Energy Distribution Of Protons Research Articles

Acceleration and radiation of ultra-high energy protons in galaxy clusters

Clusters of galaxies are believed to be capable to accelerate protons at accretion shocks to energies exceeding 10^18 eV. At these energies, the losses caused by interactions of cosmic rays with photons of the Cosmic Microwave Background Radiation (CMBR) become effective and determine the maximum energy of protons and the shape of the energy spectrum in the cutoff region. The aim of this work is the study of the formation of the energy spectrum of accelerated protons at accretion shocks of galaxy clusters and of the characteristics of their broad band emission. The proton energy distribution is calculated self-consistently via a time-dependent numerical treatment of the shock acceleration process which takes into account the proton energy losses due to interactions with the CMBR. We calculate the energy distribution of accelerated protons, as well as the flux of broad-band emission produced by secondary electrons and positrons via synchrotron and inverse Compton scattering processes. We find that the downstream and upstream regions contribute almost at the same level to the emission. For the typical parameters characterising galaxy clusters, the synchrotron and IC peaks in the spectral energy distributions appear at comparable flux levels. For an efficient acceleration, the expected emission components in the X-ray and gamma-ray band are close to the detection threshold of current generation instruments, and will be possibly detected with the future generation of detectors.

Transport mechanism of MeV protons in tapered glass capillaries

To investigate the transport mechanism of MeV protons in tapered glass capillaries, spatially resolved energy spectra were measured for proton microbeams focused by 20-μm-outlet capillaries having various taper angles. Three-dimensional Monte Carlo (MC) simulations were also performed to support the experiments and trace each particle in the capillary in more detail. The dependence of the proton energy distribution on the outgoing angle proved that the capillary-focused proton beam consists of two different components, protons traveling straight through the capillary without colliding with the capillary wall and protons scattered by the capillary inner wall. Moreover, the focusing effect of the tapered glass capillary was found to be mainly due to the scattered beam component. The MC simulations well reproduced the experimental results and showed that beam focusing ratios of 1.6–2.4 are possible with capillaries having a convex inner wall. The flight distance of the scattered proton in the capillary glass body was found to play an important role in determining transport efficiency of the protons through the capillary.

Estimates of Carrington-class solar particle event radiation exposures on Mars

Radiation exposure estimates for crew members on the surface of Mars are made for solar particle event proton radiation environments comparable to the Carrington event of 1859. We assume that the proton energy distributions for these Carrington-type events are similar to those measured for other, more recent large events. The fluence levels of these hypothetical events are normalized to the value for the Carrington event, as reported from measurements in ice core data. In this work, we use the BRYNTRN radiation transport code, originally developed at NASA Langley Research Center, and the Computerized Anatomical Male and Female human geometry models to estimate exposures for aluminum shield areal densities similar to those provided by a spacesuit, a surface lander, and a permanent habitat located at various altitudes in the Mars atmosphere. Comparisons of the predicted organ exposures with current NASA Permissible Exposure Limits are made.

MO-A-BRA-03: Promises and Perils of Proton Therapy

Proton therapy enables lowering of the integral dose to the patient due to the finite range of protons. The basis for the reduction of integral dose is the proton's Bragg peak which increases the dose deposited in the tumour while reduces that to the normal tissue at the distal side of the target volume. Protonradiotherapy reduces the volume of normal tissue exposed to low doses, which is clinically significant with respect to the risk of second malignancies. That risk is notably more pronounced for younger patients than older ones as younger patients are more at risk to future radiation induced cancers. However, proton therapy is less tolerant than photon therapy to uncertainties in both treatment planning and treatmentdelivery. For example, tissue inhomogeneity has a greater effect on protondose distributions than on photondose distributions. In planning proton therapy, the density of tissue along the proton path must be precisely determined and accounted for in order to obtain the required proton energy distribution to achieve the planned dose distribution in the patient. Failure to allow for a zone of higher density could result in a near zero dose in a distal segment of the target volume due to the reduced range of the protons. Conversely, neglecting to account for an air cavity upstream of the target volume would, for proton beams; result in a high dose being deposited in distal normal structures. Furthermore, motion and mis‐registration of the target volume with the radiation beams have far more severe consequences in proton therapy compared to photon therapy. If the target volumes are to be adequately irradiated, and adjacent OARs are to be protected in proton therapy, it is essential: that the causes and possible magnitudes of motion and misregistration are understood; that their possible consequences are understood; that measures are taken to minimize motion and mis‐registration to the extent possible and clinically warranted. It is almost impossible to get rid of all uncertainties in radiation therapy. Therefore, it is important to understand the sources of these uncertainties, quantify their magnitude, and develop mitigation and/or minimization strategies. In proton therapy margins are added to account for uncertainty sources that include; stopping power of tissues,dose calculation approximations, biological considerations, setup and anatomical variations, and internal movements of low and high density organs into the beam path. These margins reduce the benefit of proton therapy in treatment sites where the physical properties of protons could make a significant difference, such as lung cancer. The focus of this presentation is to; a) understand the potential sources of dosimetric uncertainties in proton therapy b) evaluate the impact of these uncertainties on the accuracy and conformity of dosedelivered to patients and c) suggest potential strategies that translate physical advantage of proton therapy into a maximized dosimetric benefit in the patient. Learning Objectives: 1. Describe the need for knowing potential sources of treatment planning and delivery uncertainties in proton therapy. 2. Summarize strategies to mitigate both proton therapy planning and delivery uncertainties.

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

The production mechanisms of protons in dissociation of methane by 54 eV electron impact is investigated using the reaction microscope. By measuring all three charged particles in the final state in triple coincidence, the energy deposited in the target is determined. It is found that the (2${a}_{1}$)${}^{\ensuremath{-}1}$(${\mathit{npt}}_{2}$)${}^{1}$, (2${a}_{1}$)${}^{\ensuremath{-}1}$, (1${t}_{2}$)${}^{\ensuremath{-}2}$(3${a}_{1}$)${}^{1}$, and (2${a}_{1}$)${}^{\ensuremath{-}2}$(3${a}_{1}$)${}^{1}$ states of the intermediate CH${}_{4}$${}^{+}$ make the major contributions to the formation of protons at this incident energy. The decay of each state results in a different kinetic energy distribution of protons. Possible decay mechanisms of these states are analyzed.

On the Cosmic Ray-Induced Ionization Rate in Molecular Clouds

The transformation of the energy dependence of the cosmic ray proton flux in the keV to GeV region is investigated theoretically when penetrating inside molecular clouds ( mag). The computations suggest that energy losses of the cosmic ray particles by interaction with the matter of the molecular cloud are principally caused by the inelastic (electronic) interaction potential; the transformed energy distribution of energetic protons is determined mainly by the column density of the absorbing medium. A cutoff of the cosmic ray spectrum inside clouds by their magnetic fields is also phenomenologically taken into account. This procedure allows a determination of environment-dependent ionization rates of molecular clouds. The theoretically predicted ionization rates are in good agreement with those derived from astronomical observations of absorption lines in the spectrum of the cloud connected with the Herbig Be star LkH 101.

A novel high resolution ion wide angle spectrometer

A novel ion wide angle spectrometer (iWASP) has been developed, which is capable of measuring angularly resolved energy distributions of protons and a second ion species, such as carbon C(6 +), simultaneously. The energy resolution for protons and carbon ions is better than 10% at ∼50 MeV/nucleon and thus suitable for the study of novel laser-ion acceleration schemes aiming for ultrahigh particle energies. A wedged magnet design enables an acceptance angle of 30°(∼524 mrad) and high angular accuracy in the μrad range. First, results obtained at the LANL Trident laser facility are presented demonstrating high energy and angular resolution of this novel iWASP.

Charge collection of single event effects at Bragg’s peak

Using Geant4 Monte Carlo code and Technology Computer-Aided Design (TCAD) simulation, energy deposition and charge collection of single event effects (SEE) are studied, which are induced by low-energy protons and α particles in small feature size devices. We analyzed charge collection of SEE especially at Bragg’s peak and obtained two types of deposited energy distributions of protons and α particles at different incident energies. The two components of the total charge collected are quantified, which are due to drift current of the space charge region and current in the funnel region separately. Results explain the high soft error rate in experiments of low energy proton.

An imaging proton spectrometer for short-pulse laser plasma experiments

The ultraintense short pulse laser pulses incident on solid targets can generate energetic protons. In addition to their potentially important applications such as in cancer treatments and proton fast ignition, these protons are essential to understand the complex physics of intense laser plasma interaction. To better characterize these laser-produced protons, we designed and constructed a novel spectrometer that will not only measure proton energy distribution with high resolution but also provide its angular characteristics. The information obtained from this spectrometer compliments those from commonly used diagnostics including radiochromic film packs, CR39 nuclear track detectors, and nonimaging magnetic spectrometers. The basic characterizations and sample data from this instrument are presented.

Direct evidence of the surface track potential

Angular and energy distributions of fragment protons dissociated from HeH${}^{+}$ during grazing-angle scattering from a KCl $(001)$ surface are measured. The surface of KCl $(001)$ is heated at ${180}^{\ifmmode^\circ\else\textdegree\fi{}}$C and the beam current is kept lower than 1 fA to prevent macroscopic surface charging. The angular distribution of the fragment protons shows a well-defined peak similarly to the grazing-angle scattering of atomic ions. The observed peak, however, is shifted from the specular angle toward larger scattering angles. The observed angular shift for the trailing proton is larger than that for the leading proton. These results clearly indicate that the motion of the fragment protons is affected by the surface track potential induced by the partner He ion.

A simulation of neutron interaction from Am–Be source with the CR-39 detector

Abstract Presented in this paper is a simulation of the interaction of neutrons emitted from a cylindrical Am–Be source with a CR-39 detector. A Fortran90 program, called Neutron.f90, has been written to determine the specifications of secondary particles (alpha particle or proton) and the kinematics of the interactions. A Monte Carlo method was used to simulate which interactions occurred with the constituents of the CR-39 detector, H, C and O atoms. Due to the detector composition, elastic and nonelastic scattering of neutrons is possible. In this paper, nonelastic scattering includes: inelastic scattering; the emission of an alpha particle (n,α) reaction and the emission of a proton (n,p) reaction. Cross sections of other reactions are very small and negligible in comparison with the above mentioned. The energy deposited per unit mass per one neutron was calculated. In addition the contribution to the energy deposited by the alpha particles and protons were determined separately. The program Neutron.f90 computes the coordinates of points in which interactions occur i.e. where secondary particles appear. The energy and angular distributions of protons are also represented in this paper. Another Fortran90 program, called Track_Visibility.f90, was written to calculate the number of visible proton tracks and to calculate the energy deposited per one neutron per one visible track.

Effect of magnetospheric convection on the energy distribution of protons from the Earth radiation belts

The structure of energetic protons from the Earth radiation belts, averaged for a magnetically quiet period, can be explained by the equilibrium between the radial diffusion transfer, loss due to Coulomb collisions, charge exchange with ambient neutral hydrogen of the geocorona, and drift of protons under the influence of magnetospheric convection. By transfer we mean diffusion owing to fluctuations related to substorms in the large-scale electric and magnetic fields. Equatorially mirroring protons with energies of 1–750 keV have been considered, and the theoretical predictions of the proton energy spectra for L = 1.0−6.6 have been compared with the observations on several satellites.

Energy and charge distributions of fast hydrogen ions and atoms reflected from Cu in the case of grazing incidence

The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence angles are measured at energies of incident particles (H+ and H0) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in the material.

Investigations for InAs/GaAs multilayered quantum-dot structure treated by high energy proton irradiation

This paper focuses on the high energy proton irradiation effect of InAs/GaAs multilayers quantum-dot (QD) wafer and photodetector. With high energy proton path simulation, the releases of proton energy and trap distribution in QD multilayers are predicted well. Treated by 1 and 3 MeV protons, all protons almost penetrate the multilayers of QD structures and stop deeply in GaAs substrate. InAs QD multilayer structures/Infrared photodetector have been irradiated by protons with different energies (1 and 3 MeV) and doses (1 × 10 9∼ 1 × 10 13 protons/cm 2). The photoluminescence (PL) and photoresponsivity (PR) spectrum of samples were measured and discussed with as grown and post irradiation.

Simulation of non-equilibrium energy distributions of current carriers in proton-conducting oxides with perovskite structure

A simulation method based on the integral equation for the sticking probability of ion in well was discussed for its application to study energy distributions of protons carried in simple and complex perovskite-like structures. In the terms of the Wiener—Hopf computational technique, a numerical algorithm was developed to detect deviations of the energy distribution function from the Boltzmann distribution near the potential barrier peak due to random interaction of ion with the nearest environment. Being considered as non-equilibrium in this sense, the derived distributions essentially deviated from the equilibrium distribution for a wide energy loss range of protons carried from one lattice position to another. The developed simulation algorithm may be of methodological interest in general practice for numerical solution of the Wiener—Hopf equations, because the known solution techniques for integral equations of this type are inapplicable to the studied problems of electrochemical kinetics due to their essentially different boundary conditions.

Interaction of intense laser pulses with hydrogen atomic clusters

The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.

Performance of a Pb-spallation target surrounded by a U-blanket during irradiations with 1.6 and 2.5GeV deuteron beams: Comparison with relativistic proton beams

Neutron and proton yields, spatial and energy distributions were determined on an electronuclear set-up irradiated with relativistic deuteron beams. The experimental results, acquired using both passive and active methods, are compared with the data obtained using MC simulation. The U-blanket performance in terms of fission production rate as well as plutonium accumulation is discussed. An evaluation between the data obtained using relativistic deuteron and proton beams is presented regarding to study the set-up efficiency to incinerate and/or transmute the actinides and fission products.

PINO—a tool for simulating neutron spectra resulting from the 7Li(p,n) reaction

The 7Li(p,n) reaction in combination with a 3.7 MV Van de Graaff accelerator was routinely used at FZK to perform activation as well as time-of-flight measurements with neutrons in the keV-region. Planned new setups with much higher proton currents like SARAF and FRANZ and the availability of liquid-lithium target technology will trigger a renaissance of this method. A detailed understanding of the neutron spectrum is not only important during the planning phase of an experiment, but also for the analysis of activation experiments. Therefore, the Monte-Carlo based program PINO (Protons In Neutrons Out) was developed, which allows the simulation of neutron spectra considering the geometry of the setup and the proton-energy distribution.

MO‐SAM‐BRB‐03: CE‐Therapy — SAM

The use of protons for radiation therapy offers theoretical advantages compared to external beam photon radiotherapy. It enables lowering of the integral dose to the patient due to the finite range of protons. However, proton therapy is less tolerant than photon therapy to uncertainties in both treatment planning and treatment delivery. For example, tissue inhomogeneity has a greater effect on proton dose distributions than on photon dose distributions. In planning proton therapy, the density of tissue along the proton path must be precisely determined and accounted for in order to obtain the required proton energy distribution to achieve the planned dose distribution in the patient. Failure to allow for a zone of higher density could result in a near zero dose in a distal segment of the target volume due to the reduced range of the protons. In contrast, for photons, because of their different energy loss processes, an increased density would cause only a modest lowering of the dose distal to the higher density region. Conversely, neglecting to account for an air cavity upstream of the target volume would, for proton beams; result in a high dose being deposited in distal normal structures while only a modestly increased dose would be deposited in the case of photon beams. Furthermore, motion and mis‐registration of the target volume with the radiation beams have far more severe consequences in proton therapy compared to photon therapy. If the target volumes are to be adequately irradiated, and adjacent OARs are to be protected in proton therapy, it is essential: that the causes and possible magnitudes of motion and mis‐registration are understood; that their possible consequences are understood; that measures are taken to minimize motion and mis‐registration to the extent possible and clinically warranted.In proton therapy treatment planning uncertainties arise from several sources that include; dose calculation approximations, biological considerations, setup and anatomical variations, and internal movements of low and high density organs into the beam path. Organ motion also has a major impact on the proton range, which is managed by adding a distal safety margin. These margins reduce the benefit of proton therapy in treatment sites where the physical properties of protons could make a significant difference, such as lung cancer. Therefore, it is important to understand the sources of uncertainties in proton therapy quantify their magnitude and develop mitigation and/or minimization strategies.The focus of this presentation is to; a) understand the potential sources of dosimetric uncertainties in proton therapy b) evaluate the impact of these uncertainties on the accuracy and conformity of dose delivered to patients and c) suggest potential strategies that translate physical advantage of proton therapy into a maximized dosimetric benefit in the patient.Learning Objectives:1. Explain the state‐of‐the‐art in proton therapy treatment planning.2. Describe the need for knowing potential sources of treatment planning and delivery uncertainties in proton therapy.3. Summarize strategies to mitigate proton therapy dosimetric uncertainties.

A Method to Obtain a Maxwell–Boltzmann Neutron Spectrum at kT = 30 keV for Nuclear Astrophysics Studies

AbstractA method to shape the neutron energy spectrum at low-energy accelerators is proposed by modification of the initial proton energy distribution. A first application to the superconductive RFQ of the SPES project at Laboratori Nazionali di Legnaro is investigated for the production of a Maxwell–Boltzmann neutron spectrum at kT = 30 keV via the 7Li(p, n)7Be reaction. Concept, solutions and calculations for a setup consisting of a proton energy shaper and a lithium target are presented. It is found that a power dentisity of 3 kW cm−2 could be sustained by the lithium target and a forward-directed neutron flux higher than 1010 s−1 at the sample position could be obtained. In the framework of the SPES project the construction of a LEgnaro NeutrOn Source (LENOS) for Astrophysics and for validation of integral nuclear data is proposed, suited for activation studies on stable and unstable isotopes.