Deuterium, scattering factor

The fact that neutron scattering factors are similar for all elements means that light atoms scatter neutrons as effectively as heavy atoms and can therefore be located in the crystal structure for example the X-ray scattering factors for deuterium and tungsten are 1 and 74, respectively, whereas the equivalent neutron values are 0.667 and 0.486. This... 

There is some disagreement in the literature as to the value of the (4He, H) elastic scattering cross section. Values differing by almost a factor of two have been reported, as reviewed by Paszti et al. (1986). The cross section is strongly non-Rutherford, but ab initio calculations have been reported that agree well with the trend of experimental data and could be used in simulation calculations (Tirira et al., 1990). The cross section for deuterium analysis has a resonance near a 4He+ energy of 2.15 MeV, which allows enhanced sensitivity. Detailed measurements of this cross section have been reported by Besenbacher et al. (1986). In practice, rather than calculate an experiment s calibration from first principles, calibration standards are usually used hydrogen-implanted silicon standard are the norm. 

In the opposite sitnation, when the carbon is exposed to D O at RH=0.87 in association with a 1 1 (v/v) mixtnre of TH and TD (THD), a large difference is observed with respect to the case where the tolnene is fnlly deuterated (Fig. 6.4, curve 4). I. shows a substantial increase, to 0.11 cm , and the contrast factor also increases as a result of the replacement of deuterium atoms in the toluene (fep=H-0.66 X10 cm) by protons (b -0.37 x 10 cm). It is also noticeable that the accumulated intensity at the peak around 1.7 A is much weaker owing to the reduced scattering power of the TH molecules. 

DDBJ—see EMBL DLS—dynamic light scattering DM—donkey s milk DNA—deoxyribonucleic acid DNCB—2,4-dinitrochlorobenzene DSC—differential scanning calorimetry DTH—delayed cellular hypersensitivity DXMS—deuterium exchange mass spectrometry EAACI—European Academy of Allergology and Clinical Immunology EAR—early anaphylactic phase ECFA—eosinophil chemotactic factors of anaphylaxis ECP—eosinophil cationic protein EDN—eosinophil-derived neurotoxin eHF—extensively hydrolyzed formula ELISA—enzyme-linked immunosorbent assay... 

A special simplification arises when a deuterated polymer is blended with its hydrogenous counterpart of exactly the same molecular weight. In this case, the interference component of the scattered intensity turns out to be simply proportional to the independent scattering component, and as a result the form factor can be determined even when the concentration of the deuterated polymer is not dilute. This will be discussed more when the technique of deuterium labeling is described in Section 6.3. 

An important application of neutron diffraction is based on the fact that the dependence of scattering power on atomic number is different for neutrons and X rays. For X rays, the atomic form factor is directly proportional to the atomic number, but the relationship is more complicated for neutron radiation, and there is a correlation with the energy states of isotopes. Between hydrogen and deuterium, for example, there is an appreciable difference in scattering power. The fact that neutrons, unlike X-ray quanta, are scattered by atomic nuclei means that the scattering power is virtually independent of the diffraction angle. A further advantage of the use of neutrons is the lower absorption. 

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