First results from the CARIBU facility: mass measurements on the r-process path

Area of Science:

• Nuclear Physics
• Nuclear Astrophysics
• Rare Isotope Science

Background:

• The astrophysical rapid neutron-capture (r) process is crucial for nucleosynthesis of heavy elements.
• Accurate nuclear mass data is essential for modeling r-process nucleosynthesis, particularly at waiting points.

Purpose of the Study:

• To precisely measure the masses of 33 neutron-rich nuclides around the 132Sn double shell closure.
• To investigate the impact of these new mass data on astrophysical r-process simulations.

Main Methods:

• Utilized the Canadian Penning Trap mass spectrometer for high-precision mass measurements.
• Received rare isotopes from the Californium Rare Isotope Breeder Upgrade facility at Argonne National Laboratory.

Main Results:

• Achieved typical measurement precision at the 100 parts-per-billion (ppb) level or better.
• Measured masses for nuclides with Z from Indium (In) to Cesium (Cs), including Sn isotopes up to A=135.
• Simulations incorporating direct mass measurements showed significantly increased waiting times at Tin (Sn) and Antimony (Sb) isotopes.

Conclusions:

• The new mass data reveals critical discrepancies with existing nuclear mass models.
• Current models are inadequate for accurate r-process calculations due to insufficient precision in predicting masses near the 132Sn region.
• These findings necessitate revised nuclear mass models for a better understanding of heavy element formation.