|January 18||MARTIN LUTHER KING DAY||No Seminar|
|January 25||Sven Binder
|Effective field theory in the harmonic oscillator||Self|
|February 1||Charlie Rasco
|Recent β-Decay Studies with the Modular Total Absorption Spectrometer(MTAS)||Dr. Kate Jones|
|February 8||Kate Jones
|Direct Reaction involving the Halo Nucleus 11Be||Self|
|February 15||Tony Thomas
|The role of quarks and gluons in nuclear binding: a deeper understanding of nuclear structure||Dr. Jirina Stone|
|February 22||Carla Fröhlich
|Nuclear physics and theh origin of heavy elements||Dr. Kate Jones|
|February 29||Alfredo Estrade
Central Michigan University
|Nuclear structure and astrophysics at the edge of the nuclear landscape||Robert Grzywacz|
|March 7||Leah Broussard
|Ultracold Neutrons: Fundamental Science and Applications||Nadia Fomin|
|March 14||SPRING BREAK||No Seminar|
|March 21||Kemper Talley
|Updating Nuclear Beta-Decay Data and Models for SCALE||Self|
|March 28||Art Ruggles
UTK Nuclear Engineering
|Positron emission particle tracking (PEPT) for flow measurement and simulation validation||Kate Jones|
|April 4||Marija Vostinar
|Spectroscopic studies of 257,258Db||Self|
|April 11||Alex Lepailleur
|Spectroscopy of 26F and 28Na to probe proton-neutron forces close to the drip line||Kate Jones|
|April 18||James Matta
|Collective Nuclear Structure: Transverse Wobbling in 135Pr and 6Li as a Probe of the ISGMR||Kate Jones|
Effective field theory in the harmonic oscillator
We develop interactions from chiral effective field theory (EFT) that are tailored to the harmonic oscillator basis. As a consequence, ultraviolet convergence with respect to the model space is implemented by construction and infrared convergence can be achieved by enlarging the model space for the kinetic energy. By fitting to realistic phase shifts and deuteron data we construct an effective interaction from chiral EFT at next-to-leading order. Many-body coupled-cluster calculations of nuclei up to 132Sn exhibit a fast convergence of ground-state energies and radii in feasible model spaces.
Recent β-Decay Studies with the Modular Total Absorption Spectrometer(MTAS)
The NaI(Tl) based Modular Total Absorption Spectrometer (MTAS) was constructed to measure improved β-decay feeding patterns from neutron-rich nuclei. MTAS was designed and built because it is difficult to measure all of the γ-rays from β-decay with high precision γ-ray measurements due to the low efficiency of high precision detectors, which is known as the Pandemonium Effect. There are several important applications of improved measurements of β-decay feeding patterns by total absorption spectroscopy; improve understanding of elemental abundances in the universe, help with stockpile stewardship, contribute to understanding of underlying nuclear structure, and improve β-decay feeding measurements to calculate accurately the ν spectra needed to evaluate reactor neutrino measurements. In addition to measuring γ-rays from β-decays, MTAS is directly sensitive to high energy νe particles and to neutrons, all of which are present in many neutron rich nuclei. We will discuss several techniques and present a general framework for analyzing γ-rays, β particles, and neutrons in MTAS. Finally we present β-decay feeding results of several “priority one” measurements relevant to decay heat calculations and some results which are large individual contributors to the νe uncertainty of the reactor anomaly.
Direct Reaction involving the Halo Nucleus 11Be
Close to particle emission thresholds, nuclei can form clusters reducing an A-body problem into an n-body problem, where A is the mass number representing the sum of the number of neutrons and protons and n is the number of clusters. An extreme case of this phenomenon can exist close to a single-nucleon emission threshold where A-1 nucleons cluster into a core and the last, weakly-bound nucleon forms a diffuse halo. In addition to proximity to a particle-emission threshold, usually characterized by a small separation energy, a well-formed nuclear-halo system requires small potential barriers. The last neutron in 11Be has a separation energy of just, Sn = 0.502 MeV, compared to a typical value of 7−8 MeV for stable isotopes. The 1/2+ ground state is in large part a result of the lower- ing of the nlj = 2s1/2 single-particle state. The lack of a strong Coulomb or centrifugal barrier, leads to a one-neutron halo.
The degree to which the nlj = 2s1/2 single-particle state contributes to the ground-state halo of 11Be is usually characterized by the spectroscopic factor, S. Spectroscopic factors can be extracted from data taken in direct reaction measurements by comparing differential cross sections with those calculated with a reaction theory.
The structure of 11Be, the architypal one-neutron halo, has been studied using many methods including β decay neutron knockout, and transfer reactions as well as many theoretical studies. Large discrepancies remained for the 11Be ground state S, and the two measurements for the first excited state gave S = 0.63±0.15 and 0.9.
To aid in resolving these issues, an extensive series of measurements were performed using a primary beam of 10Be at the Holifield Radioactive Ion Beam Facility, at Oak Ridge National Laboratory. The value of S extracted at each of four beam energies, using two global optical models, were compared. Subsequent studies by Deltuva using Faddeev-type reaction theory shows that core excitation, which is not included in our DWBA/ADWA analyses, is an important effect in this reaction.
The role of quarks and gluons in nuclear binding: a deeper understanding of nuclear structure
The fundamental theory of the strong force in QCD, with quarks and gluons the relevant degrees of freedom. Since the discovery of the neutron the standard approach to nuclear structure has been to calculate nuclear properties using many-body theory with the protons and neutrons as the elementary degrees of freedom. While this has proven extremely successful, at a deeper level one might ask whether the structure of the clusters of quarks and gluons that we call nucleons might not be altered by immersion in a nuclear medium. We explain why this should indeed be the case; how this might allow us to derive more fundamental effective forces and finally how one might test this idea experimentally.
Nuclear physics and the origin of heavy elements
The origin of the elements heavier than iron and in particular of the "lighter heavy elements" is a long-standing open question. Current hydrodynamical simulations of core-collapse supernovae find early proton-rich ejecta. Under these conditions, the neutrino-p-process can take place, synthesizing elements beyond iron (Ge, Sr, Y, Zr, and possibly up to Sn). I will review our current understanding of the nucleosynthesis in proton-rich neutrino-driven winds, the sensitivity of the resulting abundance pattern to nuclear reactions, and the implications on the role of the neutrino-p-process in the context of the origin of heavy elements.
Nuclear structure and astrophysics at the edge of the nuclear landscape
The continuous development of the capabilities of radioactive ion beam facilities, and associated experimental techniques, have made an increasing number of unstable isotopes accessible to experiments. The study of such isotopes provides a new light to understand the basic properties of the atomic nucleus, as well as critical data for diverse applications of nuclear physics. Our research involves experiments with sensitive experimental techniques that can be applied to neutron-rich isotopes very far from β-stability. In particular, I will present the work of the time-of-flight mass measurement collaboration at the National Superconducting Cyclotron Laboratory in East Lansing, including recent results on the evolution of the nuclear shell structure around N=28. I will also discuss our program of β-decay experiments using the new Advanced Implantation Detector Array at the Radioactive Ion Beam Factory in RIKEN, Japan, to study isotopes relevant to nucleosynthesis during the rapid-neutron capture process (r-process).
Ultracold Neutrons: Fundamental Science and Applications
Ultracold Neutrons (UCN) provide an excellent laboratory for precision studies of the Standard Model of particle physics, and can be used as a novel tool to probe the properties of other materials. The Los Alamos Neutron Science Center is home to major experimental efforts to use UCN to determine the neu- tron beta decay lifetime, the angular correlations between the neutron spin and the decay proton and electron, and a new search for the electric dipole moment of the neutron. We have recently demonstrated the use of UCN to control the distance of fission events from the material surface, enabling a new set of studies of surface damage and sputtering caused by fission fragments. This seminar will introduce you to the unique properties of ultracold neutrons and highlight recent accomplishments in the experimental program at Los Alamos.
Updating Nuclear Beta-Decay Data and Models for SCALE
Advancements in experimental and theoretical nuclear physics at have yielded new data and models that can be implemented in SCALE, a widely used nuclear engineering code. A new decay mode, β2n, has been added into SCALE for three nuclei heavier than iron: 86Ga, 98Rb, 100Rb. While these nuclei have low branching ratios and low abundance in nuclear reactors, experiments performed at the Holifield Radioactive Ion Beam Facility (HRIBF) at ORNL have also yielded significant changes in our knowledge of βn branching ratios for nuclei in the region of interest (yield and decays following the fission of 235U). New theoretical models have been developed to more accurately reproduce these new data within the region of interest. I present the results of using a few such models for several calculations of interest to nuclear engineers. A change of up to 7% in the abundance of key isotopes such as 135I is predicted by the inclusion of one such model.
Positron emission particle tracking (PEPT) for flow measurement and simulation validation.
Detection system advances allow radio tracer tracking to achieve high levels of performance. Algorithms are presented optimized for tracking particles labeled with positron emitters. Multiple particles are tracked in water flows using pre-clinical PET scanners and performance comparable to conventional optical flow measurement is achieved. Flow measurements inside a stainless heat exchanger are offered to further illustrate the value of the technique in engineering applications.
Spectroscopy studies of 257,258Db
Investigations on the nuclear structure in the region around N=152 deformed shell gap provide an understanding of the existence of superheavy elements (Z>104). Recent experimental studies have led to the determination of the size and the strength of this gap. Its influence was studied for nuclei like 255103Lr152 and 256104Rf152. Valuable information can be obtained by studying further the evolution of the N=152 deformed shell gap. To this purpose, the isotopes of 257105Db and 258105Db were produced and are the subject of this talk. Even though these two isotopes were previously studied, the currently available data are limited and the level schemes are still not fully determined. The 257Db was produced through the fusion-evaporation reaction 209Bi(50Ti,2n)257Db at GANIL. The two previously observed long lived states of 257Db were confirmed in this experiment, as well as the two isomeric states of its decay daughter 253Lr. The 258Db was produced through the fusion-evaporation reaction 209Bi(50Ti,1n)258Db at GSI. A strong indication of the existence of two states in 258Db with different half-lives was observed. A new γ-ray transition of 250Md (granddaughter) was identified and its placement in the partial level scheme is proposed. The α decay of 258Rf was also observed, suggesting a smaller branching ratio than previously reported.
Spectroscopy of 26F and 28Na to probe proton-neutron forces close to the drip line
Nuclear forces play a decisive role to account for the creation and modifications of shell gaps, to explain deformed nuclei, to permit the development of halo structures and to fix the limits of particle stability. To probe the evolution of the proton-neutron interaction when going from the stability toward the neutron drip-line, we studied the odd-odd N=17 isotones on the neutron rich side. These nuclei exhibit a πd5/2×νd3/2 coupling which leads to a quadruplet of states J=1-4 of positive parity. The determination of all of these states in the nuclei of 30Al, 28Na and 26F was required to achieve our goal.
The weakly bound neutron-rich 26F is a benchmarking nucleus for studying this interaction close to the drip line. As lying close to the 24O doubly magic nucleus, its nuclear structure at low excitation energy can be viewed as the interaction between a single deeply bound proton d5/2 (~ -15.1 (3) MeV) and a single unbound neutron d3/2 (~ +0.77 (20) MeV) on top of a closed 24O core. Its structure has been investigated at GANIL and GSI using three experimental techniques: in-beam gamma-ray spectroscopy using the fragmentation method for the J = 2+ state , study of the isomeric decay for J = 4+ , and in-beam neutron spectroscopy using the one proton knock-out reaction for the unbound J = 3+. Comparing the experimental results to shell model calculations, we found a reduction of the residual interaction for this nucleus.
We studied the 28Na through the β-decay of 28Ne at GANIL and the in-beam γ-ray spectroscopy technique at the NSCL facility. Combining these two experiments we have established two new levels of J = 3+1 and 4+1 , completing the quadruplet J = 1+ - 4+ (J = 1+ and 2+ previously known ). Combined with the previously studied 30Al experimental results , we find a systematic deviation between experimental and theoretical binding energies along the N=17 isotones: while the states are calculated too bound in 26F, they are not enough bound in 30Al (which lies close to stability). This suggests that the effective proton-neutron interaction used in the shell model should better take into account the proton-to-neutron binding energy to model nuclei from the valley of stability to the drip line.
 M. Stanoiu et al., Phys. Rev. C 85, 017303, 2012.
 A. Lepailleur et al., Phys. Rev. Lett.110, 082502, 2013.
 A. Lepailleur et al., Phys. Rev. C 92, 05309, 2015.
 V. Tripathi et al., Phys. Rev. C 73, 054303, 2006.
 D. Steppenbeck et al., Nuc. Phys. A 847, 2010.
Collective Nuclear Structure: Transverse Wobbling in 135Pr and 6Li as a Probe of the ISGMR
The nucleus is a many splendored thing. It boasts a dizzying array of complex phenomena at low and high spins, low and high excitation energies, and low and high mass numbers. The study of these properties can be carried out in a wide variety of ways. Despite their simplicity, the techniques of coincidence gamma-ray spectroscopy and inelastic scattering can yield interesting and useful results, albeit in very different regimes of nuclear structure. In this seminar I will discuss two projects I worked on as a graduate student which used these techniques. In transverse wobbling a nucleus with a triaxial core and an unpaired nucleon produce a motion that is the quantum mechanical analog of an asymmetric top. Using coincidence gamma-ray spectroscopy with the Gammasphere array at ANL its existence in the nucleus 135Pr was established. This opened a new mass region to searches for the wobbling phenomena. Additionally it suggested a new interpretation for the wobblers seen in the A~160 region. The Iso-Scalar Giant Monopole Resonance (ISGMR) is a highly collective oscillation of the nuclear radius. This compression mode allows the measurement of the nuclear incompressibility, an important term in the nuclear equation of state which governs neutron star radii, stellar collapse, and heavy-ion collisions. In inverse kinematics, the preferred probe of this oscillation, 4He, works poorly as an active target, however, there is little information about alternative probes. Therefore a normal kinematics study of the ISGMR using 6Li was performed using inelastic scattering with the Grand Raiden magnetic spectrograph in the RCNP at Osaka University to determine 6Li's suitability as a probe of the ISGMR.
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