Wandering gap

A traveling gap is a filter for measuring beam intensities that are above the maximum permissible for the detector used .

The wandering gap consists of an absorbent plate with a narrow slit that is automatically moved back and forth at a defined speed. The traveling gap is introduced into the beam path so that the gap completely sweeps over the beam profile during the back and forth movement. The width of the slit is set so that the detector cannot be blinded at any time . During a predetermined number of traveling gap passes , the counting rate of the detector is integrated , and the beam intensity is then determined with the aid of the known beam profile and the known speed and width of the gap.

Traveling slits are used in particular to characterize the primary beam for absolute measurements in X-ray scattering .