Seminars

Tuesday, Sep 26 at 11:00 AM
NSCL Lecture Hall 1200
Linda Hlophe, NSCL/FRIN
6Li in a Three-Body Model with Realistic Forces: Separable vs. Non-separable Approach

Abstract:  Faddeev equations in momentum space have a long tradition of utilizing separable interactions in order to arrive at sets of coupled integral equations in one variable. However, it needs to be demonstrated that their solution based on separable interactions agrees exactly with solutions based on non-separable forces. I will discuss calculations of the 6 Li ground state via momentum space Faddeev equations using the CD-Bonn neutron-proton force and a Woods- Saxon type neutron(proton)- 4 He force. For the latter the Pauli-forbidden s-wave bound state is projected out. Two methods for evaluating the 6 Li three-body ground state are considered. First, we solve the bound state Faddeev equations directly using the afore-mentioned two-body potentials. In the second approach, the interactions in the two-body subsystems are represented by separable interactions derived in the Ernst-Shakin-Thaler (EST) framework. We find that by utilizing the full parameter space of the EST separable expansion, one can attain a precision of upto four significant figures in three-body binding energy. It is also shown that the three-body binding energy computed in this manner agrees fully with the one obtained directly within the stated numerical precision. The momentum distributions computed in both approaches also fully agree with each other.

Wednesday, Sep 27 at 4:10 PM
NSCL Lecture Hall 1200
Paul Garrett, University of Guelph
On the nuclear structure of the Cd isotopes: do they possess low-lying vibrational states?

Abstract:  The nuclear structures of the even-even Cd isotopes near stability, especially 110-116Cd, were long thought to be prime examples of spherical nuclei possessing low-lying vibrational states. Their level schemes display nearly harmonic spacings of one, two, and three-phonon levels. Due to their importance as paradigms of vibrational motion, their structures have been investigated by a variety of reactions. These reactions were essential for establishing the location of levels and their main decay branches, together with level lifetimes, but for many levels they lacked the sensitivity to probe the weak low-energy decay branches that are necessary to assess the degree of collectivity that the states possess. In order to complement the data used to test the collectivity present in the Cd isotopes, high-statistics [beta]-decay experiments using the 8[pi] spectrometer at the TRIUMF radioactive-beam facility have been performed. The goal of these experiments was to achieve a sufficient sensitivity to weak, lowenergy branches amongst the multi-phonon levels so that the collective branches would either be observed, or very stringent upper limits set. Thus far, we have examined the decay of 110In to 110Cd, and 112In/112Ag to 112Cd. These experiments have revealed that the individual low-spin multi-phonon states do not decay in the expected manner. Further, and much more surprising, the missing E2 strength is not due to fragmentation (i.e., mixing) amongst the levels. While the breakdown of vibrational motion at the 3-phonon level is perhaps not surprising, combining data from complementary measurements, especially Coulomb excitation and E0 strengths, has enabled us to rule out the existence of the 0+ member of the 2-phonon triplet. This lack of the E2 strength has forced a re-evaluation of the structure, suggesting that the Cd isotopes do not possess low-lying multiphonon vibrations about a spherical shape as envisioned in the Bohr picture. The results on the Cd isotopes raises the issue that if our long-standing paradigms of spherical vibrations can no longer be considered as such, are there any spherical vibrational nuclei?

Thursday, Sep 28 at 11:00 AM
NSCL Lecture Hall 1200
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Highlights in Progress
Monday, Oct 02 at 2:00 PM
NSCL Lecture Hall 1200
G.F. Grinyer, University of Regina
ACTAR TPC: a high-luminosity detection system for low-intensity beams

Abstract:  The Active Target and Time Projection Chamber (ACTAR TPC) is an ambitious European project whose goal is to design and construct a high-luminosity gas-filled detector to study reactions and decays of rare isotopes. The core detection system will consist of one (or possibly several) micro-pattern gaseous detectors (MPGDs) coupled to a highly pixelated pad plane with a pitch of only 2x2 mm2. Both the channel density (25 channels/cm2) and total number of electronics channels (16384) are the highest that have been achieved by any nuclear physics detector to date. In this presentation I will provide an overview of the project, discuss the principal challenges associated with constructing such a device and present the day one physics programs for ACTAR TPC when it goes online at the GANIL laboratory in France in 2018.

Tuesday, Oct 03 at 11:00 AM
NSCL Lecture Hall 1200
Willem Dickhoff, Washington University in St. Louis
A UNIFIED APPROACH TO THE DESCRIPTION OF NUCLEAR REACTIONS AND STRUCTURE

Abstract:  The era of FRIB will further clarify that one can never unambiguously extract structure information without a proper reaction description when strongly interacting probes are involved. An outline of an ambitious plan to tackle this issue in a consistent manner will be presented with emphasis on the dispersive optical model (DOM) that treats the structure and reaction domain simultaneously at least for single proton or neutron propagation. Apart from upgrading this framework to include nonlocality of the potentials and the treatment of pairing open-shell nuclei, attention will be given to an extension of this approach involving the deuteron in the initial or final state. A fresh analysis of the (e,e’p) reaction indicates that a consistent approach is indeed possible. Predictive features of the DOM include the neutron skin with results for 48Ca and (preliminary) 208Pb. The efficacy of this approach is further illustrated by considering the current state of the art of the (d,p) and (p,d) reaction. Additional insights into where binding is generated in the nucleus are discussed with future applications to asymmetric nuclei.

Wednesday, Oct 04 at 4:10 PM
NSCL Lecture Hall 1200
Sami Tantawi, SLAC National Accelerator Laboratory
Perspectives on Ultra-Compact High Gradient RF Accelerator Technology

Abstract:  Accelerating particles over shorter distances than ever before opens new doors in many areas of science. To this end, we have been exploring RF breakdown phenomena in high vacuum structures. We have been able to engineer some of the materials used in the accelerator structure and modify its geometry to achieve extremely high gradients~175 MV/m. Now, our research effort have to also include practical engineering developments to transform these advances into practical devices that can be applied to photon science, high-energy physics, medical, industrial and national security uses. In this talk We will describe our progress on high gradient RF accelerators and the equally advanced developments for compact RF sources capable of driving these new types of accelerators. We will also describe some of the applications being enabled by these developments. For photon sciences, we are looking at compact high repetition rate coherent X-ray sources. For high energy physics application we are looking at the next generation of accelerators for linear colliders. For medical applications we are exploring a new paradigm shift in radiation therapy that will enable dose delivery at an extremely fast time scale; enough to freeze motion and hence enhance precision.

Thursday, Oct 05 at 12:30 PM
NSCL Lecture Hall 1200
Peter Knudsen, FRIB
Efficient and Cost Effective Small 2 K Systems for Laboratory Use

Abstract:  There is a need for small 1.8 K to 2.1 K refrigeration systems for SRF systems and component testing in the laboratories, which can provide 50 to 100 W, that are cost effective, efficient, and relatively easy to implement. This capacity and temperature range is not practically or efficiently handled by cryo-coolers. These are very energy intensive applications and it is not uncommon for these small systems to require up to 7000 Watts per 1 Watt of cooling at 2 K, which is approximately an order of magnitude higher input power for the same cooling capacity as compared to large systems. For these small (capacity) systems, a very modest additional capital investment can substantially improve the performance to less than 2000 Watts per Watt, and these can be packaged to work with a standard commercial 4.5 K liquefier. This talk will discuss possible design options and the projected performance for these small systems.

Monday, Oct 09 at 12:30 PM
Biomedical & Physical Sciences Bldg., Rm. 1400
James Lawler, University of Wisconsin
Elemental r-process Abundance Patterns in Metal-Poor (old) Stars

Abstract:  Heavy nuclei beyond the Fe-group are made primarily via r(apid)-process and s(low)-process n(eutron)-capture events. Although the s-process n-capture is fairly well understood, the r-process n-capture events remain poorly understood. The relative role of Core Collapse Supernova and n-star mergers will likely be understood in the next few decades. I will discuss recent studies of old Metal-Poor stars that are revealing some new details of nucleosynthesis. This progress is due to the availability of high resolution spectra from large ground based telescopes, access to the UV via the Hubble Space Telescope, and better laboratory data.

Tuesday, Oct 10 at 11:00 AM
NSCL Lecture Hall 1200
Jangho Kim, NSCL/FRIB
QCD Phase Boundary in the Strong Coupling Regime.

Abstract:  Strong coupling lattice QCD in the dual representation allows to study the full \\mu-T phase diagram, due to the mildness of the finite density sign problem. This has been done in the chiral limit, both at finite N_t and in the continuous time limit. We extend the phase diagram to finite quark masses and finite inverse gauge coupling. I present numerical results from direct Monte Carlo simulations via worm algorithm.

Tuesday, Oct 17 at 11:00 AM
NSCL Lecture Hall 1200
Ian Thompson, Lawrence Livermore National Laboratory
Using experiments and theories for nuclear data evaluations

Abstract:  That would be a high-level view of the whole process of making nuclear data. It will explain how theories and experiments and models all get combined. Especially relevant if FRIB is to make nuclear data for new nuclides.

Wednesday, Oct 18 at 4:10 PM
NSCL Lecture Hall 1200
Silvia Jurisson, University of Missouri
High Specific Activity Radiometal and Radiometalloid Chemistry for Development of Potential Radiopharmaceuticals

Abstract:  Rhenium-186 (186Re), arsenic-77 (77As), and rhodium-105 (105Rh) are radionuclides with nuclear properties suitable for “theranostics” in that they emit both beta particles for radiotherapy and gamma rays for imaging, with 90 h, 38.8 h and 35.4 h half-lives, respectively. Additionally, 72As is a positron emitter that is a true “matched pair” radioisotope for 77As. All of these radionuclides can be produced in high specific activity at either an accelerator or nuclear reactor. High specific activity 77As and 105Rh are produced by thermal neutron irradiation of 76Ge or 104Ru, followed by beta decay, with the 77As and 105Rh separated from the enriched targets. High specific activity 186Re can be produced by either proton or deuteron irradiation of enriched 186W or by proton irradiation of enriched Os targets, again followed by separation of the 186Re- from its target material. Sulfur-containing chelates (either thiols or thioethers) are used to form stable complexes with these radionuclides. The chemistry and radiochemistry from production through preliminary biological studies will be presented.