Proton Background Research Articles

PAMELA experiment on board of the resurs-DK1 satellite

The main goals of the RIM Pamela experiment on investigation of antimatter in cosmic rays are considered. The magnetic spectrometer mounted on board of the Resurs DK1 satellite no. 1 will make it possible to measure spectra of antiprotons in the energy range from 80 MeV to 190 GeV and positrons in the range from 50 MeV to 270 GeV against the background of protons and electrons. The main parameters of the spectrometer detectors, the characteristics of the instrument on the whole, and the experimental conditions on orbit are considered.

Cosmic-ray positron fraction measurement from 1 to 30 GeV with AMS-01

A measurement of the cosmic ray positron fraction $e^{+}/(e^{+}+e^{−})$ in the energy range of 1–30 GeV is presented. The measurement is based on data taken by the AMS-01 experiment during its 10 day Space Shuttle flight in June 1998. A proton background suppression on the order of 10$^{6}$ is reached by identifying converted bremsstrahlung photons emitted from positrons.

Performance of a Prototype Tracking Detector With Waveform Sampling Electronics

A straw tracking detector was proposed for the MECO experiment in order to measure the parameters of the helical trajectory of electrons emitted from stopped muon decays. The events of interest are expected to be embedded in an intense background of both energetic electrons and low-energy protons. A prototype of the proposed detector with its DAQ system was built, tested, and compared to a simulation. The results are reported in this paper. They provide the information required to improve the computer simulation of the MECO experiment, and in general, the design of any high-rate DAQ system that is required to efficiently select minimum ionizing tracks from an environment of highly ionizing particles

The electron–hadron separation performance of the PAMELA electromagnetic calorimeter

A silicon-tungsten sampling imaging calorimeter has been designed and built for the PAMELA satellite-borne experiment. The main physics goals of the experiment are the measurement of the flux of antiprotons (80 MeV–190 GeV) and positrons (50 MeV–270 GeV) in the cosmic radiation. The calorimeter has been designed to identify antiprotons from an electron background and positrons in a background of protons with a high efficiency and rejection power. This work presents the electron–hadron separation capabilities of the calorimeter as obtained using both Monte Carlo and test beam data. The calorimeter is found to have sufficient performance to reach the primary scientific objectives of PAMELA, providing a proton rejection factor of ∼10 5 while keeping a ∼90% efficiency in selecting electrons and positrons. From simulations, an electron rejection factor of ∼10 5 in antiproton measurements (∼90% antiproton identification efficiency) is demonstrated.

The Unusual Relativistic Solar Proton Events of 1979 August 21 and 1981 May 10

Sixty-nine ground level events (GLEs) caused by relativistic solar protons have been observed from 1942 to 2005. GLEs are characteristically associated with intense solar flares [having peak ~9 GHz flux densities SP(9 GHz) > 103 sfu] and fast (>1000 km s-1) coronal mass ejections (CMEs). The small GLEs on 1979 August 21 and 1981 May 10 provide an exception to these rules of thumb. In comparison with other GLEs, they were associated with significantly weaker flares [SP(9 GHz) 1000 times the normal background because of preceding SEP events originating in active regions that were located in each case ~100° east of the active region responsible for the GLE. We suggest that the relativistic solar protons observed in these two events resulted from CME-driven shock acceleration of an elevated coronal seed population, reflecting the enhanced background proton intensity at 1 AU. For this scenario, the timing onset of the relativistic protons in the two events indicates that the shocks had access to the energetic seed particles within ~2-5 R☉ of the solar surface. While an elevated ~10 MeV proton background at Earth is a favorable/common condition for GLE occurrence, it is not a requirement.

RADIAL GRADIENTS OF THE LOW-ENERGY PROTON BACKGROUND BETWEEN 20 AND 80 AU

The radial variation of the ~ 0.5 – 2 MeV proton background is estimated at 20 – 80 AU during low solar activity periods using Voyager 1 LECP data. The estimation of proton radial gradient suggest an intensity drop between about 30 and 60 AU and a change of the gradient sign from negative to positive beyond about of 70 AU.

The AMS TRD. A gasdetector designed for operation in space

The Alpha Magnetic Spectrometer AMS02 will be equipped with a large transition radiation detector TRD to achieve a proton background suppression necessary for dark matter searches. The AMS02 TRD consists of 20 layers of fleece radiator each with Xe/CO2 proportional wire straw tubes read out by a dedicated low-power data-acquisition system. A space qualified TRD design and production process will be presented. The detector performance and its GEANT simulation is verified with a 20 layer prototype tested at CERN with electrons, muons and pions up to 100 GeV and protons up to 250 GeV. The detector is under construction at RWTH Aachen, the gas system is built at MIT, slow-control at MIT and INFN Rome and DAQ at TH Karlsruhe. This project is funded by the German Space Agency DLR, the US Department of Energy DOE and NASA.

A New Amide Proton R1ρ Experiment Permits Accurate Characterization of Microsecond Time-scale Conformational Exchange

A new off-resonance spin-lock experiment to record relaxation dispersion profiles of amide protons is presented. The sensitivity-enhanced HSQC-type sequence is designed to minimize the interference from cross-relaxation effects and ensure that the dispersion profiles in the absence of micros-ms time-scale dynamics are flat. Toward this end (i) the proton background is eliminated by sample deuteration (Ishima et al., 1998), (ii) 1H spin lock is applied to two-spin modes 2(H(x)Sin theta + H(z)Cos theta) N(z), and (iii) the tilt angle theta approximately 35 degrees is maintained throughout the series of measurements (Desvaux et al. Mol. Phys., 86 (1995) 1059). The relaxation dispersion profiles recorded in this manner sample a wide range of effective rf field strengths (up to and in excess of 20 kHz) which makes them particularly suitable for studies of motions on the time scale < or = 100 micros. The new experiment has been tested on the Ca2+-loaded regulatory domain of cardiac troponin C. Many residues show pronounced dispersions with remarkably similar correlation times of approximately 30 micros. Furthermore, these residues are localized in the regions that have been previously implicated in conformational changes (Spyracopoulos et al. Biochemistry, 36 (1997) 12138).

The AMS-02 transition radiation detector

The Alpha Magnetic Spectrometer AMS02 will be equipped with a large transition radiation detector (TRD) to achieve a proton background suppression necessary for dark matter searches. The AMS02 TRD consists of 20 layers of fleece radiator each with Xe / CO 2 proportional wire straw tubes read out by a dedicated low-power data-acquisition system. A space-qualified TRD design will be presented. The performance of a 20-layer prototype was tested at CERN with electron, myon and pion beams up to 100 GeV and with protons up to 250 GeV. The beam-test results will be compared to Geant3 MC predictions. The detector is under construction at RWTH Aachen; the gas system will be built at MIT, slow-control at MIT and INFN Rome and DAQ at TH Karlsruhe. This project is funded by the German Space Agency DLR, the US Department of Energy DOE and NASA.

Surface charge evolution of mineral-organic complexes during pedogenesis in Hawaiian basalt

Changes in surface charge of soil particles that accompany mineral transformations during soil formation were measured for a humid tropical chronosequence in Hawaiian basalt ranging in lava flow age from 0.3 to 4100 kiloyears (ky). Parent mineralogy is dominated by glass, olivine, pyroxene, and feldspar, whereas poorly crystalline (PC) weathering products (allophane, microcrystalline gibbsite, ferrihydrite) accumulate in early to intermediate weathering stages (through 400 ky), and crystalline secondary minerals (kaolinite, gibbsite, goethite) are dominant in the oldest (1400 and 4100 ky) soils. Detailed characterization of the solid phase was accomplished with chemical extractions, X-ray diffraction analysis, and molecular spectroscopy (FTIR and 13C MAS NMR). Simultaneous proton titration and background ion adsorption measurements were made on LiCl saturated soils over a range in pH (2–9) and ionic strength (0.001 and 0.01 M LiCl). Dependence of variable surface charge on solution composition reflects the changing nature of mineral-organic interactions over the course of pedogenesis. Points of zero net proton charge (PZNPC) ranged from 3.4 to 6.2 and 2.0 to 5.8 at 0.001 and 0.01 M ionic strength ( I), respectively. Intermediate-aged soils containing the highest mass concentration of humified soil organic matter (SOM) and its complexes with PC minerals gave rise to the steepest charging curves (largest pH dependence) and highest PZNPC values. Surface charge properties of these soils most closely reflected their weakly acidic Al and Fe hydroxide constituents, which is consistent with metal hydroxide saturation of organic functional groups, rather than organic coating of mineral surfaces. Charging curves were less steep and PZNPC values were lower for the older soils, consistent with SOM coating of more crystalline goethite, kaolinite, and gibbsite surfaces in a soil system less impacted by labile Al and Fe.

High‐Energy Deuteron Measurement with the CAPRICE98 Experiment

We report the first measurement of the deuterium abundance in cosmic rays above 10 GeV nucleon � 1 of kinetic energy. The data were collected by the balloon-borne experiment CAPRICE98, which was flown on 1998 May 28–29 from Fort Sumner, New Mexico. The detector configuration included the NMSU-WiZard/CAPRICE superconducting magnet spectrometer equipped with a gas RICH detector, a silicon-tungsten calorimeter, and a time-of-flight system. By combining the information from the spectrometer and the RICH detector, it was possible to separate deuterons from protons in the kinetic energy range from 12 to 22 GeV nucleon � 1 .I n order to estimate the proton background and the deuteron selection efficiency, we developed an empirical model for the response of the instrument, based on the data collected in this experiment. The analysis procedure is described in this paper, and the result on the absolute flux of deuterium is presented. We found that the deuterium abundance at high energy is consistent with the hypothesis that the propagation mechanism of light nuclei is the same as that of heavier secondary components. Subject headings: balloons — cosmic rays — Galaxy: abundances — ISM: abundances

Positron/Proton Separation Using the AMS-02 TRD

AMS-02 is a cosmic ray experiment that will be placed on the International Space Station. One of its goals is to search for WIMP Dark Matter, specifically from anomalous features in the positron spectrum. In order to identify positrons at high energy from the large background of protons, a Transition Radiation Detector (TRD) will be used. Here we will present studies of positron/proton separation using the TRD from the AMS-02 Simulation.

The AMS-02 transition radiation detector

The Alpha Magnetic Spectrometer AMS02 will be equipped with a large transition radiation detector (TRD) to achieve a proton background suppression necessary for dark matter searches. The AMS02 TRD consists of 20 layers of fleece radiator each with Xe / CO 2 proportional wire straw tubes read out by a dedicated low-power data-acquisition system. A space-qualified TRD design will be presented. The performance of a 20-layer prototype was tested at CERN with electron, myon and pion beams up to 100 GeV and with protons up to 250 GeV. The beam-test results will be compared to Geant3 MC predictions. The detector is under construction at RWTH Aachen; the gas system will be built at MIT, slow-control at MIT and INFN Rome and DAQ at TH Karlsruhe. This project is funded by the German Space Agency DLR, the US Department of Energy DOE and NASA.

A RICH detector for strangeness physics in Hall A at Jefferson Lab

The high-resolution hypernuclear spectroscopy experiment at Jefferson Lab, Hall A (E94-107), needs unambiguous kaon identification. Due to the huge pion and proton background, the standard Hall A hadron particle identification, based on a time of flight and two aerogel threshold Cherenkov detectors, is not sufficient. For this task a proximity focusing C 6F 14/CsI RICH has been built. Recently, after some improvements to the mechanical structure of its wire chamber and to its electronics rate capability, the RICH has been tested with cosmic rays. This paper represents a status report of the RICH detector.

High-Resolution Alpha-Autoradiography with Contact Microscopy Technique

We have been developing a novel method for high-resolution neutron-induced alpha-autoradiography (NIAR) using CR-39 plastic track detectors and an atomic force microscope (AFM) with contact microscopy technique. In this technique,sliced samples such as tissues including boron compounds are mounted on CR-39 plates, and then irradiated by thermal neutrons. The irradiated samples are exposed to soft X-rays, and then etched in NaOH solution for short time.Etch pits for alpha/lithium particle tracks and relief for transmission X-ray image of the specimen can be observed on the CR-39 surface with an AFM at about 100 nm resolution. In the NIAR, discrimination of proton background is required for quantification of boron concentration, and incident angle measurement is significant for accurate positioning of the alpha/lithium tracks on the specimen image. These properties were tested for the measurement of small etch pits observed with an AFM. It was confirmed that alpha/lithium particles and protons could be distinguished by etch pit size, and that incident angle of those charged particles could be measured at the accuracy of several degrees. These informations approve the reliability of the NIAR, especially for the subcellular measurement of boron compound distribution inside a cell in boron neutron capture therapy (BNCT).

Magnetic collapse of a neutron gas: Can magnetars indeed be formed?

A relativistic degenerate neutron gas in equilibrium with a background of electrons and protons in a magnetic field exerts its pressure anisotropically, having a smaller value perpendicular to than along the magnetic field. For critical fields the magnetic pressure may produce the vanishing of the equatorial pressure of the neutron gas. Taking this as a model for neutron stars, the outcome could be a transverse collapse of the star. This fixes a limit to the fields to be observable in stable neutron star pulsars as a function of their density. The final structure left over after the implosion might be a mixed phase of nucleons and a meson condensate, a strange star, or a highly distorted black hole or black ”cigar”, but not a magnetar, if viewed as a superstrongly magnetized neutron star. However, we do not exclude the possibility of superstrong magnetic fields arising in supernova explosions which lead directly to strange stars. In other words, if any magnetars exist, they cannot be neutron stars.

A transition radiation detector for AMS

For cosmic particle spectroscopy on the International Space Station the AMS experiment will be equipped with a Transition Radiation Detector to improve proton background supression up to 300 GeV. The TRD has 20 layers of fleece radiator with Xe/CO2 proportional-mode straw-tube chambers. They are supported in a conically shaped octagon structure made of CFC-Al-honeycomb. For low power consumption VA analog multiplexers are used as front-end readout. A 20 layer prototype has achieved proton rejections above 100 at 90% electron efficiency for beam energies up to 250 GeV. The detector is under construction at RWTH Aachen, the gas system will be built at MIT, slow-control and DAQ at TH Karlsruhe.

High-energy deuteron measurement with the CAPRICE98 experiment

The CAPRICE98 balloon-borne instrument was flown on 28–29 May 1998 from Fort Sumner (New Mexico, USA). The detector configuration included the NMSU-WiZard/CAPRICE superconducting-magnet spectrometer equipped with a gas RICH, a silicon-tungsten calorimeter and a time-of-flight system. By combining the information from the spectrometer and the RICH, which was used as a threshold device, it was possible to separate 2H from 1H in the kinetic energy range from 12 to 22 GeV/n. In order to estimate the proton background and the deuteron selection efficiency, an empirical model for the response of the instrument, based on the data collected in this experiment, was developed. The analysis procedure is described in this paper and the results on the absolute flux of 2H and 2H/He ratio are presented. These data on 2H abundance represent the only measurements above 10 GeV/n.

Identification of K +-mesons from subthreshold pA collisions with ANKE at COSY-Jülich

The spectrometer ANKE has been put into operation at the accelerator COSY of the Forschungszentrum Jülich in spring 1998. An initial scientific goal is to study K +-production in pA collisions at subthreshold energies far below the free NN-threshold at T p=1.58 GeV. This requires the identification of K +-mesons in a background of pions and protons, about 10 6 times more intense. In this paper the sophisticated detection system and the software procedures for kaon identification are described. With the help of TOF, energy-loss and range measurements as well as the track information from wire chambers, it is possible to measure d 2σ/ dΩ dp for deep subthreshold K + production at beam energies down to T p=1.0 GeV.

A high granularity imaging calorimeter for cosmic-ray physics

An imaging calorimeter has been designed and is being built for the PAMELA satellite-borne experiment. The physics goals of the experiment are the measurement of the flux of antiprotons, positrons and light isotopes in the cosmic radiation. The calorimeter is designed to perform a precise measurement of the total energy deposited, to reconstruct the spatial development of the showers (both in the longitudinal and in the transverse directions), and to measure the energy distribution along the shower itself. From this information, the calorimeter will identify antiprotons from an electron background and positrons in a background of protons with an efficiency of about 95% and a rejection power better than 10 −4. Furthermore, a self-trigger system has been implemented with the calorimeter that will be employed to measure high-energy (from about 300 GeV to more than 1 TeV) electrons. The instrument is composed of 22 layers of tungsten, each sandwiched between two “views” of silicon strip detectors ( X and Y). The signals are read out by a custom VLSI front-end chip, the CR1.4P, specifically designed for the PAMELA calorimeter, with a dynamic range of 7.14 pC or 1400 minimum ionizing particle (mip). We report on the simulated performance and prototype design.