281 research outputs found
Resonant X-Ray Magnetic Scattering from CoO
We analyze the recent experiment [W. Neubeck {\em et al.}, Phys. Rev. B
\vol(60,1999,R9912)] for the resonant x-ray magnetic scattering (RXMS) around
the K edge of Co in the antiferromagnet CoO. We propose a mechanism of the RXMS
to make the states couple to the magnetic order: the intraatomic exchange
interaction between the and the states and the - mixing to the
states of neighboring Co atoms. These couplings induce the orbital moment
in the states and make the scattering tensor antisymmetric. Using a
cluster model, we demonstrate that this modification gives rise to a large RXMS
intensity in the dipole process, in good agreement with the experiment. We also
find that the pre-edge peak is generated by the transition to the states
in the quadrupole process, with negligible contribution of the dipole process.
We also discuss the azimuthal angle dependence of the intensity.Comment: 15 pages, 8 figure
Expression of Interest: The Atmospheric Neutrino Neutron Interaction Experiment (ANNIE)
Submitted for the January 2014 Fermilab Physics Advisory Committee meetingSubmitted for the January 2014 Fermilab Physics Advisory Committee meetingSubmitted for the January 2014 Fermilab Physics Advisory Committee meetingSubmitted for the January 2014 Fermilab Physics Advisory Committee meetingNeutron tagging in Gadolinium-doped water may play a significant role in reducing backgrounds from atmospheric neutrinos in next generation proton-decay searches using megaton-scale Water Cherenkov detectors. Similar techniques might also be useful in the detection of supernova neutrinos. Accurate determination of neutron tagging efficiencies will require a detailed understanding of the number of neutrons produced by neutrino interactions in water as a function of momentum transferred. We propose the Atmospheric Neutrino Neutron Interaction Experiment (ANNIE), designed to measure the neutron yield of atmospheric neutrino interactions in gadolinium-doped water. An innovative aspect of the ANNIE design is the use of precision timing to localize interaction vertices in the small fiducial volume of the detector. We propose to achieve this by using early production of LAPPDs (Large Area Picosecond Photodetectors). This experiment will be a first application of these devices demonstrating their feasibility for Water Cherenkov neutrino detectors
Expression of Interest: The Atmospheric Neutrino Neutron Interaction Experiment (ANNIE)
Neutron tagging in Gadolinium-doped water may play a significant role in
reducing backgrounds from atmospheric neutrinos in next generation proton-decay
searches using megaton-scale Water Cherenkov detectors. Similar techniques
might also be useful in the detection of supernova neutrinos. Accurate
determination of neutron tagging efficiencies will require a detailed
understanding of the number of neutrons produced by neutrino interactions in
water as a function of momentum transferred. We propose the Atmospheric
Neutrino Neutron Interaction Experiment (ANNIE), designed to measure the
neutron yield of atmospheric neutrino interactions in gadolinium-doped water.
An innovative aspect of the ANNIE design is the use of precision timing to
localize interaction vertices in the small fiducial volume of the detector. We
propose to achieve this by using early production of LAPPDs (Large Area
Picosecond Photodetectors). This experiment will be a first application of
these devices demonstrating their feasibility for Water Cherenkov neutrino
detectors.Comment: Submitted for the January 2014 Fermilab Physics Advisory Committee
meetin
Relativistic theory of magnetic scattering of x rays: Application to ferromagnetic iron
We present a detailed description of a first-principles formalism for magnetic scattering of circularly polar- ized x rays from solids in the framework of the fully relativistic spin-polarized multiple-scattering theory. The scattering amplitudes are calculated using a standard time-dependent perturbation theory to second order in the electron-photon interaction vertex. Particular attention is paid to understanding the relative importance of the positive- and negative-energy solutions of the Dirac equation to the scattering amplitude. The advantage of the present theory as compared with other recent works on magnetic x-ray scattering is that, being fully relativistic, spin-orbit coupling and spin-polarization effects are treated on an equal footing. Second, the electron Green’s function expressed in terms of the path operators in the multiple-scattering theory allows us to include the contribution of the crystalline environment to the scattering amplitude. To illustrate the use of the method we have done calculations on the anomalous magnetic scattering at the K , L_II , and L_III absorption edges of ferromagnetic iron
Instability of the rhodium magnetic moment as origin of the metamagnetic phase transition in alpha-FeRh
Based on ab initio total energy calculations we show that two magnetic states
of rhodium atoms together with competing ferromagnetic and antiferromagnetic
exchange interactions are responsible for a temperature induced metamagnetic
phase transition, which experimentally is observed for stoichiometric
alpha-FeRh. A first-principle spin-based model allows to reproduce this
first-order metamagnetic transition by means of Monte Carlo simulations.
Further inclusion of spacial variation of exchange parameters leads to a
realistic description of the experimental magneto-volume effects in alpha-FeRh.Comment: 10 pages, 13 figures, accepted for publication in Phys. Rev.
The Majorana experiment: an ultra-low background search for neutrinoless double-beta decay
The observation of neutrinoless double-beta decay would resolve the Majorana
nature of the neutrino and could provide information on the absolute scale of
the neutrino mass. The initial phase of the Majorana experiment, known as the
Demonstrator, will house 40 kg of Ge in an ultra-low background shielded
environment at the 4850' level of the Sanford Underground Laboratory in Lead,
SD. The objective of the Demonstrator is to determine whether a future 1-tonne
experiment can achieve a background goal of one count per tonne-year in a
narrow region of interest around the 76Ge neutrinoless double-beta decay peak.Comment: Presentation for the Rutherford Centennial Conference on Nuclear
Physic
The MAJORANA DEMONSTRATOR: A Search for Neutrinoless Double-beta Decay of Germanium-76
The observation of neutrinoless double-beta decay would determine whether the
neutrino is a Majorana particle and provide information on the absolute scale
of neutrino mass. The MAJORANA Collaboration is constructing the DEMONSTRATOR,
an array of germanium detectors, to search for neutrinoless double-beta decay
of 76-Ge. The DEMONSTRATOR will contain 40 kg of germanium; up to 30 kg will be
enriched to 86% in 76-Ge. The DEMONSTRATOR will be deployed deep underground in
an ultra-low-background shielded environment. Operation of the DEMONSTRATOR
aims to determine whether a future tonne-scale germanium experiment can achieve
a background goal of one count per tonne-year in a 4-keV region of interest
around the 76-Ge neutrinoless double-beta decay Q-value of 2039 keV.Comment: Submitted to AIP Conference Proceedings, 19th Particles & Nuclei
International Conference (PANIC 2011), Massachusetts Institute of Technology,
Cambridge, MA, USA, July 24-29, 2011; 3 pages, 1 figur
- …