- Unless otherwise noted, the nuclear physics seminar are held in Room 304 of the Nielsen Physics Building on Mondays at 2:20.
- The
**Physics Department Colloquium**,**ORNL Physics Division Seminar Schedule**and the**UT Math Department Seminar Calendar**might also be of interest. - Speakers are kindly requested to read the notes given
**here.**

University of Tennessee

**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 ^{132}Sn exhibit a fast convergence of ground-state energies and radii in feasible model spaces.

UTK/ORNL/JINPA

**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 ν_{e} 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 ν_{e} uncertainty of the reactor anomaly.

UTK

** Direct Reaction involving the Halo Nucleus ^{11}Be **
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

The degree to which the nlj = 2s

The structure of

To aid in resolving these issues, an extensive series of measurements were performed using a primary beam of

Jefferson Lab

**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.

NCSU

** 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.

Central Michigan University

**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).

ORNL

**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.

UTK

**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: ^{86}Ga, ^{98}Rb, ^{100}Rb. 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 ^{235}U). 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 ^{135}I is predicted by the inclusion of one such model.

UTK, Nuclear Engineering

**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.

UTK

**Spectroscopy studies of ^{257,258}Db**

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 ^{255}_{103}Lr_{152} and ^{256}_{104}Rf_{152}. Valuable information can be obtained by studying further the evolution of the N=152 deformed shell gap. To this purpose, the isotopes of ^{257}_{105}Db and ^{258}_{105}Db 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 ^{257}Db was produced through the fusion-evaporation reaction ^{209}Bi(^{50}Ti,2n)^{257}Db at GANIL. The two previously observed long lived states of ^{257}Db were confirmed in this experiment, as well as the two isomeric states of its decay daughter ^{253}Lr.
The ^{258}Db was produced through the fusion-evaporation reaction ^{209}Bi(^{50}Ti,1n)^{258}Db at GSI. A strong indication of the existence of two states in ^{258}Db with different half-lives was observed. A new γ-ray transition of ^{250}Md (granddaughter) was identified and its placement in the partial level scheme is proposed. The α decay of ^{258}Rf was also observed, suggesting a smaller branching ratio than previously reported.

Rutgers University

**Spectroscopy of ^{26}F and ^{28}Na 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 πd_{5/2}×νd_{3/2} 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 ^{30}Al, ^{28}Na and ^{26}F was required to achieve our goal.
The weakly bound neutron-rich ^{26}F is a benchmarking nucleus for studying this interaction close to the drip line. As lying close to the ^{24}O doubly magic nucleus, its nuclear structure at low excitation energy can be viewed as the interaction between a single deeply bound proton d_{5/2} (~ -15.1 (3) MeV) and a single unbound neutron d_{3/2} (~ +0.77 (20) MeV) on top of a closed ^{24}O 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 [1], study of the isomeric decay for J = 4^{+} [2], 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 ^{28}Ne 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 [3], completing the quadruplet J = 1^{+} - 4^{+} (J = 1^{+} and 2^{+} previously known [4]). Combined with the previously studied ^{30}Al experimental results [5], we find a systematic deviation between experimental and theoretical binding energies along the N=17 isotones: while the states are calculated too bound in ^{26}F, they are not enough bound in ^{30}Al (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.

[1] M. Stanoiu et al., Phys. Rev. C 85, 017303, 2012.

[2] A. Lepailleur et al., Phys. Rev. Lett.110, 082502, 2013.

[3] A. Lepailleur et al., Phys. Rev. C 92, 05309, 2015.

[4] V. Tripathi et al., Phys. Rev. C 73, 054303, 2006.

[5] D. Steppenbeck et al., Nuc. Phys. A 847, 2010.

ORNL/UTK

**Collective Nuclear Structure: Transverse Wobbling in ^{135}Pr and ^{6}Li 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 ^{135}Pr 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, ^{4}He, works poorly as an active target, however, there is little information about alternative probes. Therefore a normal kinematics study of the ISGMR using ^{6}Li was performed using inelastic scattering with the Grand Raiden magnetic spectrograph in the RCNP at Osaka University to determine ^{6}Li's suitability as a probe of the ISGMR.

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