Electron Volt Range Research Articles

Constraints on axion-like particles with the Perseus Galaxy Cluster with MAGIC

Axion-like particles (ALPs) are pseudo-Nambu–Goldstone bosons that emerge in various theories beyond the standard model. These particles can interact with high-energy photons in external magnetic fields, influencing the observed gamma-ray spectrum. This study analyzes 41.3 h of observational data from the Perseus Galaxy Cluster collected with the MAGIC telescopes. We focused on the spectra the radio galaxy in the center of the cluster: NGC 1275. By modeling the magnetic field surrounding this target, we searched for spectral indications of ALP presence. Despite finding no statistical evidence of ALP signatures, we were able to exclude ALP models in the sub-micro electronvolt range. Our analysis improved upon previous work by calculating the full likelihood and statistical coverage for all considered models across the parameter space. Consequently, we achieved the most stringent limits to date for ALP masses around 50 neV, with cross sections down to gaγ=3×10−12 GeV−1.

The evolution of Saturn’s radiation belts modulated by changes in radial diffusion

Globally magnetized planets, such as the Earth 1 and Saturn 2 , are surrounded by radiation belts of protons and electrons with kinetic energies well into the million electronvolt range. The Earth’s proton belt is supplied locally from galactic cosmic rays interacting with the atmosphere 3 , as well as from slow inward radial transport 4 . Its intensity shows a relationship with the solar cycle 4,5 and abrupt dropouts due to geomagnetic storms 6,7 . Saturn’s proton belts are simpler than the Earth’s because cosmic rays are the principal source of energetic protons 8 with virtually no contribution from inward transport, and these belts can therefore act as a prototype to understand more complex radiation belts. However, the time dependence of Saturn’s proton belts had not been observed over sufficiently long timescales to test the driving mechanisms unambiguously. Here we analyse the evolution of Saturn’s proton belts over a solar cycle using in-situ measurements from the Cassini Saturn orbiter and a numerical model. We find that the intensity in Saturn’s proton radiation belts usually rises over time, interrupted by periods that last over a year for which the intensity is gradually dropping. These observations are inconsistent with predictions based on a modulation in the cosmic-ray source, as could be expected 4,9 based on the evolution of the Earth’s proton belts. We demonstrate that Saturn’s intensity dropouts result instead from losses due to abrupt changes in magnetospheric radial diffusion. Saturn’s proton radiation belts are quite an isolated system and can be used as a laboratory for endogenous impacts on planetary radiation belts. Their evolution over a solar cycle shows variations associated with changes in magnetospheric radial diffusion.

Four-wave mixing experiments with extreme ultraviolet transient gratings.

Four wave mixing (FWM) processes, based on third-order non-linear light-matter interactions, can combine ultrafast time resolution with energy and wavevector selectivity, and enables to explore dynamics inaccessible by linear methods.1-7 The coherent and multi-wave nature of FWM approach has been crucial in the development of cutting edge technologies, such as silicon photonics,8 sub-wavelength imaging9 and quantum communications.10 All these technologies operate with optical wavelengths, which limit the spatial resolution and do not allow probing excitations with energy in the eV range. The extension to shorter wavelengths, that is the extreme ultraviolet (EUV) and soft-x-ray (SXR) range, will allow to improve the spatial resolution and to expand the excitation energy range, as well as to achieve elemental selectivity by exploiting core resonances.5-7,11-14 So far FWM applications at these wavelengths have been prevented by the absence of coherent sources of sufficient brightness and suitable experimental setups. Our results show how transient gratings, generated by the interference of coherent EUV pulses delivered by the FERMI free electron laser (FEL),15 can be used to stimulate FWM processes at sub-optical wavelengths. Furthermore, we have demonstrated the possibility to read the time evolution of the FWM signal, which embodies the dynamics of coherent excitations as molecular vibrations. This result opens the perspective for FWM with nanometer spatial resolution and elemental selectivity, which, for example, would enable the investigation of charge-transfer dynamics.5-7 The theoretical possibility to realize these applications have already stimulated dedicated and ongoing FEL developments;16-20 today our results show that FWM at sub-optical wavelengths is feasible and would be the spark to the further advancements of the present and new sources.

Effect of Concentration on the Energetics and Dynamics of Li Ion Transport in Anatase and Amorphous TiO2

We report on the energetics and dynamics of Li diffusion in bulk anatase and amorphous TiO2 using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Using MD simulations, for both anatase and amorphous TiO2, diffusion characteristics are first studied for an isolated Li ion, followed by simulations of Li concentrations ranging from 10% to 100% in order to explore the concentration effect on the diffusivity. The isolated Li diffusion mechanism, revealed from the MD simulations, occurs via zigzag hops between the octahedral sites in anatase. The corresponding barrier for this process obtained from DFT-NEB calculations is 480 meV. MD simulations also show that isolated Li ion diffusivity is much slower in the amorphous TiO2 than in anatase TiO2. DFT-NEB results for the diffusion in amorphous titania indicate that Li encounters deep energy wells within the amorphous network that are in the electronvolt range, confirming our MD observation of low Li diffusivity. A monotonic d...

Use of CR-39 films for nuclear radiation shielding efficacy evaluation of lining materials for combat vehicles

All materials provide, to a lesser or greater extent, shielding against nuclear radiations. Armoured fighting vehicles (AFVs) have steel as the structural material, which appears to be a reasonably good gamma and neutron shield material but a shield of pure iron would not be equally effective against whole range of neutron energies as it has a few resonances in electron volt range, and it reduces energy of fast neutrons to lower energy neutrons. These neutrons will be absorbed through radiative capture and emit gamma radiations. Thus it is essential that an effective shield should contain a large amount of moderating material, hydrogen being preferred with low atomic number materials (B, C, Li) and lead (Pb) to ensure that the neutrons do not diffuse at intermediate energies in the shield as well as gamma attenuation will also take place.In order to have a suitable shield material for armoured vehicles which serves as neutron and gamma radiation attenuator, polyethylene polymer with fillers lining materials are preferred. These materials were evaluated against gamma and fast neutrons using radioactive sources for suitability to fitment into combat vehicle as per the requirement of protection factor values. The detector for gamma radiation was used as Nal(Tl) while for neutron, CR-39 film was used.

Transition from tungsten erosion to carbon layer deposition with simultaneous bombardment of tungsten by helium and carbon

Simultaneous bombardment of tungsten layers with helium and carbon ions leads to both erosion of tungsten and implantation of carbon. The underlying processes have been investigated numerically and experimentally as a function of the carbon fraction in the incident ion flux for ion energies in the kilo electron volt range. Tungsten layers were deposited on polished single-crystal silicon substrate by magnetron sputter deposition to eliminate the influence of surface roughness on the experimental results. The fluence-dependent dynamics of the surface composition was measured in situ by ion beam analysis. The given projectile-target system is subject only to kinematic processes, and is therefore particularly suitable for benchmarking of purely kinematic simulations based on the binary-collision approximation, as implemented in the TRIDYN code. TRIDYN calculations match the experimental results very well, which demonstrates the validity of the kinematic description. In particular, the simulations allow us to predict the change of surface composition by bombardment with gaseous and nonvolatile ions, as well as the transition point from W erosion to C deposition as function of the carbon fraction in the incident ion flux.

Attosecond Neutron Compton Scattering from Protons Entangled with Adjacent Electrons

The effect of “anomalous” scattering of neutrons and electrons from protons in the electron-volt energy-transfer range is considered, and related experimental results are mentioned. A recent independent confirmation of this effect with a new data analysis procedure is presented. Due to the very short characteristic scattering time, there is no well defined separation of time scales of electronic and protonic motions. An outline of a proposed theoretical interpretation is presented, which is based on the fact that scattering protons represent open quantum systems, thus being subject to decoherence.

Specific boundary conditions for the simulation of extraction for ECRIS, LIS, and H−-sources

The necessity of a three-dimensional simulation of the extraction has been accepted for electron cyclotron resonance ion sources (ECRIS) as well as for negative ion sources. For an ECRIS, the magnetic hexapole together with the solenoidal mirror field defines a minimum B structure which confines the plasma. Depending on the magnetic flux density distribution, the plasma density in front of the extraction electrode might be non-homogeneous. In H−-sources, magnetic filter fields are used to separate electrons with different energies or to separate electrons from negative ions. These magnetic filters influence the ions as well. Besides these asymmetry effects other quantities have to be considered, namely the correct formulation of initial conditions of all present charged particles. For ECRIS the initial conditions for ions are assumed to be in the electronvolt range, whereas it can be in the kilo electronvolt range for laser ion sources. Another quantity of interest is the electron energy and the distribution of electrons in real space and their movability if magnetic fields are present.

Diffusion of a megagauss field into a metal

The plane one-dimensional problem of the diffusion of a megagauss field into a metal wall is solved taking into account heat conduction and radiation transfer. At the interface, the magnetic field is assumed to be constant, and in this sense, the problem is close to the self-similar diffusion problem with parameters dependent on the self-similar variable x/\(\sqrt t \). It is shown that if heat conduction and radiation transfer are taken into account, in megagauss fields (in the examined formulation for fields B > 1.6 MGs) there is no loss of conductivity of the material evaporated by the magnetic field because of the formation of a plasma layer at the interface with a temperature in the electronvolt range. However, the role of the plasma layer in the structure of the skin layer remains insignificant up to fields B ≈ 10 MGs.

Neutrino unification.

Present neutrino data are consistent with neutrino masses arising from a common seed at some "neutrino unification" scale M(X). Such a simple theoretical ansatz naturally leads to quasidegenerate neutrinos that could lie in the electron-volt range with neutrino mass splittings induced by renormalization effects associated with supersymmetric thresholds. In such a scheme the leptonic analog of the Cabibbo angle straight theta(middle dot in circle) describing solar neutrino oscillations is nearly maximal. Its exact value is correlated with the smallness of straight theta(reactor). The two leading mass-eigenstate neutrinos present in nu(e) form a pseudo-Dirac neutrino, avoiding conflict with neutrinoless double beta decay.

Light sterile neutrino from extra dimensions and four-neutrino solutions to neutrino anomalies

We propose a four-neutrino model which can reconcile the existing data coming from underground experiments in terms of neutrino oscillations, together with the hint from the LSND experiment and a possible neutrino contribution to the hot dark matter of the Universe. It applies the idea that extra compact dimensions, probed only by gravity and possibly gauge-singlet fields, can lower the fundamental scales such as the Planck, string or unification scales. Our fourth light neutrino $\nu_s$ ($s$ for sterile) is identified with the zero mode of the Kaluza-Klein states. To first approximation \nu_sterile combines with the nu_mu in order to form a Dirac neutrino with mass in the eV range leaving the other two neutrinos massless. The smallness of this mass scale (suitable for LSND and Hot Dark Matter) arises without appealing neither to a see-saw mechanism nor to a radiative mechanism, but from the volume factor associated with the canonical normalization of the wave-function of the bulk field in the compactified dimensions. % On the other hand the splitting between \nm and \nu_sterile (atmospheric scale) as well as the mass of the two other neutrinos (solar mass scale) arise from the violation of the fermion number on distant branes. We also discuss alternative scenarios involving flavour-changing interactions. In one of them \ne can be in the electron-volt range and therefore be probed in beta decay studies.

Surface Modification Using a Commercial Triple Quadrupole Mass Spectrometer

We report instrumental modifications to a commercial mass spectrometer that allow surface modification experiments to be performed using low-energy (electronvolt range) mass-selected ion beams. The design of the detector housing allows placement of the surface on the ion optical axis and some distance beyond the off-axis detector. Manipulation of the potentials applied to the final lens, detector housing, conversion dynode, and electron multiplier allow the ions to pass through the detector housing and impinge upon the surface without loss of the normal mode of detector operation. Ex situ analysis of the modified surface is performed using a home-built multisector mass spectrometer. The ability to modify organic thin films is demonstrated by a number of soft landing and surface modification experiments including (i) soft landing of (CH3)2SiNCS+ ions formed from trimethylsilyl isothiocyanate upon a fluorinated self-assembled monolayer (F-SAM) surface, (ii) soft landing and dissociative soft landing of the pseudomolecular cation of triphenylpyrylium tetrafluoroborate, viz. the triphenylpyrylium cation, upon an F-SAM surface, (iii) dissociative soft landing of 35ClCH2(CH3)2SiOSi(CH3)2+ formed from 1,3-bis(chloromethyl)disiloxane upon an F-SAM surface, (iv) surface passivation by reaction of the trimethylsilyl cation, Si(CH3)3+, with a hydroxyl-terminated self-assembled monolayer (OH-SAM), and (v) transhalogenation by reaction of CCl3+ (m/z 119) with an F-SAM surface.

Extremely High Energy Neutrinos, Neutrino Hot Dark Matter, and the Highest Energy Cosmic Rays

Extremely high energy (up to 10**(22) eV) cosmic neutrino beams initiate high energy particle cascades in the background of relic neutrinos from the Big Bang. We perform numerical calculations to show that such cascades could contribute more than 10% to the observed cosmic ray flux above 10**(19) eV if neutrinos have masses in the electron volt range. The required intensity of primary neutrinos could be consistent with astrophysical models for their production if the maximum neutrino energy reaches to 10**(22) eV and the massive neutrino dark matter is locally clustered. Future observations of ultra high energy cosmic rays will lead to an indirect but practical search for neutrino dark matter.

Contribution of low‐energy ionospheric protons to the plasma sheet

The magnetospheric transport of low‐energy ionospheric ions is examined by means of three‐dimensional particle codes. Emphasis is placed on the behavior of polar wind and cleft originating protons. It is demonstrated that, via nonadiabatic motion inside the neutral sheet, these ions can significantly contribute to the populations of the plasma sheet. The importance of this contribution is found to depend critically upon the dynamics of particles originating from the highest latitudes, as these possibly have access to the distant tail. Hence it is shown that polar wind H+ expelled into the magnetosphere at very low energies (in the electron volt range) preferentially feed the plasma sheet during quiet times, experiencing accelerations up to several kiloelectron volts upon return into the inner magnetosphere. In contrast, during disturbed times, the intensifying magnetospheric convection confines this population to low L shells where it travels in a nearly adiabatic manner. As for the protons originating from the cleft fountain, the simulations reveal that they can be transported up to the vicinity of the distant neutral line in the nightside sector. Via interaction with the neutral sheet, these ionospheric ions are rapidly raised to the characteristic plasma sheet energy range. The density levels contributed by these populations are quite substantial when compared to those measured in situ. These simulations establish an active role of low‐energy ionospheric ions in the overall magnetospheric dynamics.

High resolution depth profiling in near-surface regions of solids by narrow nuclear reaction resonances below 0.5 MeV with low energy spread proton beams

The application of proton-induced narrow resonances in nuclear reactions as probes for depth profiling near-surface regions of solids has been investigated at projectile energies below 400 keV. The measurements were performed at the Universität Münster 400 kV accelerator, which provided intense proton beams with an energy spread of about 15 eV. The energy stability of the accelerator was better than ±3 eV. Narrow resonances in the reactions 18O(p, γ) 19F, 18O(p, α) 15N, 23Na(p, γ) 24Mg, and 29Si(p, γ) 30P were studied. For resonances with an intrinsic width in the electronvolt range, the thermal Doppler broadening dominates the effective energy resolution. With such narrow resonances as probes, contaminants on the surface with a thickness as small as some atomic layers have a significant influence on the shape of the yield curve and for optimal results uhv conditions are required. The method is illustrated with depth profiling experiments of 18O and 23Na with potential near-surface depth resolutions of some tens of Ångstroms.

Collision induced dissociation of peptide ions.: Part 3. Comparison of results obtained using sector—quadrupole hybrids with those from tandem double-focusing instruments

Two series of peptides, viz., dynorphin fragments (up to 9 residues) and oligomers of phenylalanine, have been studied by collision induced dissociation (CID) of their protonated forms produced by fast atom bombardment (FAB) ionization. Spectra were obtained using both a four-sector tandem instrument (CID in the kiloelectronvolt range) and a tandem hybrid instrument (CID at a few tens of electronvolts). The four-sector instrument provided fragment spectra of excellent quality under conditions simulating a real-world analytical situation, i.e. 1–2 nmol of material available, although the FAB efficiency for Phe 8, was so low (precursor ion beam current ∼ 10 −14 A) that no useful fragment spectra were obtained. The hybrid instrument provided abundant fragment ions for smaller precursors (molecular weights < 500–600 Da) but for larger precursors (≥ 800 Da or so) the CID efficiency was much reduced and highly susceptible to composition effects, particularly the presence of highly basic amino acid residues. The information content of these spectra was evaluated objectively via two complementary computer algorithms. The limitations of CID in r.f.-only quadrupole collision cells are not due primarily to ion transmission effects, since examples of good quality spectra for large precursors are presented. The low efficiency of collisional activation of organic ions of m/z ≥ 800 Da or so, under conditions typical of quadrupole collision cells, was confirmed by the observation that in those cases where abundant fragment ions were obtained the corresponding spectra obtained in absence of collision gas were of comparable quality. The differences between collisional activation of such ions in the kiloelectronvolt range and in the electronvolt range, as well as the dramatic differences between low energy CID of large and small precursor ions, are discussed in terms of fundamental considerations of inelastic collisions. Finally, the qualitatively different kinds of fragmentation reactions, observed in the two regimes of collision energy, are described. In both cases the well-known peptide sequence fragments were observed. The high-energy CID also produced intense fragments arising from cleavage of all or part of sidechains (d, s, v and w series) which were entirely absent from the low-energy spectra. The latter contained abundant internal cleavage ions (both N- and C-terminus residues lost) which were relatively weak in the high-energy spectra. Loss of the C-terminus residue was observed in both regimes as a low-energy process in the absence of collision gas, although the compositional conditions giving rise to this process have not been determined in the present work.

Consequences of an electron neutrino in the few-eV range

If the mass of the electron neutrino ν e turned out to be in the few electronvolt range, this would have interesting consequences. We show that if m ν e ⪆2 eV , the present experimental constraints from neutrino oscillation and from neutrinoless double beta decay imply that the electron neutrino would be degenerate with the muon neutrino to order Δm 2 ⪅ 4·10 −4 eV 2, or degenerate with the tau neutrino to order Δm 2 ⪅ 10 −2 eV 2, or degenerate with both, to order Δm 2 ⪅ 0.1 eV 2. This possibly indicates that the ν e would be a pseudo-Dirac neutrino. Triple degeneracy would also be consistent with requirements from the solar neutrino deficiency problem and the problem with the missing atmospheric muon neutrinos.

Internal energy distributions of isolated ions after activation by various methods

A number of activation methods have been compared by approximating internal energy distributions, P( E), of selected activated ions. The ions chosen allow simplifying assumptions to be made concerning the determination of the energy distributions since they fragment by several simple consecutive reactions. Ion abundance data, in combination with known energetics of unimolecular fragmentation, are utilized to estimate the internal energy distributions. Determination of P( E) is therefore not based on a specialized instrument or technique and may be applied to ions which do not have stable neutral counterparts. The data obtained are used to account for several important features of tandem mass spectrometry and to examine and compare different methods of varying ion internal energy. The results show, inter alia, that (i) the general shapes of the energy distributions resulting from collisional activation are relatively insensitive to ion structure; (ii) the average energy of ions activated by collision in the kiloelectron volt or electron volt range of collision energy can be comparable; (iii) in contrast to low energy collisional activation, the distribution of internal energies produced by a kiloelectron volt collision is characterized by a finite probability of depositing very high energies; (iv) the average energy of fragmenting (C 2H 5) 4Si +. ions appears to vary linearly with the collision energy in the 5–28 eV range. As the collision energy increases, the width of the internal energy distribution appears to broaden.

Theoretical investigation of neutron scattering cross sections in Si and Ge.

The development of high-flux high-energy pulsed neutron sources makes it possible to study electronic transitions in solids which are in the electron-volt range. A theoretical study has been carried out to determine the feasibility of using such sources to obtain information about the band structure of semiconductors. Calculations of the inelastic neutron scattering cross sections for germanium and silicon based on an empirical pseudopotential description of the energy bands have been com- pleted. This study is an extension of previous work to more realistic (larger) momentum transfers. The calculated cross sections were found to be quite small for realistic experimental conditions. Measurement of these relatively small cross sections could, however, provide important information about the band structure of semiconductors which cannot be obtained from most other experimental techniques.

A Time-of-Flight Chemical Accelerator for Low Center-of-Mass Energy Spreads

An apparatus to obtain high resolution of relative kinetic energy for collision experiments in the electron volt range is described. Because it is the center-of-mass system that is important in the interpretation of experiments, energy spreads in both the projectiles and the targets are considered. We achieve high resolution in a primary beam with a time-of-flight technique. The target particles are in the form of a crossed beam. Basically, the scheme consists of observing only those reaction products that are formed in a short range of primary-beam flight times. This means that good resolution may be obtained in spite of any inherent energy spread in the beam. The measured quantity is modeled mathematically to show the effect of the energy spreads that remain. These calculations may be used to arrive at the true velocity dependence of the center-of-mass cross sections.