Cerium is a rare earth metal with numerous technological applications, such as some types of light bulbs and flat-screen televisions. Although this element is rare in the Earth’s crust, it is slightly more common in the universe. However, not much is known about how it is synthesized in stars.

Now, in a new study published Physical Examination LettersThe n_TOF collaboration at CERN is investigating how cerium is formed in stars. The results differed from what was expected from theory; This pointed out that the mechanisms thought to be responsible for the production of cerium and other heavy elements in the universe needed to be reconsidered.

“Our measurement allowed us to identify never-before-observed nuclear resonances in the energy range relevant to cerium production in stars,” explains Simone Amaducci of the INFN Southern National Laboratory and first author of the study. “This is due to the very high energy resolution of the experimental apparatus at CERN and the availability of a very pure sample of cerium 140.”

The many elements heavier than iron observed in stars (such as tin, silver, gold, and lead) can be represented mathematically by assuming the existence of two neutron capture processes: the slow (s) process and the fast (r) process. .

The s-process corresponds to a neutron flux of 10 million neutrons per cubic centimeter, while the r-process has a flux of over one million billion neutrons per cubic centimeter. This process is thought to account for about half of the elements heavier than iron in the universe, including cerium.

CERN’s Neutron Time-of-Flight facility (n_TOF) is designed to study neutron interactions occurring in stars. In this study, scientists used a device to measure the nuclear reaction of the cerium 140 isotope with a neutron to produce the isotope 141.

According to complex theoretical models, this reaction plays a crucial role in the synthesis of heavy elements in stars. Specifically, scientists studied the reaction cross section: a physical quantity that expresses the probability of a reaction occurring. Scientists measured the cross section over a wide energy range with 5% higher accuracy than previous measurements.

The results raise new questions about the chemical composition of the universe. “We were initially intrigued by the discrepancy between theoretical models of the stars and observational data for cerium in the stars of the M22 globular cluster in the constellation Sagittarius,” explains Sergio Cristallo of the INAF Astronomical Observatory of Abruzzo, who proposed the experiment.

“The new nuclear data differ significantly from data found in nuclear databases currently in use by up to 40% and are certainly beyond the predicted uncertainty.”

These results have remarkable astrophysical implications; It shows a 20% reduction in the s-process contribution to excess cerium in the universe. This means that a paradigm shift is needed in the theory of cerium nucleosynthesis: other physical processes not currently included must be taken into account in calculations of stellar evolution. The new data also has important implications for scientists’ understanding of the chemical evolution of galaxies; This evolution also affects the production of heavier elements in the universe.