Abstract
In recent years, neutron radiography and tomography have been applied at different beam lines at Los Alamos Neutron Science Center (LANSCE), covering a very wide neutron energy range. The field of energy-resolved neutron imaging with epi-thermal neutrons, utilizing neutron absorption resonances for contrast as well as quantitative density measurements, was pioneered at the Target 1 (Lujan center), Flight Path 5 beam line and continues to be refined. Applications include: imaging of metallic and ceramic nuclear fuels, fission gas measurements, tomography of fossils and studies of dopants in scintillators. The technique provides the ability to characterize materials opaque to thermal neutrons and to utilize neutron resonance analysis codes to quantify isotopes to within 0.1 atom %. The latter also allows measuring fuel enrichment levels or the pressure of fission gas remotely. More recently, the cold neutron spectrum at the ASTERIX beam line, also located at Target 1, was used to demonstrate phase contrast imaging with pulsed neutrons. This extends the capabilities for imaging of thin and transparent materials at LANSCE. In contrast, high-energy neutron imaging at LANSCE, using unmoderated fast spallation neutrons from Target 4 [Weapons Neutron Research (WNR) facility] has been developed for applications in imaging of dense, thick objects. Using fast (ns), time-of-flight imaging, enables testing and developing imaging at specific, selected MeV neutron energies. The 4FP-60R beam line has been reconfigured with increased shielding and new, larger collimation dedicated to fast neutron imaging. The exploration of ways in which pulsed neutron beams and the time-of-flight method can provide additional benefits is continuing. We will describe the facilities and instruments, present application examples and recent results of all these efforts at LANSCE.
Highlights
More than 80 years after the first neutron image was produced [1,2] and 70 years after publication [1,3], advances in accelerator and, potentially, laser-driven neutron sources, as well as in detector technology and computing are creating imaging capabilities that are unique, powerful and complementary to X-ray and charged particle imaging
In the early 2000’s very successful thermal neutron imaging programs were underway at PSI [6], FRM-2 [7], HZB [8] and NIST [9], with cold neutron advancements following [10]
Neutron imaging is available at J-PARC [11,12], ISIS [13] and other reactor and accelerator facilities with support from universities, government laboratories and companies
Summary
More than 80 years after the first neutron image was produced [1,2] and 70 years after publication [1,3], advances in accelerator and, potentially, laser-driven neutron sources, as well as in detector technology and computing are creating imaging capabilities that are unique, powerful and complementary to X-ray and charged particle imaging. The short (270 ns for Target 1 and < 1 ns for Target 4) proton beam pulses are uniquely well-suited for fast, time-gated imaging, both for nuclear resonances (eV to keV) to perform isotope- and element-specific imaging and at MeV energies to develop improved detectors and techniques for very-penetrating high-energy neutron imaging. The high-energy neutron imaging detector developed at LANSCE has been employed with a state of the art laser-driven neutron source in a first demonstration of the potential for this new type of neutron source This laser source creates possibilities for (1) very small source sizes (magnification and excellent resolution); (2) fast timing for flash neutron radiography and (3) reduced radiation backgrounds due to the directional nature of the source [34,35,36].
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