Current Schedule

Speaker = Prof. Mark Spieker of Florida State

Host = Uthayakumaar, Sivi uthayaku@frib.msu.edu

When = 2025-09-03 Wednesday 15:30

Where = FRIB 1300

Please feel free to sign up below, but note that some slots may need to be re-assigned to accommodate those with a specific need to meet the speaker. If this happens, the Admin or Speaker Host will reach out to you via email.

Title: Experimental studies of the pygmy dipole resonance

Abstract

In atomic nuclei, the term pygmy dipole resonance (PDR) has been commonly used for the electric dipole (E1) strength around and below the neutron-separation energy. It has been shown that the PDR strength strongly impacts neutron-captures rates in the s- and r-process, which synthesize the majority of heavy elements in our universe. A precise understanding of the PDR's microscopic structure is essential to pin down how it contributes to the gamma-ray strength function often used to calculate neutron-capture rates with statistical approaches. In fact, the different responses to isovector and isoscalar probes highlighted earlier the complex structure of the PDR and emphasized that different underlying structures would indeed need to be disentangled experimentally if stringent comparisons to microscopic models wanted to be made. In this seminar, I will give a broad overview on recent experimental investigations of the PDR and how associated results help to better understand its structure. I will specifically feature recent one-neutron (d,p) transfer studies of the PDR in 208Pb, 120Sn, 62Ni, and 50Ti, which illuminate its neutron single-particle character. For 208Pb, the new data will be briefly compared to the large suite of complementary, experimental data available highlighting how our collaboration established (d,p) as an additional, valuable, experimental probe to study the PDR and its collectivity.

To highlight future possibilities, I will also present first results from a new experimental setup recently commissioned at the Super-Enge Split-Pole Spectrograph at Florida State University for particle-gamma coincidence experiments, called CeBrA, and highlight the value other particle transfer reactions could add to studying the microscopic structure of the PDR. Ideas for performing similar experiments at Argonne National Laboratory and the Facility for Rare Isotope Beams (FRIB) at Michigan State University will be discussed if time permits.

The low-energy nuclear physics group at Florida State University acknowledges support by the U.S. National Science Foundation (NSF) under Grant Nos. PHY-2012522, PHY-2412808, PHY-2405485, and by the U.S. Department of Energy, National Nuclear Security Administration (NNSA) under Grant No. DE-NA0004150 [Center for Excellence in Nuclear Training And University-based Research (CENTAUR)] as part of the Stewardship Science Academic Alliances Centers of Excellence Program. Support by Florida State University is also gratefully acknowledged.

Relevant background with commentary from Speaker:

• stuff and things