Fall 2017 Nuclear Physics Seminar


Seminars are Mondays 2:20 PM in Nielsen 304. Please contact Miguel Madurga for questions (mmadurga@utk.edu).


Aug. 28        Jeremy Bungaard           UTK

High Precision Measurements Using The NIFFTE fissionTPC

                                                        

Abstract: The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) collaboration has developed the fission Time Projection Chamber (fissionTPC) to make new, high precision fission cross section measurements as called for by the Nuclear Energy and Stockpile Stewardship communities. The fissionTPC is annually deployed to the Los Alamos Neutron Science Center (LANSCE) where it operates in beam, colliding neutrons with heavy actinide tar- gets, inducing fission. This detector was developed at the Lawrence Livermore National Laboratory’s (LLNL) TPC lab, where it routinely measures spontaneous fission (SF) from radioactive sources, typically 252Cf and 244Cm, to characterize detector response, gauge performance, and evolve the design. An important aspect of these source mea- surements is to develop analyses and demonstrate the fissionTPC’s performance abilities/limitations by measuring the α/SF branching ratio of 252Cf; our method benchmarks the fissionTPC’s ability to deduce the α/SF branching ratio with sub-percent precision. The talk will discuss the need for improved fission measurements, details of how the detector operates to create 3D ionization tracks, and analysis methods developed for the 252Cf α/SF branching ratio measurements. The results from the NIFFTE collaboration’s recent publication (submitted June 2017 to PRC) of the neutron induced fission cross section ratio of 238U/235U will also be summarized.

                                


Sept. 11        Xesus Pereira              UTK

                                        

Study of transfer reactions induced by a 16C beam

                                                        

Recent experiments have evidenced the existence of new nuclear shell gaps at N=14 and N=16 in neutron-rich oxygen isotopes associated with the vanishing of the N=20 shell gap. However, in the neutron-rich carbon isotopes, the extent to which these gaps persist is unclear. In an effort to answer this question we have attempted to probe the low-lying level structure of 17C using the (d,p) transfer reaction to locate the single-particle orbitals involved in the formation of the N=14 and N=16 shell gaps.        

The experiment was carried out at the GANIL facility. A 16C beam at 17.2 AMeV produced by fragmentation was used to bombard a CD2 target. The light ejectiles were detected using the TIARA silicon strip array while a Si-Si-CsI telescope was placed at zero degrees to identify beam-like residues. In addition, four HPGe-EXOGAM clover detectors were used to measure the gamma-rays arising from 17C bound excited states.

The measured angular distributions confirm the spin and parity assignments of 3/2+, 1/2+ and 5/2+ for the ground and the first and second excited states located at 217 keV and 335 keV respectively. The spectroscopic factors deduced for these excited states indicate a large single particle strength, in agreement with shell model calculations. With a strong l = 0 valence neutron component and a low separation energy, the first excited state of 17C appears as a good one-neutron halo candidate.


Sept. 18        Gaute Hagen               ORNL

Coupled-cluster computations of atomic nuclei

This talk reviews recent progress in coupled-cluster computations of atomic nuclei based on state-of-the-art interactions from chiral effective-field-theory. An optimization of an interaction from chiral effective field theory to few-nucleon systems and oxygen isotopes yielded much improved binding energies and charge radii in light and medium-mass nuclei. The computation of the nucleus 48Ca showed that its neutron skin (difference between the radii of the neutron and proton distributions) is smaller than previously thought, and we made prediction for its dipole polarizability which has recently been measured. We performed coupled-cluster computations of neutron rich calcium isotopes complementing a recent measurement of charge radii in 49,51,52Ca obtained from laser spectroscopy experiments at ISOLDE, CERN. This experiment found an unexpectedly large charge radius for 52Ca that questions its magicity. We also predicted the 2+ state in 78Ni from a correlation with the 2+ state in 48Ca using chiral nucleon-nucleon and three-nucleon interactions. Our results confirm that 78Ni is doubly magic. It was also found that continuum effects play an important role in the level ordering of 79Ni. I will also show recent results for neutron deficient tin isotopes, where in particular we make predictions for the structure of 100Sn from first principles.


Sept. 25        Rin Yokoyama             UTK

Shape evolution of neutron-rich midshell nuclei around A~160 studied by gamma-ray spectroscopy.

 

Study of the nuclear deformation of midshell nuclei is important to understand how the shell effect drive macroscopic shape of nuclei to have different shapes at different proton or neutron numbers. In neutron-rich A~160 region, onset of higher-order deformations such as octupole () or hexadecupole () deformations are predicted. Such exotic shapes of unstable nuclei are not well understood. However, those deformation can change single particle levels and consequently affect the decay property of the nuclei. Properties of the nuclei in this region is also important in astrophysical point of view because they are on the decay path of nuclei produced in r-process. I am going to present some of the results from isomer and beta-gamma spectroscopy experiments at a fragmentation facility, RIBF, at RIKEN Nishina Center in Japan and discuss on the various shapes of the nuclei in this region.

 


Oct. 2            Adam Matyja               UTK


Oct. 9


Oct. 16         Aaron Sprow                UKY


Oct. 23         Jason Fry                     UVA


Oct. 30         Yuri Efremenko            UTK


Nov. 6           Jonas Braun


Nov. 13        


Nov. 20        


Nov. 27         James Matta                ORNL


Dec. 4          (Grad. Students talk)