Physics Seminar

Thursday, October 08, 2026 at 2:00pm to 3:30pm

Zooom
Dr. Renuka Rajapakse
rrajapakse@umassd.edu
https://umassd.zoom.us/j/96467854751?pwd=VNpsXZMMdIRO6I2j3Mo5QOcNNb1U2v.1

Abstract:

⁷⁸Ni is a doubly magic nucleus far from stability, which was identified as an early “waiting point” for r-process nucleosynthesis. Recent measurements indicate that decays of nuclei beyond N=50 can be understood as the decay of the ⁷⁸Ni core, with the valence neutrons outside N=50 playing only a spectator role (Madurga et al.). In this experiment, the focus was extended to also study the decay of nearby ⁷⁹Cu. The N=50 isotones near ⁷⁸Ni were studied for the first time using total-absorption spectroscopy, with the beta-decay strength distribution measured at the FRIB Decay Station initiator (FDSi). The experiment employed the Modular Total Absorption Spectrometer (MTAS) to measure complete γ-ray cascades following decays to neutron-bound states in ⁷⁹Cu. The isotopes were implanted at the second focal plane of the FDSi into a Yttrium Ortho-silicate(YSO) segmented scintillator detector system inside the MTAS. An ion-beta correlation was performed on the collected isotopes, and the optimal correlation radius was found to acquire the best signal-to-background ratio. Further analysis will be performed using the Geant4 simulations to obtain the MTAS response functions. A complete deconvolution of MTAS spectra allows for the extraction of β-decay strength distribution for ⁷⁹Cu. The experimental findings will be compared with the nuclear shell models to study the evolution of the N=50 shell closure in the region.

Biography:

Prabodha earned his BSc degree in physics from the University of Peradeniya, Sri Lanka. After that, he began an MS in physics at UMass Dartmouth and graduated in 2023. Under Prof. Robert Fisher, he researched viscous evolution in Astrophysical disks. That same year, he started his PhD in physics at the University of Tennessee, Knoxville, and is currently a fourth-year PhD student there. After working in computational astrophysics, Prabodha shifted his interests to Experimental Nuclear physics, where he focuses on nuclear structure and nuclear astrophysics. His current research focuses on studying the decay of neutron-rich isotopes near the 78Ni shell closure, and Prof. Robert Grzywacz advises him.