Beta decay of 71,73Co; probing single particle states approaching doubly magic 78Ni

Low-energy excited states in 71,73Ni populated via the {\beta} decay of 71,73Co were investigated in an experiment performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). Detailed analysis led to the construction of level schemes of 71,73Ni, which are interpreted using systematics and analyzed using shell model calculations. The 5/2- states attributed to the the f5/2 orbital and positive parity 5/2+ and 7/2+ states from the g9/2 orbital have been identified in both 71,73Ni. In 71Ni the location of a 1/2- {\beta}-decaying isomer is proposed and limits are suggested as to the location of the isomer in 73Ni. The location of positive parity cluster states are also identified in 71,73Ni. Beta-delayed neutron branching ratios obtained from this data are given for both 71,73Co.Comment: Accepted for publication in PR

Advanced X-Ray Timing Array Mission: Conceptual Spacecraft Design Study

The Advanced X-Ray Timing Array (AXTAR) is a mission concept for submillisecond timing of bright galactic x-ray sources. The two science instruments are the Large Area Timing Array (LATA) (a collimated instrument with 2-50-keV coverage and over 3 square meters of effective area) and a Sky Monitor (SM), which acts as a trigger for pointed observations of x-ray transients. The spacecraft conceptual design team developed two spacecraft concepts that will enable the AXTAR mission: A minimal configuration to be launched on a Taurus II and a larger configuration to be launched on a Falcon 9 or similar vehicle

Z-Pinch Magneto-Inertial Fusion Propulsion Engine Design Concept

Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. Magneto-Inertial Fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small fusion reactor/engine assembly (1). The Z-Pinch dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an estimated axial current of approximately 100 MA. Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4) (2). The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this is repeated over short timescales (10(exp -6) sec). This plasma formation is widely used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, as well as in fusion energy research. There is a wealth of literature characterizing Z-Pinch physics and existing models (3-5). In order to be useful in engineering analysis, a simplified Z-Pinch fusion thermodynamic model was developed to determine the quantity of plasma, plasma temperature, rate of expansion, energy production, etc. to calculate the parameters that characterize a propulsion system. The amount of nuclear fuel per pulse, mixture ratio of the D-T and nozzle liner propellant, and assumptions about the efficiency of the engine, enabled the sizing of the propulsion system and resulted in an estimate of the thrust and Isp of a Z-Pinch fusion propulsion system for the concept vehicle. MIF requires a magnetic nozzle to contain and direct the nuclear pulses, as well as a robust structure and radiation shielding. The structure, configuration, and materials of the nozzle must meet many severe requirements. The configuration would focus, in a conical manner, the Deuterium-Tritium (D-T) fuel and Lithium-6/7 liner fluid to meet at a specific point that acts as a cathode so the Li-6 can serve as a current return path to complete the circuit. In addition to serving as a current return path, the Li liner also serves as a radiation shield. The advantage to this configuration is the reaction between neutrons and Li-6 results in the production of additional Tritium, thus adding further fuel to the fusion reaction and boosting the energy output. To understand the applicability of Z-Pinch propulsion to interplanetary travel, it is necessary to design a concept vehicle that uses it. The propulsion system significantly impacts the design of the electrical, thermal control, avionics, radiation shielding, and structural subsystems of a vehicle. The design reference mission is the transport of crew and cargo to Mars and back, with the intention that the vehicle be reused for other missions. Several aspects of this vehicle are based on a previous crewed fusion vehicle study called Human Outer Planet Exploration (HOPE), which employed a Magnetized Target Fusion (MTF) propulsion concept. Analysis of this propulsion system concludes that a 40-fold increase of Isp over chemical propulsion is predicted. This along with a greater than 30% predicted payload mass fraction certainly warrants further development of enabling technologies. The vehicle is designed for multiple interplanetary missions and conceivably may be suited for an automated one-way interstellar voyage

Systematics of low energy collective states in neutron-rich Cd isotopes

It has been shown that there are significant deviations from the expected U(5) dynamical symmetry for 110,112,114,116Cd. However, there is very significant mixing with intruder states in this region. In this paper, we investigated states in the heavier 120,124,126Cd populated via beta decay. These nuclei exhibit similar patterns to the lighter Cd isotopes even though the intruder states are much higher in energy. © Published under licence by IOP Publishing Ltd

Xenia Mission: Spacecraft Design Concept

The proposed Xenia mission will, for the first time, chart the chemical and dynamical state of the majority of baryonic matter in the universe. using high-resolution spectroscopy, Xenia will collect essential information from major traces of the formation and evolution of structures from the early universe to the present time. The mission is based on innovative instrumental and observational approaches: observing with fast reaction gamma-ray bursts (GRBs) with a high spectral resolution. This enables the study of their (star-forming) environment from the dark to the local universe and the use of GRBs as backlight of large-scale cosmological structures, observing and surveying extended sources with high sensitivity using two wide field-of-view x-ray telescopes - one with a high angular resolution and the other with a high spectral resolution

Long-lived isomeric states and quasiparticle band structures in neutron-rich Gd 162,164 nuclei from β decay

Neutron-rich nuclei Eu162,164 were produced by bombarding a proton beam on a U238 target at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory and mass separating the Eu162,164 products. New level schemes and new γ-ray transitions of the daughters Gd162,164 were identified from β-decay spectroscopy studies. Half-lives of the Eu162,164 were remeasured to clarify the previous ambiguous results. Two quasiparticle band structures were built and compared with neighboring nuclei. The β and γ bands were extended in Gd162 and a γ band was extended in Gd164. Half-lives of the isomeric states at (6-) 1449 keV in Gd162 and (4-) 1096 keV in Gd164 were measured to be 99(3) μs and 0.56(3) μs, respectively. Projected shell model calculations were performed and found to be in good agreement with all of the experimental data

Complete β -decay pattern for the high-priority decay-heat isotopes i 137 and Xe 137 determined using total absorption spectroscopy

Background: An assessment done under the auspices of the Nuclear Energy Agency in 2007 suggested that the β decays of abundant fission products in nuclear reactors may be incomplete. Many of the nuclei are potentially affected by the so called pandemonium effect and their β-γ decay heat should be restudied using the total absorption technique. The fission products I137 and Xe137 were assigned highest priority for restudy due to their large cumulative fission branching fractions. In addition, measuring β-delayed neutron emission probabilities is challenging and any new technique for measuring the β-neutron spectrum and the β-delayed neutron emission probabilities is an important addition to nuclear physics experimental techniques. Purpose: To obtain the complete β-decay pattern of I137 and Xe137 and determine their consequences for reactor decay heat and νe emission. Complete β-decay feeding includes ground state to ground state β feeding with no associated γ rays, ground state to excited states β transitions followed by γ transitions to the daughter nucleus ground state, and β-delayed neutron emission from the daughter nucleus in the case of I137. Method: We measured the complete β-decay intensities of I137 and Xe137 with the Modular Total Absorption Spectrometer at Oak Ridge National Laboratory. We describe a technique for measuring the β-delayed neutron energy spectrum, which also provides a measurement of the β-neutron branching ratio, Pn. Results: We validate the current Evaluated Nuclear Structure Data File (ENSDF) evaluation of Xe137β decay. We find that major changes to the current ENSDF assessment of I137β-decay intensity are required. The average γ energy per β decay for I137β decay (γ decay heat) increases by 19%, from 1050-1250 keV, which increases the average γ energy per U235 fission by 0.11%. We measure a β-delayed neutron branching fraction for I137β decay of 7.9±0.2(fit)±0.4(sys)% and we provide a β-neutron energy spectrum. Conclusions: The Modular Total Absorption Spectrometer measurements of I137 and Xe137 demonstrate the importance of revisiting and remeasuring complex β-decaying fission products with total absorption spectroscopy. We demonstrate the ability of the Modular Total Absorption Spectrometer to measure β-delayed neutron energy spectra

β-Decay study of neutron-rich bromine and krypton isotopes

Short-lived neutron-rich nuclei including 93Br, 93Kr, and 94Kr were produced in proton-induced fission of 238U at the Holifield Radioactive Ion Beam Facility in Oak Ridge. Their β decay was studied by means of a high-resolution online mass separator and β-γ spectroscopy methods. The half-life of T1/2 = 152(8) ms and β-delayed branching ratio of Pn = 53-8+11% measured for 93Br differs from the previously reported values of T1/2 = 102(10) ms and Pn = 68(7)%. At the same time the half-life of 94Kr T1/2 = 227(14) ms and both the half-life of T1/2 = 1.298(54) s and β-delayed branching ratio of Pn = 1.9-0.2+0.6% of 93Kr are in very good agreement with literature values. The decay properties of 93Br include previously unreported γ transitions following β-delayed neutron emission. © 2013 American Physical Society

Impact of Modular Total Absorption Spectrometer measurements of β decay of fission products on the decay heat and reactor ν e flux calculation

We report the results of a β-decay study of fission products Br86, Kr89, Rb89, Rb90gs, Rb90m, Kr90, Rb92, Xe139, and Cs142 performed with the Modular Total Absorption Spectrometer (MTAS) and on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10 000 s after fission of U235 and Pu239 by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor νe flux used to analyze reactor νe interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, U235, U238, Pu239, and Pu241, amounts to 0.976, 0.986, 0.983, and 0.984, respectively