Particle Energy Deposition Research Articles

Multispectral observations of Jupiter's aurora

Remote sensing of Jupiter's aurora from x-ray to radio wavelengths has revealed much about the nature of the jovian aurora and about the impact of ionosphere-magnetosphere coupling on the upper atmosphere of Jupiter. As indicated by the combination of x-ray and ultraviolet observations, both energetic heavy ions and electrons energized in the outer magnetosphere contribute to auroral excitation. Imaging with the Hubble Space Telescope in the ultraviolet and with the InfraRed Telescope Facility at infrared wavelengths shows several distinct regions of interaction: 1) a dusk sector where turbulent auroral patterns extend well into the polar cap; 2) a morning sector generally characterized by a single spatially confined auroral arc originating in the outer or middle magnetosphere of Jupiter; 3) diffuse emissions associated with the Io plasma - spectroscopy has provided important information about the thermal structure of Jupiter's auroral atmosphere and the altitude distribution of auroral particle energy deposition, while Lyman alpha line profiles yield clues to the nature of thermospheric dynamical effects. Galileo observations at visible wavelengths on the nightside offer a new view of the jovian aurora with unprecedented spatial information. Infrared observations have added much to the understanding of thermal structure at all latitudes, the dynamics of the thermospheric wind system, and auroral morphology, and may hold the key to understanding the role of Joule heating in Jupiter's thermosphere. ROSAT observations have revealed soft x-ray emissions from Jupiter's lower latitudes as well as from the auroral zones, implying that energetic particle precipitation also occurs at low latitudes in regions magnetically linked to the inner radiation belts. In this review, multispectral observations of jovian auroral emissions are presented within a theoretical/modeling framework that is intended to provide some insight into magnetosphere-ionosphere coupling and its effects on the upper atmosphere.

A potential application to the study of microscopic energy deposition in a solid by means of heavy charged-particle induced photochromic alterations in a tissue-equivalent matrix

A theoretical study was carried out to investigate the feasibility of using the radiation-induced colour decay of photochromic molecules embedded in a polymer matrix as a probe for studying the microscopic energy deposition of heavy charged particles (HCPs) in a tissue-equivalent solid. The theoretical treatment makes use of the radial dose distribution function as derived from gas-phase physics, together with the effects of the increase in temperature and of matrix degradation on the colour-decay kinetics of the photochromic molecules, according to empirical models derived for the solid state. Bearing in mind the non-stochastic nature of the model, the use of gas-phase physics at the level of radiation interaction, and the fact that some empirical quantities used have been established macroscopically, all factors which signify that extra caution is required in the interpretation of the results, it is shown that when the optimum information retrieval time (after track formation) is considered the technique may be able to resolve differences in the energy deposition pattern by different HCPs in the nanometre range (1-10 nm; material's mass density ) from the track axis. Most importantly, though, the present study aims to erect a theoretical framework for the possible application of the technique and to highlight those aspects which are likely to be critical to its practical usage, such as particle type and energy range, and spatial scale and magnitude of the expected effect together with its dependence on time, the physical characteristics of the matrix, and the kinetic behaviour of the type of photochromic molecule studied. Furthermore, it establishes a rationale for interpreting the experimentally observed (if available) colour changes in the HCP track in terms of the microscopic distribution of energy deposition in it.

Usage of a corrected Bethe–Bloch formula for charge identification of fast ions with Z⩾30 recorded in polycarbonate track detectors

The Bethe–Bloch formula is commonly used to calculate energy losses and ranges of charged massive (m≫me) particles when they penetrate into a given absorber. In order to make the formula applicable to ions of any charge and energy travelling inside any given material, several corrections must be introduced. To identify the charge of unknown ions employing SSNTDs, a track formation model, based on the energy deposition of the incident particles in the absorber, is needed. The Restricted Energy Loss (REL) model assumes that only the energy deposition due to distant collisions of the incident ion with the absorber atoms contributes effectively to track formation. In this work, the effect on the charge identification process of considering the corrections to the Bethe–Bloch formula is studied, as well as the possible effect of considering a contribution of the close collisions to the REL model. The identification procedure is applied to the Ultra Heavy cosmic ray ions recorded in the Ultra Heavy Cosmic Ray Experiment.

UARS observations of Birkeland currents and Joule heating rates for the November 4, 1993, storm

Magnetic field and particle observations from the Upper Atmosphere Research Satellite particle environment monitor (UARS/PEM) are used to estimate field‐aligned currents, electron precipitation energy flux, ionospheric conductivities, and Joule heating rates during the main phase of the November 4, 1993, geomagnetic storm. From 0300 to 1200 UT on November 4 the auroral oval expanded equatorward of 65° magnetic latitude (MLAT), and UARS encountered the polar cap on seven consecutive passes during the storm main phase. These passes provide data appropriate to determine field‐aligned currents and estimate ionospheric Joule heating. For this storm, UARS sampled the midnight to dawn sector in the northern hemisphere and the noon to dusk sector in the southern hemisphere. The maximum net currents on the day side and nightside are comparable and reach 1 A/m for several hours. The average Joule heating rates are comparable at midnight, early morning, and noon, where they are 9.2, 6.6, and 7.7 GW/h, respectively, but have a strong peak in the late afternoon, where they are 25.6 GW/h. In contrast, the electron precipitation energy deposition is highest near midnight at 5.6 GW/h but drops to less than half this level to 2.4 GW/h and 1.9 GW/h in the early morning and at dusk, respectively, but is very small near noon, only 0.24 GW/h. The Joule to particle energy deposition rate ratio thus varies by roughly an order of magnitude with local time, being over 40 near noon, about 20 at dusk, 3 near dawn, and 2 at midnight. The hemispherical Joule and electron precipitation heating rates, HJ and Helec, are estimated to have been 290 GW and 50 GW, respectively, giving HJ/Helec = 4.5 and HJ + Helec = 340 GW. Differences between these averages and assimilative mapping of ionospheric dynamics (AMIE) results, HJ = 200 GW and Helec = 80 GW, reflect time variability during the storm and are largely resolved when AMIE results only at the times of UARS passes are considered.

Propagation velocity and structure of thermonuclear deflagration waves

Structure and propagation speeds have been determined for thermonuclear deflagration waves (fusion flames) in idealized, magnetically confined, deuterium - tritium plasmas. A one-dimensional time-dependent numerical code using multi-fluid and magnetohydrodynamic equations and detailed treatments of alpha particle energy deposition and radiative energy transfer was used. In all cases studied, deflagration waves with well defined structures form and propagate through the plasma with a speed of , where is the ion density , B is the magnetic field (T), and u is the local plasma fluid velocity.

Irradiation-induced Ag-colloid formation in ion-exchanged soda-lime glass

Ion-exchanged glass samples were obtained by immersing soda-lime slides in molten salt baths of molar concentration in the range 1–20% AgNO 3 in NaNO 3, at temperatures varying from 320 to 350°C, and processing times of the order of a few minutes. Irradiations of exchanged samples were subsequently performed by using H +m, He +, N + ions at different energies in order to obtain comparable projected ranges. The fluence was varied between 5 × 10 15 and 2 × 10 17 ions/cm 2. Most of the samples were treated at current densities lower than 2 μA/cm 2, in order to avoid heating effects. Some samples were irradiated with 4 keV electrons, corresponding to a range of 250 nm. The formation of nanoclusters of radii in the range 1–10 nm has been observed after irradiation, depending on the treatment conditions. The precipitation process is governed by the electronic energy deposition of incident particles. The most desirable results are obtained for helium implants. The process was characterized by the use of Secondary Ion Mass Spectrometry (SIMS) and nuclear techniques (Rutherford Backscattering (RBS), Nuclear Reactions (NRA)), in order to determine concentration-depth profiles and by optical absorption and Transmission Electron Microscopy (TEM) measurements for the silver nanoclusters detection and size evaluation.

The temperature of the track

The energy deposition of swift charged particles penetrating solids is accompanied by such processes as particle (electron, atom, ion, molecular ion, photon …) emission and/or a change of the solid along the particle track. The energy, velocity and mass distribution of such secondary particles obtained from thin solids (such as carbon, polyhydrocarbon, isolators and conductors) penetrated by projectiles (e.g. Ar 1.8 MeV) was measured quantitatively. A number of direct and indirect production mechanisms contribute to the internal source of electrons and secondary ions. The analysis of the ejected radicals give information on the emission processes, the temperature, the charge and the time scale of energy deposition near the surface of the solid which, eventually, become responsible for the track formation.

Experimental Verification of a Superheated Liquid Droplet (Bubble) Neutron Detector Theoretical Model

Abstract Superheated liquid droplet ('bubble') neutron detectors utilise thousands of microscopic droplets of freon-based compounds suspended in a viscous matrix material. Neutrons can interact with the atoms of the superheated liquid droplets, resulting in the formation of energetic charged recoil ions. These ions transfer their energy to the liquid in the droplets, sometimes resulting in the droplets vaporising and producing visible bubbles. The basis of bubble detector operation is identical to that of bubble chambers, which have been well characterised by researchers such as Wilson, Glaser, Seitz and others since the 1950s. Each of the microscopic superheated liquid droplets behaves like an independent bubble chamber. This paper presents a theoretical model that considers the three principal aspects of detector operation: nuclear reactions, charged particle energy deposition, and thermodynamic bubble formation. All possible nuclear reactions were examined and those which could reasonably result in recoil ions sufficiently energetic to vaporise a droplet were analysed in detail. Feasible interactions having adequate cross sections include elastic and inelastic scattering, n-proton, and n-alpha reactions. Ziegler's transport of ions in matter (TRIM) code was used to calculate the ions' stopping powers in various compounds based on the ionic energies predicted by standard scattering distributions. If the ions deposit enough energy in a small enough volume then the bubble of vapour that forms will grow to 'critical' size, and spontaneously vaporise the rest of the entire droplet without further energy input. Various theories as to the vaporisation of droplets by ionising radiation were studied and a novel method of predicting the critical (minimum) energy was developed. This method can be used to calculate the minimum required stopping power for the ion, from which the threshold neutron energy is obtainable. Experimental verification of the model was accomplished by measuring the response of two different types of bubble detectors to monoenergetic thermal neutrons, as well as to neutrons from the polyenergetic spectra of bare and moderated californium spontaneous fission sources. The model's predicted response compared favourably with the experimental data.

Particle penetration through frozen gases

The energy deposition of swift charged particles penetrating solids is accompanied by such processes as particle (electrons, atoms, photons …) production or phase transition along the particle track. The electron yield obtained with thin copper foils covered with solid CO2 (or Xe) and the erosion of frozen CO2 (or Xe) by transmission of protons (1 MeV) was measured quantitatively. The obtained CO2 (or Xe) thickness was related 1. to the yield of convoy electrons (Ee ≃ 540eV) being emitted along the beam direction (Θ=O°) with a vector velocity ve equal to the projectile vector velocity vp and 2. to the intensity of low energy “true” secondary electrons (Ee < 50eV). The adsorbate thickness dependence of both electron yields is found to be independent of their electron transport lengths 1(Ee.

Heavy ion and fusion particle stopping power in inertial confinement fusion (abstract)

In inertial confinement fusion (ICF), the energy deposition of, first, heavy ions in the hohlraum and, second, charged fusion products in the plasma pellet is an essential issue. This can be quite subtle because the targets experience a series of phase transitions (solid→gas→partially ionized plasma→fully ionized plasma) and, most importantly, charged particle energy deposition depends on whether the charged particles are in the ‘‘fast,’’ ‘‘intermediate,’’ or ‘‘slow’’ regime, which depends on the plasma temperature. (The regime is defined as xi/e=vi2/vthe2. vi is ion velocity and vthe is electron thermal velocity. xi/e≫1, xi/e∼1, and xi/e≪1 correspond to fast, intermediate, and slow regimes, respectively.) A physical model based on the theory of binary interactions and plasma collective effects is being applied to the stopping power in these different regimes, especially in the transition regime (xi/e∼1), which is almost always ignored. From this model, we describe the physical picture of the evolution in energy deposition in both holhraum and the compressed pellet. Taking the typical ICF parameters for holhraum−ion energy ∼1 MeV/amu, electron density ∼1024 cm−3, and plasma temperature from a few eV to 1 keV −the scale sizes for both collisional energy exchange and electron plasma wave damping have been estimated and the energy relaxation rates of both mechanisms calculated. The significance of nuclear stopping and electron degeneracy effects will also be considered for fusion products in the core of pellet plasma. Finally, we briefly extend this model to the Solar core. This work was supported by U. S. Department of Energy Grant No. DE-FG02-91ER54109 and LLNL Subcontract B116798.

Energy deposition in antimatter meteors

Antimatter meteors, like ordinary ones, can be heated during their infall flight. However, this could happen by a completely different process than in the case of koinomatter meteors, since in the latter case the annihilation interactions mechanism is absent. In case of antimatter meteors, the temperature may be increased mainly due to the energy deposition effect, caused by the passage of the annihilation secondaries penetrating throughout the meteor. The energy deposition of the secondary particles produced in matter antimatter annihilation interactions as a function of the dimensions of an antimatter meteor is described in this paper.

Energy deposition in direct nuclear pumped optical cavities

A two-dimensional, time-dependent model has been developed to determine the coupled fluid dynamic and charged particle transport behavior of a flowing gas, nuclear pumped laser cavity. Stationary results are presented for a typical cavity that uses a flowing He buffer gas pumped with charged particles produced by the 10B(n,α)7Li reaction. The boron is coated on fuel plates mounted parallel to the flow direction. The effects of changing the buffer gas inlet flow velocity and outlet pressure are investigated. For a fixed inlet velocity, the results presented show that the gradients of the charged particle energy deposition and density increase in magnitude primarily in the direction perpendicular to the gas flow, i.e., normal to the fuel plates, as the outlet pressure is increased. With increasing inlet velocity and a fixed outlet pressure, the density variations decrease, whereas the variations in energy deposition increase in the direction perpendicular to the flow and decrease in the direction parallel to the gas flow. For higher inlet velocity cases, the deposition is nearly one-dimensional, varying primarily in the direction perpendicular to the flow. Qualitatively similar results can be found with an argon buffer gas and fission fragment pumping for similar charged particle ranges. In general, for a fixed cavity geometry similar charged particle energy deposition behavior can be obtained for different laser gases by adjusting the outlet pressure and charged particle source.

Plasma discharge in N 2 + CH 4 at low pressures: Experimental results and applications to Titan

We report the yields of gaseous hydrocarbons and nitriles produced in a continuous flow, low-dose, cold plasma discharge excited in a 10% CH 4, 90% N 2 atmosphere at 295 K and pressures p of 17 and 0.24 mbar, and use the results to compute expected abundances of minor constituents in Titan's atmosphere. These experiments are, by design, relevant to the atmospheric chemistry induced by cosmic rays in Titan's troposphere and (at the lower pressure) to chemistry initiated by Saturnian magnetospheric electrons and other charged particle sources which excite stratospheric aurorae. At p = 17 mbar, 59 gaseous species including 27 nitriles are detected in overall yield 4.0 (C + N) atoms incorporated into products per 100 eV (heV). At p = 0.24 mbar, 19 species are detected, including six nitriles and three other unidentified N-bearing compounds; the yield is 0.79 (C + N)/heV, a mild decrease with pressure. The types of molecules formed change more markedly, with high degrees of multiple bonding at 0.24 mbar prevailing over more H-saturated molecules at 17 mbar. The molecules and yields at 0.24 mbar bear a striking resemblance to the minor constituents found in Titan's atmosphere, all of which are abundant products in the laboratory experiment. Using the altitude-integrated flux of charged particle energy deposition at Titan, the laboratory yields at p = 0.24 mb, and a simple eddy mixing model, we compute absolute stratospheric column abundances and mole fractions. These are found to be in very good agreement with the Voyager IRIS observations. Except for the primarily photochemical products, C 2H 6 and C 3H 8, the match is much better than that obtained by photochemical-kinetic models, demonstrating that properly designed laboratory experiments are directly applicable to modeling radiation-chemical processes in planetary atmospheres. On the basis of this agreement we expect CH 3CN (ethanenitrile = acetonitrile) CH 2CHCHCH 2 (1,3-butadiene), CH 2CCH 2 (1,2-propadiene = allene), and CH 2CHCCH (1-buten-3-yne) to be present at mol fractions X > 10 −9, and CH 2CHCN (propenenitrile), CH 3CHCH 2 (propene), and CH 3CH 2CN (propanenitrile) at X > 10 −10 in Titan's atmosphere.

MCPT: A Monte Carlo code for simulation of photon transport in tomographic scanners

MCPT is a special-purpose Monte Carlo code designed to simulate photon transport in tomographic scanners. Variance reduction schemes and sampling games present in MCPT were selected to characterize features common to most tomographic scanners. Combined splitting and biasing (CSB) games are used to systematically sample important detection pathways. An efficient splitting game is used to tally particle energy deposition in detection zones. The pulse height distribution of each detector can be found by convolving the calculated energy deposition distribution with the detector's resolution function. A general geometric modelling package, HERMETOR, is used to describe the geometry of the tomographic scanners and provide MCPT information needed for particle tracking. MCPT's modelling capabilities are discribed and preliminary experimental validation is presented.

Measurement of dose distributions of linear energy transfer in matter irradiated by fast neutrons

A detector has been developed and used to measure dose distributions versus linear energy transfer to thin gas targets in spherical geometry from fast neutron irradiation of tissue-equivalent plastic and carbon. The detector is a hemispherical proportional counter with a Cs(T1) scintillator at the center of the hemisphere. The coincidence of the proportional counter signals constrain the measurements to charged particles traversing the radius of the hemisphere. The charged particle energy deposition distributions are directly measured for a known pathlength. The A-150 kerma factor was measured at a neutron energy of 14.8 MeV and is in agreement with tabulated values. The carbon kerma factor measurements are less than the tabulated value at 14.8 MeV. The alpha-particle production in carbon was measured for neutron energies from 14.1 to 14.8 MeV and is compared with existing data.

A simple model of auroral electrodynamics compared with HILAT measurements

Simultaneous measurements of cold plasma drift velocities, magnetic field perturbations, and precipitating electron fluxes with instrumentation on board the HILAT satellite provide an opportunity to correlate Birkeland current densities, electric fields, and ionospheric conductivities in the region of an auroral form. Typical plasma parameters such as ion density, temperature, and composition and electron density and temperature are also available. On July 17, 1983, the satellite crossed the northern auroral zone in the early morning, magnetic local time sector. As the satellite crossed a bright auroral form, recorded by the auroral imager‐mapper, the particle spectrometer detected a 2 orders of magnitude increase in the flux of &gt;10‐keV electrons. The precipitating electrons of this event produced a double inverted‐V structure embedded in the large‐scale, region 2 field‐aligned current sheet. This paper presents calculations of the component of the electric field along the satellite trajectory and perpendicular to the auroral form, given the Birkeland current feeding the auroral form and conductivities derived from particle precipitation data. This electric field component emerges as a solution to the current continuity equation j∥ = −▽ · (Σ · E) in the infinite current sheet approximation with appropriate boundary conditions. Emphasis is placed on accurately representing the Birkeland current density in the region of the bright auroral form. In general, large‐scale features are well represented by the calculations. Although small‐scale features are not well tracked, calculations of the auroral zone potential drop and the height‐integrated Joule heating varied by less than 2% from measured values. During this particular pass the ionospheric Joule heating exceeded the particle energy deposition along the satellite trajectory by a factor of 2.6.

Study of energy deposition of GeV particles in nuclei

The highly-inelastic process in hadron-nucleus reactions at several GeV has been studied to investigate mechanisms of energy deposition of GeV particles in nuclei and possibilities to search for any signature of unusual phenomena.

4. Particle Tracks and Energy Deposition

4. Particle Tracks and Energy Deposition

4. Particle Tracks and Energy Deposition

4. Particle Tracks and Energy Deposition

Energetic electron precipitation due to gyroresonant interactions in the magnetosphere Involving coherent VLF waves with slowly varying frequency

A test particle simulation model (Inan et al., 1982) of the gyroresonance wave‐particle interaction in the magnetosphere is extended to study the transient particle precipitation fluxes induced by various coherent VLF waves with slowly varying frequency propagating along the earth's magnetic field lines. For moderate wave intensities (Bw ≤ 10 pT at L = 4) a comparison between input signals with linearly rising and falling frequencies shows that they induce the same amount of precipitated particle energy deposition. However, when the wave growth near the principal interaction region is considered, the precipitation induced by a riser is considerably higher than that induced by a faller. The effect of the frequency‐time slope (df/dt) of the input signal on the induced precipitation energy flux is found to be small. Our results indicate, however, that the precipitation energy flux depends strongly on the falloff in energy of the trapped particle distribution function. The model is applied for computing the transient precipitation energy fluxes induced by a triggered rising emission, a hooklike signal and a one‐hop whistler. The total precipitated energy deposition for these various signals is found to be comparable to that induced by a linear ramp having the same input wave energy density.