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

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.