317 research outputs found
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Fission Detection Using the Associated Particle Technique
A beam of tagged 14 MeV neutrons from the deuterium-tritium (DT) reaction is used to induce fission in a target composed of depleted uranium. The generator yield is 107 neutrons/second radiated into a 4π solid angle. Two 4 in.×4 in. NaI detectors are used for gamma-ray detection. The fission process is known to produce multiple gamma-rays and neutrons. Triple coincidences (α-γ-γ) are measured as a function of neutron flight time up to 90 ns after fission, where the α-particle arises from the DT reaction. A sudden increase in the triple coincidence rate at the location of the material is used to localize and detect fission in the interrogated target. Comparisons are made with experiment runs where lead, tungsten, and iron were used as target materials. The triple coincidence response profile from depleted uranium is noted to be different to those observed from the other target materials. The response from interrogation targets composed of fissile material is anticipated to be even more unique than that observed from depleted uranium
The intrinsic features of the specific heat at half-filled Landau levels of two-dimensional electron systems
The specific heat capacity of a two-dimensional electron gas is derived for
two types of the density of states, namely, the Dirac delta function spectrum
and that based on a Gaussian function. For the first time, a closed form
expression of the specific heat for each case is obtained at half-filling. When
the chemical potential is temperature-independent, the temperature is
calculated at which the specific heat is a maximum. Here the effects of the
broadening of the Landau levels are distinguished from those of the different
filling factors. In general, the results derived herein hold for any
thermodynamic system having similar resonant states.Comment: 11 pages, 1 figure, to appear in J Low Temp Phys (2010
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Multiple-Coincidence Active Neutron Interrogation of Fissionable Materials
Using a beam of tagged 14.1 MeV neutrons to probe for the presence of fissionable materials, we have measured n-γ-γ coincidences from depleted uranium (DU). The multiple coincidence rate is substantially above that measured from lead, tungsten, and iron. The presence of coincidences involving delayed gammas in the DU time spectra provides a signature for fissionable materials that is distinct from non-fissionable ones. In addition, the information from the tagged neutron involved in the coincidence gives the position of the fissionable material in all three dimensions. The result is an imaging probe for fissionable materials that is more compact and that produces much less radiation than other solutions
Persistent spin splitting of a two-dimensional electron gas in tilted magnetic fields
By varying the orientation of the applied magnetic field with respect to the
normal of a two-dimensional electron gas, the chemical potential and the
specific heat reveal persistent spin splitting in all field ranges. The
corresponding shape of the thermodynamic quantities distinguishes whether the
Rashba spin-orbit interaction RSOI, the Zeeman term or both dominate the
splitting. The interplay of the tilting of the magnetic field and RSOI resulted
to an amplified splitting in weak fields. The effects of changing the RSOI
strength and the Landau level broadening are also investigated.Comment: 10 pages, 5 figure
Tunneling spectroscopy in the magnetic superconductor TmNi2B2C
We present new measurements about the tunneling conductance in the
borocarbide superconductor TmNiBC. The results show a very good
agreement with weak coupling BCS theory, without any lifetime broadening
parameter, over the whole sample surface. We detect no particular change of the
tunneling spectroscopy below 1.5K, when both the antiferromagnetic (AF) phase
and the superconducting order coexist.Comment: Submitted to Phys. Rev. B, Rapid Communication
Phonon-mediated anisotropic superconductivity in the Y and Lu nickel borocarbides
We present scanning tunneling spectroscopy and microscopy measurements at low
temperatures in the borocarbide materials RNi2B2C (R=Y, Lu). The characteristic
strong coupling structure due to the pairing interaction is unambiguously
resolved in the superconducting density of states. It is located at the
superconducting gap plus the energy corresponding to a phonon mode identified
in previous neutron scattering experiments. These measurements also show that
this mode is coupled to the electrons through a highly anisotropic
electron-phonon interaction originated by a nesting feature of the Fermi
surface. Our experiments, from which we can extract a large electron-phonon
coupling parameter lambda (between 0.5 and 0.8), demonstrate that this
anisotropic electron-phonon coupling has an essential contribution to the
pairing interaction. The tunneling spectra show an anisotropic s-wave
superconducting gap function.Comment: 5 pages, 3 figure
Cardiometabolic health in offspring of women with PCOS compared to healthy controls: a systematic review and individual participant data meta-analysis
BACKGROUND: Women diagnosed with polycystic ovary syndrome (PCOS) suffer from an unfavorable cardiometabolic risk profile, which is already established by child-bearing age. OBJECTIVE AND RATIONALE: The aim of this systematic review along with an individual participant data meta-analysis is to eva
Modeling of Thermodynamic Properties and Phase Equilibria for the Al-Sm Binary System
The thermodynamic properties and associated phase equilibria for the Al-Sm binary system are examined, and experimental results regarding the stability of the Al3Sm, Al11Sm3, and Al4Sm intermetallics are incorporated. In the analysis presented, the liquid phase is described using a three-species association model, the intermediate phases are treated as stoichiometric compounds, and the terminal phases are treated as solid solutions with a single sublattice model. In addition to the stable phases, thermodynamic descriptions of the metastable Al11Sm3-α and Al4Sm-γ phases are employed, and both stable and metastable phase equilibria are presented over the full composition range, providing a general model, which is consistent with available experimental data. Metastable liquidus curves are examined with respect to the observed crystallization behavior of amorphous Al-Sm alloys
The Stability of Al11Sm3 (Al4Sm) Phases in the Al-Sm Binary System
The relative stability of Al11Sm3 (Al4Sm) intermetallic phases was experimentally investigated through a series of heat treatments followed by microstructural, microchemical, and X-ray diffraction (XRD) analyses. The principal findings are that the high-temperature tetragonal phase is stable from 1655 to 1333 K and that the low-temperature orthorhombic phases, α and γ, have no range of full stability but are metastable with respect to the crystalline Al and Sm reference states down to 0 K. Thermodynamic modeling is used to describe the relative energetics of stable and metastable phases along with the associated two-phase mixtures. Issues regarding transition energetics and kinetics are discussed
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