Answer to Question #574 Submitted to "Ask the Experts"

Q

Is ¹⁴C concentrated during the process of turning wood products into charcoal (such as ventilation purification media)? In other words, would the number of picocuries per gram increase due to driving off the moisture and some of the vegetation material during the process? A second question along the same lines is: Would atmospheric ¹⁴C be expected to be filtered out of an air stream by activated charcoal such as used in ventilation systems and thus increase the ¹⁴C content of the charcoal media?

A

Merril Eisenbud's text Environmental Radioactivity notes the specific activity of ¹⁴C in living carbon and CO₂, prior to input from the 1950s and 60s weapons tests, was about 7.5 picocuries per gram. In that the process of charcoal production requires driving off water, tars, etc., by baking at moderate temperature, one might expect some increase in ¹⁴C concentration. However, the production of activated charcoal has an added step of adding oxygen at the end to cause a great increase in surface area by opening up millions of tiny pores. Surface areas are of 300 to 2,000 square meters per gram. Thus, that would perhaps have an opposite effect on ¹⁴C concentration. Regardless, the detection of environmental levels of ¹⁴C requires very low background counting systems. As far as filtration of ¹⁴C, activated charcoal might adsorb some CO₂ with a natural concentration of ¹⁴C, as well as other organics with ¹⁴C. Having said all that, if you burn charcoal or wood, you'll also expect to see potassium concentrations increase in the ash, with a respective increase in natural ⁴⁰K. Also there have been reports of increased concentrations of weapons testing fallout fission products (i.e., ⁹⁰Sr and ¹³⁷Cs) found in the wood ash in the northeast United States.

Dave Allard, CHP