Laboratory breakthrough clarifies ancient star chemistry

• Astronomers have resolved a decades-old mystery regarding excess strontium in Carbon-Enhanced Metal-Poor (CEMP) stars by accurately determining the neutron capture rate of Krypton-88.
• Scientists previously struggled to reconcile observed strontium levels with theoretical "i-process" (intermediate neutron-capture) models because the specific nuclear data for Krypton-88 was unknown.

The Scientific Challenge

• Astrophysicists use three main processes to explain the creation of heavy elements (metals): the slow s-process, the rapid r-process, and the i-process.
• CEMP stars, among the oldest in the universe, consistently showed higher levels of strontium than models predicted.
• The discrepancy hinged on the behavior of radioactive Krypton-88, which can either capture a neutron to become heavier or undergo beta decay into strontium.

Experimental Solution

• Researchers at the Argonne National Laboratory's Californium Rare Isotope Breeder Upgrade facility conducted a surrogate experiment.
• They bombarded Bromine-89 (half-life of 4.357 seconds) with neutrons to observe its decay into Krypton-89.
• Using a specialized Summing NaI (SuN) detector, the team measured Nuclear Level Density and the gamma-ray Strength Function.
• These values allowed researchers to reverse-engineer the neutron capture rate of Krypton-88, providing the missing link that successfully reconciled the chemical ratios in star simulations.