Project

Discipline

neutron imaging; radiography; fast neutrons; neutron detectors; process tomography; multiphase flow

Lead
Lay summary
Imaging with neutrons has always been considered as a useful complement to the use of X-rays and gamma radiation thanks to a specific sensibility to material containing nuclides of low mass number, which creates contrast conditions interesting for many applications. This is especially useful for investigating robust objects containing heavy elements in construction materials. The recent international trend is to develop time-resolved, high spatial resolution tomographic imaging techniques with X-rays controlled by deflecting or pulsing of electron beams to vary the aspect angle during acquisition of projections necessary for tomographic image reconstruction. The proposed PhD project will be part of a feasibility study on the application of similar techniques to apply neutrons instead of X-rays. The feasibility study will be performed as a combination of theoretical modeling and experiments. The test of chosen detector configurations is carried out experimentally. In this line, the Laboratory of Nuclear Energy Systems (LKE) of ETH Zurich in cooperation with the Laboratory of Thermal-hydraulics (LTH) at PSI, is setting up a pulsed deuterium-deuterium (D-D) fusion based compact neutron generator. It is a one-of-a-kind device developed in cooperation with and constructed by Prof. Ka-Ngo Leung from the University of California, Berkley. The strength of the source is not sufficient to perform fast tomography, but allows determining the efficiency of combinations of appropriate scintillator materials coupled to photon detectors, to demonstrate the spatial resolution necessary for radiographic and tomographic imaging and to perform first imaging experiments. On the other hand, the output of the source is not sufficient for fast imaging or tomography. For this, a considerable future effort is needed to upgrade the source or to change to alternative processes for the neutron generation, whereas the detector configurations resulting from the proposed PhD project can be directly used for the final purpose of tomography with fast neutrons. They are independent from the speed of the imaging in a wide range of measuring rates and can be applied also for time averaging tomography. Options for a direct use of the results as well as alternatives to a tomography will be investigated as well. In case of the successful demonstration of the feasibility of fast tomographic imaging with fast neutrons, the way will be open towards a prototype facility with unique features that can find wide application as a user facility for different fields of research and technology.

Direct link to Lay Summary

Last update: 21.02.2013

Title	Year

Number	Title	Start	Funding scheme

In the context of non-intrusive measuring techniques and process tomography, imaging with neutrons has always been considered as a useful complement to the use of X-rays and gamma radiation thanks to their specific advantages: on one hand, neutrons are more sensible and contrast giving for materials containing light elements and on the other hand experience a much lower attenuation in the walls of bulky, robust objects containing heavy elements in construction materials. These features of neutron imaging provide significant advantages for studying two-phase and multi-phase flows occurring in energetic and process industries, but also for many other applications. Often additional challenges arise from the transient character of the flow, which requires high imaging rates. The majority of the neutron radiography/tomography studies are performed around a few large-scale, static devices like research reactors or large accelerator-based (spallation) sources, where mechanical rotation of the studied object is required to obtain a sufficient number of projections under different angles that is necessary for the numerical tomographic reconstruction process. This however cannot be performed with a high speed, i.e. high time resolution, for bulky, heavy specimens. The recent international trend is to develop time-resolved, high spatial resolution tomographic imaging techniques with X-rays controlled by deflecting or pulsing of electron beams to vary the aspect angle during acquisition of projections necessary for tomographic image reconstruction. The present PhD project will be part of a feasibility study on the application of similar techniques to apply neutrons instead of X-rays. The feasibility study will be performed as a combination of theoretical modeling and experiments. The method of choice for theoretical modeling of the interaction of neutrons and the detector system are Monte Carlo calculations. They allow predicting both efficiency and energy sensibility as well as spatial resolution of the neutron detection in the process of design iterations. The test of chosen detector configurations is carried out experimentally. In this line, the Laboratory of Nuclear Energy Systems (LKE) of ETH Zurich in cooperation with the Laboratory of Thermal-hydraulics (LTH) at PSI, is setting up a deuterium-deuterium (D-D) fusion based compact neutron generator. It is a one-of-a-kind device developed in cooperation with and constructed by Prof. Ka-Ngo Leung from the University of California, Berkley, producing pulses of an integral output of 10^8 neutrons per second with an energy of 2.45 MeV. This is sufficient to determine the efficiency of combinations of appropriate scintillator materials coupled to photon detectors, to demonstrate the spatial resolution necessary for radiographic and tomographic imaging and to perform first imaging experiments. On the other hand, the output of the source is not sufficient for fast imaging or tomography. For this, a considerable future effort is needed to upgrade the source or to change to alternative processes for the neutron generation, whereas the detector configurations resulting from the proposed PhD project can be directly used for the final purpose of tomography with fast neutrons. They are independent from the speed of the imaging in a wide range of measuring rates and can be applied for time averaging tomography as well. Options for a direct use of the results are therefore given. The scope of work is a challenging, multidisciplinary topic for a promotion of a graduate in physics or electronics. The present application requests the funding of the position of this PhD student, together with financial means in order to develop and construct a neutron detector assembly.