A new approach to the determination of the uncertainty in neutron diffraction experiments with isotopic substitution method

摘要

Nudeutron diffraction experiment with isotopically substituted substances is audpowerful approach claiming to yield unambiguous information about the local atomicudstructure in disordered materials. This information is expressed in the partial structureudfactorsud, and extracting them from a series of measurements requires solution of a setudof linear equations that is affected by experimental errors. In this article, we suggest audmethod for the determination of the optimal set of H/D compositions with or withoutudtaudking into account the experimental error. For the case of water, our investigationsudshow that the selection of the isotope concentrations and the distribution ofudmeasurement time among the various samples have critical role if one wants to utilizeudthe limiudted neutron beam time efficiently.udIt is well known that measurements of pure Hud2udO introduce fairly large errors in theudpartial structure factors due to its very strong incoherent scattering. On water andudmethanol as examples, we investigated the propagatioudn of random errors to the partialudstructure factors using partial pairud-udcorrelation functions from molecular dynamics simulation. It is shown on the example of water that it is not worthwhile measurudingudpure Hud2udO.