Anomalous dispersion neutron

In recent papers we have shown that small-angle X-ray scattering (SAXS) is a highly suitable method to investigate stiff-chain polyelectrolytes [71]. In particular, it has been demonstrated there that the effect of anomalous dispersion [72] can be applied to discern the contribution of the counterions to the measured scattering intensity I(q). Here the main points of this analysis that is based on earlier work by small-angle neutron scattering (SANS [73-76]) and by SAXS [77, 78] are presented and discussed. 

The physical process of resonance neutron scattering is through the formation of a compound nucleus . Cd, and Gd belong to the small class of nuclei which exhibit a resonance in the thermal energy region. In the case of Cd the compound nucleus Cd will either eject a neutron in an (n, n) process or emit y-rays in an (n, y) process the latter being inelastic. Unlike in X-ray anomalous dispersion, in the present case both the elastic (n, n) and inelastic (n, y) processes contribute to b"(0) ... 

Wright AC, Cole JM, Newport RJ, Fisher CE, Clarke SJ, Sinclair RN, Fischer HE, Cuello GJ (2007) The neutron diffraction anomalous dispersion technique and its application to vitreous Sm203-4P205. Nucl Instrum Methods Phys Res Sect A 571(3) 622-635... 

The first term / (k) is the X-ray atomic scattering factor and the other two terms are the dispersion corrections. Similar anomalous scattering occurs for neutrons also and the neutron scattering factor is formulated in a similar way. 

Nuclear spin dependent neutron scattering relies on polarisation variation, i.e. on a change of the order of the nuclear spin system. Resonant (or anomalous) X-ray scattering is a concomitant feature of core electron ionisation (Eq. (2)). The dispersion of the resonant coherent scattering is very small compared to the rise of absorption (and fluorescence) due to electronic excitation. It typically amounts to... 

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