Southeastern Universities Research Association Research Articles

Band mixing in 96,98Mo isotopes * *Supported by the National Natural Science Foundation of China (11875171, 11675071, 11747318), the U. S. National Science Foundation (OIA-1738287, ACI -1713690), U. S. Department of Energy (DE-SC0005248), the Southeastern Universities Research Association, the China-U. S. Theory Institute for Physics with Exotic Nuclei (CUSTIPEN) (DE-SC0009971), and the LSU–LNNU joint research program (9961)

We use the two lowest weight states to fit E2 strengths connecting the and transitions in Mo. Our results confirm that the and states are maximally mixed, and that the states are weakly mixed in both nuclei. An appropriate Hamiltonian to represent the band mixing is found to be exactly solvable, and its eigenstates can be expressed as the basis vectors in the configuration mixing scheme and interacting boson model. The interacting boson model and coexistence mixing configuration under the solvable methods are suitable models for analyzing the band mixing with high accuracy.

The Evolution and Outcomes of a Collaborative Testbed for Predicting Coastal Threats

Beginning in 2003, the Southeastern Universities Research Association (SURA) enabled an open-access network of distributed sensors and linked computer models through the SURA Coastal Ocean Observing and Predicting (SCOOP) program. The goal was to support collaborations among universities, government, and industry to advance integrated observation and modeling systems. SCOOP improved the path to operational real-time data-guided predictions and forecasts of coastal ocean processes. This was critical to the maritime infrastructure of the U.S. and to the well-being of coastal communities. SCOOP integrated and expanded observations from the Gulf of Mexico, the South Atlantic Bight, the Middle Atlantic Bight, and the Chesapeake Bay. From these successes, a Coastal and Ocean Modeling Testbed (COMT) evolved with National Oceanic and Atmospheric Administration (NOAA) funding via the Integrated Ocean Observing System (IOOS) to facilitate the transition of key models from research to operations. Since 2010, COMT has been a conduit between the research community and the federal government for sharing and improving models and software tools. SCOOP and COMT have been based on strong partnerships among universities and U.S. agencies that have missions in ocean and coastal environmental prediction. During SURA’s COMT project, which ended September 2018, significant progress was made in evaluating the performance of models that are progressively becoming operational. COMT successes are ongoing.

Exact solution of U(5)–O(6) transitional description in interacting boson model with two-particle and two-hole configuration mixing * * Support from the National Natural Science Foundation of China (11675071, 11975009, 11575076), the Liaoning Provincial Universities Overseas Training Program (2019-46), the U. S. National Science Foundation (OIA-1738287 and ACI-1713690), U. S. Department of Energy (DE-SC0005248), the Southeastern Universities Research Association, and the

The exact solution of the U(5)-O(6) transitional description in the interacting boson model with two-particle and two-hole configuration mixing is derived based on the Bethe ansatz approach. The Bethe ansatz equations are provided to determine the model's eigenstates and corresponding eigen-energies. N= 2 and N= 4 cases are considered as examples to demonstrate the solution features. As an example of the application, some low-lying level energies and B(E2) ratios of 108Cd are fitted and compared with the corresponding experimental data.

A close look at the competition of isovector and isoscalar pairing in A=18 and 20 even-even N≈Z nuclei * * Supported by the National Natural Science Foundation of China (11675071 and 11375080), the U. S. National Science Foundation (OIA-1738287 and ACI -1713690), U. S. Department of Energy (DE-SC0005248), the Southeastern Universities Research Association, the China-U. S. Theory Institute for Physics

The competition of isovector and isoscalar pairing in A=18 and 20 even-even N≈Z nuclei is analyzed in the framework of the mean-field plus the dynamic quadurpole-quadurpole, pairing and particle-hole interactions, whose Hamiltonian is diagonalized in the basis in the L = 0 configuration subspace. Besides the pairing interaction, it is observed that the quadurpole-quadurpole and particle-hole interactions also play a significant role in determining the relative positions of low-lying excited 0+ and 1+ levels and their energy gaps, which can result in the ground state first-order quantum phase transition from J = 0 to J = 1. The strengths of the isovector and isoscalar pairing interactions in these even-even nuclei are estimated with respect to the energy gap and the total contribution to the binding energy. Most importantly, it is shown that although the mechanism of the particle-hole contribution to the binding energy is different, it is indirectly related to the Wigner term in the binding energy.

A nucleon-pair and boson coexistent description of nuclei**Supported by National Natural Science Foundation of China (11375080, 11675071), the U.S. National Science Foundation (OCI-0904874 and ACI-1516338), U. S. Department of Energy (DE-SC0005248), the Southeastern Universities Research Association, the China-U. S. Theory Institute for Physics with Exotic Nuclei (CUSTIPEN) (DE-SC0009971), and the LSU–LNNU joint research program (9961) is acknowledged

We study a mixture of s-bosons and like-nucleon pairs with the standard pairing interaction outside an inert core. Competition between the nucleon-pairs and s-bosons is investigated in this scenario. The robustness of the BCS-BEC coexistence and crossover phenomena are examined through an analysis of pf-shell nuclei with realistic single-particle energies, in which two configurations with Pauli blocking of nucleon-pair orbits due to the formation of the s-bosons is taken into account. When the nucleon-pair orbits are considered to be independent of the s-bosons, the BCS-BEC crossover becomes smooth, with the number of the s-bosons noticeably more than that of the nucleon-pairs near the half-shell point, a feature that is demonstrated in the pf-shell for several values of the standard pairing interaction strength. As a further test of the robustness of the BCS-BEC coexistence and crossover phenomena in nuclei, results are given for values of even-even 102–130Sn with 100Sn taken as a core and valence neutron pairs confined within the 1d5/2, 0g7/2, 1d3/2, 2s1/2, 1h11/2 orbits in the nucleon-pair orbit and the s-boson independent approximation. The results indicate that the B(E2) values are reproduced well.

Architecture of a Community Infrastructure for Predicting and Analyzing Coastal Inundation

The Southeastern Universities Research Association (SURA) has advanced the SURA Coastal Ocean Observing and Prediction (SCOOP) program as a multi-institution collaboration to design and prototype a modular, distributed system for real-time prediction and visualization of the coastal impacts from extreme atmospheric events, including hurricane inundation and waves. The SCOOP program vision is a community “cyberinfrastructure” that enables advances in the science of environmental prediction and coastal hazard planning. The system architecture is a coordinated and distributed network of interoperable, modularized components that include numerical models, information catalogs, distributed archives, computing resources, and network infrastructure. The components are linked over the Internet by standardized web-service interfaces in a service-oriented architecture (SOA). The design philosophy allows geographically disparate partnering institutions to provide complementary data-provider and integration services. The overall system enables coordinated sharing of resources, tools, and ideas among a virtual community of coastal and computer scientists. The distributed design builds on the notion that standards enable innovation, and seeks to leverage successes of the World Wide Web by creating an environment that nurtures interaction between the research community, the private sector, and government agencies working together on behalf of the nation.

Hall C raster veto/flag generator

Due to the high intensity and small size of the continuous electron beam produced at Jefferson Lab, 1 1 The Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility for the United States Department of Energy under contract DE-AC05-84ER40150. one must raster it over the target to keep the properties of the target stable during an experiment. Rastering the beam using sign-wave control signals to produce a Lissajous pattern, however, causes the beam to remain at the edges of the target longer than the center. In these regions, the local heating can be much higher than the central region generating considerable luminosity losses affecting the quality of the data. This circuit tracks the X and Y raster waveforms and sends out NIM and TTL VETO/FLAG pulses when X 2+ Y 2 is greater than a user set threshold based on the percentage of the peak voltage on the Y input. The VETO/FLAG can be used to limit the acquisition/analysis of the data to a circular region in the center of the raster pattern. This circuit automatically compensates for changing frequency and voltage to maintain a constant percent trigger from 0.4 to 5 V peak to the peak of the raster waveform.

Local meeting discusses SNS and HFIR

A local meeting entitled the SNSl HFIR Workshop was held from February 26-27, 1998, and was jointly sponsored by Oak Ridge Associated Universities, Oak Ridge National Laboratory (ORNL), Southeastern Universities Research Association and the University of Tennessee. The purpose was primanly to promote opportunities for neutron science at the existing HFIR and the proposed SNS.

CEBAF Readies Its Electron Beam for Studies of Nucleons and Nuclei

In April 1983 the Southeastern Universities Research Association won an intense competition for construction and operation of a continuouswave electron accelerator in the energy range 0.5–4.0 GeV designed for studies in high‐energy nuclear physics. Four years later Hermann Grunder, director of SURA's proposed Continuous Electron Beam Accelerator Facility at Newport News, Virginia, initiated a radical change in the design of the accelerator from one that would stretch a pulsed beam to one that used superconducting cavity technology, just then becoming viable for large‐scale applications, to create an intrinsically continuous beam. (See PHYSICS TODAY, July 1983, page 57; February 1986, page 18; and April 1992, page 19.) Construction of CEBAF began in 1987 and is now nearing completion

CEBAF — a high energy, high duty factor electron accelerator for nuclear physics

The Nuclear Science Advisory Committee has recommended the construction of the Continuous Electron Beam Accelerator Facility (CEBAF) as proposed by the Southeastern Universities Research Association (SURA), a consortium of more than thirty institutions in the southeastern United States. The accelerator will be capable of delivering intense ( I ave > 100 μA), quasi-continuous (duty Factor > 90%) beams of electrons with energies up to 4.8 GeV. Short (1.2 μs), intense ( I pk = 200 mA) pulses of electrons will be accelerated by passing twice through a conventional pulsed linac. The pulses then will be injected into and stored in a pulse stretcher ring, the circumference of which is close to the length of the electron pulse. During the period between pulses (1ms) the stored electrons will be extracted to yield a high duty factor beam. Delivery of arbitrarily polarized beams will be possible. Experimental facilities will include three end stations. Two will be used for experiments utilizing the primary electron beam; the third will serve as a tagged photon facility.

An Energy Independent Electron Spin Precessor

The delivery on target of a polarized electron beam from a linear accelerator is straightforward. With circular accelerators this delivery becomes understandably more difficult. In order to maintain the polarization of an electron beam in a circular machine such as a synchrotron or pulse stretcher ring the electron spins must be oriented vertically so as to be parallel to the dominant guide fields. Extraction from these machines occurs in the horizontal plane so the extracted beam retains the vertical polarization. It is generally desirable to have not vertical but longitudinal polarization of the beam at the target; this requires a reorientation of the spins. The straightforward solution to this problem is to put a solenoid in the beam line to precess the spin into the horizontal plane followed by a horizontally deflecting dipole to precess the spin into the momentum direction. The angle of spin precession is energy dependent. What is needed is a method of varying the effective bend angle. One method used with polarized protons from the ZGS at Argonne involved a movable beam line. An alternative method is to utilize the noncommutativity of rotations in three dimensions. To do this requires two or more solenoids and twomore » or more dipoles. This paper discusses the theory and implementation of this method and describes a solenoid-dipole-solenoid-dipole configuration beam line suitable for the 4 GeV electron accelerator proposed by the Southeastern Universities Research Association.« less