TUNL Seminar Series

September 23, 2021

Tom Clegg

UNC Chapel Hill

TUNL's History

Our seminar this week will be given by Tom Clegg and will provide a view of the formation and development of the nuclear physics activities amongst the Triangle area universities.

September 30, 2021

Wei Jia Ong

Lawrence Livermore National Laboratory

Presolar grains as constraints on the origin of the p-nuclei.

There are ~30 naturally existing nuclei on the proton-rich side of the valley of stability which origin cannot be explained by neutron-capture processes. The nuclear astrophysical process (or combination of processes) that lead to the synthesis of these nuclei is not well understood or constrained. Since these p-nuclei are less abundant than the other isotopes of the same elements, astronomical spectroscopy is currently a limited source of data that can be used to constrain the astrophysical environment of origin. Presolar grains, or stellar condensates, can preserve single-event nucleosynthetic signatures from their parent star and can be exploited as a source of information on the formation of the p-nuclei. I will discuss the ongoing cosmochemical and nuclear physics efforts to investigate the origin of the p-nuclei.

October 7, 2021

Joule Othman

UNC Chapel Hill and TUNL

The CAGE Scanner: Investigating Surface Backgrounds in High-Purity
Germanium Detectors

The neutrino is an elusive particle that has challenged our models of the universe. With the discovery of neutrino oscillations, we know that neutrinos have mass, which disagrees with the Standard Model (SM) of particle physics. However, we still do not know the mechanism by which neutrinos obtain their mass.  The discovery of neutrinoless double-beta decay would have a profound impact on our understanding of neutrinos and the universe. It would show that the neutrino is its own antiparticle, ie. a Majorana particle, that lepton number is not a conserved quantity, and would give us insight into the matter-antimatter asymmetry. Next-generation searches for neutrinoless double-beta decay, such as LEGEND, are working to build ton-scale experiments with the goal of discovering neutrinoless double-beta decay.  To discover such a rare process, experiments must be extremely low-background to mitigate unwanted signals that may obscure the signal of interest from neutrinoless double-beta decay. This is accomplished primarily by locating experiments underground to shield against cosmic rays, using very radiopure materials, active vetos, and using pulse shape discrimination in analysis. The LEGEND experiment will operate 76Ge-enriched pointcontact High-Purity germanium (HPGe) detectors directly immersed in a liquid argon (LAr) active veto.

A significant background expected in LEGEND is from radiation interacting near the surfaces of the detectors. Thin passivated surfaces are particularly susceptible to shallowly impinging alpha and beta radiation. To help further mitigate against surface backgrounds on passivated surfaces, dedicated test stands can help us understand the detector response to surface backgrounds and develop cuts to remove them from our data, maximizing our discovery sensitivity to neutrinoless double-beta decay. In this dissertation, we introduce the Collimated Alphas, Gammas, and Electrons (CAGE) test stand, which we built to study passivated surfaces for HPGe detector geometries that will be used in LEGEND. CAGE utilizes collimated radiation sources to study the effect of shallowly impinging radiation on specific locations on the passivated surfaces of HPGe detectors. We improve on previous surface scanning systems by offering more protection from infrared (IR) shine on passivated surfaces and more  flexibility in positioning the collimated source beam, most notably the ability to change the incidence angle of the source beam with respect to the passivated surface of the detector. We show that CAGE is able to operate stably and show the first results from a radial scan of a P-type Point-Contact detector using a 241Am alpha and gamma source. We present the results of a study of the risetimes of the 59.5 keV gamma from 241Am and show that certain risetime parameters can be useful in discriminating against surface backgrounds in LEGEND. We conclude by discussing the future goals of the CAGE test stand.

October 14, 2021

DNP Meeting, no seminar this week

October 21, 2021

Rachel Carr

Assistant Professor, US Naval Academy

Title:  Results of the Nu Tools Study: Exploring Practical Roles for Neutrinos in Nuclear Energy and Security

Abstract:  For decades, physicists have used neutrinos from nuclear reactors to advance basic science. These pursuits have inspired many ideas for applications of neutrino detectors in nuclear energy and security. While developments in neutrino science are now making some of these ideas technically feasible, it has not been clear how practically they mesh with the needs, budgets, and other constraints of end users such as the International Atomic Energy Agency. In 2019, the National Nuclear Security Administration's Office of Defense Nuclear Nonproliferation R&D commissioned a community study on this question. The study, called Nu Tools, included extensive interviews with over 40 nuclear security and energy professionals. Perhaps surprisingly, these experts do see practical niches for neutrino detectors, but not in the places neutrino physicists have often seen them. This talk will review the Nu Tools study and findings, available in full at: https://nutools.ornl.gov/

October 28, 2021

Eric Wulf

November 4, 2021

HIγS Celebration

Mohammad Ahmed

November 11, 2021

HIγS Celebration

Werner Tornow, Vladimir Litvinenko, Norbert Pietralla

November 18, 2021

SESAPS Meeting: no seminar

November 25, 2021

Thanksgiving, no seminar

December 2, 2021

Leendert Hayen

December 9, 2021

Jon Engel

December 16, 2021