How to Prepare Linen for Radiocarbon Dating
Radiocarbon dating is a common technique to determine the age of a sample. Dating ancient linen samples such as found, for example, on mummy shrouds is a complex process involving cleaning the sample to remove neutron contamination on the external layers of the fiber. Such contamination skew results and can occur over the years from any one of a number of sources such as smoke. Thorough cleaning leaves the inner core as a more reliable source for accurate dating.
Using a Lab Homogenizer to Prepare Samples
Dating ancient samples such as linen is a delicate process made more so by the scarcity of samples. That’s why practice runs are made to refine the process by using small samples of regularly available product that has been purposely neutron irradiated.
Process development is complex. Among other things it involves cutting a well-washed sample of neutron irradiated linen into small squares such as 1 cm2. The optimum sample size may vary depending on the texture of the linen.
These squares are homogenized to reduce samples to a size permitting accurate analysis of organic chlorine isotopes, an element present in linen as chlorine-35 and -37. Neutron irradiation causes chlorine-35 to capture a neutron to make chlorine-36.
The analysis to determine the chlorine-36/chlorine-35 ratio is done on an accelerator mass spectrometer. Otherwise stated, knowing the total chlorine content in the linen irradiated with a known amount of neutrons would determine the chlorine-36/chlorine-35 ratio to look for in the real sample.
In this example a CAT Unidrive X-1000 homogenizer drive motor is paired with a 20 mm G-20 Knife shaft with ceramic seals and slip-ring bearings.
Establishing the Homogenizing Procedure
Experimentation may be necessary to develop the optimum homogenizing procedure because samples from different sources may have different properties. In general, however, use a 1500 mL flask filled with approximately 250 mL of water.
Attach the homogenizer drive motor on its mounting stand in such a way that you can move the flask up and down as well as tilt it during the homogenizing process. With the generator immersed in the water turn the unit on. If you are using the CAT X-1000 homogenizer set the speed control to 5 or 25,000 RPM.
Add the linen sample (s) to the flask quickly but one-by-one, not as a batch. The purpose of this is to avoid samples clumping at the generator intake. The immediately grasp the flask and move in slightly up and down as well as on a tilt to aid the homogenizing process. This is not generally required but is done in this instance due to the nature of linen.
Note that the flask will quickly get hot. Consider wearing hand protection such as racing gloves.
When homogenization is complete – that is you notice that all the samples have been processed through the rotor-stator generator – drain the flask through a filtering cloth such as a membrane filter so you can isolate the product, which is now ready for analysis on the accelerator mass spectrometer.
After the sample prep run your homogenizer in clean water or distilled water to flush out sample remnants that could affect the analysis of ongoing tests.