I wonder what sort of 14C signal remains in the atmosphere - as bomb 14C
being diluted by 14C-poor CO2 from fossil fuels. I guess it depends upon
when the linseed was grown.
One might be able to use the 13C signal - as the 13C:12C ratio of
atmospheric CO2 is decreasing as a result of fossil fuel-derived CO2.
I seem to remember reading somewhere that a group of researchers tried
use bomb 14C as a tracer for soil carbon turnover and sequestration in
rainforest soils. I recall that they had great difficulty in detecting a
signal - sorry, cannot remember the reference.