Sample preparation and radiocarbon measurement
Penn State's Radiocarbon Laboratory provides radiocarbon measurements on carbon-bearing materials spanning the last 45,000 years. This includes materials such as wood, charcoal, bone, carbonates, and soils from the Pleistocene and Holocene time periods.
The lab's services are available to Penn State researchers and external academic and industrial clients.
Results and research support
Combustion and graphitization
Purified samples are then sealed on a vacuum line, combusted using a Barnstead programmable muffle furnace, and graphitized: combusted CO2 is converted to graphite via hydrogen reduction onto a Fe catalyst.
Once graphitization is complete, AMS 14C measurements are made through the Radiocarbon Laboratory.
Preparation laboratory equipment
The Radiocarbon Prep Laboratory at Penn State includes both dry and wet-lab areas for sample storage and preparation with standard laboratory equipment including:
- Fume hood
- Barnstead NanoPure water purifier
- Drying oven
- Freezer
- Freeze-dry lyophilizer
- Balances
Preparation systems and quality controls
The combustion and graphitization lines are made with Swagelok Ultra-Torr fittings on stainless steel drawn by oil-free Pfeiffer turbo pumps and have been modeled on lines in use at KCCAMS at the University of California, Irvine. The lab has been swiped for the presence of 14C tracer and maintains constant quality controls on radiocarbon processing with KCCAMS through use of international and internal known-age lab standards (e.g., OX-1, OX2, Prophet River Wood, Beaufort Whale, FIRI secondaries).
Accelerator Mass Spectrometer
Equipment full name
National Electrostatics Corporation 500kV 1.5SDH-1 Compact Accelerator Mass Spectrometer (AMS)
Description
The Radiocarbon Laboratory is equipped with a National Electronics Corporation compact AMS with a 0.5MV accelerator (NEC 1.5SDH-1) installed in April 2016.
The AMS is optimized with a second einzel lens and solid ion source capable of routinely generating 12C- beam currents in the range of 120-150 µA on small (0.3-0.7 mg C) samples, roughly twice the current of similar low-energy AMS systems available to researchers. This allows for high-precision measurements of small individual samples and reduces the need for bulk or mixed materials to generate sufficient carbon for measurements. Thus, changes in 14C can be measured in incremental growth samples, such as:
Incremental growth samples
- Tree rings
- Marine shell
- Speleothems
- Seeds
- Leaves
- Hair
- Other biologicals tissues
Technical specifications and measurement precision
The primary modifications impacting analytical measurement error are the use of a spherical ionizer ion source operating at high cathode voltage (7V) to generate intense C- beams, plus injection beam line changes for better ion-optical matching to the accelerator. The injector modifications include a second einzel lens plus an increased ion source bias voltage running at 47.5 kV combined with a redesigned large-gap injector magnet (DF01319; Beverly et al. 2010).
These alterations allow for analytical error in the 2-3‰ range for near modern samples under currents of up to 200 µA of 12C- and routinely generating 120-150µA of 12C- from ~0.7mg C samples. Radiocarbon ages are corrected for mass-dependent fractionation with δ13C values measured on the AMS and normalized to OXII standards (SRM-4990C). Sample sizes of 0.7mg C are routine, with somewhat lower precision on samples smaller than 0.3mg C. Any carbon-bearing material may be analyzed using the AMS.
How it works
Ionization and acceleration
An accelerator mass spectrometer measures the amounts of different isotopes within a sample. For carbon dating, the process starts in an ionizing chamber, where sample carbon atoms are given a negative charge and initially accelerated to an injection magnet where the particle beam is split by mass and sequentially injected into the accelerator.
Isotope separation and measurement
Penn State's accelerator imparts almost 1 million electron volts to the ions and breaks apart interfering molecules. A larger analyzing magnet separates the sequential beam by bending the ions according to mass and directing them into two Faraday cups (for 12C and 13C mass) and a solid-state detector (for 14C mass radiocarbon). The ratio of 14C vs 12C in a sample and the known rate of 14C decay is used to estimate the age of the sample.
Sample sizes
AMS allows for high-precision 14C measurement on relatively small samples, with our optimal target being 0.7 mg of carbon. Lower precision 14C measurement is possible with smaller samples. The table below gives recommended size ranges for submitted materials. These guidelines are generally conservative because carbon content and state of preservation varies widely among organic and inorganic materials, among depositional context, and with age.
That is, the values list below do not represent minimum samples. Please contact us if you have questions on specific material types.
| Material | Recommended amount |
|---|---|
| wood (unburned) | 20-100 mg |
| charcoal | 5-50 mg |
| bulk sediment/peat | 10-100 g |
| bone | 200-1000 mg |
| bone collagen | >5 mg |
| hair/fibers | 10-100 mg |
| carbonates | 25-50 mg |
| calcined bone | 1-5 g |
Results and research support
Research design and sample selection
Our lab staff can assist with developing research designs, sampling strategies, and analysis of radiocarbon data at every stage of their projects from conception to conclusion.
The Radiocarbon Lab produces precise and accurate radiocarbon measurements. However, that 14C/12C ratio will be most useful if your samples are carefully chosen to answer your research question.
Interpreting your data
Background corrections and comparison with a known-age secondary standard are included in the per-sample cost. Lab staff can assist with the calibration of radiocarbon ratios and interpretation of your data for an additional cost. Please let us know if you want assistance with calibration and interpretation.
Ready to Discuss a Project?
Connect with laboratory staff early to assess project fit, sample selection, preparation requirements and measurement goals.