[en] Although the production of PuBe neutron sources has discontinued, hundreds of sources with unknown or inaccurately declared plutonium content are in existence around the world. Institutions have undertaken the task of assaying these sources, measuring, and calculating the isotopic composition, plutonium content, and neutron yield. The nominal plutonium content, based off the neutron yield per gram of pure ²³⁹Pu, has shown to be highly inaccurate. New methods of measuring the plutonium content allow a more accurate estimate of the true Pu content, but these measurements need verification. Using the TENDL 2012 nuclear data libraries, MCNP6 has the capability to simulate the (α, n) interactions in a PuBe source. Theoretically, if the source is modeled according to the plutonium content, isotopic composition, and other source characteristics, the calculated neutron yield in MCNP can be compared to the experimental yield, offering an indication of the accuracy of the declared plutonium content. In this study, three sets of PuBe sources from various backgrounds were modeled in MCNP6 1.2 Beta, according to the source specifications dictated by the individuals who assayed the source. Verification of the source parameters with MCNP6 also serves as a means to test the alpha transport capabilities of MCNP6 1.2 Beta with TENDL 2012 alpha transport libraries. Finally, good agreement in the comparison would indicate the accuracy of the source parameters in addition to demonstrating MCNP's capabilities in simulating (α, n) interactions.

[en] Current pulsed laser and synchrotron x-ray sources provide new opportunities for Time-Of- Flight (TOF) based photoemission spectroscopy to increase photoelectron energy resolution and efficiency compared to current standard techniques. The principals of photoelectron timing front formation, temporal aberration minimization, and optimization of electron beam transmission are presented. We have developed these concepts into a high resolution Electron Optical Scheme (EOS) of a TOF Electron Energy Analyzer (TOF-EEA) for photoemission spectroscopy. The EOS of the analyzer includes an electrostatic objective lens, three columns of transport lenses and a 90 degree energy band pass filter (BPF). The analyzer has two modes of operation: Spectrometer Mode (SM) with straight passage of electrons through the EOS undeflected by the BPF, allowing the entire spectrum to be measured, and Monochromator Mode (MM) in which the BPF defines a certain energy window inside the scope of the electron energy spectrum

[en] University of Dallas (UD) physics majors are offered a variety of undergraduate research opportunities in nuclear physics through an established program at the University of Kentucky Accelerator Laboratory (UKAL). The 7-MV Model CN Van de Graaff accelerator and the neutron production and detection facilities located there are used by UD students to investigate how neutrons scatter from materials that are important in nuclear energy production and for our basic understanding of how neutrons interact with matter. Recent student projects include modeling of the laboratory using the neutron transport code MCNP to investigate the effectiveness of laboratory shielding, testing the long-term gain stability of C₆D₆ liquid scintillation detectors, and deducing neutron elastic and inelastic scattering cross sections for ¹²C. Finally, results of these student projects are presented that indicate the pit below the scattering area reduces background by as much as 30%; the detectors show no significant gain instabilities; and new insights into existing ¹²C neutron inelastic scattering cross-section discrepancies near a neutron energy of 6.0 MeV are obtained.

[en] The pressing need for high-precision data on neutron-induced reactions of interest for emerging nuclear technologies and nuclear astrophysics has triggered the development of new methods and experiments, especially on capture cross-section measurements of fissile nuclei. In these measurements, radiative capture γ-rays are hidden in a large background of fission γ-rays. The latter has then to be subtracted via a veto method, by detecting fission events with a very good efficiency. This efficiency is limited by the backscattering and the self-absorption of the fission fragments (FF) in the target, and by the alpha radioactivity of the sample. An accurate determination of the fission efficiency is rather difficult. It is often determined by using known fission cross sections if the neutron flux is given. However, in some cases, the fission cross section is not well known and the neutron flux cannot be measured with sufficient accuracy. Another method to determine the fission efficiency is based on the detection of prompt fission neutrons in coincidence or anti-coincidence with the fission detector. Different examples are presented and advantages and disadvantages of this method will be discussed. (authors)

[en] Superlattices of the repeated structure La_1.56Sr_0.44CuO₄/La₂CuO₄ (LSCO-LCO), where none of the constituents is superconducting, show a superconducting transition of T(prime)_c 25 K. In order to elucidate the nature of the superconducting state we have performed a low-energy μSR study. By applying a magnetic field parallel (Meissner state) and perpendicular (vortex state) to the film planes, we could show that superconductivity is sheet like, resulting in a very anisotropic superconducting state. This result is consistent with a simple charge-transfer model, which takes into account the layered structure and the difference in the chemical potential between LCO and LSCO, as well as Sr interdiffusion. Using a pancake-vortex model we could estimate a strict upper limit of the London penetration depth to 380 nm in these superlattices. The temperature dependence of the muon depolarization rate in field cooling experiments is very similar to what is observed in intercalated BSCCO and suggests that vortex-vortex interaction is dominated by electromagnetic coupling but negligible Josephson interaction.

[en] We discuss the importance of the fermion nodes for the quantum Monte Carlo (QMC) methods and find two cases of the exact nodes. We describe the structure of the generalized pairing wave functions in Pfaffian antisymmetric form and demonstrate their equivalency with certain class of configuration interaction wave functions. We present the QMC calculations of a model fermion system at unitary limit. We find the system to have the energy of E = 0.425Efree and the condensate fraction of = 0.48. Further we also perform the QMC calculations of the potential energy surface and the electric dipole moment along that surface of the LiSr molecule. We estimate the vibrationally averaged dipole moment to be D =0 = 0.4(2).

[en] In this contribution the current status and future perspectives of the Karlsruhe Tritium Neutrino (KATRIN) Experiment are presented. The prime goal of this single β-decay experiment is to probe the absolute neutrino mass scale with a sensitivity of 200 meV (90% CL). We discuss first results of the recent main spectrometer commissioning measurements, successfully verifying the spectrometer's basic vacuum, transmission and background properties. We also discuss the prospects of making use of the KATRIN tritium source, to search for sterile neutrinos in the multi-keV mass range constituting a classical candidate for Warm Dark Matter. Due to the very high source luminosity, a statistical sensitivity down to active-sterile mixing angles of sin"2θ < 1 · 10"-"7 (90% CL) could be reached

[en] Prompt K x-ray production yields in U-238(n,f) have been measured for the first time at fast and intermediate neutron energies using the GEANIE array of germanium detectors at the Los Alamos Neutron Science Center. Results are compared with calculations and used to investigate fission charge yields as a function of incident neutron energy. (authors)

[en] The characteristics of the fission fragments (FF) as well as those of the prompt neutrons and gammas can be deduced using FIFRELIN Monte Carlo simulation code. The quality of the results obviously depends on the experimental entry data, the theoretical and phenomenological models, and the various assumptions done in the code. The goal of this paper is to highlight new features of the code and to present some selected new results focusing on the use of a temperature-dependent spin cut-off, the prompt gamma de-excitation capability, a ROOT-based tool for the analysis of the FF histories, the estimation of correlated quantities, and so on. The influence of some experimental data on the neutron multiplicity and the influence of the level density parameter models on fission observables are also presented. Finally a preliminary result concerning the neutron spectrum for the ²³⁸U(n,f) reaction at 1.8 MeV is shown. (authors)

[en] From the I-V characteristics for as-grown and irradiated Bi₂Sr₂CaCu₂O_8+δ single crystals at T=5 K (i.e. T → 0) in a magnetic field applied parallel to c axis, we have seen two types of vortex dynamics above the depinning threshold, depending on the vortex-vortex interaction strength (λ_ab)/a₀). For the as-grown sample, at a low field, the I-V curves show steps that clearly indicate a 'fingerprint phenomenon' since they reflex the current dependence of the differential resistance r_d(I). This can be ascribed to vortices flowing through uncorrelated channels for the highly defective lattice. As field sufficiently increase, these peaks merge to become broader ones indicating a crossover from filament type to braid river type. In contrast, in the irradiated sample, the pinning is found to be individual at low fields and collective when the vortex-vortex interactions are involved. (authors)