First experiment on neutron resonance radiography with a Micromegas detector at the Back-n white neutron source

The element identification and imaging methods with a white neutron beam by using different detectors are under development at the Back-n white neutron source of China Spallation Neutron Source. The paper presents the preliminary experimental results with a Micromegas detector. The detector was developed for the beam profile measurements in the Back-n beamline. With upgraded electronics, this system can record the time-of-flight information of the neutrons together with the 2D imaging. The structure of the Micromegas, the improvement of electronics and the experimental setup are presented. A detailed data analysis including the noise suppression, the signal recognition and the event reconstruction are described. In the neutron time-of-flight (TOF) spectrum obtained from the neutron resonance radiography experiment, there are obvious dips due to the resonance absorption of the sample. Subsequently, clear resonance peaks from different elements can be identified form the processed neutron TOF spectrum, which is obtained by subtracting the sample-in spectrum from the sample-out spectrum. By selecting the corresponding resonance peaks, the shapes of different elements including Ag, In and W in a composite sample are successfully identified.