The rapid neutron capture process, or r-process, is a stellar phenomenon responsible for synthesizing nuclei heavier than iron. The r-process utilizes thousands of nuclei and occurs far from stability. Its precise nuclear path is dependent on multiple environmental factors and the stellar site, making simulations key in understanding its nature. There are important experimental quantities that affect r-process simulations: the mass of nuclei along the path, their lifetimes, neutron capture rates, neutron density and the neutron energy distribution from this decay. This neutron density and energy distribution are affected by beta-delayed neutron (BDN) emission, a type of exotic decay that occurs in nuclei with beta decay Q-values greater than the neutron separation energy. A given nucleus has two pieces of information in a BDN decay – the neutron emission probability and the neutron energy distribution – but existing techniques only measure one of the two.

At Argonne National Laboratory, we have developed a new technique for studying BDN emission and getting both the probability and energy spectrum simultaneously. Isotopes are sent to the beta Paul trap (BPT), which detects the recoiling ion when it decays, in lieu of the neutron. Eight isotopes were studied at the Californium Rare Isotope Breeder Upgrade (CARIBU) using the BPT. The trapping technique allows for multiple independent calculations of the probability by having three ways to calculate the total number of decays: detecting the recoiling ions, betas, and gammas.