Emission Of Neutral Particles Research Articles

Heliospheric effects caused by Sun-originating versus LISM-advected fluctuations

Context. We investigate the response of the heliosphere to fluctuations in the local interstellar medium (LISM) as compared to the influence of solar-cycle fluctuations. Aims. We discuss the differences between effects coming from the two types of drivers of time-dependent effects in the heliosphere in the context of the shape of the heliosphere, the thickness of the inner heliosheath, and the position of the ribbon of enhanced energetic neutral particle emission, as observed by the IBEX mission. Methods. Our study is based on a comparison of fully time-dependent simulations obtained with a three-dimensional (3D) model of the heliosphere. Results. We show that density fluctuations, taking the form of entropy waves and originating from the LISM, may reduce the thickness of the inner heliosheath to a similar extent as the solar-cycle effects. However, the relative motions of the termination shock and the heliopause in the two types of simulations are different. The amplitude of variation of the heliopause position is greater for the LISM fluctuation. The IBEX ribbon position is shown to be not significantly affected by the two types of drivers, although the effect of LISM fluctuation is stronger than that of the solar cycle. In this context, slight systematic changes of the position of the IBEX ribbon in its different sectors (i.e., changes in the heliospheric nose followed by variations in the heliospheric flanks) may serve as an indicator of the passage of a density fluctuation in the LISM, as suggested by our study. We also discuss the difficulties in fitting the LISM parameters in the presence of time-dependent effects.

The Sun at TeV energies: Gammas, neutrons, neutrinos and a cosmic ray shadow

High energy cosmic rays reach the surface of the Sun and start showers with thousands of secondary particles. Most of them will be absorbed by the Sun, but a fraction of the neutral ones will escape and reach the Earth. Here we incorporate a new ingredient that is essential to understand the flux of these solar particles: the cosmic ray shadow of the Sun. We use Liouville’s theorem to argue that the only effect of the solar magnetic field on the isotropic cosmic ray flux is to interrupt some of the trajectories that were aiming to the Earth and create a shadow. This shadow reveals the average solar depth crossed by cosmic rays of a given rigidity. The absorbed cosmic ray flux is then processed in the thin Solar surface and, assuming that the emission of neutral particles by low-energy charged particles is isotropic, we obtain (i)a flux of gammas that is consistent with Fermi-LAT observations, (ii) a flux of 100–300 neutrons/(year m2) produced basically in the spallation of primary He nuclei, and (iii) a neutrino flux that is above the atmospheric neutrino background at energies above 0.1–0.6 TeV (depending on the solar phase and the zenith inclination). More precise measurements of the cosmic ray shadow and of the solar gamma flux, together with the possible discovery of the neutron and neutrino signals, would provide valuable information about the magnetic field, the cycle, and the interior of the Sun.

Effects of entrance channels on the deexcitation properties of the same compound nucleus formed by different pairs of collision partners

The properties of deexcitation of the same $^{220}$Th compound nucleus (CN) formed by different mass (charge) asymmetric reactions are investigated. It is demonstrated that the effective fission barrier $<B_{\rm fis}>$ value being a function of the excitation energy $E^*_{\rm CN}$ is strongly sensitive to the various orbital angular momentum $L=\ell\hbar$ distributions of CN formed with the same excitation energy $E^*_{CN}$ by the very different entrance channels $^{16}$O+$^{204}$Pb, $^{40}$Ar+$^{180}$Hf, $^{82}$Se+$^{138}$Ba and $^{96}$Zr+$^{124}$Sn. Consequently, the competition between the fission and evaporation of light particles (neutron, proton, and $\alpha$-particle) processes along the deexcitation cascade of CN depends on the orbital angular momentum distribution of CN. Therefore, the ratio between the evaporation residue cross sections obtained after emission of neutral and charged particles and neutrons only for the same CN with a given excitation energy $E^*_{CN}$ is sensitive to the mass (charge) asymmetry of reactants in the entrance channel.

Role of charged particle emission on the evaporation residue formation in the 82Se+138Ba reaction leading to the 220Th compound nucleus

We present detailed results of a theoretical investigation on the production of evaporation residue nuclei obtained in a heavy ion reaction when charged particles (proton and α-particle) are also emitted with the neutron evaporation along the deexcitation cascade of the formed compound nucleus. The almost mass symmetric 82Se+138Ba reaction has been studied since there are many experimental results on individual evaporation residue (ER) cross sections after few light particle emissions along the cascade of the 220Th compound nucleus (CN) covering the wide 12–70 MeV excitation energy range. Our specific theoretical results on the ER cross sections for the 82Se+138Ba are in good agreement with the available experimental measurements, but our overall theoretical results concerning all possible relevant contributions of evaporation residues are several times greater than the ERs measured in experiment. The discrepancy could be due to the experimental difficulties in the identification of ER nuclei after the emission of multiple neutral and charged particles, nevertheless the analysis of ER data is very important to test the reliability of the model and to stress the importance on the investigation of ER nuclei also obtained after charged particle emissions.

Secondary emission of neutral and charged particles from intermetallic single-crystal

Sputtering, secondary ion and secondary electron emission were studied experimentally for an intermetallic Ni4Mo compound with high corrosion resistance and great hardness, which is used as material for constructing components of rockets and nuclear reactors. The process of sputtering was analyzed by molecular dynamics simulations of Ni4Mo (111) face for unchanged and changed composition (with segregation) of topmost layers of a disordered and ordered crystal. Predominant exit of Ni and Mo atoms in close-packed directions was observed and explained by correlated collisions. Both nickel and molybdenum atoms are ejected in the same crystallographic directions for a disordered crystal. For an ordered crystal the nickel atoms deviate from these directions. The origin of sputtering and number of ejected particles generated has been calculated. For secondary electron emission from the (111) Ni4Mo face the maxima in close-packed directions were obtained experimentally and explained by scattering of primary and secondary electrons on atoms located in the lateral sides of open channels.

Spontaneous decay of small copper-cluster anionsCun−(n=3–6), on long time scales

We have measured the spontaneous neutral particle emission from copper cluster anions (Cu$_n^-$, $n=3-6$) stored at cryogenic temperatures in one of the electrostatic ion storage rings of the DESIREE (Double ElectroStatic Ion Ring ExpEriment) facility at Stockholm University. The measured rate of emission from the stored Cu$_3^-$ ions follows a single power law decay for about 1 ms but then decreases much more rapidly with time. The latter behavior may be due to a decrease in the density of available final states in Cu$_3$ as the excitation energies of the decaying ions approach the electron detachment threshold. The emissions from Cu$_4^-$, Cu$_5^-$ and Cu$_6^-$ are well-described by sums of two power laws that are quenched by radiative cooling of the stored ions with characteristic times between a few and hundreds of milliseconds. We relate these two-component behaviors to populations of stored ions with higher and lower angular momenta. In a separate experiment, we studied the laser-induced decay of Cu$_6^-$ ions that were excited by 1.13 eV or 1.45 eV photons after 46 milliseconds of storage.

LHCf Experiment: Physics Results

LHCf is an experiment designed to study the forward emission of neutral particles produced in proton-proton and proton-nucleus collisions at the LHC. The detectors consists of a pair of electromagnetic sampling calorimeters installed on both sides of the ATLAS interaction point IP1 at a distance of 140 m, covering the pseudorapidity range from 8.4 to infinity. The experiment has successfully measured the energy spectra of gamma rays, neutral pions and neutrons in p-p collisions at 0.9 TeV and 7 TeV, and of neutral pions in p-Pb collisions at 5.02 TeV and in p-p collisions at 2.76 TeV. The most recent data set has been acquired during a special physics run of p-p collisions at 13 TeV in June 2015 after the restart of the LHC. This set of measurements represent an useful contribution to the calibration and tuning of the hadronic interaction models used for the simulation of atmospheric showers induced by very-high energy cosmic rays, as the measured energy interval corresponds to the range 1014 - 1017 eV in the laboratory frame.

Penrose process in a charged axion–dilaton coupled black hole

Using the Newman–Janis method to construct the axion–dilaton coupled charged rotating black holes, we show that the energy extraction from such black holes via the Penrose process takes place from the axion/Kalb–Ramond field energy responsible for rendering the angular momentum to the black hole. Determining the explicit form for the Kalb–Ramond field strength, which is argued to be equivalent to spacetime torsion, we demonstrate that at the end of the energy extraction process, the spacetime becomes torsion free with a spherically symmetric non-rotating black hole remnant. In this context, applications to physical phenomena, such as the emission of neutral particles in astrophysical jets, are also discussed. It is seen that the infalling matter gains energy from the rotation of the black hole, or equivalently from the axion field, and that it is ejected as a highly collimated astrophysical jet.

Spontaneous decay of small copper cluster anions, Cu−N = 3 − 6

SynopsisWe have measured the spontaneous neutral particle emission from beams of copper cluster anions (Cu−N, N = 3 − 6) stored in an electrostatic storage ring. These experiments have show that multiple structural isomers may be present in the beam.

Spontaneous ejection of high-energy particles from ultra-dense deuterium D(0)

High-energy particles are detected from spontaneous processes in an ultra-dense deuterium D(0) layer. Intense distributions of such penetrating particles are observed using energy spectroscopy and glass converters. Laser-induced emission of neutral particles with time-of-flight energies of 1–30 MeV u−1 was previously reported in the same system. Both spontaneous line-spectra and a spontaneous broad energy distribution similar to a beta-decay distribution are observed. The broad distribution is concluded to be due to nuclear particles, giving straight-line Kurie-like plots. It is observed even at a distance of 3 m in air and has a total rate of 107–1010 s−1. If spontaneous nuclear fusion or other nuclear processes take place in D(0), it may give rise to the high-energy particle signal. Low energy nuclear reactions (LENR) and so called cold fusion may also give rise to such particles.

Assessment and improvements of Geant4 hadronic models in the context of prompt-gamma hadrontherapy monitoring

Monte Carlo simulations are nowadays essential tools for a wide range of research topics in the field of radiotherapy. They also play an important role in the effort to develop a real-time monitoring system for quality assurance in proton and carbon ion therapy, by means of prompt-gamma detection. The internal theoretical nuclear models of Monte Carlo simulation toolkits are of decisive importance for the accurate description of neutral or charged particle emission, produced by nuclear interactions between beam particles and target nuclei. We assess the performance of Geant4 nuclear models in the context of prompt-gamma emission, comparing them with experimental data from proton and carbon ion beams. As has been shown in the past and further indicated in our study, the prompt-gamma yields are consistently overestimated by Geant4 by a factor of about 100% to 200% over an energy range from 80 to 310 MeV/u for the case of 12C, and to a lesser extent for 160 MeV protons. Furthermore, we focus on the quantum molecular dynamics (QMD) modeling of ion–ion collisions, in order to optimize its description of light nuclei, which are abundant in the human body and mainly anticipated in hadrontherapy applications. The optimization has been performed by benchmarking QMD free parameters with well established nuclear properties. In addition, we study the effect of this optimization on charged particle emission. With the usage of the proposed parameter values, discrepancies reduce to less than 70%, with the highest values being attributed to the nucleon–ion induced prompt-gammas. This conclusion, also confirmed by the disagreement we observe in the case of proton beams, indicates the need for further investigation on nuclear models which describe proton and neutron induced nuclear reactions.

NEUTRAL MASSIVE SPIN ½ PARTICLES EMISSION IN A RINDLER SPACE

The Unruh effect for the rate of emission and absorption of neutral massive Majorana spinor particles — plausible constituents of the Dark Matter — in a Rindler space–time is thoroughly investigated. The corresponding Bogoliubov coefficients are explicitly calculated and the consistency with Fermi–Dirac statistics and the Pauli principle is actually verified.

Resonant neutral particle emission in collisions of electrons with protonated peptides with disulfide bonds at high energies

Electron–ion collisions were studied for various protonated peptide monocations with disulfide bonds, using an electrostatic storage-ring equipped with a merged-electron-beam device. Resonant neutral particle emissions at the energies of 6–7eV were observed, as well as a rise towards zero-energy, which are typical electron-capture dissociation profiles. The presence of disulfide (S–S) bonds tends to enhance the resonant bump heights. Chemical nature of the amino-acid residues adjacent to cysteines appears to correlate with the bump strength. Molecular-dynamical simulations help clarify the role of molecular vibration modes in the electron-capture dissociation process.

Resonant neutral-particle emission in collisions of electrons with protonated and sodiated nucleotide monocations in a storage ring

Electron-ion collisions have been studied for protonated and sodiated single-strand dinucleotide monocations with various base compositions and sequences by using an electrostatic storage ring equipped with a merged-electron-beam device. Plots of neutral-particle production rates against collision energy show typical electron-capture-dissociation profiles, which increase for energies close to zero and contain a bump at high energies. The height of the resonant bumps varies with the number of Na+ ions as well as the base composition and sequence; in most cases, the height increases with an increase in the number of Na+ ions. Molecular mechanics and semiempirical quantum-chemical calculations suggest that the rate is correlated with various base-base interactions.

Resonant neutral-particle emission in collisions of electrons with protonated and sodiated nucleotide monocations in a storage ring

Electron-ion collisions have been studied for protonated and sodiated single-strand dinucleotide monocations with various base compositions and sequences by using an electrostatic storage ring equipped with a merged-electron-beam device. The plots of neutral-particle production rates against collision energy show typical electron-capture-dissociation profiles, which are characterized by an increase in the production rate at energies close to zero and a bump at high energies. The height of the resonant bumps varies with the number of Na+ ions as well as the base composition and sequence; in most cases, the height increases with the number of Na+ ions. Molecular mechanics and semiempirical quantum-chemical calculations suggest that the rate is correlated with various base-base interactions.

Resonant neutral-particle emission correlated with base–base interactions in collisions of electrons with protonated and sodiated dinucleotide monocations

Electron–monocation collisions for protonated and sodiated single-stranded dinucleotides with various base compositions and sequences have been studied using an electrostatic storage ring equipped with a merging-electron-beam device. Resonant neutral-particle emissions have been observed at a collision energy of 4–5 eV. The strength of the resonant bumps changes depending on the number of sodium, as well as the DNA base composition and sequence, which mostly increases with an increase in number of sodium. The results were compared with theoretical structures generated and studied by molecular mechanics and semiempirical quantum-chemistry calculations. It is deduced that the rate correlates with various base–base interactions.

Neutral-particle emission from multiply charged biomolecular ions in collisions with electrons

Electrostatic storage rings are suitable for storing macromolecules, such as biomolecules. The combination of electrostatic storage rings and electron targets opens up a new aspect for studying electron-biomolecular ion collisions with well-defined energies in the gas-phase. Neutral-particle emissions in collisions of electrons with biomolecular ions, studied by the electrostatic storage rings with the electron targets, are reviewed. In electronbiomolecular anion collisions, high threshold energies for producing neutrals are a common remarkable feature. Meanwhile, in electron-biomolecular cation collisions, resonant neutral particle emissions were observed in some specific ions and at particular energies. The origins of these phenomena are discussed based on well-known concepts in physics, chemistry and biology.

Energy distribution of particles ejected by laser-generated aluminium plasma

A study of laser-generated plasma by visible laser ablation of aluminium, in high vacuum (3×10−7mbar), by using 3ns Nd:YAG laser radiation, is reported. Nanosecond pulsed ablation, at intensity of the order of 1010W/cm2, gives an emission of neutral and charged particles. A special mass quadrupole spectrometer, operating in the 1–300amu mass range, was used to analyse the energetic atomic emission produced by the laser ablation. Neutrals show typical Boltzmann distributions, directly correlated to the plasma temperature, while ions show Coulomb–Boltzmann-shifted distributions depending on their charge state. Surface profiles of the craters and microscopy investigations permitted to study the ablation threshold and the ablation yields. The multi-component structure of the plasma plume emission is investigated in terms of charge state, neutrals and ions temperature. A special regard is given to the study of the ion acceleration process occurring inside the plasma due to a high electrical field generated in the non-equilibrium plasma. The angular distributions of the neutral and ion particles are also presented and discussed.

Resonant neutral-particle emission after collisions of electrons with base-stacked oligonucleotide cations in a storage ring

Electron-cation collisions have been studied for various protonated deoxyoligonucleotide monocations, using an electrostatic storage ring equipped with a merged-electron-beam device. Resonant neutral-particle emissions have been observed at a collision energy of about 4.5 eV for some of them. The resonance parameters depend on DNA base composition and sequence, and the resonances occur only in oligonucleotide monocations with base stacking. The resonance widths increase with oligonucleotide length, but saturate at trimers. Quantum-chemical estimations performed here help explain these results.

Dayside H + circulation at Mercury and neutral particle emission

In this study we discuss the proton circulation and the neutral atom emission at Mercury. The H + distribution in space, energy and pitch angle has been simulated by means of a single-particle Monte Carlo model. The applied electric and magnetic field model has been parameterized to take into account different boundary conditions such as interplanetary magnetic field and cross-tail potential drop. Particular attention has been paid to the estimation of the surface-sputtered neutral atoms and the energetic neutral atoms generated via charge-exchange process. The peculiar configuration of the hermean magnetosphere, as it is expected after the Mariner-10 observation of a weak magnetic field, allows a significant part of the incoming solar wind to enter Mercury's environment. For the B z < − 10 nT conditions, intense ion fluxes are expected in the cusp regions, which are extremely large when compared to the Earth's ones. The solar wind particles are likely to rapidly leave the hermean magnetosphere or precipitate onto the planetary surface, thus originating neutral particle emission via ion-sputtering. Two instruments, proposed to fly on board ESA mission BepiColombo (namely: the NPA-IS SERENA suite on the MPO segment and the ENA instrument on the MMO segment) will monitor the neutral signal as well as the precipitating ion particles. The modeled distribution presented here may be considered as a reference tool for the future observations.