03/25/2026
By Muzafar Ibrahim

The Kennedy College of Science, Department of Physics and Applied Physics, invites you to attend a Master's Thesis defense by Muzafar Ibrahim on: "Experimental Study of the Electromagnetic Transitions in Neutron-rich 22F."

Defense Date: Friday, April 10, 2026
Time: noon-2 p.m.
Location: Pinanski 202

Committee:

  • Advisor: Peter Bender, Ph.D., Assistant Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Andrew Rogers, Ph.D., Associate Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Hugo Ribeiro, Ph.D., Assistant Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell

Abstract:

Exotic nuclei have revealed that nuclear shell structure evolves as a function of proton–neutron imbalance. In the nuclear shell model, “magic numbers” arise from large energy gaps between major shells that lead to enhanced stability for specific proton or neutron numbers. However, experiments on neutron-rich nuclei have shown that these shell gaps can change far from stability, demonstrating that the nucleus behaves as a quantum many-body system whose structure depends sensitively on its nucleon composition.

A prominent example occurs near neutron number N=20, where neutron-rich isotopes of Ne, Na, and Mg exhibit strong quadrupole deformation and ground states dominated by intruder configurations originating from the neighboring shell. This region is known as the “Island of Inversion” (IoI), where cross-shell excitations become energetically favorable and the conventional sd-shell ordering breaks down.
In the present work, excited states of the neutron-rich nucleus 22F, were populated using the 9Be(18O, αp)22F fusion-evaporation reaction. A 3 MeV/u 18O beam was delivered by the Argonne Tandem Linac Accelerator System (ATLAS). Prompt γ-ray emission was measured with the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA), consisting of 12 high-purity germanium (HPGe) models and positioned to cover polar-angles between 70◦ < θ < 170◦ relative to the beam axis. The recoiling 22F residues were identified and selected using the Fragment Mass Analyzer (FMA).

Doppler-corrected γ-γ coincidence spectra enabled the construction of an expanded level scheme, revealing new excited states and previously unobserved transition branches. Spin and parity assignments are deduced from aligned angular distribution and linear polarization measurements.

The deduced level scheme is compared with the state-of-the-art "ab initio" calculations derived from the chiral effective field theory, providing new insights into exotic neutron-rich nuclei.