Alexander "Sasha" Chemey: From raw materials to fission studies

URL: https://enppreview.tamu.edu/events/fr...

ABOUT THE SPEAKER: Alexander “Sasha” Chemey is currently employed as a Postdoctoral Scholar in the Loveland Group at Oregon State University in the Department of Chemistry. His work there has been split between fundamental fission studies, actinide target-making, and new electronics development. He received his PhD in Chemistry in the Thomas Albrecht-Schönzart (previously Albrecht-Schmitt) group at Florida State University, where his dissertation was titled “Actinide Fluorides.” While at Florida State, he was a leader in the Department of Energy’s “Early Career Network,” organizing a symposium on the Federal R&D Budget Process for the 2017 National Meeting. He also received an award from the Department of Energy Office of Nuclear Technology in 2019 with the “Innovations in Nuclear Technology” program. His undergraduate research at Michigan State University was at the NSCL, working with Sean Liddick on algorithms for covert nuclear weapons tests by measurement of xenon isotopes.

ABSTRACT: Nuclear fission is a vital area of study for reasons of energy generation and national security. Production of rare isotopes in nuclear reactors and from natural sources enables new physical phenomena to be examined. The production of targets suitable for heavy ion spectroscopy, such as is appropriate with fission fragments, remains a challenge. Understanding the influence of target chemistry is important for proper interpretation of fission physics results due to the large influence of target composition on stopping power.

While thermal-spectrum fission energy release is well understood, the influence of neutrons faster than ~ 20 MeV remains uncertain, and unexpected observations are still being made. In particular, the influence of fast neutron energy on total kinetic energy (TKE) release remains somewhat less than quantitative in description, even with commonly-studied isotopes such as 233U, 237Np, and 239Pu. This is important, as fission fragment TKE is over 80% of the energy released in fission. Recent experiments measuring the TKE release in (n, f) reactions have determined an unexpected plateau for the region of (30 MeV less than En less than 70 MeV). Additional information regarding the configuration of the fissioning nucleus can be obtained by comparison of nuclear distortion at the scission point as a function both of mass and incident neutron energy. Discussion of results from just above the fission barrier to 100 MeV will be presented.

Oregon State University has recently obtained an upgraded digital data acquisition system (DDAS) for use in fission studies. The use of MVME software and MDPP-16 data modules (both produced by Mesytec) are tested with simultaneous alpha particle and fission fragment detection at the Oregon State TRIGA Reactor. The flexibility and stability of this system is demonstrated with after-the-fact searches for ternary fission fragments perpendicular to the path of principal fission fragments. Time, energy, and mass relationships between putative ternary particles and principal fission fragments are examined and used to benchmark the MDPP-16 module time and energy resolutions. Insights into the influence of effective target and backing thickness are presented from these data, including the use of alpha decay energy loss as an internal calibration for these variables.