ok, so i still dont have the actual figure for % yield for carbon-11, but if it were 0.1%, then the amount in a reactor when you shut it down will equal the equilibrium value reached during continuous operation; as above, we have 7.18 x 10^18 reactions per second; hypothetically * 0.001 = 7.18 x 10^15 carbon-11 atoms created per second. (x 20.334 minutes = 8.76 x 10^18 atoms created during one half-life period).
at equilibrium, decay rate equals creation rate, so there would be twice this, or 1.752 x 10^19 atoms in the reactor, when you shut it down, or 320 micrograms.
make adjustments for actual yield
