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Search Results: 1 - 10 of 250796 matches for " H. O. Back "
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Pulse-Shape discrimination with the Counting Test Facility
H. O. Back et al.
Physics , 2007, DOI: 10.1016/j.nima.2007.09.036
Abstract: Pulse shape discrimination (PSD) is one of the most distinctive features of liquid scintillators. Since the introduction of the scintillation techniques in the field of particle detection, many studies have been carried out to characterize intrinsic properties of the most common liquid scintillator mixtures in this respect. Several application methods and algorithms able to achieve optimum discrimination performances have been developed. However, the vast majority of these studies have been performed on samples of small dimensions. The Counting Test Facility, prototype of the solar neutrino experiment Borexino, as a 4 ton spherical scintillation detector immersed in 1000 tons of shielding water, represents a unique opportunity to extend the small-sample PSD studies to a large-volume setup. Specifically, in this work we consider two different liquid scintillation mixtures employed in CTF, illustrating for both the PSD characterization results obtained either with the processing of the scintillation waveform through the optimum Gatti's method, or via a more conventional approach based on the charge content of the scintillation tail. The outcomes of this study, while interesting per se, are also of paramount importance in view of the expected Borexino detector performances, where PSD will be an essential tool in the framework of the background rejection strategy needed to achieve the required sensitivity to the solar neutrino signals.
New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility
Borexino collaboration,H. O. Back
Physics , 2003, DOI: 10.1016/S0370-2693(03)00636-1
Abstract: The results of background measurements with the second version of the BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso Underground Laboratory, were used to obtain limits on the instability of nucleons, bounded in nuclei, for decays into invisible channels ($inv$): disappearance, decays to neutrinos, etc. The approach consisted of a search for decays of unstable nuclides resulting from $N$ and $NN$ decays of parents $^{12}$C, $^{13}$C and $^{16}$O nuclei in the liquid scintillator and the water shield of the CTF. Due to the extremely low background and the large mass (4.2 ton) of the CTF detector, the most stringent (or competitive) up-to-date experimental bounds have been established: $\tau(n \to inv) > 1.8 \cdot 10^{25}$ y, $\tau(p \to inv) > 1.1 \cdot 10^{26}$ y, $\tau(nn \to inv) > 4.9 \cdot 10^{25}$ y and $\tau(pp \to inv) > 5.0 \cdot 10^{25}$ y, all at 90% C.L.
Response to a critique of the Borexino result in "A new experimental limit for the stability of the electron" by H.V. Klapdor-Kleingrothaus, I.V. Krivosheina and I.V. Titkova
Borexino collaboration,H. O. Back
Physics , 2007,
Abstract: A recently published article by Klapdor-Kleingrothaus et al. critiques the limit on the stability of the electron obtained by the Borexino collaboration. We respond here to the criticisms raised by Klapdor-Kleingrothaus and his colleagues, and re-establish that our result is based on very conservative premises and that the "indication of a signal of 1.4 $\sigma$" for the decay of the electron in the $\gamma+\nu$ channel, reported by Klapdor-Kleingrothaus and colleagues, is excluded by the Borexino result.
Spin Hall effect
Jairo Sinova,Sergio O. Valenzuela,J. Wunderlich,C. H. Back,T. Jungwirth
Physics , 2014,
Abstract: Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Although first observed only a decade ago, these effects are already ubiquitous within spintronics as standard spin-current generators and detectors. Here we review the experimental and theoretical results that have established this sub-field of spintronics. We focus on the results that have converged to give us a clear understanding of the phenomena and how they have evolved from a qualitative to a more quantitative measurement of spin-currents and their associated spin-accumulation. Within the experimental framework, we review optical, transport, and magnetization-dynamics based measurements and link them to both phenomenological and microscopic theories of the effect. Within the theoretical framework, we review the basic mechanisms in both the extrinsic and intrinsic regime which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. We also review the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin-generation which has proven important in the measurements of the spin Hall angle. We further connect the spin-current generating spin Hall effect to the inverse spin galvanic effect, which often accompanies the SHE, in which an electrical current induces a non-equilibrium spin polarization. These effects share common microscopic origins and can exhibit similar symmetries when present in ferromagnetic/non-magnetic structures through their induced current-driven spin torques. Although we give a short chronological overview, the main body is structured from a pedagogical point of view, focusing on well-established and accepted physics.
First Large Scale Production of Low Radioactivity Argon From Underground Sources
H. O. Back,F. Calaprice,C. Condon,E. de Haas,R. Ford,C. Galbiati,A. Goretti,T. Hohman,An. Inanni,B. Loer,D. Montanari,A. Nelson,A. Pocar
Physics , 2012,
Abstract: We report on the first large-scale production of low radioactivity argon from underground gas wells. Low radioactivity argon is of general interest, in particular for the construction of large scale WIMP dark matter searches and detectors of reactor neutrinos for non-proliferation efforts. Atmospheric argon has an activity of about 1 Bq/kg from the decays of 39Ar; the concentration of 39Ar in the underground argon we are collecting is at least a factor of 100 lower than this value. The argon is collected from a stream of gas from a CO2 well in southwestern Colorado with a Vacuum Pressure Swing Adsorption (VPSA) plant. The gas from the well contains argon at a concentration of 400-600 ppm, and the VPSA plant produces an output stream with an argon concentration at the level of 30,000-50,000 ppm (3-5%) in a single pass. This gas is sent for further processing to Fermilab where it is purified by cryogenic distillation. The argon production rate is presently 0.5 kg/day.
Low-Background gamma counting at the Kimballton Underground Research Facility
P. Finnerty,S. MacMullin,H. O. Back,R. Henning,A. Long,K. T. Macon,J. Strain,R. M. Lindstrom,R. B. Vogelaar
Physics , 2010, DOI: 10.1016/j.nima.2011.03.064
Abstract: The next generation of low-background physics experiments will require the use of materials with unprecedented radio-purity. A gamma-counting facility at the Kimballton Underground Research Facility (KURF) has been commissioned to perform initial screening of materials for radioactivity primarily from nuclides in the 238U and 232Th decay chains, 40K and cosmic-ray induced isotopes. The facility consists of two commercial low-background high purity germanium (HPGe) detectors. A continuum background reduction better than a factor of 10 was achieved by going underground. This paper describes the facility, detector systems, analysis techniques and selected assay results.
The Effects of Dissolved Methane upon Liquid Argon Scintillation Light
B. J. P. Jones,T. Alexander,H. O. Back,G. Collin,J. M. Conrad,A. Greene,T. Katori,S. Pordes,M. Toups
Physics , 2013, DOI: 10.1088/1748-0221/8/12/P12015
Abstract: In this paper we report on measurements of the effects of dissolved methane upon argon scintillation light. We monitor the light yield from an alpha source held 20 cm from a cryogenic photomultiplier tube (PMT) assembly as methane is injected into a high-purity liquid argon volume. We observe significant suppression of the scintillation light yield by dissolved methane at the 10 part per billion (ppb) level. By examining the late scintillation light time constant, we determine that this loss is caused by an absorption process and also see some evidence of methane-induced scintillation quenching at higher concentrations (50-100 ppb). Using a second PMT assembly we look for visible re-emission features from the dissolved methane which have been reported in gas-phase argon methane mixtures, and we find no evidence of visible re-emission from liquid-phase argon methane mixtures at concentrations between 10 ppb and 0.1%.
Clinical and pharmacological properties of new oral anticoagulants for the prevention of cerebral thromboembolism: Factor Xa and thrombin inhibitors  [PDF]
Yaroslav Winter, Richard Dodel, Alexei Korchounov, Martin Grond, Wolfgang H. Oertel, Tobias Back
World Journal of Neuroscience (WJNS) , 2012, DOI: 10.4236/wjns.2012.21002
Abstract: Vitamin K antagonists, such as warfarin and phen-procoumon, are the first-line oral anticoagulants for primary and secondary prevention of cerebral embo-lism in patients with atrial fibrillation. Although vitamin K antagonists can significantly decrease the risk of stroke, their use is limited by several important drawbacks, such as a narrow therapeutic window, the risk of intracranial and gastrointestinal bleeding, interactions with a number of drugs and nutrients, and the need for regular laboratory tests for therapy adjustment. Currently, new oral anticoagulants, such as direct thrombin inhibitors (e.g., dabigatran) and direct factor Xa inhibitors (e.g., apixaban, rivaroxaban), are being developed and tested in clinical trials. Dabigatran and rivaroxaban were recently approved for prevention of cerebral embolism in patients with atrial fibrillation. The ad-vantages of dabigatran in comparison to warfarin are a lower rate of major bleedings with dabigatran 110mg bid, a better efficacy with dabigatran 150mg bid, no clinically relevant interactions with other drugs and no need for routine coagulation monitoring. The disadvantages are the absence of antidote and the absence of routine laboratory tests for precise mea-surements of anticoagulant effect of direct thrombin/ factor Xa inhibitors. This review will focus on throm-bin and factor Xa inhibitors, which are new and promising oral anticoagulants for the prevention of cerebral embolism. We will discuss their pharmacol-ogical and clinical properties and provide the most recent updates on their clinical trials.
First Commissioning of a Cryogenic Distillation Column for Low Radioactivity Underground Argon
H. O. Back,T. Alexander,A. Alton,C. Condon,E. de Haas,C. Galbiati,A. Goretti,T. Hohmann,An. Ianni,C. Kendziora,B. Loer,D. Montanari,P. Mosteiro,S. Pordes
Physics , 2012,
Abstract: We report on the performance and commissioning of a cryogenic distillation column for low radioactivity underground argon at Fermi National Accelerator Laboratory. The distillation column is designed to accept a mixture of argon, helium, and nitrogen and return pure argon with a nitrogen contamination less than 10 ppm. In the first commissioning, we were able to run the distillation column in a continuous mode and produce argon that is 99.9% pure. After running in a batch mode, the argon purity was increased to 99.95%, with 500 ppm of nitrogen remaining. The efficiency of collecting the argon from the gas mixture was between 70% and 81%, at an argon production rate of 0.84-0.98 kg/day.
Structural and magnetic dynamics of a laser induced phase transition in FeRh
S. O. Mariager,F. Pressacco,G. Ingold,E. Mancini,A. Caviezel,E. M?hr-Vorobeva,P. Beaud,S. L. Johnson,C. J. Milne,S. Moyerman,E. Fullerton,R. Feidenhans'l,C. H. Back,C. Quitmann
Physics , 2011, DOI: 10.1103/PhysRevLett.108.087201
Abstract: We use time-resolved x-ray diffraction and magnetic optical Kerr effect to study the laser induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (\tau_1 ~ 30ps). This is significantly faster than the magnetic response (\tau_2 ~ 60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases co-exist on short time-scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.
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