A known method for analysis of material by neutron interrogation is based on the emission of neutrons towards the material to be analysed, on detection, by a gamma ray detector, of gamma photons emitted during the first interaction of neutrons with the material to be analysed and on detection, by an alpha particle detector, of the alpha particles associated with the emitted neutrons. This method of analysis by detection of associated alpha particles is commonly referred to as the “API” (Associated Particle Imaging) method. The API method not only allows determination of the presence of certain elements, but also three-dimensional localisation of these elements in the material analysed. Such a method is described for example in patent document FR 2945631.
Although this method is generally satisfactory, the gamma ray detector data acquisition time is relatively long, which may be problematic for some applications. This is the case for example of applications in which the material to be analysed and the analysis device move in relation to each other and in which all the data required for the analysis need to be acquired during this movement.
In order to overcome this drawback, a solution would involve increasing the neutron flux emitted to increase the number of interactions with the material. Thus, more data would be collected during an acquisition period and the length of this period could be reduced. However, increasing the neutron flux would require a neutron generator that is more powerful, therefore larger, heavier and consuming more electrical energy. Moreover, by increasing the neutron flux, the surrounding radioactivity would increase and provision would need to be made for thicker shielding to protect the users against this radioactivity. Ultimately, the mass and overall dimensions of the device would be significantly increased, which would represent a disadvantage in applications in which the analysis device is mobile, such as for example applications in which the device is mounted on a vehicle.
Consequently, there is a need for a new type of device for analysis of material by neutron interrogation, making it possible to offset, at least in part, the above-mentioned drawbacks.