Standard Service turnaround is estimated between 4-6 weeks. Express Service turnaround is guaranteed 15 business days (bone) or 10 business days (all other services), from date of submitter approval. The submitter will be notified of any delay in reporting.
Once AMS measurement is complete, our data analysts and quality control personnel finalize the data and generate the report. Submitters will receive a pdf report at the email address provided on the Submission Form. Our standard report provides:
- DirectAMS ID
- Submitter ID
- Sample type
- Fraction of modern, 1-sigma error
- Radiocarbon age, 1-sigma error
Results are presented in units of percent modern carbon (pMC) and the uncalibrated radiocarbon age before present (BP). All results have been corrected for isotopic fractionation with an unreported d13C value, measured on the prepared carbon by the AMS. the pMC reported requires no further correction for fractionation.
Calibrating Radiocarbon Age
DirectAMS results are not calibrated, nor corrected for the marine reservoir effect, as a number of site-specific calibration curves may be considered. Calibrations performed by programs like CALIB and OxCal incorporate the compilations of INTCAL13. Such programs can be utilized generally or tailored for specific needs. The CALIB program is capable of performing marine calibrations as well as local reservoir corrections, useful in Shell dating.
Not Distinguishable from Background
After ~40,000 years, less than 1% of the original 14C remains in a sample, reducing the precision of measurement. For DirectAMS, any measurement that falls below 0.369 pMC, exceeding 45,000, is not able to be distinguished from the measured level of background carbon.
Avoiding unexpected results starts at the beginning, with appropriate sample selection and control of potential contamination. Appropriate pretreatment is required to ensure potential contaminants have been eliminated and is vital to the accuracy of results. It is important to provide contextual information on the Submission Form, as many potential contaminants can be assumed based on context (e.g. rat urine in desert environments). Portioning and chemical pretreatment protocols are then tailored to address site-specific contaminants.
Careful consideration of the known caveats that influence radiocarbon dates and data interpretation is also key in understanding AMS data. The Old Wood Effect and the Carbon Exchange Reservoirs are just two well-characterized pitfalls for radiocarbon dating.
If unexpected results are received, please contact us immediately with concerns. Numerous records are maintained throughout the handling of samples. We are able to review:
- Appearance of original sample submission
- Preparation notes before pretreatment, contextual information
- Pretreatment steps performed and any pertinent observations
- Organic combustion or shell digestion quantities
- Concurrently processed and measured samples
- Data analysis observations
- Results of standards and blanks measured with the sample(s)
Repeat analysis will automatically be performed at no additional charge if an error in processing cannot be eliminated. In situations where other radiocarbon laboratories have reported different results than those provided by DirectAMS, we will provide repeat processing and analysis, with additional consulting from archaeological/geological experts, at the standard service fee.