Abstract
The techniques of neutron interferometry and neutron diffraction were
used to determine the coherent and incoherent neutron scattering lengths of 13C.
From a neutron interferometry measurement of the optical path difference in liquid
samples: 13CS2 versus natCS2, we obtain a bound coherent scattering length of
bcoh,13C = 6.502 � 0.003 fm which differs appreciably from the standard tabulated
value of 6.19 � 0.09 fm. The resulting contrast of only 0.146(3) fm with respect to
bcoh,natC = 6.6484 � 0.0013 fm has consequences for neutron diffraction experiments
involving 13C isotopic substitution. Combining our result for bcoh,13C with precise
neutron diffraction measurements of the self-scattering intensities of liquid samples:
13CS2 versus natCS2, and 13CO2 versus 12CO2, we deduce a bound incoherent
scattering length of bincoh,13C = −0.73 � 0.14 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.
