Round Table: Novel Opportunities for Cooperation between France and Germany in Neutron Science

During the Spring Meeting of the Condensed Matter Section of the German Physical Society (DPG), held in Dresden in March 2026, a round table was held on the theme ‘Novel Opportunities for Cooperation between France and Germany in Neutron Science’. The discussion counted on the participation of the directors of the French and German facilities and of representatives of the neutron user association in both countries, SFN and KFN.

How to get to the neutrons

The first discussion topic concerned the access to neutron beams and triggered considerable interest and questions from the audience. It became clear that researchers that do not have prior work experiences in large scale facilities don’t find it necessarily easy to take the first steps – a certain barrier is perceived. In response, all the facility managers express their interest in attracting new users – in view of expanding their user base, but also because new ideas and research topics are crucial for the development of the field.

The representatives of KFN and SFN underlined the existence of a variety of training opportunities – from three-day practical courses in international instruments at ILL (Collaborative Research Group instruments, CRG), to one- or two-week long school (as organised by ILL/Montpellier or JCNS), or the five- week Hercules school at ILL. Some of these schools, such as the thematic schools organised by SFN, publish freely downloadable textbooks. SFN and KFN also run annual meetings, originally focused on either the French (JDN) or German (DN, SNIB) user community, but nowadays with a strong international focus.

Beamtime access practicalities

Several questions from the audience concerned the technical aspects of access to neutron beam time. The mechanism of beamtime distribution currently implemented in virtually all facilities worldwide was outlined: the proposal system with regular calls (typically twice a year) and expert committees deciding on beamtime allocation. The drawbacks of this system were not hidden: it is relatively slow (about six months from request to experiment); decisions may come late and are not always positive, in particular when instruments are strongly requested. While it was considered that a ‘normal’ overbooking (typically around 2) usually allows for most promising experiments to be granted beamtime, this number may nevertheless discourage new users.

Facility directors generally agreed that a delay of two to three months from the proposal to the experiment is an achievable goal. Importantly, new users were strongly encouraged to team up with experienced users, or to contact directly the instrument responsible scientists for advice. It was also pointed out that all facilities offer alternative beamtime access modalities: for projects with a strong time pressure (fast, or easy access) and for test measurements allowing to check a hypothesis before submitting a full proposal, (which can usually be done during in-house beamtime, or director’s discretion time). Along the same line, virtual instruments (digital twins) will be increasingly available to estimate measurement times and statistics for given types of samples. For future sources, facility management teams are currently rethinking the way to allocate beamtime, taking into account new and emerging ways of doing research. Given the increasing data production rates, the question of the management of big data is becoming increasingly relevant.

But why neutrons?

An aspect addressed in the discussion with the audience were the potentially lengthy data acquisition times, in particular in comparison with X-ray scattering. Indeed, due to the underlying physics, incoming neutron fluxes are orders of magnitude lower. It was emphasised that some measurements, in particular those sensitive to hydrogen atoms or magnetic moments, can only be done with neutrons. Moreover, modern sources aim at higher and higher brilliance – there is “plenty of space at the top”, creating many opportunities for young scientists.

The round table participants reminded that experiments that are feasible with X-rays should be done with X-rays, leaving the most important neutron applications to this rarer resource. In some cases, the complementarity between X-rays and neutrons beneficial or even key for the success of the experiments, as they may highlight different aspects of the same process or structure (e.g. exact positions of heavy vs. light elements).

The challenge of data analysis

Owing to the nature of the processes involved, conclusions are usually inferred indirectly in scattering experiments. Data analysis is thus part of the experimental workflow. Users should leave with pre-treated data, enabling them to focus on the science rather than in solving technical issues.

Moreover, powerful data analysis programs are available, and considerable efforts are pursued in the sources to implement more efficient data reduction and processing. Artificial intelligence is expected to become increasingly helpful, and it is being actively explored at the facilities. Given the increase in computing power, “on the fly” data analysis may become feasible in specific applications.

Finally, dedicated workshop and schools for data analysis are regularly held in the French-German research landscape. Once more, the importance of adequate training and of collaborating with experienced groups was emphasised in the discussion.

A wealth of opportunities

The remaining of the discussion, focusing on ‘international jobs in neutron facilities, now and in the future’ and ‘scientific and instrumental collaboration between France and Germany was relatively brief due to time constraints. The explicit question to be answered by the panel was ‘Could there be a job for me in neutron scattering?’

The international nature of such jobs and working environments was emphasised – increasingly, not only for scientists but also for technicians and engineers. In this context, it was underlined that French-German partnerships are in place not only in the sources represented in the discussion but also at ESS, where common beamlines exist. The possibility of opportunities in growing areas, as for example neutron imaging, was also stressed. On the scientific project side, two opportunities were mention in the discussion.

Firstly, the new science strategy developed by ILL. Leveraging on recent and major instrument and facility upgrades, the science strategy proposes to concentrate forces on specific topics of societal relevance using different types of project organisation, such as hubs and showcase experiments. Secondly, the well-known ANR-DFG joint research program. Over the last 10 years, the program enabled the funding of about 60 projects per year involving at least one French and one German institution, in a total budget of around 200 M€ in each country.

The final message seems clear: there are many opportunities in neutron science for young researchers – in scientific projects as in instrument development; in France and in Germany; in existing facilities, in ESS beamlines with French/German participation or in facilities yet to come, like ICONE and HBS-1.