The Accelerator Mass Spectrometry (AMS) technique for radiocarbon dating accounts for a substantial number of the analysis requests Beta Analytic receives each day. There can be considerable advantages to using the AMS technique in many dating applications, making it possible to extend radiocarbon dating into many new areas of research. AMS also permits applications in important situations that cannot be dated by the radiometric dating technique.
Beta Analytic has been providing routine AMS radiocarbon dating services to the international scientific community since 1983. The company routinely delivers AMS radiocarbon dating results within 14 business days.
The AMS measurement is done on graphite produced by hydrogen reduction of the CO2 sample over a cobalt catalyst. The CO2 is obtained from the combustion of the sample at 800°C+ under a 100% oxygen atmosphere. The CO2 is first dried with methanol/dry ice then collected in liquid nitrogen for the subsequent graphitization reaction. The identical reaction is performed on reference standards, internal QA samples, and backgrounds to ensure systematic chemistry.
The analytical result ("BP" or "pMC") is obtained by measuring sample C14/C13 relative to the C14/C13 in Oxalic Acid II (NIST-4990C) in one of our multiple in-house particle accelerators using SNICS ion source. Quality assurance samples are measured along with the unknowns and reported separately in a "QA report". We require results for the QA samples to fall within expectations of the known values prior to accepting and reporting the results for any given sample.
The d13C used to correct for isotopic fractionation associated with the analysis is obtained by placing a small portion of the sample graphite into an elemental analyzer (EA), connected directly to an isotope-ratio mass spectrometer (IRMS). The EA oxidizes the organics to CO2 and the IRMS provides the separation of the carbon masses and calculation of the d13C.
Your samples are included in a “full wheel" of graphite targets, including backgrounds, modern and known-age standards prepared by Beta Analytic. These additional materials undergo the same chemical pretreatments and graphite syntheses as do your samples. This is indispensable for precision radiocarbon dating. They are interspersed throughout the accelerator wheel to provide reference measurements for the age calculations and verifications. Only with rare exception that it is acceptable to analyze unknowns prepared separately from the reference standards.
Results of AMS carbon 14 dating analysis are reported within 14 business days for the Standard AMS Delivery Service, and within 6 business days for the Priority AMS Delivery Service. These quoted delivery times are independent of the quantity of samples sent for radiocarbon dating analysis. When your samples are received, we quote an expected terminal delivery date in a correspondence letting you know the samples arrived safely.
Beta Analytic begins the chemical treatments immediately. At the same time, backgrounds, modern and known-age samples are also being carbon dated. The complete wheel of samples is sent to the accelerator. We then calibrate the results to calendar years, apply isotopic ratio corrections (where needed), and report the carbon 14 dating results to you.
More researchers are using a mix of both AMS and radiometric dating in order to properly answer the complex questions posed by their research. The AMS radiocarbon dates are systematically the same or consistent with any of the radiometric dating results provided by Beta Analytic since 1979.
In addition to reference standards, we circulate "blind" known-age samples, which were measured radiometrically at Beta Analytic to ensure non-biased results. Also, we have an unprecedented quality control program (which we would be glad to send you a copy). Furthermore, we participate in all international standard measurements and use international conventions for our radiocarbon dating calculations.
We are always available to answer your questions.
Please don't hesitate to call, fax, or e-mail us. We have many years experience in all aspects of radiocarbon dating; you're very welcome to take advantage of this expertise, mail to firstname.lastname@example.org.