Experimental studies on nuclide identification radiography with a CMOS camera at Back-n white neutron source

As an advanced neutron imaging technique, nuclide identification radiography (NIR) using neutron resonance or cross-section differences is a promising technique for investigating nuclide spatial distribution inside samples. Since its proposal in 1980s, this technique has advanced very slowly due to many limitations in neutron source, detector efficiency and resolution. At the Back-n white neutron source at China Spallation Neutron Source, the NIR technique based on gated CMOS camera has been developed by taking the advantage of very high neutron flux and suitable energy spectrum of the Back-n neutron beam. Heavy nuclides, medium-mass nuclides and light nuclides have been tested to validate the effectiveness of the technique, covering the resonances from eV to MeV regions. Typical heavy elements such as Ag, In, Au and W, medium-mass elements such Al, Fe and Cu, light elements such as O have been used for experiments. The study shows, that nuclides with resonance peaks in the eV region can be easily identified, while the nuclides with resonance peaks above keV are difficult to be identified individually due to their narrow resonance peaks affecting the signal-to-noise ratio in the camera measurements. However, these nuclides can be differentiated for imaging by using adjacent multiple resonance peaks or distinct cross-section differences over wider energy ranges. The experiments are perhaps the first ones that demonstrate the NIR technique for the identification and imaging of nuclides with cross-section resonances covering from eV to several MeV.