New measurements of the coherent and incoherent neutron scattering lengths of 13C

The techniques of neutron interferometry and neutron diffraction were used to determine the coherent and incoherent neutron scattering lengths of (13)C. From a neutron interferometry measurement of the optical path difference in liquid samples, (13)CS(2) versus (nat)CS(2), we obtain a bound coherent scattering length of b(coh, 13C) = 6.542 +/- 0.003 fm, which differs appreciably from the standard tabulated value of 6.19 +/- 0.09 fm. The resulting contrast of only 0.106(3) fm with respect to b(coh, natC) = 6.6484 +/- 0.0013 fm has consequences for neutron diffraction experiments involving (13)C isotopic substitution. Combining our result for b(coh, 13C) with precise neutron diffraction measurements of the self-scattering intensities of liquid samples, (13)CS(2) versus (nat)CS(2), and (13)CO(2) versus (12)CO(2), we deduce a bound incoherent scattering length of b(incoh, 13C) = - 0.42 +/- 0.24 fm that is consistent with the standard tabulated value of -0.52 +/- 0.09 fm. The results presented here have required accurate measurements of small effects, for which particular attention has been given to the data analysis.