ESS Lund hosted the NEUWAVE-5 Workshop (promoting energy-selective neutron imaging) in April 2013

The 5^th Meeting of the NEUWAVE series took place in Lund coinciding with the initiation of the neutron imaging instrument project ODIN at the upcoming European Spallation Source ESS.

Since the first NEUtron WAVElength dependent Imaging (NEUWAVE) meeting held 2006 in Munich/Garching the compact community dealing with the advanced methods for imaging, in particular also at pulsed sources, meets regularly for dedicated workshops.

Related to the fact that advanced imaging methods, like imaging with polarized neutrons or using a grating interferometer for phase and dark-field imaging, required either a monochromatic neutron beam or wavelength dependent measurements, like in the case of Bragg edge imaging, a number of new developments has been triggered in the field. Not only different means of monochromatisation have been tested and implemented at state-of-the-art neutron imaging stations, but also method development has seen considerable progress. In this framework not at least pulsed neutron sources became especially attractive for neutron imaging. The time-of-flight (TOF) approach has not only proven highly efficient for novel methods, but also having a significant potential for methods utilizing only monochromatic beams before. In the latter case especially quantitative approaches can profit a lot. However, the TOF strategy also requires corresponding imaging detectors, providing not only high spatial resolution but also according time resolution. This provides the context in which the NEUWAVE meetings have become an important means of communication, exchange and development in the field of neutron imaging.

In parallel to the according detector development and corresponding to the significant progress of methodical development a new generation of neutron imaging beamlines at the upcoming pulsed spallation sources is a central task of this workshop.

Four different projects have been initiated meanwhile resulting in four beam line initiatives:

• ERNIS at J-PARC (Japan)
• IMAT at ISIS-TS 2 (UK)

both of which are under construction in the meantime and are expected to enter the commissioning phase in 2015, as well as

• VENUS at SNS (USA)
• ODIN at ESS (Europe, Scandinavia)

both of which are in a final design phase looking for approval and final funding to enter the construction phase.

The progress of these instrument projects but also possible novel applications and the growing scope of neutron imaging are core topics of the NEUWAVE meetings nowadays as well.

The recent NEUWAVE-5 meeting at the ESS in Lund was highlighted by the message that the ESS Scientific Advisory Committee (SAC) has strongly recommended the ODIN project to be among the first two beam lines to be constructed at this future spallation source. Hence, the project is waiting for a corresponding final approval by the ESS Steering Committee (STC) expected in autumn this year in order to enter the construction phase.

The meeting in Lund was attended by 50 experts in the fields of neutron imaging, material research, detectors, neutron scattering and even X-ray diffraction, all dealing with topics around the mentioned projects.

However, energy selective imaging is already utilized at the world leading existing neutron imaging facilities where the energy bands are tuned by means of turbine type devices, monochromators or band filters, which triggered the above outlined developments. Correspondingly and despite the limited performance compared to the one expected at the major spallation sources important new approaches and results were obtained and reported at the NEUWAVE-5 meeting. The program hence conveyed contributions dealing with the newest results concerning e.g. strain mapping of construction materials in imaging geometry, measuring and visualizing textures and other crystalline information partly complementing transmission imaging with diffraction data, which was e.g. additionally measured by imaging devices in diffraction geometry. Applications have been addressed dealing amongst others with engineering materials, nuclear materials, cultural heritage but also fuel cell research and development.

Furthermore wavelength resolved measurements with polarized neutrons have been reported, which successfully target magnetic properties such as super-conductivity (Meissner effect) and enable direct observations, visualization and quantification of magnetic field distributions in and around samples with high spatial resolution.

A wavelength dependent analysis of refraction artifacts at the edges of materials, supporting earlier reports, has been presented and the potential to utilize those for defect analysis in structural materials has been outlined.

Last but not least also the state of detector developments for TOF imaging, which is indispensible for the novel beamlines at pulsed sources, has been presented by several groups from Europe, America and Japan. Not only prototypes and test measurements but also significant applications have been introduced in this context as well.

As common in all previous NEUWAVE workshops, the kick-off in advance to the presentations and discussions has to be a hiking tour to bring the participants together in a more relaxed atmosphere. Due to the lack of challenging mountains in the area of Lund, the hiking was replaced by fishing on the Oresund on Sunday afternoon (under blue sky and sunshine and with great success €“ see picture). The fishes were prepared and eaten during the reception dinner.

NEUWAVE-6 will be organized in 2014 again by the institute which initiated and hosted already the first meeting at FRM-2 at TU Munich in Garching.

Eberhard H. Lehmann