Brownian Shape Motion in Fission: A marriage between structure & dynamics

Abstract: Ever since its discovery 85 years ago, nuclear fission has posed serious theoretical challenges but, at the same time,

the phenomenon presents unique opportunities to gain insights into the nuclear system.  Over the past dozen years or so,

the field has experienced a renaissance due to significant improvements in both instrumentation and modeling.  This talk focusses on the latter.

Although the nuclear many-body system resembles a (charged) liquid drop, its nucleons have long mean free paths and move

in a 'mean' field, occupying specific single-particle orbitals.  Consequently, the nuclear system displays both macroscopic and

microscopic features.

When the nucleus undergoes a shape change, as during the fission process, the associated change of the mean field agitates the nucleons, thus heating up the system.  This mechanism causes the dynamics to be strongly dissipative, so the shape evolution is akin to Brownian motion.  The fission process can therefore be simulated as a random walk in the space of nuclear shapes.

The resulting treatment, which in effect constitues a 'marriage' between macroscopic dynamics and microscopic structure, provides a novel and powerful theoretical tool for calculating a variety of fission observables.  For the first time, the fission fragment mass (and charge) yields can now be fairly reliably calculated for any fissionable nucleus.  Moreover, when the shape-dependent miscroscopic structure in the density of states is incorporated, more detailed features can be understood, such as the possibility of a non-monotonic energy dependence of the mmass yields and the sawtooth fragment-mass dependence of the mean neutron multiplicity.

Advanced Technology for Positron Emission Tomography and Applications in Human Biomedical Research

Positron emission tomography (PET) imaging is an important clinical tool for staging and monitoring treatment response in cancer patients and has diagnostic and research applications in the heart and brain.  A new generation of PET systems have been developed recently which result in a quantum leap in imaging performance, and in doing so open new opportunities for the application of PET in biomedical research and in the clinic.  This presentation will focus on these new advanced imaging systems and highlight some of the research opportunities they bring for new discoveries about how the human body functions, both in health and disease.

One key development has been the first total-body PET scanners which cover the entire human body and allow radiotracer kinetics to be measured with high sensitivity across all organs and tissues.  The design and performance of the first total-body PET scanner will be presented along with examples of several applications that demonstrate the power of using this technology for quantitative measurements of function across the human body, including total-body perfusion imaging and total-body assays of T-cells. The role of dynamic imaging, kinetic modeling and parametric imaging using total-body PET will be illustrated.

A second key development are new generations of dedicated PET scanners for imaging the human brain with much improved spatial resolution and/or detection sensitivity.  Three such systems are currently under development with funding from the NIH Brain Initiative in the USA, and early results and images from one of these systems, which has recently been completed, will be presented.

Finally, opportunities for developing even better PET scanners will be discussed, focusing primarily around improvements in time-of-flight performance, which, ultimately could lead to real-time and reconstruction-free imaging of positron-labeled radiopharmaceuticals.  Such systems would approach the theoretical performance limits for imaging radiotracers and permit novel imaging geometries, providing an exquisitely sensitive and quantitative imaging and measurement tool for biomedical research in human subjects.

Recent Progress of J-PARC Facilities in Japan

J-PARC finished its construction 14 years ago, in 2009. In this talk, I review its progress, primarily in particle and nuclear physics. First, the neutrino experiments are described on determining q-13 followed by their efforts towards CP violation. Next, nuclear physics experiments with hyperons are described, including double hypernuclei, kaon in nuclei, etc. In the third, particle physics experiments other than the above neutrino experiments will be mentioned, followed by the fourth topic of material science with neutron and muon beams. Finally, future projects, including heavy-ion acceleration at J-PARC, are discussed.

Let there be light: next generation neutrino detection at Theia

Neutrinos are some of the most fascinating particles that occur in nature. Over one billion times lighter than the proton, the neutrino was once thought to be massless and to travel at the speed of light. The Nobel-Prize winning discovery of neutrino oscillations demonstrated that neutrinos have non-zero mass, which opens up the unique possibility of the neutrino being its own antiparticle, known as a Majorana fermion. This talk will discuss the physics landscape, and present recent technological advances that enable a new kind of “hybrid" neutrino experiment, which would combine two highly successful detection techniques: the topological information of Cherenkov detectors, with the high light yield of scintillators. The Theia detector would be capable of combining both signals to achieve unprecedented levels of particle and event identification, offering a rich program of science across high-energy particle, nuclear and astrophysics. If deployed as one of the “modules of opportunity” at the DUNE far site, Theia could offer insights into both CP violation, and the search for Majorana neutrinos: the two ingredients necessary to shed light on the source of the matter antimatter asymmetry in our Universe.

Fundamental Physics with Nuclei

Next-generation experiments are poised to explore lepton-number violation, discern the neutrino mass hierarchy, understand the particle nature of dark matter, and answer other fundamental questions aimed at testing the validity and extent of the Standard Model. Nuclei are used for these high-precision tests of the Standard Model and for searches of physics Beyond the Standard Model. Without a thorough understanding of nuclei, including electroweak structure and reactions, we will not be able to meaningfully interpret the experimental data nor can we disentangle new physics signals from underlying nuclear effects. To describe nuclear properties, I use many-body nuclear interactions and electroweak currents derived in chiral effective field theory, and Quantum Monte Carlo methods to solve for the nuclear structure and dynamics of the many-body problem for nuclei. This microscopic approach yields a coherent picture of the nucleus and its properties, and indicates that many-body effects are essential to accurately explain the data. In this talk, I will report on recent progress in Quantum Monte Carlo calculations of electron and neutrino interactions with nuclei in a wide range of energy and momentum transfer and their connections to current experimental efforts in fundamental symmetries and neutrino physics.

Nuclear Electric Dipole Moments

The size of the matter-antimatter asymmetry strongly suggests that there are additional sources of CP violation beyond those of the standard model.  One consequence could be the generation of measurable neutron and nuclear electric dipole moments (edms).  Certain nuclei are of particular interest because of parity doublets that will greatly enhance the edm.  The most spectacular opportunities are associated with octupole deformed nuclei.   I’ll describe perhaps the strangest case — the rare isotope 229Pa — where the separation of the doublet is small even compared to atomic scales.  Interest in 229Pa is being driven by the FRIB isotope harvesting program, which will produce for the first time the needed yields.

Radiation Detection, Localization, and Tracking in Urban Environments

The ability to detect, identify, and localize illicit radiological/nuclear sources in real-world environments is a key component of nuclear security and nuclear non-proliferation efforts across the world.  In this presentation, I will describe ongoing LBNL-led efforts to develop new technologies for radiation detection, localization, and tracking.  These technologies include advanced vehicle-based detection systems and intelligent sensor networks that exploit advances in contextual sensing, telecommunications, and edge and cloud computing to provide new capabilities for radiation detection in urban environments.