07/23/2026
By Christian Burns

The Kennedy College of Sciences, Department of Physics, invites you to attend a doctoral dissertation defense by Christian Burns on "Prompt Spectroscopy of 254No."

Candidate Name: Christian Burns
Degree: Doctoral
Defense Date: Tuesday, Aug. 4, 2026
Time: Noon to 1:30 p.m.
Location: Room 202, Pinanski Hall, North Campus, UMass Lowell and via Zoom

Thesis/Dissertation Title: Prompt Spectroscopy of 254No

Committee Members:

  • Advisor: Partha Chowdhury, Ph. D., Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Andrew Rogers, , Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell
  • Hugo Ribeiro, Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell

Brief Abstract:

For the heaviest elements in the universe, as the proton number (Z) increases, the delicate competition between long-range repulsive Coulomb forces and short-range attractive nuclear forces dictates the existence of the heaviest nuclei, with valence gaps in the quantum energy levels of specific nuclei increasing their stability. These superheavy nuclei cannot be produced in quantities where their excited levels can be probed via spectroscopic techniques. The current spectroscopic frontier is at Z ≲ 106, where data are available to test superheavy theories.

This thesis presents a combined analysis of two recent experiments that populated the nucleus 254No via the 208Pb(48Ca,2n)254No fusion-evaporation reaction at Argonne National Laboratory. The relatively high production cross-section for the nucleus 254No (Z = 102, N = 152) makes it a "gateway" nucleus for such studies.

The nucleus is axially deformed and exhibits robust collective rotation perpendicular to its symmetry axis. In addition, proton and neutron pairs occupy valence orbitals with large projections (K) of their intrinsic angular momenta along the symmetry axis. The pairs break and combine to form 2- and 4-quasiparticle (qp) high-K isomeric states, leading to an interplay between intrinsic and collective excitations.

The excitations of 254No were investigated using in-beam gamma-ray spectroscopy (Gammasphere array) coupled with recoil-decay-tagging techniques (AGFA spectrometer). Rotational excitations populating the 4-qp 16⁺ isomeric state are identified for the first time, along with new transitions extending the ground-state rotational band. These new spectroscopic observations provide important constraints on the structure of 254No, laying a foundation for future high-statistics experiments and a more complete understanding of single-particle and collective excitations in this region, where shell effects govern the stability of the heaviest nuclei.