Thanks to a FuseNet mobility grant, I spent 6 months at IPFN, the fusion research institute of Instituto Superior Técnico in Lisbon, working on my Master's thesis on nuclear reaction cross sections relevant to fusion materials.
Why this matters
One of the challenges of future fusion reactors is protecting the walls facing the plasma. Liquid lithium is a strong candidate coating for these components, partly because it can also breed the tritium fuel reactors will need. But before lithium-based components can be used, they have to be characterized and one of the best tools for this is Nuclear Reaction Analysis (NRA) with a 3He ion beam.
This master thesis project was designed because when 3He hits lithium, it doesn't just trigger the reaction you're interested in, it also triggers several competing reactions. One of them, 6Li(3He,p1)8Be, produces a proton peak so broad that it overlaps with the signal used to measure retained deuterium in these materials, contaminating the very measurement researchers are trying to make. To correct for this, you need to know the cross section of that overlapped reaction very precisely, as a function of both energy and angle. That's exactly what my thesis set out to measure.
What I actually did
At IPFN, I used the 2.5 MV Van de Graaff accelerator at CTN (Bobadela) to irradiate a thin 6Li target with 3He ions at energies between 1.2 and 2.5 MeV, collecting spectra at four different detector angles. A big part of the work was careful spectral analysis: because the peak of interest is very broad, I had to estimate its center and width from reaction kinematics, model it as a Gaussian, and define a consistent window to extract the net counts, on top of properly subtracting the background under it. I also had to calibrate the solid angle of each detector using a beryllium reference target and reaction, before I could turn raw counts into an actual cross section.
What I learned
Beyond the physics, this project taught me how much real experimental work depends on getting the details right (background subtraction, calibration, uncertainty propagation) before you can trust a single data point. I also got hands-on experience with tools like SRIM and WiNDF, and with the day-to-day logistics of running a beamline experiment.
Living the experience
Lisbon itself made the whole experience special. It's a young, open city, and the perfect place to build both friendships and academic connections. The lab welcomed me from day one and made me feel part of the team right away. I shared the experience with several other students my age, from different parts of the world, all doing their own internships there which enriched the whole trip. I'd strongly encourage any student interested in experimental nuclear physics to apply for a similar placement, there's no substitute for spending weeks at an actual accelerator facility to understand the experimental side of what each of us in this field have studied.
by Colella Amleto, Politecnico di Milano — Nuclear Engineering
