Proton Background Research Articles

Macroscopic effects in cold magnetized nucleons and electrons with anomalous magnetic moments

A model of a degenerate neutron gas in chemical equilibrium with a background of degenerate electrons and protons in a constant uniform ultrastrong magnetic field is applied to describe the state of matter in the cores of strongly magnetized neutron stars. Expressions for the thermodynamic quantities are obtained including the anomalous magnetic moments of the fermions. It is shown that (1) the inclusion of the anomalous magnetic moments of charged fermions leads to nonperiodic magnetic oscillations of their thermodynamic quantities in strong magnetic fields, (2) the total stress energy tensor relevant for neutron star structure must include contributions from both the magnetized matter and the magnetic field and as a result the total pressure produced is anisotropic, and (3) complete spin polarization of neutrons occurring in superstrong magnetic fields must lead to an increase in the degeneracy pressure compared with the zero field case at the same neutron densities. It is hoped that the results obtained will have applications for the structure in neutron stars with ultrastrong frozen-in magnetic fields.

Silica aerogel threshold Cherenkov counters for the JLab Hall A spectrometers: improvements and proposed modifications

Recently approved experiments at Jefferson Lab Hall A require a clean kaon identification in a large electron, pion, and proton background environment. To this end, improved performance is required of the silica aerogel threshold Cherenkov counters installed in the focal plane of the two Hall A spectrometers. In this paper we propose two strategies to improve the performance of the Cherenkov counters which presently use a hydrophilic aerogel radiator, and convey Cherenkov photons towards the photomultipliers by means of mirrors with a parabolic shape in one direction and flat in the other. The first strategy is aerogel baking. In the second strategy we propose a modification of the counter geometry by replacing the mirrors with a planar diffusing surface and by displacing in a different way the photomultipliers. Tests at CERN with a 5 GeV/c multiparticle beam revealed that both the strategies are able to increase significantly the number of the detected Cherenkov photons and, therefore, the detector performance.

The balloon-borne electron telescope with scintillating fibers (BETS)

We describe a new detector system developed for high-altitude balloon flights to observe the cosmic-ray electrons above 10 GeV. The Balloon borne Electron Telescope with Scintillating (BETS) fibers instrument is an imaging calorimeter which is capable of selecting electrons against the large background of protons. The calorimeter is composed of a sandwich of scintillating optical-fiber belts and lead plates with a combination of three plastic scintillators for shower trigger. The total thickness of lead is 40 mm (∼ 7.1 r.l.) and the number of fiber belts is nine. In each belt, alternating layers are oriented in orthogonal ( x and y) directions. Two sets of an intensified CCD camera are adopted for read-out of the scintillating fibers in the x and y direction, respectively. The accelerator beam tests were carried out to study the performance of detector for electrons in 1996 and for protons in 1997 at CERN-SPS. The instrument was successfully flown aboard high-altitude balloon in 1997 and 1998. It is demonstrated by the flight data that a reliable identification of the electron component has been achieved in 10– 100 GeV and the energy spectrum has been obtained.

First results from subthreshold K +-production measurements with ANKE

The new spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich. An initial scientific goal is to study K +-production in pA collisions at subthreshold energies below the free NN-threshold of T = 1.58 GeV. First measurements of double differential cross sections in p 12C collisions at emission angles around 0° have been performed at T = 1.0, 1.2 and 2.0 GeV. The challenge is to identify the kaons in a huge background of pions and protons, since the signal to background ratio decreases to about 10 −6 at T = 1.0 GeV. For background suppression detectors and a trigger system based on energy-loss and time-of-flight measurements have been developed. In the analysis the decay of kaons ( τ = 12.4 ns) stopped in the detection system into μ + and π + is exploited as well as the track information from the wire chambers.

New measurement of the electron flux from 10 GeV to 100 GeV with the bets instrument

Abstract The BETS (balloon-borne electron telescope with scintillating fibers) instrument has been developed for high-altitude balloon flights to observe the cosmic ray electrons with energies of 10 GeV to several 100 GeV. The detector is a Lead/SciFi sampling calorimeter consisting of 36 SciFi belts (each 280 mm wide) and 8 lead plates (each 5 mm thick). The electron identification is performed by triggering the electro-magnetic showers on board and by analyzing the three-dimensional shower images by an intensified CCD camera. It is demonstrated in the flight data in 1995 and 1997 that a reliable identification of the electron component against the proton background is achieved up to a few 100 GeV. The performance of detector was tested by the CERN-SPS electron beams in 1996 and with the proton beams in 1997. The obtained energy spectrum is consistent with the recent observation by HEAT, although our result still has a little room for improvement. The energy spectrum from 10 GeV to 1000 GeV which is obtained by combining these data and the emulsion chamber data (Nishimura 1997) suggests that the diffusion constant is about 1 × 10 28 ( E/GeV ) 0.3 cm 2 /sec in the energy range between 10 GeV and 1000 GeV. A hump in the energy spectrum is observed around several hundred GeV, which is expected from a nearby source.

Possibility of increasing proton rejection by detecting primary cosmic radiation electrons using an ionization-neutron calorimeter

Measurements were made of the neutron yields from a lead absorber 60 cm thick in electromagnetic cascades initiated by 200–600 MeV electrons. A comparison between the neutron yields obtained for electrons and the results of similar measurements for protons and pions suggests that the rejection factor of the proton background is increased ∼102 times when an ionization-neutron calorimeter is used to measure primary cosmic radiation electrons at energies above 100 GeV.

The High-Energy Antimatter Telescope (HEAT): An instrument for the study of cosmic-ray positrons

The HEAT (High-Energy Antimatter Telescope) instrument has been developed for a series of observations in cosmic-ray astrophysics that require the use of a superconducting magnet spectrometer. This paper describes the first configuration of HEAT which is optimized for the detection of cosmic-ray electrons and positrons below 100 GeV. In addition to the spectrometer, a combination of time-of-flight scintillators, a transition radiation detector, and an electromagnetic shower counter, provides particle identification, energy measurement, and powerful discrimination against the large background of protons. The instrument was successfully flown aboard high-altitude balloons in 1994 and 1995. The design and construction of the spectrometer and of the detector systems are described, and the performance of the instrument is demonstrated with data obtained in flight.

Neutron Laue diffraction study of concanavalin A The proton of Asp28

Neutron Laue data collection, which harnesses a broader wavelength band emitted from the neutron source, opens up the prospect of studying larger proteins and/or using smaller protein crystals than is possible with monochromatic neutron protein crystallography data collection methods. Concanavalin A, a 25 kDa† protein was used in this study, albeit with a rather large crystal of 1.2×1.8×2.2 mm. Data in a resolution range of 8–2.75 Åwere used to refine the protein structure, which included many H/D sites; the final R-factor for the protein model and 61 waters was 0.207 (Rfree = 0.310) for 4909 unique reflections. In particular, for example, the proton on Asp28 of concanavalin A, located previously by our 0.94 Åsynchrotron X-ray study, was also found in this neutron study; thus the two methods confirm each other. The Asp28 proton was found not to exchange, under the deuteriation conditions used. Negative neutron density was also observed for the manganese binding site consistent with the negative neutron scattering factor for this element. Concanavalin A is one of the first proteins studied by the neutron Laue technique. The limited exchange of H for D almost certainly can be improved upon thus reducing the proton background in the diffracton pattern. This in turn would allow the weaker, high-resolution reflections, to be recorded.

K +-meson production inpBe interactions atT p=2.9 GeV

The production ofK+ andπ+ mesons and protons inpBe collisions atTp=2.9 GeV has been studied at the ITEP proton synchrotron. Ejectiles with a momentum ofp=545 MeV/c were observed under an emission angle ϑ=17°. The detectors which have been developed for the identification of kaons out of a six orders of magnitude more intense background of pions and protons are described. A cross-section ratio d2σK+/dΩdp: d2σp/dΩdp: d2σp/dΩdp of (1±0.34):(85±1):(31±1) has been measured. Normalization with existing pion data yields an invariant differential cross sectionE·d3σK+/d3p=(3.1±1.2) mbGeV−2c3sr−1 and a total cross section of σtot(pBe)=(3.7±1.5) mb. These cross sections are compared with existing data and theoretical predictions. TheA dependence ofK+ production in the few-GeV range is analyzed.

Competing processes of plasma wave instabilities driven by an anisotropic electron beam: Linear results and two‐dimensional particle simulations

A magnetoplasma made up of a background of isotropic electrons and protons and a beam of anisotropic electrons (T⊥/T‖ > 1), with drift velocity parallel to the ambient magnetic field, can feed different unstable modes. Numerical solution of the dispersion equation in the wavenumber plane (k‖, k⊥) reveals several unstable modes with islets of oblique growth unconnected to the unstable parallel modes. The mechanisms involved in the growth and saturation of the fastest instability do not necessarily exclude later developments of other instabilities. Competing processes among the coexisting unstable waves are expected. Linear analysis or one‐dimensional computer simulations cannot properly address this problem; there would not be interaction of modes propagating at different angles to the static magnetic field. Linear and nonlinear evolutions of the modes are studied via computer simulation with a two‐dimensional particle code (KEMPO2). Results show that several modes are excited with different timescales. Some modes are only temporarily excited, while others persist in the system. The distribution function is significantly changed by the first excited modes, the beam‐mode waves. In later stages of development, forward and backward oblique whistler mode waves are excited. A final stage is characterized by coexistence of several waves with different frequencies and wavelengths. The beam‐mode waves have frequencies close to the plasma frequency, whereas the frequencies of the whistler mode waves fall near a half of the cyclotron frequency. These results may be relevant to the interpretation of wave activities observed in the Earth's magnetosphere by the GEOS 1, GEOS 2, and GEOTAIL satellites or in the Uranian bow shock by Voyager 2.

Minor heavy ion electromagnetic beam–plasma interactions in the solar wind

It is shown that the velocity threshold of the right‐hand‐polarized ion‐ion resonant instability decreases with decreasing gyrofrequency values of the beam ions, and also, the system can become unstable for very small beam concentrations. In order to illustrate the results, a plasma consisting of a proton background and a very tenuous O+ ion beam is considered. It is shown that for an ion beam of nO+/np = 10−4, the threshold velocity is VO+ ∼ 1.36VA (VA is the Alfvén velocity), and the maximum growth rate is of the order of 10−3Ωp (Ωp is the proton gyrofrequency). We apply these results to high‐speed solar‐wind‐type plasmas consisting of a proton background, an alpha particle beam, and a beam of O+ ions. It is also shown that the presence of alpha particles reduces the velocity instability threshold of the O+‐p resonant instability.

The superconducting kaon spectrometer — SKS

A superconducting kaon spectrometer has been installed in the north experimental hall of the KEK 12-GeV proton synchrotron. The spectrometer was designed to serve for nuclear physics experiments with meson beams in the 1 GeV/ c region, particular emphasis being laid on study of Λ-hypernuclei via ( π +, K +) reactions. In order to obtain Λ-hypernuclear data with better statistics and energy resolution, it was designed to have a good momentum resolution of 0.1% FWHM and a large acceptance of 100 msr. It consists of a large superconducting dipole magnet, tracking chambers, and trigger counters that can efficiently select kaons from large background of pions and protons. The overall energy resolution for scattering is realized together with a beam-line spectrometer in the K6 beam line, the momentum resolution of which was also designed to be better than 0.1% FWHM. A good energy resolution of better than 2 MeV FWHM has been confirmed in π −- 12C elastic scattering and in the ( π +,K +) reaction on 12C.

Surface charge characteristics of kaolinitic tropical soils

Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs + adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1–10 mmol L −1 and pH value 2–6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density.

Surface charge characteristics of kaolinitic tropical soils

Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs+ adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1–10 mmol L−1 and pH value 2–6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density.

High resolution study ofhyperon-nucleon interactions by associated strangeness production in pp collisions

The associated strangeness production in pp collisions was studied at bombarding energies of 2.3 and 2.7 GeV by detecting the outgoing K + particles with a high resolution magnetic spectrometer at forward angles up to 23.5° laboratory angle. The kaons were separated from an immense background of protons and pions by a highly resolving TOF electronics addition to vetoes from Čerenkov detectors utilizing either β differing Čerenkov light cones in lucite or different thresholds for light production in aerogel. The hyperon-nucleon missing mass spectra obtained show strong deviations from pure phase space which is ascribed to final state interactions of the pΛ and the Nσ systems. The structures found are discussed and compared with results from K −d → π −YN experiments, with theoretical calculations in the frame of OBE models, and with the prediction of sharp strange dibaryon resonances from several quark-bag models.

Phase separation observed by 1H-NMR in YBa 2Cu 3O 7 − δH x

We report on 1H-NMR experiments on protonated samples of YBa 2Cu 3O 7 − δ. Phase separation into an antiferromagnetic (AFM) phase with high 1H-concentration and a metallic/superconducting (SC) phase with a low 1H-concentration is observed. Cooling experiments suggest that this phase separation takes place already during the protonation process. Even unprotonated samples show high proton background 1H-NMR signals (about 0.25 1Hs per unit cell). Comparison of the linewidth of the AFM spectra with model calculations leads us to the conclusion that the protons in the AFM phase are located within 1.2 Å above or below the Cu-chain layer.

Real-time data processes in a balloon-borne apparatus

In a balloon-borne experiment signals from detectors are processed in a balloon-borne apparatus to fit the data bandwidth of storage devices installed in the apparatus. The process begins at front-end processors receiving signals from detectors and proceeds under successive stages by dedicated processors. Event data are finally fed to a computer bank where the events are further selected before being written into the storage devices. The computer bank is made of transputer modules. The transputers are widely employed and some processors are implemented with the transputers. The integration of the processors is described and the function and implementation of the individual processors are outlined. The authors are planning a series of balloon-borne experiments searching for antiparticles of cosmic origins. Firstly the authors will measure the antiproton flux. Antiprotons need to be identified under the overwhelming background of protons. >

Oxygen-17 and Proton Mr Microscopy in Materials Analysis

ABSTRACTPreliminary results of two applications of 17O/lH NMR microimaging (MRμI) are described. In the first case, it is shown that oxygen-17 MRμI presents a unique advantage in situations where a strong proton background hinders the analysis of water ingress in polymeric materials. This is illustrated with 17O-enriched water diffusion into an agar gel from a central well. While proton imaging cannot readily distinguish between exogenous and endogenous water, 17O imaging makes a clear differentiation, due to the fact that the natural abundance gel has virtually no 17O background. In the second case, proton MRμI was used to analyze the structure and performance of commercial time-release pellets (ProMacR) containing an active ingredient (surfactant) dispersed into an inert matrix. This was done after leaching the detergent with natural abundance water or after drying the leached sample and refilling the pores with water. Pores ranging in size from 25 to 325 μm diameter are clearly visualized. The 1H images have been quantitated with commercial image analysis software in terms of the total porosity and the individual pore characteristics. Two types of water can be separately imaged: “bound” water with restricted mobility (interacting with the polymer matrix), and “free” water (in large pools). The majority of water is in the bound state. It is possible to evaluate the control-release performance of the product from the size of the pores, the uniformity of dispersion and the time course of detergent-water exchange.

Studies on nitrogen mapping by various CR-39 track detectors

The possibility of using CR-39 track detectors for nitrogen distribution measurements via 14 N(n,p) 14 C reaction is studied. In this respect the proton detection properties of different CR-39 products have been analyzed. By PIXE and neutron activation methods the possible disturbing impurity content of the detector sheets is determined. It is found that the main contaminant is chlorine which remains in the CR-39 monomer during its manufacture. The variation of background track density induced in the bulk of detectors is examined under different conditions of neutron irradiation. The analysis of our experimental data has led to the conclusion that the sources of proton background tracks are the fast neutron component of neutron source, chlorine in detector and nitrogen diffused from air into the upper layer of detector. Efforts have been made to decrease the nitrogen content of diffusion origin by removing the upper detector layer and by outgassing the CR-39 sheet in vacuum before irradiation. Finally the “signal/noise” ratio for steel specimen and the sensitivity of nitrogen determination are given.

Zero field NMR and NQR with selective pulses and indirect detection

Zero field NMR and NQR spectra are obtained by the application of dc magnetic field pulses to a demagnetized sample. Pulsed dc fields allow for selective excitation of isotopic species and provide a means for coherent manipulation of the spin system in zero field. Using these selective pulses and level crossing techniques, indirect detection of a quadrupolar nucleus may be accomplished via protons without obtaining the proton background signal in the NQR spectrum. Experimental results from a variety of 1H, 2H, and 14N homo- and heteronuclear systems are presented as an illustration of these techniques.