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Mikhail Avdeev (J I Nuclear Res (JINR)) Q: What is the obstacle (beam "monitor") before the sample? Is it necessary to do the beam weaker? The beam monitor is a detector with very low efficiency (order of 0.001), which is placed in the incident beam. Its task is to follow possible temporal osciallations in the reactor power and, hence, in the neutron beam flux. Because of the low efficiency, it has no actual effect on the beam flux, but its counting is proportional to the incident flux/intensity (statistics is perfect for 10 - 60 min measuring time, this is direct beam (!) with about 10^7 neutrons/s/cm^2). After the measurments of the scattered intensities (studied sample, background, calibration sample, empty sample cell) we devide all the curves by the corresponding monitor count (obtained simultaneously with a given curve), thus avoiding the influence of the beam flux variation during the measurements. Q: If the mixture of powders consists of both isotropic and anisotropic particles, is it possible to estimate the ratio of isotropic and anisotropic parts? If I understand the question correctly, one asks, if one has a fraction of oriented anisotropic particles and a fraction of the disoriented anisotrpic particles (i.e. one has somewhat partial texture in the powder sample), then is it possible to find out these fractions? The answer is you need to model the 2D pattern in this case, which consists of the anisotropic 2D scattering cross-section (dependence on both the absolute value and orientation of momentum transfer) and isotropic cross-section (dependence on the absolute q-value only) multiplied by the corresponding fractions (to be fitted together with other unknown particle parameters). If there is just a mixture of isotropic (let's say spheres) and anysotropic (let's say elongated ellipsoids) particles, and the particles of the second kind are disoriented, then you have a mixture of two kinds of isotrpic scattering curves with the coefficients corresponding to the fractions. Again you should model this sum by varying the fraction coefficients together with the unknown particle parameters. I cannot exclude that in some cases there can be simple rules how to find out the asked ratio taking into account the scattering from the known forms. Never met.