Key Points
- Finnish researchers measured the atomic masses of radioactive lanthanum isotopes with high precision.
- The study revealed an unexpected “bump” in neutron separation energies when neutrons increased from 92 to 93.
- Findings impact astrophysical models of the r-process, essential for heavy element formation in space.
- New mass values changed neutron-capture reaction rates by up to 35% and reduced uncertainties significantly.
Researchers at the Accelerator Laboratory of the University of Jyväskylä, Finland, have made a groundbreaking discovery in nuclear physics by precisely measuring the atomic masses of radioactive lanthanum isotopes. Their findings reveal an unexpected anomaly in nuclear binding energies, providing new insights into the production of heavy elements in the universe.
The study, published in Physical Review Letters, challenges current nuclear models and calls for further research into the nuclear structure of these isotopes.
The researchers utilized the Ion Guide Isotope Separation On-Line (IGISOL) facility to produce neutron-rich lanthanum isotopes. Due to their short-lived nature, these isotopes are difficult to study. However, using the highly sensitive phase-imaging ion cyclotron resonance technique with the JYFLTRAP Penning trap mass spectrometer, they were able to measure the masses of six lanthanum isotopes with exceptional precision. Notably, the masses of the two most exotic isotopes, lanthanum-152 and lanthanum-153, were recorded for the first time.
One of the study’s key findings was a surprising anomaly in neutron separation energies, which measure the energy required to remove a neutron from an isotope. When the number of neutrons increased from 92 to 93, a sharp “bump” was observed, an unprecedented feature in nuclear physics. This phenomenon may indicate an abrupt change in the nuclear structure, but further investigation using complementary techniques such as laser or nuclear spectroscopy is required.
The discovery is significant for astrophysics, particularly in understanding the rapid neutron capture process (r-process) in neutron star mergers. The researchers found that their new mass values altered neutron-capture reaction rates by up to 35%, significantly reducing uncertainties in astrophysical models. These findings challenge existing nuclear mass models, which fail to predict this anomaly, highlighting the need for theoretical advancements.
