CERN n_TOF experiment resolves molybdenum-94 anomaly in presolar grains
Spanish researchers measured the neutron capture rate of niobium-94 for the first time, explaining isotopic anomalies in ancient meteorites.
Physicists from the Institute of Corpuscular Physics (IFIC), a joint center of CSIC and the University of Valencia, measured a fundamental nuclear reaction key to stellar nucleosynthesis at CERN's n_TOF facility in Geneva, according to El Debate eldebate.com
El Debateeldebate.comOpen source ↗. The experimental data, published in Physical Review Letters, reproduces the observed levels of molybdenum-94 discovered inside presolar grains preserved in primitive meteorites.
Presolar grains condensed before the formation of the Solar System and preserve the isotopic signatures of ancient stars. For decades, astrophysical models failed to explain an anomalously high concentration of molybdenum-94 identified in these particles. Heavy elements synthesize inside dying stars, where radioactive isotopes compete between beta decay and neutron capture before matter is ejected into interstellar space.
Neutron capture on niobium-94
The synthesis of molybdenum-94 depends directly on the behavior of the radioactive isotope niobium-94 under stellar conditions. Depending on the local neutron flux and core dynamics, niobium-94 either undergoes beta decay or captures an additional neutron, a critical branch point that dictates final isotopic abundances.
Prior to this study, the probability of neutron capture on niobium-94 had never been measured experimentally, forcing stellar models to rely purely on theoretical estimates eldebate.com
El Debateeldebate.comOpen source ↗. Using the time-of-flight neutron facility n_TOF at CERN, the researchers directly quantified the capture cross section.
Constraining stellar nucleosynthesis models
The empirical value obtained aligns closely with certain prior theoretical calculations, substantially reducing the input uncertainty for stellar evolution codes. By incorporating this cross section, the authors accurately matched the molybdenum-94 abundance measured in presolar meteorite samples.
The international collaboration included the Leibniz Institute for Solid State and Materials Research Dresden, the Institut Laue-Langevin, and the Paul Scherrer Institute. The authors note that full resolution of the nucleosynthetic pathway requires future measurements of other competing nuclear channels in niobium-94 that currently remain unverified experimentally.
