Neutron contrast factor

Small angle neutron scattering measurements were carried out with the PACE diffractometer at the Laboratoire Leon Brillouin, (CE Saclay, France). The q range observed was 3.4 lO" to 0.2 A l. Samples were prepared in deuterated instead of ordinary water to achieve a suitable value for the neutron contrast factor. 

The intensity of the scattered neutron beam is related to numerous parameters, but a full discussion of these is not appropriate here. There are several texts that give a more detailed account of these variables and of SANS in general (e.g., Richards, 1989). However, one of the most important parameters in the determination of the pattern and intensity of scattered radiation is the contrast factor, as defined in Eq. 2,... 

Z(9) differential scattering cross section per volume unit K contrast factor for neutron scattering... 

Now we have to use the contrast factor for neutron scattering, denoted ATn, and it is given by... 

The choice of the most appropriate scattering technique depends upon two main requirements the contrast factor and/or the need for time-resolved experiments. Presently, time-resolved experiments can be essentially carried out with X-rays thanks to the extremely high flux of photons delivered by synchrotron radiation facilities. In some high flux neutron facilities, such as ILL in Grenoble, some apparatuses allow one to do near-time-resolved experiments under certain experimental setup conditions (low sample-detector distances). 

The contrast factor is by far the characteristic difference between neutrons and X-rays. As was said in Section 4.1, these particles do not see matter the same way. 

S A N S can be employed to study both homogeneous as well as heterogenous blends and various information can be derived by analysis of the differential scattering cross-section, d2(Q)/dQ (cm ), where d2(Q) (neutron s ) is the number of neutrons scattered per second into a small solid angle, dQ. The measured intensity, I Q), is related to d 2(Q)/d Q and depends on various parameters such as the incident flux, resolution of the detector, detector efficiency, and so on. It is also a function of the contrast factor (Ag), which is defined as the square of the difference of the scattering length density of the scattering centers, for example, the particle and the matrix. This quantity is calculated from ... 

The prerequisite for an experimental test of a molecular model by quasi-elastic neutron scattering is the calculation of the dynamic structure factors resulting from it. As outlined in Section 2 two different correlation functions may be determined by means of neutron scattering. In the case of coherent scattering, all partial waves emanating from different scattering centers are capable of interference the Fourier transform of the pair-correlation function is measured Eq. (4a). In contrast, incoherent scattering, where the interferences from partial waves of different scatterers are destructive, measures the self-correlation function [Eq. (4b)]. 

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