Superheated emulsions for the detection of special nuclear material

A novel solution for the detection and smuggling interdiction of special nuclear materials is presented here consisting of large detector modules which contain superheated emulsions and which are readout with an optical approach. The detectors can be produced to be fully sensitive to prompt fission neutrons and totally insensitive to the interrogation beam, whether X-rays or neutrons below a chosen energy threshold. Therefore, the detectors are able to operate while the selected interrogation beam is on and they will only pick up the signal from fission neutrons. A position-sensitive readout mechanism is used in our design, relying on the scattering of light by neutron-induced bubbles. A beam of coherent light crosses the active area of the detector, and local variations in scattered light due to the presence of bubbles are detected in real time by arrays of silicon planar photodiodes affixed along the whole length of the detector. The system may offer a variety of advantages compared to current approaches, such as the possibility of simultaneous irradiation and detection, i.e. a 100% duty cycle, without requiring complex signal analysis, and high signal-to-noise ratio, minimizing costly nuisance alarms, thanks to its inherent insensitivity to photons.