Shape Of Energy Spectrum Research Articles

Direct observations of galactic cosmic rays

The mysterious “radiation ... entering our atmosphere from above” discovered by Hess in 1912 is now known to be dominated by relativistic charged particles, mostly with energies in the GeV-range, but extending to energies higher by many orders of magnitude. As none of these particles can penetrate the earth’s atmosphere without interaction, detailed studies of their composition and energy spectra require observations with high-altitude balloons or spacecraft. This became possible only towards the middle of the 20th century. The direct measurements have now revealed much detail about the Galactic cosmic rays below 1015eV, but do not yet provide much overlap with the air-shower region of energies. A historic overview of the measurements is given, beginning with the realization that the majority of the cosmic rays are protons. The discovery and astrophysical significance of the heavier nuclei, and of the ultra-heavy nuclei beyond iron and up to the actinides, are then described, and measurements of the isotopic composition are discussed. Observations of the individual energy spectra are reviewed, and finally, the detection of electrons, positrons, and anti-protons in the cosmic rays, and the searches for exotic or unusual phenomena are summarized. Emphasis is given to the fact that all of these discoveries have become possible through the evolution of increasingly sophisticated detection techniques, a process that is continuing through the present time. The precise knowledge of the abundance distributions of the elements in the cosmic rays and of their isotopic composition permits a comparison with the “universal abundance scale” and provides strong constraints on the origin of the cosmic-ray material in the interstellar medium. “Clock-isotopes” reveal the time history of the particles. The shapes of the energy spectra of the individual cosmic-ray components are related to evolving ideas about particle acceleration and propagation in the Galaxy. In conclusion, prospects for future work are briefly discussed.

THE CHARACTERISTICS OF GRBs WITH PRESENCE OF HIGH ENERGY COMPONENT IN THEIR SPECTRA

The properties of GRBs with presence of high energy emission in spectra are discussed. The temporal profiles of part of events are similar in various energy bands in prompt phase (as for GRB 080528, GRB 021008) but during some events extended high energy emission was detected (for example, GRB 090902B). For other part of GRBs temporal profiles are quite different in various energy bands during prompt phase (as for GRB 050525B), but for some such events extended high energy emission was observed too – for example, GRB 080514B. Moreover, high energy precursors were registered for several GRBs: some photons in energy band 30 MeV - 30 GeV were detected by AGILE during GRB 080514B. The shape of energy spectra of GRBs with presence of high energy emission can follows the Band model (or power law or broken power law) up to some tens or hundreds of MeV (as for GRB 021008) or contains additional high energy power law component (for example, GRB 050525B and GRB 090902B). Following this criteria it is possible to separate two main subclasses of GRBs with high energy emission. Both types of GRBs observed since CGRO mission beginning. The analysis of their energy spectra has shown that the break between additional high energy component and Band (or power law or broken power law) component was in energy region 2-200 MeV. Both types can have got extended high energy emission including component with E > 500 MeV for some events and low energy precursors. The special features of second class of GRBs by the results of preliminary data analysis are the absence of hard to soft evolution in the low energy band and (or) presence of the high energy precursors for some events.

Quantification of the effects of uncertainties in turbulent flows through generalized Polynomial Chaos

Statistical methodologies based on surrogate-models have proved to be an efficient approach to quantify the physical properties of turbulent flows. The underlying idea is to parametrize the space of possible solutions via a computationally inexpensive approximation model, which is then used to generate samples for the statistical tool at hand.In the following homogeneous isotropic turbulence (HIT) decay and Large-eddy simulation (LES) subgrid-scale modeling are considered as stochastic processes and their sensitivity to uncertainties in the energy spectrum shape is investigated by a surrogate-model approach based on the generalized Polynomial Chaos (gPC) approximation.The initial spectrum shape at large scales drives the long-time evolution of the physical quantities in HIT: this sensitivity is recovered even at high Reynolds number. In particular, a universal asymptotic behavior in which kinetic energy decays as t−1 is not observed.The statistical average of the Smagorinsky subgrid model constant is close to the asymptotic Lilly-Smagorinsky value if the LES filter cut is applied in the inertial range at high Reynolds numbers, while a significant variance is recovered if the cut if performed in the dissipation range or if moderate Reynolds number are considered.

Neutrino Mass Experiment at The University of Texas at Austin (NEXTEX)

NEXTEX is the next generation experiment designed to determine the electron antineutrino mass to at least 0.5 eV. The experiment is based on the shape of the beta endpoint energy spectrum from gaseous tritium molecules. Two high throughput electrostatic differential electron analyzers coupled with spherical deflection accelerator are key components of the apparatus. The voltages at the electrodes of the spectrometers ultimately determine the energy of the electrons reaching the detector. The correlations between voltages and the energy of the transmitted electrons will be calibrated with diffraction on the T 2 gas of electrons emitted from the auxiliary gun. The coherent electron diffraction pattern from T 2 will provide a series of calibration markers for the spectrum with uncertainties better than 100 mV. Extremely low background count-rates from cosmic rates of less than one count a day at the detector has been already demonstrated. A numerical model predicts residual background from tritium sources of few counts per day. The tritium source and its recycling system is designed to prevent the formation of HT to better than 1% during the fiduciary runs.

The effects of shielding around the source on neutron energy spectra

The knowledge of neutron energy spectra contributes to unambiguous identification of neutron sources in the fields of nuclear safeguards and nuclear non-proliferation. Since a real scenario situation includes the presence of shielding around the source, we have investigated the influence of the potential shielding surrounding the source on the shape of energy spectra for a few neutron sources. We have applied the maximum-likelihood, expectation–maximisation (MLEM) method with one-step-late (OSL) algorithm for neutron spectra unfolding. The pulse height distributions used in the unfolding procedures were simulated with the high accuracy by using the MCNP-PoliMi code based on the Monte Carlo method. A possibility to identify the shielded neutron sources by using the unfolding method was examined with two continuous-in-energy sources, such as 252Cf and 241Am–Be in source-shielding configurations with lead (Pb) and polyethylene (PE) blocks. The results of calculations have shown that the identification of 252Cf and 241Am–Be sources with 2.5 cm of Pb and PE shield can be achieved successfully by using the MLEM method with the OSL algorithm. However, the unfolded results for 252Cf and 241Am–Be sources with 10 cm of PE shield significantly deviate from the reference spectra and the sources cannot be correctly identified on the basis of their unfolded energy spectra.

On the detectability of high-energy galactic neutrino sources

With the arrival of km 3 volume scale neutrino detectors the chances to detect the first astronomical sources of TeV neutrinos will be dramatically increased. While the theoretical estimates of the neutrino fluxes contain large uncertainties, we can formulate the conditions for the detectability of certain neutrino sources phenomenologically. In fact, since most galactic neutrino sources are transparent for TeV γ-rays, their detectability implies a minimum flux of the accompanying γ-rays. For a typical energy-dependence of detection areas of km 3 volume neutrino detectors, we obtain the quantitative condition I γ ( 20 TeV ) > 2 × 10 - 15 ph/cm 2 s , that thanks to the normalization of the γ-ray spectrum at 20 TeV appears to be quite robust, i.e. almost independent of the shape of energy spectrum of neutrinos. We remark that this condition is satisfied by the young supernova remnants RX J1713.7-3946 and RX J0852.0-4622 (Vela Jr) – two of the strongest galactic γ-ray sources. The preliminary condition for the detectability of high energy neutrinos is that the bulk of γ-rays has a hadronic origin: A new way to test this hypothesis for RX J1713.7-3946 is proposed. Finally, we assess the relevance of a neutrino detector located in the Northern hemisphere for the search for galactic neutrino sources. In particular, we argue that if the TeV neutrino sources correlate with the galactic mass distribution, the probability that some of them will be observed by a detector in the Mediterranean Sea is larger by a factor of 1.4–2.9 compared to the one of IceCube.

Luminosity measurement in H1

The HERA luminosity was determined by measuring the flux of bremsstrahlung photons emitted at zero degree off electrons in the field of protons in the interaction region. After the HERA upgrade, the H1 Collaboration developed a new luminosity system which measured all the emitted photons in a bunch crossing. We describe the expression of this photon flux in the luminosity detector which is used in the simulation of the detector. The total energy method, based on the measurement of the bremsstrahlung photon energy flux in the calorimeter, is the standard method for the off-line luminosity measurement. In this study, we propose a new method to calculate the luminosity. This new method is based on the shape of the bremsstrahlung photon energy spectrum measured in the luminosity detector. The two methods are compared. A good agreement is observed.

Reynolds-number dependency in homogeneous, stationary two-dimensional turbulence

Turbulent solutions of the two-dimensional Navier–Stokes equations are a paradigm for the chaotic space–time patterns and equilibrium distributions of turbulent geophysical and astrophysical ‘thin’ flows on large horizontal scales. Here we investigate how homogeneous, stationary two-dimensional turbulence varies with the Reynolds number (Re) in stationary solutions with large-scale, random forcing and viscous diffusion, also including hypoviscous diffusion to limit the inverse energy cascade. This survey is made over the computationally feasible range in Re ≫ 1, approximately between 1.5 × 103 and 5.6 × 106. For increasing Re, we witness the emergence of vorticity fine structure within the filaments and vortex cores. The energy spectrum shape approaches the forward-enstrophy inertial-range form k−3 at large Re, and the velocity structure function is independent of Re. All other statistical measures investigated in this study exhibit power-law scaling with Re, including energy, enstrophy, dissipation rates and the vorticity structure function. The scaling exponents depend on the forcing properties through their influences on large-scale coherent structures, whose particular distributions are non-universal. A striking result is the Re independence of the intermittency measures of the flow, in contrast with the known behaviour for three-dimensional homogeneous turbulence of asymptotically increasing intermittency. This is a consequence of the control of the tails of the distribution functions by large-scale coherent vortices. Our analysis allows extrapolation towards the asymptotic limit of Re → ∞, fundamental to geophysical and astrophysical regimes and their large-scale simulation models where turbulent transport and dissipation must be parameterized.

Dose‐rate distribution of ‐glass microspheres for intra‐arterial brachytherapy

The intra-arterial administration of radioactive glass microspheres is an alternative therapy option for treating primary hepatocellular carcinoma, the main cause of liver cancer death, and metastatic liver cancer, another important kind of cancer induced in the liver. The technique involves the administration of radioactive microspheres in the hepatic artery, which are trapped preferentially in the tumor. In this work the GEANT4 toolkit was used to calculate the radial dose-rate distributions in water from 32P-loaded glass microspheres and also from 90Y-loaded glass microspheres. To validate the toolkit for this application, the authors compared the dose-rate distribution of 32P and 90Y point sources in water with data from the International Commission on Radiation Units and Measurements report 72. Tables of radial dose-rate distributions are provided for practical use in brachytherapy planning with these microspheres. The simulations with the microspheres show that the shape of the beta ray energy spectra with respect to the 32P and 90Y sources is significantly modified by the glass matrix.

Measurement of the isotope composition of hydrogen in carbon materials using elastically scattered electron peak spectroscopy

The quantitative composition of hydrogen and helium isotopes in the surface layers of structural materials is reconstructed using the developed technique for processing the energy spectra of electrons scattered from plane-parallel layers of solids into a preset solid angle element. These are the spectra measured with a high energy resolution ΔE ∷ 0.2−0.4 eV. The change in the shape of peaks for elastically scattered electrons is analyzed depending on the probe electron beam energy and experimental geometry. The theory of electrons scattered from plane-parallel layers of solids is constructed using the solution of the boundary value problem for the transfer equation by invariant immersion methods. The analytic solution to the system of equations is found in the small-angle approximation for the reflection and transmission functions. The results of calculations are compared with experimental data on electron scattering from polyethylene. The shape of the energy spectra of electron scattering from deuterium and tritium is predicted. The sensitivity threshold of the method relative to percentage concentration of hydrogen isotopes in hydrocarbons is analyzed.

Investigation of the PCR energy spectrum shape by the means of the local EAS muon density technique

The results of studying the primary cosmic radiation (PCR) flux in the energy range 1015–1018 eV at the NEVOD-DECOR experimental array using local muon density spectra are reported. The experimental distributions and the spectra obtained by simulation of EAS muon LDF using the CORSIKA code are compared. Possibilities of using a new method for analysis of muon bundle events on the basis of the primary energy estimator are discussed.

Measurements of high energy cosmic rays above 10 PeV with KASCADE-Grande

In the present work, different aspects of the measurement and reconstruction of extensive air showers generated by cosmic rays in the energy range between 10 16 eV and 10 18 eV are investigated. KASCADE-Grande detects charged particles of extensive air showers at ground level. From the energy deposits and the arrival times of the particles in the detector stations, the main parameters of the extensive air showers are reconstructed: the impact point, the direction of the shower axis, the total number of electrons (N e ), and the total number of muons (Nμ) of the shower at observation level. The nurnbers of electrons and muons are related to the mass and energy of the primary particle and are the basis for further analysis. The shape of the electron number spectrum reflects the shape of the cosmic ray energy spectrum. Knowing the reconstruction accuracies, the N e spectrum of the KASCADE- Grande data is studied in order to identify possible spectral features. It is found, that observed structures are consistent with the detector resolution and the reconstruction uncertainties. On the basis of the correlation between the total number of muons in the showers and the total number of charged particles, a composition estimation is carried out. A k Nearest Neighbours (kNN) classification procedure is developed: a measured air shower is classified as proton-like or iron-like by finding its nine nearest neighbours in the parameter space of the selected mass sensitive observables. The total number of charged particles (N ch ) and the total number of muons (N μ ) are found to be suitable observables for this purpose. The parameter space is populated by a set of simulated proton and iron induced air showers and an air shower is assigned to the class most common among its neighbours. The misclassification errors, as obtained in the training phase, are taken into account. An increase of the relative number of iron-like induced air showers is observed between 10 16 eV and 3.2·10 16 eV, which could be associated with the decrease of the cosmic ray light component (He, CNO group) due to the break in its energy spectrum. Above 3.2·10 16 eV, about 70% of the events result to be iron-like and ≈ 30% proton-like. At the highest observed energies an increase of light primaries is indicated. The results presented in this work constitute a first attempt to carry out composition analysis with KASCADE-Grande data.

Mesoscale to Submesoscale Transition in the California Current System. Part III: Energy Balance and Flux

Abstract This is the last of a suite of three papers about the transition that occurs in numerical simulations for an idealized equilibrium, subtropical, eastern-boundary upwelling current system similar to the California Current. The transition is mainly explained by the emergence of ubiquitous submesoscale density fronts and ageostrophic circulations about them in the weakly stratified surface boundary layer. Here the high-resolution simulations are further analyzed from the perspective of the kinetic energy (KE) spectrum shape and spectral energy fluxes in the mesoscale-to-submesoscale range in the upper ocean. For wavenumbers greater than the mesoscale energy peak, there is a submesoscale power-law regime in the spectrum with an exponent close to −2. In the KE balance an important conversion from potential to kinetic energy takes place at all wavenumbers in both mesoscale and submesoscale ranges; this conversion is the energetic counterpart of the vertical restratification flux and frontogenesis discussed in the earlier papers. A significant forward cascade of KE occurs in the submesoscale range en route to dissipation at even smaller scales. This is contrary to the inverse energy cascade of geostrophic turbulence and it is, in fact, fundamentally associated with the horizontally divergent (i.e., ageostrophic) velocity component. The submesoscale dynamical processes of frontogenesis, frontal instability, and breakdown of diagnostic force balance are all essential elements of the energy cycle of potential energy conversion and forward KE cascade.

Comparison of two forms of the S-matrix element of strong-field photoionization

We numerically compare ionization rates and photoelectron energy spectra resulting from the so-called length gauge (LG) and velocity gauge (VG) forms of the Keldysh–Faisal–Reiss (KFR) theory for a circularly polarized laser field. To this end, we use the well-known analytical formulae for the ground state of a hydrogen atom and we derive analogous formulae for its first excited (degenerate) state. It appears that both forms of the KFR theories show qualitatively different behaviour of ionization rate as a function of frequency and intensity of the laser field. In the LG KFR theory, one obtains much smaller stabilization of the hydrogen atom than in the VG KFR theory. Unlike the latter one, the LG KFR theory shows that for sufficiently strong laser field (in the non-relativistic and dipole approximations) ionization rate from a given initial state is only a function of intensity, but not of frequency of the laser field. We also find substantial differences in the shape of photoelectron energy spectra for both theories. In contrast to the VG KFR theory, the LG one shows a minimum in photoelectron energy spectra for some initial states of the hydrogen atom. We discuss our results by comparing them, where possible, to other theoretical calculations.

The WITCH experiment: Acquiring the first recoil ion spectrum

The standard model of the electroweak interaction describes β-decay in the well-known V–A form. Nevertheless, the most general Hamiltonian of a β-decay includes also other possible interaction types, e.g. scalar (S) and tensor (T) contributions, which are not fully ruled out yet experimentally. The WITCH experiment aims to study a possible admixture of these exotic interaction types in nuclear β-decay by a precise measurement of the shape of the recoil ion energy spectrum. The experimental set-up couples a double Penning trap system and a retardation spectrometer. The set-up is installed in ISOLDE/CERN and was recently shown to be fully operational. The current status of the experiment is presented together with the data acquired during the 2006 campaign, showing the first recoil ion energy spectrum obtained. The data taking procedure and corresponding data acquisition system are described in more detail. Several further technical improvements are briefly reviewed.

A study of time correlations in lattice Boltzmann-based large-eddy simulation of isotropic turbulence

As one of statistical characteristics of turbulent flow, space-time correlation is important when studies contribute to understanding of the mechanism of sound radiation and wave scattering by turbulence. This paper combines large-eddy simulations (LES) with the lattice Boltzmann method (LBM) to study the effects of subgrid models on time correlations in decaying isotropic turbulence. The performance of the inertial-range (IR) consistent model and the classical Smagorinsky model is evaluated in terms of two-time Eulerian velocity correlations at the LBM framework. The present study compares the correlations evaluated by LES and the direct numerical simulations based on the lattice Boltzmann equation and Navier–Stokes (NS) equations, respectively. It shows that the lattice Boltzmann subgrid models yield an underestimation of the magnitude of the time correlation on different time intervals and on a variety of wavenumber modes, similar to NS subgrid models. It is also observed that the calculated decorrelation time scale is in good agreement with the theoretical analysis for the Eulerian time microscale and scales nearly as τ(k)∝(Vk)−1. It appears that τ(k) may be either underestimated or overestimated depending on the shape of initial energy spectrum to some extent. Furthermore, compared to the classical Smagorinsky model with different initial spectra, the IR consistent subgrid model shows promising performance on the prediction of the time-space correlations in turbulent flows.

Energy spectrum shape of low energy ion scattering from insulators and its similarity to asymmetric spectrum shape observed in core level XPS from metals

The energy spectrum of low energy ion scattering (LEIS) from insulators is studied theoretically. The energy spectrum could be analyzed by using the Doniach–Sunsic line-shape function, which is routinely used as a fitting function to the asymmetric shape of the spectrum observed in core level X-ray photoemission spectroscopy (XPS) for metallic targets. The common nature between LEIS and XPS is discussed in terms of a singular behavior of physical processes involved in LEIS and XPS. In the case of XPS, it is known that the infrared divergence of electron–hole pair excitations leads to the asymmetric shape of line spectrum, whereas, in the case of LEIS, the multiple elastic scatterings lead to a similar asymmetric shape of the spectrum.

Neutron Spectrum from the Renewed Cold Neutron Source in JRR-3 and Expectation for the Future Upgrade Project

The neutron flux and energy spectrum from the renewed cold neutron source was measured at the C2-1 beam port in the guide hall of JRR-3. We confirmed that both the absolute flux of 2×1012n/m2s and the shape of energy spectrum were reproduced after the replacement of the liquid hydrogen tank. JAEA has a plan to increase cold neutron flux ten times as strong as that at present by introducing a new type of hydrogen tank and super mirror neutron guide in the next term.

A NEW STUDY ON THE ENERGY SPECTRUM AND COMPOSITION OF PRIMARY COSMIC RAY FLUX AT ENERGIES ~ 1014 – 1016 EV USING THE GRAPES-3 ARRAY AT OOTY

Data collected with the 217-detector air shower array and the 560 m2 area tracking muon detector, being operated at Ooty in southern India by the India-Japan (Tata Institute-Osaka City University) collaboration, GRAPES, have been analyzed to study the shape of the energy spectrum and the composition around the knee. It is shown that the muon multiplicity distribution, observed with the highly modular muon detector, permits a relatively reliable measurement on the composition of primary flux which then helps in a more accurate reconstruction of the energy spectrum from the observed shower size spectrum. The highlights of the GRAPES array, the analysis procedure and the results are presented.

Sensitivity of spectral variational multiscale methods for large-eddy simulation of isotropic turbulence

Subgrid closures in the Fourier space belonging to the variational multiscale method proposed by Hughes are investigated in the case of the incompressible freely evolving isotropic turbulence in the limit of an infinite Reynolds number. Sensitivity to the closure used at small scales is shown to be high, and different hybrid spectral closures proposed in the present study which explicitly account for the computed kinetic energy spectrum shape yield good results. The original formulation of the method is observed to suffer from an unphysical energy pile-up in the large scales, which arises from the fact that the kinetic energy transfers associated with distant triadic interactions are neglected. The use of a nonorthogonal operator to define the resolved large and small scales is proved to alleviate this problem, yielding an accurate and robust spectral variational multiscale methods for high Reynolds number flows.