>one possible explanation for a smoothly varying twin fraction would be two intergrown crystals (i.e. not a twin). Intergrown crystals often do so by a rotation of 180degrees, which is not your case, but maybe the rotation just happens to be close to your twin law.
Yes, I have been mulling over such a hypothesis: my crystal is a hexagonal lozenge, so face-on, one could imagine alternating plus/minus pie slices, and if the beam is not centered on the crystal center (it was not), some of the slices would get more dose, so lower twin fraction. From the side, then, the pie-slices would get equal dose, hence 50% twin fraction.
JPK
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