account the errors of each individual tree-ring measurement on the calibration curve and then employs a “spline fit” mathematics procedure to the data as per Mathematics use for calibration scenario – A Simplified Approach to Calibrating C14 Dates, Talma, A.S., Vogel, J.C., 1993, Radiocarbon 35 (2): 317-322)

Standard Deviation

Beta Analytic does not report standard deviations of less than +/- 30 BP for single measurements since this can lead to a misinterpretation of the accuracy of the results. The only time standard deviations of less than +/-30 years BP are reported is when the lab runs a unique sample fraction (e.g. a single twig, seed, bone, shell) 2 or 3 times on portions that have been pretreated, graphitized, and AMS counted independently of each other. This ensures that as much as possible, any sample, laboratory or counting bias is accounted for in both the accuracy and quoted sigma. Once 2 or 3 measurements have been made, the lab then performs a weighted average age and error calculation and reports those values.

The detection efficiency in particle accelerators is very high, as such extremely low sigmas are possible simply by measuring more reference standards and/or counting the unknown sample for longer periods of time. While this may produce a very small numerical sigma value, that value is strictly limited to the “determinate errors” associated with counting the 14C modern standard (oxalic acid), unknown sample, and chemical blank (background).

Quoted sigmas on radiocarbon dates, unfortunately, cannot take into account “indeterminate errors” such as sample homogeneity, chemistry, and to a lesser extent, detector stability. As good as AMS machines are, simultaneous measurements of the 14C modern standard, sample, and blank cannot be done so small shifts up or down in the detection efficiency of the AMS over the course of the run will affect the accuracy of the result, which at times are outside of the smaller quoted sigma values possible. This is why Beta Analytic only quotes smaller errors by going through the additional effort and cost of running samples multiple times.