Two methods for radiocarbon measurement are available at the CAIS:
Liquid Scintillation Counting (LSC): Using the
LSC method, the amount of C-14 in a sample is determined
by measuring the amount of radioactive decay in the sample.
Carbon-containing material is converted first into carbon
dioxide gas, and then eventually into high purity benzene
through a process called benzene synthesis. The benzene is
measured for C-14 activity using low-level liquid scintillation
counting techniques and instrumentation, and the result is
compared to NIST standards and corrected for background activity.
Accelerator Mass Spectrometry (AMS): Using AMS, the amount of C-14 in a sample is determined by directly counting carbon atoms in the sample, and comparing the relative abundance of the three naturally-occurring isotopes of carbon, C-14, C-13, and C-12. Standards and backgrounds are measured coincident with samples in making the determination of C-14 activity.
Considerations: Sample size and homogeneity should be considered when choosing the best method for radiocarbon measurement. AMS offers the capability of measuring C-14 in extremely small samples comprised of as little as a single milligram of carbon, with the potential to go even smaller. This is particularly useful when the sample material is rare or precious. However, with small sample size comes an inherent variability that could potentially result in an incorrect representation of C-14 activity. Other considerations include sample analysis turnaround time and cost. LSC offers a faster turnaround time and is less expensive than AMS. The precision of both the LSC and AMS methods is good, with one-sigma standard deviations.
For further information contact Dr. Alex Cherkinsky (706) 542-6111 or Dr. Randy Culp (706) 542-6122