Neutron Scattering - JUWEL - Forschungszentrum Jülich

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