Gamma-ray spectroscopy for analysis of the decay of La-140 for nuclear forensics applications*

¹⁴⁰La is an important isotope in nuclear forensics, used primarily as a chronometer for nuclear events. The decay of ¹⁴⁰La, however, was last studied more than 30 years ago using a simple detector system. Utilizing the advancements in the instrumentation available to measure radioactive decay, we can obtain considerable improvement on the decay of ¹⁴⁰La. ¹⁴⁰La was produced through neutron irradiation of natural La (99.99% 139La) in the UMass Lowell research reactor. The Argonne National Laboratory where it was assayed with the Gammasphere array, consisting of up to 110 active high-purity Compton Suppressed germanium detectors in a spherical arrangement, can provide high-statistics measurements of low intensity gamma-rays. The analysis was carried out using a γ-γ coincidence matrix as well as a singles spectrum. Utilizing both allowed for us to determine a precise intensity on strong transitions and to better confirm weak transitions.  An angular correlation analysis was also conducted using the coincidence matrix. In this talk, I will present a new decay scheme for ¹⁴⁰La and discuss the improvements on prior measurements.