The GP2 Module will be a state-of-the-art detector for imaging and 3D reconstruction within the emergent field of energy-resolved neutron imaging (ERNI). Neutron imaging is a well-established technique in which a beam of neutrons is used to record a radiograph of a sample, the neutronic equivalent to the familiar hospital x-ray of a broken bone. However, the full potential of ERNI is yet to be realised. This is often attributed to the lack of suitable detector technology, the requirements for which are particularly complex as the detector must determine both the position and the energy of each neutron. The energy is determined by measuring the flight-time of the neutrons over a known distance from their point of creation to the detector, giving their speed and therefore kinetic energy.
If imaging detectors can be made sufficiently large, efficient and fast, a plethora of techniques will become available to the European neutron imaging community, which is already engaged with both academic and industrial sectors. ERNI is used across many scientific and industrial fields, including energy, cultural heritage, engineering, materials science, additive manufacturing and industrial manufacturing. One example is the field of clean energy research, which is concerned with the study of hydrogen in metals or lithium in batteries. Neutron imaging is ideal to study such systems, being sensitive to these light elements. If the neutron energy spectra is also recorded for each pixel, advanced diagnostics such as material composition, residual strain (related to failure mechanisms such as cracking) and the distributions of these isotopes can be investigated, non-destructively, in both 2D and 3D.
This project combines a prototype imaging detector known as ‘GP2’ with a number of innovations which will increase the neutron detection efficiency three-fold, reduce the read-out time six-fold and critically, make a flexible and multi-use module for large area coverage. This will be achieved by a novel sensor mounting design. Mounting the sensor on a long, narrow circuit board places the sensor out into free space, away from the detector electronics. The resulting modules can then be tessellated to make a row or grid of sensors, which can operate either cooperatively or independently. They can also be inserted into systems where there is very little available room due to the environment surrounding the sample.
The improvements in neutron detection efficiency are realised via the novel ‘sandwich structure’ of the sensor, where the sensor is back-ground to under 30 μm thick and neutron conversion material is deposited onto both the top and bottom of the sensor. This process gives a factor of three gain in detection efficiency and avoids having to use other gain-enhancing technology, which can introduce limitations either in stability and/or rate capability, or necessitates the use of large cumbersome vacuum vessels.