Measurement Of Energy Deposition Research Articles

Measurement of equivalent power density and RF energy deposition in the immediate vicinity of a 24-GHz traffic radar antenna

In response to reports of alleged health effects associated with the use of hand-held traffic radars, e.g., testicular cancer, a study was undertaken to quantify: (1) the distribution of the electric field (E) in the immediate vicinity of the antenna aperture of a typical 24-GHz hand-held traffic radar; and (2) the relative match and the corresponding depth of penetration of the absorbed energy when the antenna aperture is positioned in contact with material having properties similar to human tissue. The former measurements are important for assessing a large number of measurements reported by others using techniques that are not expected to be reliable indicators of power density at distances small compared with the size of the radiator; the latter are important for verifying predictions that energy from the antenna at 24-GHz will be predominantly absorbed in superficial tissue, i.e., the skin. The results of the first part of the study indicate that the equivalent-plane-wave power density in the plane of the aperture of the radar antenna is approximately one-half of the corresponding values reported in the literature; the results of the second part of the study indicate that the depth of penetration into material simulating human skin is approximately 0.5 mm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental verification of bremsstrahlung production and dosimetry predictions as a function of energy and angle

Measurements of energy deposition from bremsstrahlung production as a function of angle and beam energy (5-25 MeV) are shown to be in excellent agreement with Monte Carlo predictions. Dosimetry measurements are made and predicted in both equilibrated and underequilibrated radiation environments. In the latter case the quality of the agreement requires an accurate prediction of both the photon and electron spectra produced by the primary electron beam. An improved empirical equation for predicting bremsstrahlung production is also presented. This empirical relation can be used to estimate doses without resorting to expensive calculational efforts. It also gives an analytical relationship for dose as a function of energy and angle for a converter optimized for bremsstrahlung production using 15.5 MeV electrons. >

Thermoelectric measurements of energy deposition during shock-wave consolidation of metal powders of several sizes

The degree of shock energy localization within individual particles and between neighboring particles of different size was explored during shock-wave consolidation of spherical metal powders. The thermoelectric voltage generated by the passage of a shock wave through a copper powder-constantan powder interface was recorded. The sizes of the copper and constantan powders were varied between mean diameters of 40 and 98 μm. Shock-wave pressures of 5 GPa were applied by flyer plate impact, and the resulting voltage versus time signals were collected with a 10 ns time resolution. In order to analyze the signals, a simulation of the thermocouple system was developed to account for the effects of multiple particle interactions and a slightly nonplanar copper-constantan interface. The resulting simulated voltage versus time signals are a good match for the observed signals when the size ratio of the copper and constantan particles is less than a factor of 2, and reveal the preferential deposition of energy in smaller particles at the expense of larger particles within the size range examined. The amount of energy localized near particle surfaces was found to be a majority of all the energy, with a significant minority deposited throughout the particle bulk.

Dosimetry considerations for the high-energy photon/electron environment of HERMES III: implications for experiments and modeling

Measurements of energy deposition as a function of equilibrator thickness and position in the HERMES III radiation field are compared to ITS code predictions. These measurements demonstrate the combined photon/electron nature of the radiation field and the importance of the electron field in both measurements and calculations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dosimetry Considerations For The High-energy Photon/electron Environment Of Hermes III: Implications For Experiments And Modeling

Measurements of energy deposition as a function of equilibrator thickness and position in the HERMES III radiation field are compared to ITS code predictions. These measurements demonstrate the combined photon/electron nature of the radiation field and the importance of the electron field in both measurements and calculations. >

Measurement of energy deposition in transmission electron microscopy

Various anomalous observations, such as atomic clouds and particles spinning under electron beam irradiation, have been reported. In this note we show that it is possible to estimate the energy deposited by the electron beam from the energy-loss spectrum. This not only constrains proposed mechanisms to explain these observations but should also help elucidate the mechanism for other radiation damage processes.

Beam–plasma interaction experiments with heavy-ion beams

The progress of the experimental research program at GSI for studying beam-plasma interaction phenomena is reported. Heavy-ion beams from the new accelerator facility SIS/ESR at GSI-Darmstadt are now available for experiments, and will soon deliver ≥ 109 particles per pulse in 100 ns. Focused on a small sample of matter, the beams will be able to produce a high-density plasma and to permit investigation of interaction processes of heavy ions with hot ionized matter.For the intense beam from the new heavy-ion synchrotron (SIS), a fine-focus system has been designed to produce a high specific deposition power beam for target experiments with a beam-spot radius of 100 μm. We further discuss improvements of this lens system by nonconventional focusing devices such as plasma lenses.Intense-beam experiments at the RFQ Maxilac accelerator at GSI have already produced the first heavy-ion-induced plasma with a temperature of 0.75 eV. New diagnostic techniques for investigating ion-beam-induced plasmas are presented. The low-intensity beam from the GSI UNILAC has been used to measure energy deposition profiles of heavy ions in hot ionized matter. In this experiment an enhancement of the stopping power for heavy ions was observed. The current experimental research program tests basic plasma theory and addresses key issues of inertial confinement fusion driven by intense heavy-ion beams.

Study of energy deposition in the electron-beam-pumped laser facility HAWK

The HAWK facility has been developed as a tool to investigate the kinetics of electron-beam-pumped lasers at a pressure of 1 atm for pump rates of 0.040–1 kW/cm3 and pump times of 0.05–1 ms. The highly collimated (1 cm FWHM within the lasing medium) relativistic electron beam propagates through fast valves that separate the accelerator vacuum from a 2-m-long vacuum isolation section, a 0.4-m-long gas-filled buffer section, and 0.7 m along a lambda-geometry laser cell. A 6.5 kG magnetic field confines the 1-MeV electron beam laterally and guides it around a 30° bend into the 3.3-cm-diam laser cell. A magnetic mirror at the far end of the laser cell reflects a large portion of the transmitted electron beam, thereby protecting the laser optics from the electron beam and making the axial deposition more uniform. In this paper we describe modeling of the electron beam energy deposition in HAWK using the three-dimensional Monte Carlo electron/photon transport code acceptm and compare our results with the measured energy deposition. These numerical simulations were begun during the design phase to define the operational range of the facility. There is good agreement between the calculated energy deposition in the laser cell and the deposition inferred from measurements with a segmented, totally stopping calorimeter at different axial locations in cases where hydrodynamic effects are unimportant. ln cases where these effects are important, however, the calculations can predict too large an amount of energy deposited in the laser gas. The numerical simulations are being used to infer the radial and axial deposition profiles of the electron beam energy as an aid in determining the electron-beam-pumped laser performance.

Spatial patterns of ionization in charged-particle tracks

The physical structure of charged-particle tracks plays an important role in determining the response of a stopping material to the absorption of energy following irradiation by charged particles and neutrons. For biological systems, and for muelectronic circuits, the response is sensitive to the energy deposited in submun-size volume elements. Because of the stochastic nature of energy deposition in and near charged particle tracks, there may be wide variations in the actual quantities of energy deposited in critical volume elements. Since direct measurements of energy deposition in condensed material (solids or liquids) are not technologically feasible, the effects of charged-particle track structure are usually estimated from one of several model calculations; the most commonly used are homogeneous track structure models. Recent interest in the radiation biology of high Linear-Energy-Transfer (LET) radiation has spurred interest in testing these model descriptions of the structure of high-energy heavy-ion tracks. As one means of providing such tests, experiments were recently conducted at the GSI-Darmstadt, UNILAC accelerator, to measure energy deposition in small volumes as a function of the radial distance from the path of fast, heavy ions. These measurements, conducted in collaboration with research groups of Dr. G. Kraft at GSI and Prof. Schmidt-Böcking of the University of Frankfurt, were made for simulated tissue volumes 0.5 and 1.0 μm in diameter, located from 0 to 10 μm from the path of Ge ions having energies from 13.0- to 17.2-MeV/amu. Excellent agreement was observed between model calculations and measured dose distributions for radial distances up to a few mumeters in simulated tissue. At greater distances the actual measured dose in irradiated volumes was much more than the calculated average value. These differences reflect the stochastic nature of energy deposition in which a large fraction of the volume elements receive no dose from a given particle traversal, but elements which do receive energy receive relatively large amounts. This may have important consequences for effects which occur with a nonlinear or threshold energy response.

Prebreakdown energy absorption from intense laser pulses at 532 nm in NaCl.

Details of the photoacoustic measurement and model calculations of prebreakdown energy deposition in NaCl at 532 nm [Jones, Shen, Braunlich, Kelly, and Epifanov, Phys. Rev. B 35, 894 (1987)] are provided. The primary absorption process is shown to be four-photon excitation of valence electrons to the conduction band. Calibration of the acoustic system by two-photon absorption of 266-nm laser light indicates focal point temperature increases over 300 K are attained for nondamaging pulses at 532 nm. Interpretation of the experimental data considering secondary energy absorption by free carriers and transient crystal defects yields the result that the generalized four-photon cross section lies in the range 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}114}$ ${\mathrm{cm}}^{8}$${\mathrm{sec}}^{3}$\ensuremath{\le}${\mathrm{\ensuremath{\sigma}}}^{(4)}$\ensuremath{\le}20\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}114}$ ${\mathrm{cm}}^{8}$ ${\mathrm{sec}}^{3}$. It is further shown that avalanche generation of free carriers is not evident even for these large temperature increases. The calibrated results were obtained from reactive-atmosphere-processed ultrapure NaCl crystals; the importance of sample purity is discussed.

Measurements of off-axis energy deposition form 100 MeV electrons traversing water and liquid nitrogen

Using the US Naval Postgraduate School 100 MeV linear electron accelerator, the authors measured the dose delivered in water and liquid nitrogen near the axis of an electron beam with calcium fluoride thermoluminescent dosimeters. The measurements show that calculations can predict dose near an electron beam. Calculations were done with CYLTRAN, a Monte Carlo electron/photon transport code, but, as the physical basis for this and other members of the Integrated Tiger Series is the same, the use of other codes is not expected to provide significant differences. The uncertainties in the physical arrangement of dosimeters do not readily lend themselves to precision measurements, but data and calculation agree adequately over many orders of magnitude. A prescription is presented to extend results obtained in one medium (H/sub 2/O or LN/sub 2/) to another (air), where geometry considerations make experiments difficult. >

Iterative solution of the multistream electron transport equation: 1. Comparison with laboratory beam injection experiments

We describe a Neumann iteration method for solution of the electron transport equation with the independent variables of energy, pitch angle, and altitude. The method has been developed to study electron energy deposition in the high‐latitude thermosphere and mesosphere. It is fast and can compute numerical point response function solutions of the electron transport equation. Inelastic cross sections input to the model are empirically based but are constrained by theoretical consistency conditions. Angular elastic cross sections are also empirically based. Thus, the transport solutions obtained represent a test of compatibility between various sets of cross sections and energy deposition measurements. Energy coupling of the electron transport equation is treated using an efficient, discrete energy loss method that allows the use of a widely separated energy grid at high energy. However, there are limitations on the bin width that are due to physical considerations. This method allows separation of the electron transport equation into a system of single‐energy equations coupled in energy. The angular and spatial parts of each single‐energy equation can be solved by Neumann iteration. We employ an angular grid rather than an expansion of the angular dependence in terms of spherical harmonics. To obtain accurate phase function integrals at a low computational cost, we have developed a numerical quadrature based on the use of analytic phase function forms. We have also developed a quadrature for the spatial integration based upon the known analytic behavior expected from the solution of the transport equation. As an application of the model, we make the first published comparison between a direct solution—as opposed to a Monte Carlo method—using discrete energy loss from detailed atomic cross sections and monoenergetic, monodirectional electron beam injection experiments. Results obtained from the model for the practical range are within 10% of the observed range for electrons in N2 over the energies studied from 300 eV to 12 keV. The scaled energy deposition profiles computed by the model tend toward shape invariance at higher energies when plotted as a function of the fraction of the practical range as also seen in empirical studies. The computed shape is generally in good agreement with empirical determinations, being best at the highest incident energies.

Scrapeoff layer studies with an instrumented limiter

An instrumented limiter was used as a diagnostic to measure energy deposition and power fluxes in the scrapeoff layer. The limiter consisted of an array of 12 tiles, each equipped with a thermocouple. This arrangement represented a calorimeter array that yielded the total limiter energy and decay length of the power flux in the scrapeoff layer. Energy deposition and decay lengths are discussed for various plasma parameters.

A calorimeter for measuring energy deposition in materials and calibrating the response of dosimeters irradiated by low-energy industrial electron accelerators

A simple calorimeter with a totally-absorbing graphite body was designed and tested at a 400-keV electron accelerator. For a given conveyor speed and beam current, the calorimetric measurements are expressed as a quantity F (J·cm −2)—the absorbed energy per unit surface area—which is found to be independent of the calorimetric body size and in accordance with the measurements of absorbed dose by calibrated radiochromic film dosimeters. The use of the calorimeter for the initial calibration of the energy deposition by low-energy accelerator beams and routine calibration of thin-film dosimeters are demonstrated.

Gamma-Ray Energy Deposition Measurements in the Fast Breeder Blanket Facility

Gamma-ray energy deposition measurements were made in a simulated fast reactor blanket of the Purdue University Fast Breeder Blanket Facility (FBBF) using CaF/sub 2/:Dy thermoluminescent dosimeters (TLDs). The TLDs were encased in either stainless steel or lead sleeves, and cavity ionization theory corrections known as f factors were used to relate the TLD dose to the sleeve dose. Corrections for the neutron response of the TLDs were made by determining the relative contributions of the TLDs neutron and gamma-ray responses. Radial experimental heating rates are presented and compared to calculations. The calculations significantly underestimate the experimental gamma-ray energy deposition rates in both stainless steel and lead. The underestimation is approx. =30% in stainless steel and approx. =15% in lead at the transformer/blanket interface and increases with increasing radius, reaching approx. =50% in stainless steel and approx. =40% in lead at the outside of the 0.51-m-thick blanket. This underestimation trend is attributed to a general underprediction of the ''bulk'' neutron population by the neutron flux calculations.

A measurement of the local energy deposition by antiprotons coming to rest in tissue-like material

The measurement of the energy deposited in tissue-equivalent plastic as a beam of low-energy antiprotons slows down is described. The resulting depth-dose curve is presented and compared with that of protons measured under similar conditions. These curves indicate that the ratio of the dose in the antiproton stopping peak to that in the plateau region is about twice that found for protons. Analysis of the data shows that out of the 2 GeV available in an antiproton annihilation, on average less than 30 MeV is deposited close to the site of the interaction. This leads to the conclusion that antiprotons are unlikely to offer any marked advantage over other radiations for radiotherapeutic applications of the future.

Accelerators for critical experiments involving single-particle upset in solid-state microcircuits

Charged-particle interactions in microelectronic circuit chips (integrated circuits) present a particularly insidious problem for solid-state electronic systems due to the generation of soft errors or single-particle event upset (SEU) by either cosmic rays or other radiation sources. Particle accelerators are used to provide both light and heavy ions in order to assess the propensity of integrated circuit chips for SEU. Critical aspects of this assessment involve the ability to analytically model SEU for the prediction of error rates in known radiation environments. In order to accurately model SEU, the measurement and prediction of energy deposition in the form of an electron-hole plasma generated along an ion track is of paramount importance. This requires the use of accelerators which allow for ease in both energy control (change of energy) and change of ion species. This and other aspects of ion-beam control and diagnostics (e.g., uniformity and flux) are of critical concern for the experimental verification of theoretical SEU models.

Lightning-induced electron precipitation

The broadband very low frequency (VLF, 0.3–30 kHz) radiation from lightning propagates in the Earth–ionosphere cavity as impulsive signals (spherics) and in the dispersive plasma regions of the ionosphere and magnetosphere it propagates as tones of descending or rising frequency (whistlers)1. VLF radio waves propagating in the magnetospheric plasma scatter energetic electrons by whistler-mode wave–particle interactions (cyclotron resonance) into the atmosphere2–6. These electrons, through collisions with the atmospheric constituents, cause localized ionization, conductivity enhancement, visual and ultraviolet light emissions, and brems-strahlung X rays. We have reported previously on the precipitation of energetic electrons from the radiation belts by the controlled injection from the ground of VLF radio waves7,8. Here we report the first satellite measurements of electron precipitation by lightning. The measured energy deposition of these conspicuous lightning-induced electron precipitation (LEP) bursts (∼ 10−3 erg cm−2) is sufficient to deplete the Earth's radiation belts and to alter subionospheric radiowave propagation (≲1 MHz). A one-to-one correlation is found between ground-based measurements of VLF spherics and whistlers at Palmer, Antarctica, and low-altitude satellite (S81-1) measurements of precipitating energetic electrons.

Measurement of collisional multiphoton energy deposition by a new optothermal detector

The infrared multiphoton absorption of SF 6 under collisional condition has been measured by a new optothermal detector which is based on measuring the change of resistance of a platinum filament. The optothermal signal, i.e., the absorbance of CO 2 laser energy by SF 6, was enhanced by the addition of Ar or NH 3. But the increase of optothermal signal caused by adding NH 3 is much greater than that caused by adding Ar, mainly due to the energy siphoning from excited SF 6 molecules to NH 3 molecules.

Energy deposition measurements of a large-diameter, intense relativistic electron beam for high-power gas laser excitation

Measurements of electron-beam (e-beam) energy deposition in gaseous medium by a segmented totally stopping calorimeter and a pressure jump method are described, both of which gave the same values. Typical e-beam parameters are 2 MV, 80 kA, and 65 ns (FWHM). The e-beam cross-sectional area is 10 cm in diameter. First, the radial distribution of the e-beam current generated from the field-emission diode as a function of the axial magnetic field was measured. Next, for applications to longitudinal excitation of the high-power gas lasers, the e-beam energy deposition characteristics are measured in N2 for the propagation distance up to 2.3 m in terms of the axial magnetic field, the N2 gas pressure, and the radial e-beam distribution. As a result, the axial field equivalent to the self-magnetic field of the electron beam can acceptably control the e-beam generation and propagation uniformities.