Shape Of Energy Spectrum Research Articles

Response control of RPLGD for gamma-ray dose measurement using lead filters for BNCT

Boron Neutron Capture Therapy (BNCT) is a cell-selective radiotherapy using a neutron capture reaction of 10B. In recent years, Accelerator Based Neutron Sources (ABNS) are under development instead of nuclear reactors for the next-generation neutron irradiation system for BNCT. However, ABNS as well as nuclear reactor usually generates unavoidable secondary gamma-rays by neutron-nuclear reactions such as capture reaction. In this research, we aimed to develop a separate measurement method of only gamma-rays in a mixed field of neutrons and gamma-rays using a fluorescent glass dosimeter (RPLGD), because most dosimeters have sensitivity to both radiation types. For this purpose, we proposed a lead filter method using two RPLGDs and lead filters. However, this method has a problem that the sensitivity to low energy gamma-rays (∼100 keV) is very small. In order to improve the sensitivity to low energy gamma-rays, we devised a method using a specially shaped lead filter. From theoretical calculations, we have shown that it was possible to estimate the air dose rate of the field where the gamma-ray energy spectrum shape was known for energies up to 10 MeV. In addition, we produced the specially shaped lead filter and experimentally confirmed the validity of the lead filter method using several gamma-ray standard sources and by measurements in a nuclear fuel storage room.

Калибровка и поверка многодетекторного нейтронного спектрометра реального времени

In [1-4], the main problems of creating a real-time multi-detector neutron spectrometer are considered and simulation modeling of such a spectrometer is carried out in order to determine the optimal composition of the detection unit of such a spectrometer.
 This article states the imperfection of the metrological and methodological support of not only spectrometric, but also radiometric measurements of arbitrary neutron fluxes. To increase the reliability of the results of neutron measurements, it is proposed to verify the multi-detector real-time neutron spectrometer being developed in reference neutron fields with different and reliably known shapes of energy spectra. To create such reference neutron fields, a neutron testing and verification complex was developed, the prototype of which was studied experimentally. But taking into account the limited variety of forms of the spectra of the reference neutron fields created by this complex, it is proposed to train the neural network embedded in the neutron spectrometer on a wider set of base spectra, which includes, in addition to the spectra of the reference fields created on the test and calibration complex, reliably known spectra of neutron fluxes found in the literature. It is shown that in this case the energy errors of the spectrometer when measuring neutron fluxes with a variety of spectrum shapes will be practically eliminated, even when the spectrometer is verified in reference fields with a narrower variety of spectrum shapes.

Диагностика интенсивностей излучения и электронной концентрации в полярных сияниях по данным эмпирических моделей электронных высыпаний.

We have studied the influence of the precipitating electron spectrum shape on the integral intensity of emissions λ391.4 nm 1NG N⁺₂, λ670.4 mn 1PG N₂, λ337.1 nm 2PG N₂, λ320.0 nm VK N₂, λ127.3 nm LBH N₂, atomic oxygen emissions λ557.7 and λ630.0 nm, total electron content in the vertical column of aurora. The integral characteristics of the emission intensity and the total electron content are shown to weakly depend on the energy spectrum shape and to be determined mainly by average energy values Eev and energy flux value Fᴇ of precipitating electrons. An algorithm is proposed for diagnosing the planetary distribution of emission intensities and total electron content in auroras based on data from empirical electron precipitation models, without making a priori assumptions about the shape of the energy spectrum of precipitating electrons.

Diagnostics of emission intensities and electron density in auroras based on empirical precipitation models

We have studied the influence of the precipitating electron spectrum shape on the integral intensity of emissions λ391.4 nm 1NG N⁺₂, λ670.4 mn 1PG N₂, λ337.1 nm 2PG N₂, λ320.0 nm VK N₂, λ127.3 nm LBH N₂, atomic oxygen emissions λ557.7 and λ630.0 nm, total electron content in the vertical column of aurora. The integral characteristics of the emission intensity and the total electron content are shown to weakly depend on the energy spectrum shape and to be determined mainly by average energy values Eev and energy flux value Fᴇ of precipitating electrons. An algorithm is proposed for diagnosing the planetary distribution of emission intensities and total electron content in auroras based on data from empirical electron precipitation models, without making a priori assumptions about the shape of the energy spectrum of precipitating electrons.

Evolution of the shape of fission fragment energy spectrum with absorber thickness in two different media and effective charge correction

The energy loss behavior of fission fragments (FFs) from [Formula: see text]Cf(sf) in thin Mylar [Formula: see text] and Aluminium absorber foils has been revisited. The aim is to investigate the observed change in the well-known asymmetric energy of spontaneous fission of [Formula: see text]Cf as the fragments pass through increasingly thick absorber foils. Two different types of absorbers have been used: one elemental and the other an organic compound. The stopping powers have been determined as a function of energy for three fragment mass groups with average masses having [Formula: see text], 141.8, 125.8 corresponding to light, heavy and symmetric fragments of [Formula: see text]Cf. The energy loss data have been compared with the predictions of SRIM 2013 code. The best representations of the data have been achieved using the effective Z correction term in the stopping power relation from the classical Bohr theory. Using the effective charge (Z[Formula: see text]) in the stopping power relation in the classical Bohr theory best describes the stopping power data. Spectrum shape parameters, subsequently, have been extracted from the energy spectra of FFs for different foil thicknesses. The effective charge (Z[Formula: see text]) correction term determined from the stopping power data is then used in the simulation for the absorber thickness dependence of the shape parameters of the energy spectrum. The present simulation results are compared with the TRIM prediction. The trends of the absorber thickness dependence of the spectrum shape parameters, for both Mylar and Aluminium, are well reproduced with the present simulation.

A new linear forcing method for isotropic turbulence with controlled integral length scale

Turbulence is a common feature to all flows that surround us. Despite its ubiquity, particularly in industrial flows, it is very difficult to provide a mathematical framework for the generation of turbulent eddies. Several methods have been proposed which are able to reproduce realistic features for velocity fluctuations, exhibiting proper space- and time-correlations. Focusing on physical space forcing, these methods are usually first evaluated upon sustained homogeneous isotropic turbulence by introducing a body force to the Navier–Stokes equations. Since the pioneering work of Lundgren, these techniques usually experience difficulties in predicting the integral length scale. The present study provides a forcing through a reconstruction approach which consists in building velocity fluctuations with a prescribed energy spectrum model. The proposed approach is assessed by performing large-eddy simulations of a sustained homogeneous isotropic turbulence in a triply periodic box. Properties of this forcing technique are discussed, drawing on both spatial and time correlations and also on the shape of energy spectrum together with the level of resolved turbulent kinetic energy. A special attention is put on the control of resolved turbulent energy. In this framework, an efficient selective forcing technique is derived, making use of spectral space features. The results show that the proposed approach allows to drive efficiently the resolved kinetic energy toward its target value while preserving the integral length scale independent of the domain size. It is observed that the resulting longitudinal length scale is overestimated by 13%, while the two-time correlations are recovered when using stochastic frequencies.

Monitoring electron energies during FLASH irradiations

When relativistic electrons are used to irradiate tissues, such as during FLASH pre-clinical irradiations, the electron beam energy is one of the critical parameters that determine the dose distribution. Moreover, during such irradiations, linear accelerators (linacs) usually operate with significant beam loading, where a small change in the accelerator output current can lead to beam energy reduction. Optimisation of the tuning of the accelerator’s radio frequency system is often required. We describe here a robust, easy-to-use device for non-interceptive monitoring of potential variations in the electron beam energy during every linac macro-pulse of an irradiation run. Our approach monitors the accelerated electron fringe beam using two unbiased aluminium annular charge collection plates, positioned in the beam path and with apertures (5 cm in diameter) for the central beam. These plates are complemented by two thin annular screening plates to eliminate crosstalk and equalise the capacitances of the charge collection plates. The ratio of the charge picked up on the downstream collection plate to the sum of charges picked up on the both plates is sensitive to the beam energy and to changes in the energy spectrum shape. The energy sensitivity range is optimised to the investigated beam by the choice of thickness of the first plate. We present simulation and measurement data using electrons generated by a nominal 6 MeV energy linac as well as information on the design, the practical implementation and the use of this monitor.

Universal properties of primary and secondary cosmic ray energy spectra

Atomic nuclei appearing in cosmic rays (CRs) are typically classified as primary or secondary. However, a better understanding of their origin and propagation properties is still necessary. We analyse the flux of primary (He, C, O) and secondary nuclei (Li, Be, B) detected with rigidity (momentum/charge) between 2 GV and 3 TV by the alpha magnetic spectrometer on the International Space Station. We show that q-exponential distribution functions, as motivated by generalized versions of statistical mechanics with temperature fluctuations, provide excellent fits for the measured flux of all nuclei considered. Primary and secondary fluxes reveal a universal dependence on kinetic energy per nucleon for which the underlying energy distribution functions are solely distinguished by their effective degrees of freedom. All given spectra are characterized by a universal mean temperature parameter ∼200 MeV which agrees with the Hagedorn temperature. Our analysis suggests that QCD scattering processes together with nonequilibrium temperature fluctuations imprint universally onto the measured CR spectra, and produce a similar shape of energy spectra as high energy collider experiments on the Earth.

Suprathermal Proton Spectra at Interplanetary Shocks in 3D Hybrid Simulations

Abstract Interplanetary shocks are one of the proposed sources of suprathermal ion populations (i.e., ions with energies of a few times the solar-wind energy). Here we present results from a series of 3D hybrid simulations of collisionless shocks in the solar wind. We focus on the influence of the shock-normal angle, θ Bn , and the shock speed, V s , on producing protons with energies a few to hundreds of times the thermal energy of the upstream plasma. The combined effects of θ Bn and V s result in shocks with Alfvén Mach numbers in the range 3.0–6.0 and fast magnetosonic Mach numbers in the range 2.5–5.0, representing moderate to strong interplanetary shocks. We find that θ Bn largely organizes the shape of proton energy spectra, while shock speed controls acceleration efficiency. All shocks accelerate protons at the shock front, but the spectral evolution depends on θ Bn . Shocks with θ Bn ≥ 60° produce isolated bursts of suprathermal protons at the shock front, while shocks with θ Bn ≤ 45° create suprathermal beams upstream of the shock. Downstream proton energy spectra have exponential or smoothed broken power-law forms when θ Bn ≥ 45° and a single power-law form when θ Bn ≤ 30°. Protons downstream of the strongest shocks have energies at least 100 times the upstream thermal energy, with θ Bn ≤ 30° shocks producing the highest-energy protons and θ Bn ≥ 60° shocks producing the largest number of protons with energies at least a few times the thermal energy.

Analysis strategies and treatment of systematic effects in the KATRIN experiment

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to search for the effective electron antineutrino mass with a sensitivity of 0.2 eV/c2 (90% C.L.) from the shape of the tritium β-decay electron energy spectrum. The first measurement campaign in KATRIN dedicated to the neutrino mass took place in spring 2019 with about 22 % of the nominal tritium activity. The goal of this pilot measurement was to reach a sensitivity competitive with past results while establishing a robust bias-free analysis and good initial understanding of systematic effects. Several different analysis techniques were developed independently and cross-checked on a set of fake Monte Carlo prior to real spectra. In this paper, I present an overview of the KATRIN analysis strategies and discuss their applications on the tritium spectra. The treatment of systematic effects is also discussed in detail. I conclude with a short outlook for the future neutrino mass measurement campaigns with KATRIN.

Comment on "Is the Hydrated Electron Vertical Detachment Genuinely Bimodal?"

In a recent article, David Bartels addresses the issue of the band shape of the genuine binding energy spectrum of the hydrated electron. He essentially claims that the genuine binding energy of the hydrated electron must be Gaussian in shape independent of the photon energy used for ionization, contrary to what was found in our previous work for excitations energies in the UV (3.6-5.8 eV photon energy). Further, he alleges that the asymmetric (bimodal) distribution found for the genuine binding energy in our previous work must have resulted from deficiencies in the scattering cross sections used in the scattering calculations. Bartels concludes that these deficiencies arise from an allegedly wrong value of -1.0eV for the escape barrier used in the original fitting procedure to determine the scattering cross section. In the following, we show that these claims are unfounded and based on partly incorrect assumptions.

2D quantum turbulence in a polariton quantum fluid

The coexistence of the energy and enstrophy cascades in 2D quantum turbulence is one of the important open questions in the studies of quantum fluids. Here, we show that polariton condensates are particularly suitable for the possible observation of scaling on sufficiently large scales. The shape of raw energy spectra depends on the procedure of condensate excitation (stirring), but the energy spectra of clustered vortices always exhibit the -5/3 power law. In the optimal case, the cascade can be observed over almost 2 decades.

Synchrotron spectra of GRB prompt emission and pulsar wind nebulae

Particle acceleration is a fundamental process in many high-energy astrophysical environments and determines the spectral features of their synchrotron emission. We have studied the adiabatic stochastic acceleration (ASA) of electrons arising from the basic dynamics of magnetohydrodynamic (MHD) turbulence and found that the ASA acts to efficiently harden the injected electron energy spectrum. The dominance of the ASA at low energies and the dominance of synchrotron cooling at high energies result in a broken power-law shape of both electron energy spectrum and photon synchrotron spectrum. Furthermore, we have applied the ASA to studying the synchrotron spectra of the prompt emission of gamma-ray bursts (GRBs) and pulsar wind nebulae (PWNe). The good agreement between our theories and observations confirms that the stochastic particle acceleration is indispensable in explaining their synchrotron emission.

Scaling laws in Hall inertial-range turbulence

Abstract. There is an increasing amount of observational evidence in space plasmas for the breakdown of inertial-range spectra of magnetohydrodynamic (MHD) turbulence on spatial scales smaller than the ion-inertial length. Magnetic energy spectra often exhibit a steepening, which is reminiscent of dissipation of turbulence energy, for example in wave–particle interactions. Electric energy spectra, on the other hand, tend to be flatter than those of MHD turbulence, which is indicative of a dispersive process converting magnetic into electric energy in electromagnetic wave excitation. Here we develop a model of the scaling laws and the power spectra for the Hall inertial range in plasma turbulence. In the present paper we consider a two-dimensional geometry with no wave vector component parallel to the magnetic field as is appropriate in Hall MHD. A phenomenological approach is taken. The Hall electric field attains an electrostatic component when the wave vectors are perpendicular to the mean magnetic field. The power spectra of Hall turbulence are steep for the magnetic field with a slope of -7/3 for compressible magnetic turbulence; they are flatter for the Hall electric field with a slope of -1/3. Our model for the Hall turbulence gives a possible explanation for the steepening of the magnetic energy spectra in the solar wind as an indication of neither the dissipation range nor the dispersive range but as the Hall inertial range. Our model also reproduces the shape of energy spectra in Kelvin–Helmholtz turbulence observed at the Earth's magnetopause.

Influence of tungsten fuzz on energy spectra of helium recoiled by 10 MeV oxygen ions

The influence of fuzz-like tungsten surface structures on the shape of helium energy spectra recoiled by an incident 10 MeV 16O beam was investigated by computer simulations using the program STRUCTNRA and a phenomenological two-dimensional tungsten fuzz model. The model describes fuzz by a random distribution of inclined rectangular filaments containing tungsten and 1 at% helium. The mean width of the filaments was varied from 10 to 100 nm and the mean filament height was varied from 10 to 1500 nm while keeping the total amount of material constant. The shapes of the helium recoil energy spectra are modified by the fuzz, the deviations from the spectrum of a smooth sample increase with increasing filament widths and heights. The total numbers of detected helium recoils remain surprisingly independent of the filament widths and heights. A surrogate smooth sample with depth profile yielding a recoil energy spectrum identical to a fuzzy sample can be always found. The total amount of He can be derived robustly using the surrogate sample.

On certain heuristic approach to neutron spectrum unfolding

Abstract The paper presents uncommon approach to the processing of neutron measurement results. The purpose of the proposed algorithm is not to restore the shape of neutron energy spectrum but to quantify the phenomena occurring in investigated neutron spectrum. The method based on minimization of functional proportional to the variance of the investigated reaction rate. The variance results from the discrepancy between the spectrum approximation and the actual spectrum. Appropriate Euler–Lagrange equation of the calculus of variations is then solved to find function minimizing the functional. The proposed algorithm is applied and tested with three different measured neutron spectra and compared with commonly used deconvolution code. The results are presented and discussed.

Acceleration of plasma in current sheet during substorm dipolarizations in the Earth's magnetotail: Comparison of different mechanisms

This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some extent electrons) can be more effectively accelerated due to the mechanism (C) than the single dipolarization (B). It is found that high-frequency electric and magnetic fluctuations accompanying multiple DFs (D) can strongly accelerate electrons e− and really weakly influence other populations of plasma. The results of modeling demonstrated clearly the distinguishable spatial and temporal resonance character of particle acceleration processes. The maximum particle energies depending on the scale of the magnetic acceleration region and the value of the magnetic field are estimated. The shapes of energy spectra are discussed.This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some exten...

Inter-scale transfer of the large-scale background anisotropy under periodic conditions

In numerical simulations of three-dimensional isotropy turbulence, low-wave-number truncation leads to large-scale anisotropy, but little anisotropy is generated at small scales. As the generally accepted energy cascade theory suggests an energy transfer from large to small scale, we phenomenally guess that an inter-scale anisotropy evolution might occur in the energy transfer process. With analyses in Kolmogorov’s equation and DNS validations, we demonstrate that the large-scale anisotropy is effectively transferred by convective effect, but this anisotropy is then diminished at small scales by viscous dissipation. The inter-scale anisotropy transfer process is synchronised with the inter-scale energy transfer. Time evolution of anisotropy distribution is then investigated in free-decaying, forced and non-equilibrium isotropic turbulence. It is shown that the anisotropy distribution remains stationary if the shape of energy spectrum does not change. The objective of this work is to provide a theoretical and numerical support for the further study on anisotropy correction in post-processing results.

Proton scattering from tungsten fuzz

Abstract Tungsten fuzz is a nanostructure formed on tungsten surface under helium plasma impact. In this work, we investigate this structure using the scattering of keV-energy protons. Energy spectra of scattered protons have double-peak shape that corresponds to the scattering from fuzz and underlying pure tungsten. The energy losses of protons in fuzz are estimated as the difference between primary beam energy and the energy corresponding to the local minimum between two peaks. Computer simulations with SRIM code also demonstrate double-peak shape of energy spectra of protons scattered from fuzzy target. Fuzz and pure tungsten stopping powers for protons are compared and fuzz density relative to pure tungsten is estimated and discussed. Evolution of H+ energy spectra during fuzz irradiation by Ar+ beam is measured and discussed.

Improvement of neutron spectrum unfolding based on three-group approximation using CsI self-activation method for evaluation of neutron dose around medical linacs

We previously evaluated ambient neutron dose equivalent by using the self-activation of a CsI scintillator around a high-energy medical linear accelerator (linac) 128I saturated activities were successfully converted to neutron spectrum and ambient neutron dose equivalent by neutron spectrum unfolding with the “three-group approximation.” The principle of the three-group approximation is based on the assumption of fixed shapes of neutron energy spectra for each of the three energy regions to evaluate the neutron spectrum effectively. However, such a neutron dose evaluation with the unfolding method might be affected by the difference between the actual fast neutron energy spectrum and the assumed spectrum. In the present work, we modified the unfolding method by taking into account the differences in the shapes of fast neutron energy spectra for various medical linacs. We verified the unfolding method using Monte Carlo simulation with several neutron spectra obtained from published research articles. The modified three-group approximation evaluates the neutron doses more accurately than the conventional unfolding method.