Visualize powerful magnetic fields with neutrons

Researchers at the Paul Scherrer Institute at PSI have developed a new method for accurately measuring strong magnetic fields. They use neutrons obtained from the spallation source SINQ. In the future, it will be possible to measure the fields of magnets already installed in devices and therefore inaccessible by other sounding techniques. The researchers have now published their findings in the journal Nature Communications.

Neutrons are, as their name implies, electrically neutral and are the building blocks of almost all atomic nuclei. Neutrons interact with magnetic fields because of their spin. Researchers at the Paul Scherrer Institute, PSI, have now shown that this property can be used to visualize magnetic fields. They used polarized neutrons, which means that all neutrons have the same spin orientation.

If polarized neutron beams pass through a magnetic field, a refraction of the neutron beam can be detected behind this field. From the refraction scheme, the magnetic field and in particular the differences in field strength can be reconstructed. For the first time, this method, also called polarized neutron array interferometry (pnGI), was used to measure magnetic fields.

A million times more powerful than the Earth's magnetic field

The pnGI can be used to measure very strong magnetic fields with a gradient intensity of the order of 1 Tesla per centimeter. "This allows us to move in orders of magnitude about a million times stronger than the Earth's magnetic field," says Christian Grünzweig, a neutron scientist at the Paul Scherrer Institute of the United States. ISP. Until now, neutrons could only be used to measure considerably lower magnetic fields.

Alternators to MRI systems

Many applications are possible for the new method, in particular because neutrons penetrate most materials non-destructively. "We can also probe hard-to-access magnetic fields because they are already embedded in a device," says Jacopo Valsecchi, lead author of the study and PhD candidate working at PSI. "The applications range from car engine generators to many components of the power supply system, including magnetic fields from magnetic resonance tomography systems used in medicine."

The researchers proved that their method works by using computer models to simulate the expected results of the measurement. They then verified whether comparable results could actually be obtained with a real measure. "The simulation results and the actual measurement results are in perfect harmony," says Grünzweig.

With the new method, fluctuations in the magnetic field can also be detected. For example, even permanent magnets, such as magnetic stickers for refrigerator doors, do not have a homogeneous magnetic field. "We can now detect the possible gradients, even if the magnetic field is very powerful," says physicist Valsecchi.

The researchers have now published their findings in the journal Nature Communications.