Quasi-elastic measurements using neutron spin flippers

A method for low-resolution quasi-elastic measurements using commonly available components on a polarized neutron beam reflectometer is demonstrated. By amplitude modulation of the current in a neutron spin flipper placed between the neutron beam polarizer and polarization analyzer, the intensity of the neutron beam illuminating a sample is similarly modulated (or chopped). We show that the intensity contrast between subsequent chopped pulses is dramatically reduced by a sample that changes neutron velocity.