Stroboscopic Bragg Edge Radiography of Twin Formation in a Magnetic Shape Memory Alloy

Stroboscopic neutron imaging provides opportunities to capture fast and repetitive processes in the millisecond range, even for a slow acquisition technique such as energy-resolved neutron imaging. We have implemented an asynchronous collection mode and performed stroboscopic neutron Bragg dip imaging on a pulsed source instrument to follow dynamic microstructure changes in a Ni 2 MnGa magnetic shape memory alloy. The single crystalline alloy exhibited large elongations and contractions of a few percent upon application of a cyclic alternating magnetic field and an external force. We used a custom-made actuator and signal generator for the external magnetic field and a microchannel plate (MCP) detector in an event list mode for neutron detection. We achieved a spatial resolution of approximately 200 µm and a temporal resolution of a few milliseconds for observing crystal twinning. The stroboscopic method used to study twin formation and dynamics is essentially a 4D neutron imaging technique, combining radiographic imaging using a 512x512-pixel Timepix system with time-of-flight (TOF) and an actuator phase as additional dimensions.