Neutron Scattering - JUWEL - Forschungszentrum Jülich
Neutron Scattering - JUWEL - Forschungszentrum Jülich
Neutron Scattering - JUWEL - Forschungszentrum Jülich
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KWS-3 7<br />
Table 2. Samples for practicum; CV: samples for the contrast variation; FF, SF: sample for<br />
form and structure factor determination.<br />
�D2O 0 CV 3.6 FF, SF 10 CV 20 CV 30 CV 40 CV 50 CV 60 CV 76 FF<br />
�Spheres 1.00 0.96 0.9 0.8 0.7 0.6 0.5 0.4 0.24<br />
I(0)[10 4 cm -1 ] 103 75.2 38 6.5 0.47 12.01 33.2 55.9 75.2<br />
5 The experiment and data reduction<br />
All samples listed in Table 2 we will measure with (Sample) and without (Sample-DB)<br />
beamstop. The first one should be measured much longer than the second one. Additionally<br />
the empty cell [with (EC) and without (EC-DB) beamstop] and the black current (BC) run<br />
will be measured and used for data reduction of all datasets.<br />
What to measure?<br />
ISample, ISample-DB, IEC, IEC-DB, IBC [counts per current pixel, normalized by monitor]<br />
Sample transmission:<br />
T � I Sample�DB I EC �DB<br />
Empty cell and black current subtraction:<br />
I � (ISample � IBC ) � T� (IEC � IBC )<br />
Absolute calibration:<br />
d�<br />
d� Q<br />
I(Q)<br />
� ��<br />
d� T� �D � IEC �DB ��(Q)<br />
where d sample thickness, T sample transmission, �D detector efficiency, �� solid angle per<br />
current pixel, counts on sample.<br />
6 Experiment-Related Exercises<br />
Within our “one-day-experiment” at KWS-3 it would be nice to get as much as possible<br />
information about above mentioned sample, like:<br />
a) the form factor P(Q) of PS spheres from sample with �D2O=0.76; “real” radius R and<br />
polydispersity of the PS microspheres;<br />
b) the structure factor S(Q) in case of �D2O=0.04 and decide about the interactions<br />
between spheres: could we neglect the structure factor S(Q) during data analysis?