Total Energy Spectrum Research Articles

Modeling a Hypothetical170Tm Source for Brachytherapy Applications

Purpose: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical170Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons. Methods: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of170Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical 170Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation. Results: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (<1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively. Conclusions: A170Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of 170Tm as a brachytherapy source presents notable challenges.

Impact of the nonstationarity of a supercritical perpendicular collisionless shock on the dynamics and energy spectra of pickup ions

[1] Both hybrid and full particle simulations and recent experimental results have clearly evidenced that the front of a supercritical quasi-perpendicular shock can be nonstationary. One proposed mechanism responsible for this nonstationarity is the self-reformation of the shock front being due to the accumulation of reflected ions. On the other hand, a large number of studies have been made on the acceleration and heating of pickup ions (PIs) but most have been restricted to a stationary shock profile only. Herein, one-dimensional test particle simulations based on shock profiles issued from one-dimensional particle-in-cell simulation are performed in order to investigate the impact of the shock front nonstationarity (self-reformation) on the acceleration processes and the resulting energy spectra of PIs (protons H+) at a strictly perpendicular shock. PIs are represented by different shell distributions (variation of the shell velocity radius). The contribution of shock drift acceleration (SDA), shock surfing acceleration (SSA), and directly transmitted (DT) PI's components to the total energy spectra is analyzed. Present results show that (1) both SDA and SSA mechanisms can apply as preacceleration mechanisms for PIs, but their relative energization efficiency strongly differs; (2) SDA and SSA always work together at nonstationary shocks (equivalent to time-varying shock profiles) but SDA, and not SSA, is shown to dominate the formation of high-energy PIs in most cases; (3) the front nonstationarity reinforces the formation of SDA and SSA PIs in the sense that it increases both their maximum energy and their relative density, independently on the radius of PI's shell velocity; and (4) for high shell velocity around the shock velocity, the middle energy range of the total energy spectrum follows a power law Ek−1.5. This power law is supported by both SDA and DT ions (within two separate contributing energy ranges) for a stationary shock and mainly by SDA ions for a nonstationary shock. In both cases, the contribution of SSA ions is comparatively weak.

Alfvén waves and ideal two-dimensional Galerkin truncated magnetohydrodynamics

We investigate numerically the dynamics of two-dimensional Euler and ideal magnetohydrodynamics (MHD) flows in systems with a finite number of modes, up to 4096(2), for which several quadratic invariants are preserved by the truncation and the statistical equilibria are known. Initial conditions are the Orszag-Tang vortex with a neutral X point centered on a stagnation point of the velocity field in the large scales. In MHD, we observe that the total energy spectra at intermediate times and intermediate scales correspond to the interactions of eddies and waves, E(T)(k)~k(-3/2). Moreover, no pseudodissipative range is visible for either Euler or ideal MHD in two dimensions. In the former case, this may be linked to the existence of a vanishing turbulent viscosity whereas in MHD, the numerical resolution employed may be insufficient. When imposing a uniform magnetic field to the flow, we observe a lack of saturation of the formation of small scales together with a significant slowing down of their equilibration, with however a cutoff independent partial thermalization being reached at intermediate scales.

On the energy cascade rate of solar wind turbulence in high cross helicity flows

[1] Improved observations and analysis of solar wind fluctuations at 1 AU show that the total energy spectrum, kinetic plus magnetic, is in better agreement with the Kraichnan 3/2 scaling than with the Kolmogorov 5/3 scaling, consistent with simulations of incompressible MHD turbulence with a strong ambient magnetic field which exhibit a perpendicular energy spectrum proportional to k⊥−3/2. The Kraichnan scaling is especially clear in solar wind flows having large values of the normalized cross helicity σc. In this study, a generalization of Boldyrev's theory that applies to turbulence with nonvanishing cross helicity is used to estimate the energy cascade rate for high cross helicity flows in the solar wind at 1 AU. The analysis of 85 intervals of solar wind data from the Wind spacecraft characterized by normalized cross helicities in the range ∣σc∣ > 0.88 yields typical values of the energy dissipation rate ɛ ranging from 100 to 2400 J/kg/s. This is roughly a factor of 4 or 5 smaller than estimates of the proton heating rate at 1 AU needed to account for the nonadiabatic solar wind expansion. The results suggest that the reduction in turbulent heating in high cross helicity flows creates a tangible deficit in the heating rate required by empirical models based on average solar wind properties.

Experimental determination of the three-dimensional primary field of a seismic airgun array.

The Littoral Acoustic Demonstration Center (LADC) recorded acoustic and related data on three moored arrays and ship-deployed hydrophones, which together spanned the full water column to measure the 3-D acoustic field of a seismic airgun array, in September 2007. The seismic source vessel shot specified lines to give detailed solid angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, one-third octave band analyzes, and source directivity studies are used to characterize the field. Three-dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Longer lines were shot for propagation analyzes. Source signatures from NUCLEUS and GUNDALF are used in propagation modeling. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]

Energy Spectra of Rossby and Gravity Waves

The characteristics of energy spectrum based on 3D normal mode energetics are investigated with the global analysis dataset provided by Japan Meteorological Agency (JMA) with the resolution of TL959L60. The energy spectrum of gravity modes exactly follows the -5/3 power law in the synoptic and mesoscales. In the synoptic scale, the spectral slope of total energy follows the -3 power law because Rossby waves are dominant compared to gravity waves. The energy level of gravity modes becomes larger than that of Rossby modes around the zonal wavenumber k = 80. This scale corresponds to 350 km in 45°circle. The total energy spectrum does not show a clear transition from -3 power slope to -5/3 power slope because the energy level of Rossby and gravity modes become comparable near the transition wavenumbers.

Double-electron above-threshold ionization resonances as interference phenomena

We report calculations of double-ionization energy spectra and momentum distributions of laser-driven helium due to few-cycle pulses of wavelength 195 nm. The results are obtained from full-dimensional numerical integration of the two-electron time-dependent Schrödinger equation. A momentum-space analysis of doubly ionizing wavepackets shows that the concentric-ring structure of above-threshold double ionization, together with the associated structure of peaks in the total kinetic energy spectrum, may be attributed to wavepacket interference effects, where at least two doubly ionizing wavepackets from different recollision events populate the same spatial hemisphere.

Novel Scatter Compensation of List-Mode PET Data Using Spatial and Energy Dependent Corrections

With the widespread use of positron emission tomography (PET) crystals with greatly improved energy resolution (e.g., 11.5% with LYSO as compared to 20% with BGO) and of list-mode acquisitions, the use of the energy of individual events in scatter correction schemes becomes feasible. We propose a novel scatter approach that incorporates the energy of individual photons in the scatter correction and reconstruction of list-mode PET data in addition to the spatial information presently used in clinical scanners. First, we rewrite the Poisson likelihood function of list-mode PET data including the energy distributions of primary and scatter coincidences and show that this expression yields an MLEM reconstruction algorithm containing both energy and spatial dependent corrections. To estimate the spatial distribution of scatter coincidences we use the single scatter simulation (SSS). Next, we derive two new formulae which allow estimation of the 2-D (coincidences) energy probability density functions (E-PDF) of primary and scatter coincidences from the 1-D (photons) E-PDFs associated with each photon. We also describe an accurate and robust object-specific method for estimating these 1-D E-PDFs based on a decomposition of the total energy spectra detected across the scanner into primary and scattered components. Finally, we show that the energy information can be used to accurately normalize the scatter sinogram to the data. We compared the performance of this novel scatter correction incorporating both the position and energy of detected coincidences to that of the traditional approach modeling only the spatial distribution of scatter coincidences in 3-D Monte Carlo simulations of a medium cylindrical phantom and a large, nonuniform NCAT phantom. Incorporating the energy information in the scatter correction decreased bias in the activity distribution estimation by ~20% and ~40% in the cold regions of the large NCAT phantom at energy resolutions 11.5% and 20% at 511 keV, respectively, compared to when using the spatial information alone.

The three‐dimensional acoustic field of primary arrivals from a seismic airgun array.

The Source Characterization Study 2007 (SCS07) measured the three‐dimensional (3‐D) acoustic field of a seismic airgun array. The Littoral Acoustic Demonstration Center (LADC) performed the experiment, collecting acoustic and related data on three moored hydrophone arrays and one ship‐deployed hydrophone array which together spanned the full water column. Sensitive and desensitized phones were deployed at each position to extend the dynamic range. An ultra short baseline localization system was deployed with the EARS moorings to provide array shape. With postanalysis this results in time‐dependent positions for each of the acoustic sensors. Every channel is calibrated. A seismic source vessel shot a series of lines designed to give detailed angle and range information concerning the field of the primary arrival. Peak pressures, sound exposure levels, total shot energy spectra, and one‐third octave band analyses give important insights into details of the acoustic field. Images of these quantities are generated to show dependence on emission and azimuthal angles and range. 3‐D visualizations and two‐dimensional cuts through the data are shown. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]

The competition between quadratic and integral invariants in inviscid truncated two-dimensional and quasigeostrophic shallow-water turbulence

We investigate the behavior of spectrally truncated simulations of inviscid two-dimensional and quasigeostrophic shallow-water (QGSW) turbulence. Under the assumption that the only conserved quantities are the energy and enstrophy (the total energy and the potential enstrophy in the case of QGSW turbulence), it is possible to use arguments from statistical mechanics to predict an absolute equilibrium form for the (total) energy spectrum E(k)=ak/(k2+b), where a and b are constants. However, other robust integral invariants exist in these systems. In strictly two-dimensional turbulence the low-wavenumber spectrum has the expansion E∼Jk−1+Lk+Ik3+O(k5), where J, L, and I are various integral moments of the two-point vorticity correlation function ⟨ωω′⟩. J and L are invariants, while I is generally time dependent. In the case of QGSW turbulence, the equivalent expansion for the total energy spectrum is Et∼LkR2k−1+ÎkR2k+M̂kR2k3+N̂kR2k5+O(k7), where kR is the Rossby deformation wavenumber and Î, M̂, and N̂ are related to further integral moments of the two-point vorticity correlation function. In this system it is found that Î and M̂ are additional invariants. There must, therefore, be competition at the low-wavenumber end of the spectrum between the developing equilibrium spectrum and the region controlled by the integral invariants. We find that while the equilibrium spectrum comes to dominate an increasing range of wavenumbers, it is always blocked from the region k→0 by the presence of the integral invariants. Furthermore, the rate at which the region occupied by the equilibrium spectrum expands is almost independent of the form of both the equilibrium and low-wavenumber spectra. This can be interpreted as the inverse energy cascade, which carries the equilibrium spectrum to low k, being insensitive to the very high and very low k form of the spectrum.

Rare muon decayμ+→e+e−e+νeν¯μ

An analytical expression for the spin-averaged amplitude squared of the rare muon decay $\mu^+ \to e^+e^-e^+\nu_e\bar{\nu_\mu}$ is calculated. Monte Carlo phase space simulation using the analytical expression for the amplitude has been used to get various differential distributions of charged leptons. The approximate analytical expression for the total energy spectrum of charged leptons near the end point is presented. The dependence of branching ratio on cuts in total energy of charged leptons is studied taking into account an experimental energy resolution. It is shown that the measured branching ratio is very sensitive to the energy resolution.

Source characterization study 2007: The three-dimensional primary field of a seismic airgun array.

During September 2007 the Littoral Acoustic Demonstration Center collected acoustic and related data from three moored arrays and ship-deployed hydrophones spanning the full water column to measure the 3-D acoustic field of a seismic airgun array. A seismic source vessel shot a series of lines to give detailed angle and range information concerning the field of the primary arrival. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total energy spectra, one-third octave band, and source directivity analyses are measures used to characterize the field. Three-dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Three-dimensional visualizations are being developed using a visualization cave and software for 2-D cave emulation. [Research supported by the Joint Industry Programme through the International Association of Oil and Gas Producers.]

UV Photodissociation Dynamics of Nitric Acid: The Hydroxyl Elimination Channel

Sliced velocity mapping ion imaging technique was employed to investigate the dynamics of the hydroxyl elimination channel in the photodissociaiton of nitric acid in the ultraviolet region. The OH product was detected by (2+1) resonance enhanced multiphoton ionization via the D2 electronic state. The total kinetic energy spectra of the OH+NO2 channel from the photolysis of HONO2 show that both NO2(X2A1) and NO2(AB2) channels are present, suggesting that both 11A and 21A excited electronic states of HONO2 are involved in the excitation. The parallel angular distributions suggest that the dissociation of the nitric acid is a fast process in comparison with the rotational period of the HNO3 molecule. The anisotropy parameter for the hydroxyl elimination channel is found to be dependent on the OH product rotational state as well as the photolysis energy.

Multiphoton ionization through the triplet states of Mg by linearly and circularly polarized laser pulses

We theoretically study multiphoton ionization through the triplet states of Mg by linearly polarized and circularly polarized fs laser pulses. After the construction of the atomic basis using the frozen-core Hartree-Fock potential as well as the model potential approaches for both singlet and triplet series which show rather good agreements with the existing data in terms of state energies and dipole matrix elements, we solve time-dependent Schr\"odinger equations with $3s3p$ $^{3}P_{1}$ as an initial state, and calculate the total ionization yield and photoelectron energy spectra.

Three-dimensional data analysis for acoustic measurements of a seismic airgun array.

The Source Characterization Study 2007 measured the three‐dimensional acoustic field of a seismic airgun array. The Littoral Acoustic Demonstration Center performed the experiment, collecting acoustic and related data on three moored hydrophone arrays and one ship‐deployed hydrophone array which together spanned the full water column. Sensitive and desensitized phones were deployed at each position to extend the dynamic range. An ultra short baseline localization system was deployed with the EARS moorings to provide array shape. With post analysis this results in time‐dependent positions for each of the acoustic sensors. Every channel is calibrated. A seismic source vessel shot a series of lines designed to give detailed angle and range information concerning the field of the primary arrival. The experiment was conducted in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, and one‐third octave band analyses are me...

Characterization of semiconductor detectors of (1–30)-keV monoenergetic and backscattered electrons

Semiconductor detectors of backscattered electrons are basic elements of all modern scanning electron microscopes. Their quality is determined by the properties of planar p-n junctions and the parameters of the protective layer on the detector surface. The main characteristics of semiconductor detectors are considered, their response functions are calculated, and the threshold signal cutoff energies are found both for a monoenergetic electron beam and for detection of the total energy spectrum of backscattered electrons. The experimental results are in good agreement with the computational model data.

Gradual Eddy-Wave Crossover in Superfluid Turbulence

We revise the theory of superfluid turbulence near the absolute zero of temperature and suggest a differential approximation model for the energy fluxes in the k-space, eHD(k) and eKW(k), carried, respectively, by the collective hydro- dynamic (HD) motions of quantized vortex lines and by their individual uncorre- lated motions known as Kelvin waves (KW). The model predicts energy spectra of the HD and the KW components of the system, EHD(k) and EKW(k), which experi- ence a smooth crossover between different regimes of motion over a finite range of scales. For an experimentally relevant range of Λ ≡ ln(�/a) (� is the mean intervor- tex separation and a is the vortex core radius) between 10 and 15 the total energy flux e = eHD(k) + eKW(k) and the total energy spectrum E(k) = EHD(k) + EKW(k) are dominated by the HD motions for k< 2/� .I n this regionE(k) follows the HD spectrum with constant energy flux e � eHD =const.: E(k) ∝ k −5/3 for smaller k and tends to equipartition of the HD energy E(k) ∝ k 2 for larger k. This bottle- neck accumulation of the energy spectrum is milder than the one predicted before in (L'vov et al. in Phys. Rev. B 76:024520, 2007) based on a model with sharp HD-KW transition. For Λ = 15, it results in a prediction for the effective viscos- ity ν � � 0.004κ (κ is the circulation quantum) which is in a reasonable agreement

Modeling the three‐dimensional field of a seismic airgun array and comparison to 2003 measured data.

The full three‐dimensional field of a seismic airgun array is modeled using an enhanced parabolic equation run on a parallel cluster computer system, which is part of the Louisiana Optical Network Initiative network cluster. Source signatures are calculated using GUNDALF and NUCLEUS softwares. The calculated results are compared to available measurements collected in Green Canyon in the northern Gulf of Mexico in 2003. Three‐dimensional maps showing angular variation (both emission and azimuthal angles) and range dependence are generated, which show peak pressures, sound exposure levels, total shot energy spectra, and one‐third octave band analyses. [Research supported by the International Association of Oil and Gas Producers and the International Association of Geophysical Contractors.]

Neutrons from muons underground

Results of many-year experimental investigations of neutrons originating from cosmic-ray muons at depths of 25, 316, 570, 3650, and 5200 mwe are presented. Mechanisms of neutron generation by muons underground are outlined qualitatively. Methods of relevant measurements are described in detail, and the resulting properties of neutrons, including their total yield, flux, energy spectrum, multiplicity, and spatial distribution, are reported.

The source characterization study 2007: A detailed three dimensional acoustic field measurement of a seismic airgun array.

In September 2007 the Littoral Acoustic Demonstration Center (LADC) collected acoustic and related data from three moored arrays and ship‐deployed hydrophones spanning the full water column to measure the three‐dimensional acoustic field of a seismic airgun array. The seismic source vessel shot a series of lines to give a detailed angle and range information concerning the field. The data were collected in the western Gulf of Mexico between the East Break and Alamos Canyon regions. Peak pressures, sound exposure levels, total shot energy spectra, and one‐third octave band analyses are measures used to characterize the field. Three dimensional maps of these quantities are generated to show dependence on emission and azimuthal angles and range. Both the direct and indirect fields are characterized. Moveout analysis is done to delineate arrivals and to detect ducted and interface waves. [Research supported by the International Association of Oil and Gas Producers.]