Energy Loss Of Ions Research Articles

Effect of the nuclear charge of a fast structural ion on its internal effective stopping in collisions with atoms

The energy losses of fast structural ions in collisions with atoms have been considered in the eikonal approximation. The structural ions are ions consisting of a nucleus and a certain number of electrons bound to it. The effect of nuclear charge Z of the ion on its effective deceleration κ(p) (energy losses associated with excitation of only intrinsic ion shells) has been analyzed. It is shown that the allowance for the interaction of an atom with the ion nucleus for Z a Z/v > 1, where Z a is the charge of the atomic nucleus and v is the velocity of collisions in atomic units, considerably affects the value of κ(p), which generally necessitates taking into account nonperturbatively the effect of both charges Z a and Z on κ(p).

Visual evidence of suppressing the ion and electron energy loss on the wall in Hall thrusters

A method of pushing down magnetic field with two permanent magnetic rings is proposed in this paper. It can realize ionization in a channel and acceleration outside the channel. The wall will only suffer from the bombardment of low-energy ions and electrons, which can effectively reduce channel erosion and extend the operational lifetime of thrusters. Furthermore, there is no additional power consumption of coils, which improves the efficiency of systems. We show here the newly developed 200 W no wall-loss Hall thruster (NWLHT-200) that applies the method of pushing down magnetic field with two permanent magnetic rings; the visual evidence we obtained preliminarily confirms the feasibility that the proposed method can realize discharge without wall energy loss or erosion of Hall thrusters.

Neutron-induced fission cross-section measurement of 234U with quasi-monoenergetic beams in the keV and MeV range using micromegas detectors

Accurate data on neutron-induced fission cross-sections of actinides are essential for the design of advanced nuclear reactors based either on fast neutron spectra or alternative fuel cycles, as well as for the reduction of safety margins of existing and future conventional facilities. The fission cross-section of $^{234}$U was measured at incident neutron energies of 560 and 660 keV and 7.5 MeV with a setup based on ‘microbulk’ Micromegas detectors and the same samples previously used for the measurement performed at the CERN n_TOF facility (Karadimos et al., 2014). The $^{235}$U fission cross-section was used as reference. The (quasi-)monoenergetic neutron beams were produced via the 7Li(p,n) and the 2H(d,n) reactions at the neutron beam facility of the Institute of Nuclear and Particle Physics at the ‘Demokritos’ National Centre for Scientific Research. A detailed study of the neutron spectra produced in the targets and intercepted by the samples was performed coupling the NeuSDesc and MCNPX codes, taking into account the energy spread, energy loss and angular straggling of the beam ions in the target assemblies, as well as contributions from competing reactions and neutron scattering in the experimental setup. Auxiliary Monte-Carlo simulations were performed with the FLUKA code to study the behaviour of the detectors, focusing particularly on the reproduction of the pulse height spectra of α-particles and fission fragments (using distributions produced with the GEF code) for the evaluation of the detector efficiency. An overview of the developed methodology and preliminary results are presented.

Search for metastable heavy charged particles with large ionisation energy loss in pp collisions at √{{s}} = 13 TeV using the ATLAS experiment

Search for metastable heavy charged particles with large ionisation energy loss in pp collisions at √{{s}} = 13 TeV using the ATLAS experiment

Femtoscopy in √SNN= 5.02 TeVp-Pb collisions withATLAS

Bose-Einstein correlations between identified charged pions are measured for p +Pb collisions at √S NN = 5.02 TeV with the ATLAS detector using a total integrated luminosity of 28 nb−1 . Pions are identified using ionisation energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of average transverse pair momentum (k T ) and rapidity (y ππ *) as well as collision centrality. Pairs are selected with a rapidity −2 ππ * T T . A correlation with the local single-particle multiplicity dN ch /dy * is demonstrated. The scaling of the extracted radii with the mean number of participants is also used to compare a selection of initial-geometry models. The cross term R o1 , which couples radial and longitudinal expansion, is measured as a function of rapidity, and a departure from zero is observed with 4.8 σ combined significance for y ππ * > −1 in the most central events.

Energy loss and straggling of MeV Si ions in gases

We present measurements of energy loss and straggling of Si ions in gases. An energy range from 0.5 to 12MeV/u was covered using the 6MV EN tandem accelerator at ETH Zurich, Switzerland, and the K130 cyclotron accelerator facility at the University of Jyväskylä, Finland. Our energy-loss data compare well with calculation based on the SRIM and PASS code. The new straggling measurements support a pronounced peak in He gas at around 4MeV/u predicted by recent theoretical calculations. The straggling curve structure in the other gases (N2, Ne, Ar, Kr) is relatively flat in the covered energy range. Although there is a general agreement between the straggling data and the theoretical calculations, the experimental uncertainties are too large to confirm or exclude the predicted weak multi-peak structure in the energy-loss straggling.

Event-by-Event Identified Particle Ratio Fluctuations in Pb–Pb Collisions with ALICE using the Identity Method

The study of event-by-event fluctuations of identified hadrons may reveal the degrees of freedom of the strongly interacting matter created in heavy-ion collisions and the underlying dynamics of the system. The observable νdyn, which is defined in terms of the moments of identified-particle multiplicity distributions, is used to quantify the magnitude of the dynamical fluctuations in event-by-event measurements of particle ratios. The ALICE detector at the LHC is well-suited for the study of νdyn, due to its excellent particle identification capabilities. Particle identification based on the measurement of the specific ionization energy loss, dE/dx, works well on a statistical basis but suffers from ambiguities when applied on an event-by-event level. A novel experimental technique called the “Identity Method” is used to overcome such limitations. The first results on identified particle ratio fluctuations in Pb-Pb collisions at sNN=2.76 TeV in ALICE as a function of centrality are presented. The ALICE results for the most peripheral events indicate an increasing correlation between pions and protons which is not reproduced by the HIJING and AMPT models. On the other hand, for the most central events the ALICE results agree with the extrapolations based on the data at lower energies from CERN-SPS and RHIC.

Preliminary neutron shielding calculations of the electronics in the EAST BES systems focusing on neutron induced displacement damage

Monte Carlo N-Particle (MCNP) calculations were carried out to compare neutron shielding capabilities of three frequently used neutron shielding materials: polyethylene without neutron absorbers, polyethylene with boron absorbers and polyethylene with lithium absorbers, according to Non Ionizing Energy Loss (NIEL). The results of 1D shielding calculations showed that simple neutron moderating materials can provide sufficient and cheap shielding against 2.45MeV and 14.1MeV fusion neutrons, in terms of 1MeV neutron equivalent flux, in silicon targets, which is the most commonly used material of electronic components. Based on these results a new shielding concept is proposed which can be taken into consideration where the reduction of displacement damage is the main goal and the free space available for shielding is limited. Based on this shielding concept detailed 3D calculations were carried out to describe the properties of the neutron shielding of the Beam Emission Spectroscopy (BES) system installed at the EAST tokamak.

Energy loss of an energetic Ga ion in hot Au plasmas

Self-consistent calculations of energy loss for a Ga ion moving in hot Au plasmas are made under the assumption of wide ranges of the projectile energy and the plasma temperature with all important mechanisms considered in detail. The relevant results are found to be quite different from those of an α particle or a proton. One important reason for this is the rapid increasing of the charge state of a Ga ion at plasma temperature. This reason also leads to the inelastic stopping which does not always decrease with the increase of plasma temperature, unlike the case of an α particle. The nuclear stopping becomes very important at high enough plasma temperature due to the heavy reduced mass of a Ga and an Au ion and the above-mentioned reason. The well-known binary collision model [Phys. Rev. 126 (1962) 1] and its revised one [Phys. Rev. A 29 (1984) 2145] are not working or unsatisfactory in this case.

Structural response of titanate pyrochlores to swift heavy ion irradiation

The structure, size, and morphology of ion tracks resulting from irradiation of five different pyrochlore compositions (A2Ti2O7, A = Yb, Er, Y, Gd, Sm) with 2.2 GeV 197Au ions were investigated by means of synchrotron X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Radiation-induced amorphization occurred in all five materials analyzed following an exponential rate as a function of ion fluence. XRD patterns showed a general trend of increasing susceptibility of amorphization with increasing ratio of A- to B-site cation ionic radii (rA/rB) with the exception of Y2Ti2O7 and Sm2Ti2O7. This indicates that the track size does not necessarily increase with rA/rB, in contrast with results from previous swift heavy ion studies on Gd2Zr2-xTixO7 pyrochlore materials. For Y2Ti2O7, this effect is attributed to the significantly lower electron density of this material relative to the lanthanide-bearing pyrochlores, thus lowering the electronic energy loss (dE/dx) of the high-energy ions in this composition. An energy loss normalization procedure was performed which reveals an initial increase of amorphous track size with rA/rB that saturates above a cation radius ratio larger than Gd2Ti2O7. This is in agreement with previous low-energy ion irradiation experiments and first principles calculations of the disordering energy of titanate pyrochlores indicating that the same trends in disordering energy apply to radiation damage induced in both the nuclear and electronic energy loss regimes. HRTEM images indicate that single ion tracks in Yb2Ti2O7 and Er2Ti2O7, which have small A-site cations and low rA/rB, exhibit a core-shell structure with a small amorphous core surrounded by a larger disordered shell. In contrast, single tracks in Gd2Ti2O7 and Sm2Ti2O7, have a larger amorphous core with minimal disordered shells.

Search for metastable heavy charged particles with large ionization energy loss inppcollisions ats=13 TeVusing the ATLAS experiment

This paper presents a search for massive charged long-lived particles produced in pp collisions at $\sqrt{s}=$ 13 TeV at the LHC using the ATLAS experiment. The dataset used corresponds to an integrated luminosity of 3.2 fb$^{-1}$. Many extensions of the Standard Model predict the existence of massive charged long-lived particles, such as $R$-hadrons. These massive particles are expected to be produced with a velocity significantly below the speed of light, and therefore to have a specific ionization higher than any Standard Model particle of unit charge at high momenta. The Pixel subsystem of the ATLAS detector is used to measure the ionization energy loss of reconstructed charged particles and to search for such highly ionizing particles. The search presented here has much greater sensitivity than a similar search performed using the ATLAS detector in the $\sqrt{s}=$ 8 TeV dataset, thanks to the increase in expected signal cross-section due to the higher center-of-mass energy of collisions, to an upgraded detector with a new silicon layer close to the interaction point, and to analysis improvements. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on $R$-hadron production cross-sections and masses are set. Gluino $R$-hadrons with lifetimes above 0.4 ns and decaying to $q\bar{q}$ plus a 100 GeV neutralino are excluded at the 95% confidence level, with lower mass limit ranging between 740 GeV and 1590 GeV. In the case of stable $R$-hadrons the lower mass limit at the 95% confidence level is 1570 GeV.

Charge-state-dependent energy loss of slow ions. II. Statistical atom model

A model for charge-dependent energy loss of slow ions is developed based on the Thomas-Fermi statistical model of atoms. Using a modified electrostatic potential which takes the ionic charge into account, nuclear and electronic energy transfers are calculated, the latter by an extension of the Firsov model. To evaluate the importance of multiple collisions even in nanometer-thick target materials we use the charge-state-dependent potentials in a Monte Carlo simulation in the binary collision approximation and compare the results to experiment. The Monte Carlo results reproduce the incident charge-state dependence of measured data well [see R. A. Wilhelm et al., Phys. Rev. A 93, 052708 (2016)], even though the experimentally observed charge exchange dependence is not included in the model.

Charge-state-dependent energy loss of slow ions. I. Experimental results on the transmission of highly charged ions

We report on energy loss measurements of slow $(v\ensuremath{\ll}{v}_{0})$, highly charged $(Qg10)$ ions upon transmission through a 1-nm-thick carbon nanomembrane. We emphasize here the scaling of the energy loss with the velocity and charge exchange or loss. We show that a weak linear velocity dependence exists, whereas charge exchange dominates the kinetic energy loss, especially in the case of a large charge capture. A universal scaling of the energy loss with the charge exchange and velocity is found and discussed in this paper. A model for charge-state-dependent energy loss for slow ions is presented in paper II in this series [R. A. Wilhelm and W. M\oller, Phys. Rev. A 93, 052709 (2016)].

The FLUKA Code: An Accurate Simulation Tool for Particle Therapy.

Monte Carlo (MC) codes are increasingly spreading in the hadrontherapy community due to their detailed description of radiation transport and interaction with matter. The suitability of a MC code for application to hadrontherapy demands accurate and reliable physical models capable of handling all components of the expected radiation field. This becomes extremely important for correctly performing not only physical but also biologically based dose calculations, especially in cases where ions heavier than protons are involved. In addition, accurate prediction of emerging secondary radiation is of utmost importance in innovative areas of research aiming at in vivo treatment verification. This contribution will address the recent developments of the FLUKA MC code and its practical applications in this field. Refinements of the FLUKA nuclear models in the therapeutic energy interval lead to an improved description of the mixed radiation field as shown in the presented benchmarks against experimental data with both 4He and 12C ion beams. Accurate description of ionization energy losses and of particle scattering and interactions lead to the excellent agreement of calculated depth–dose profiles with those measured at leading European hadron therapy centers, both with proton and ion beams. In order to support the application of FLUKA in hospital-based environments, Flair, the FLUKA graphical interface, has been enhanced with the capability of translating CT DICOM images into voxel-based computational phantoms in a fast and well-structured way. The interface is capable of importing also radiotherapy treatment data described in DICOM RT standard. In addition, the interface is equipped with an intuitive PET scanner geometry generator and automatic recording of coincidence events. Clinically, similar cases will be presented both in terms of absorbed dose and biological dose calculations describing the various available features.

The Role of Nuclear Fragmentation in Particle Therapy and Space Radiation Protection.

The transport of the so-called HZE particles (those having high charge, Z, and energy, E) through matter is crucially important both in space radiation protection and in the clinical setting where heavy ions are used for cancer treatment. HZE particles are usually considered those having Z > 1, though sometimes Z > 2 is meant. Transport physics is governed by two types of interactions, electromagnetic (ionization energy loss) and nuclear. Models of transport, such as those used in treatment planning and space mission planning must account for both effects in detail. The theory of electromagnetic interactions is well developed, but nucleus–nucleus collisions are so complex that no fundamental physical theory currently describes them. Instead, interaction models are generally anchored to experimental data, which in some areas are far from complete. The lack of fundamental physics knowledge introduces uncertainties in the calculations of exposures and their associated risks. These uncertainties are greatly compounded by the much larger uncertainties in biological response to HZE particles. In this article, we discuss the role of nucleus–nucleus interactions in heavy charged particle therapy and in deep space, where astronauts will receive a chronic low dose from galactic cosmic rays (GCRs) and potentially higher short-term doses from sporadic, unpredictable solar energetic particles (SEPs). GCRs include HZE particles; SEPs typically do not and we, therefore, exclude them from consideration in this article. Nucleus–nucleus collisions can result in the breakup of heavy ions into lighter ions. In space, this is generally beneficial because dose and dose equivalent are, on the whole, reduced in the process. The GCRs can be considered a radiation field with a significant high-LET component; when they pass through matter, the high-LET component is attenuated, at the cost of a slight increase in the low-LET component. Not only are the standard measures of risk reduced by fragmentation, but it can be argued that fragmentation also reduces the uncertainties in risk calculations by shifting the LET distribution toward one that is more concentrated at low LET, where biological effects are better understood. We review previous work in this area, including measurements made by the Radiation Assessment Detector during its journey to Mars and while on the surface of Mars aboard the Curiosity rover. Transport of HZE is also critically important in heavy-ion therapy, as it is necessary to know the details of the radiation field at the treatment site. This field is substantially modified compared to the incident pure (or nearly pure) ion beam by the same mechanisms of energy loss and nuclear fragmentation that pertain to the transport of space radiation.

Calculations on charge state and energy loss of argon ions in partially and fully ionized carbon plasmas.

The energy loss of argon ions in a target depends on their velocity and charge density. At the energies studied in this work, it depends mostly on the free and bound electrons in the target. Here the random-phase approximation is used for analyzing free electrons at any degeneracy. For the plasma-bound electrons, an interpolation between approximations for low and high energies is applied. The Brandt-Kitagawa (BK) model is employed to depict the projectile charge space distribution, and the stripping criterion of Kreussler et al. is used to determine its equilibrium charge state Q(eq). This latter criterion implies that the equilibrium charge state depends slightly on the electron density and temperature of the plasma. On the other hand, the effective charge Q(eff) is obtained as the ratio between the energy loss of the argon ion and that of the proton for the same plasma conditions. This effective charge Q(eff) is larger than the equilibrium charge state Q(eq) due to the incorporation of the BK charge distribution. Though our charge-state estimations are not exactly the same as the experimental values, our energy loss agrees quite well with the experiments. It is noticed that the energy loss in plasmas is higher than that in the same cold target of about, ∼42-62.5% and increases with carbon plasma ionization. This confirms the well-known enhanced plasma stopping. It is also observed that only a small part of this energy loss enhancement is due to an increase of the argon charge state, namely only ∼2.2 and 5.1%, for the partially and the fully ionized plasma, respectively. The other contribution is connected with a better energy transfer to the free electrons at plasma state than to the bound electrons at solid state of about, ∼38.8-57.4%, where higher values correspond to a fully ionized carbon plasma.

Ion energy losses during the charge-exchange process

A method for calculating ion energy losses during the charge-exchange process is proposed. It is established that the contribution of the charge-exchange process to inelastic energy losses for ions with nuclear charges of Z = 5–10 is significant and reaches 15% for certain ions in the energy interval of 30 to 100 keV/nucleon. If a gas target is replaced with a solid one, the ion energy losses during the charge-exchange processes decrease.

Simulations of the energy loss of ions at the stopping-power maximum in a laser-induced plasma

Simulations have been performed to study the energy loss of carbon ions in a hot, laser-generated plasma in the velocity region of the stopping-power maximum. In this parameter range, discrepancies of up to 30% exist between the various stopping theories and hardly any experimental data are available. The considered plasma, created by irradiating a thin carbon foil with two high-energy laser beams, is fully-ionized with a temperature of nearly 200 eV. To study the interaction at the maximum stopping power, Monte-Carlo calculations of the ion charge state in the plasma are carried out at a projectile energy of 0.5 MeV per nucleon. The predictions of various stopping-power theories are compared and experimental campaigns are planned for a first-time theory benchmarking in this low-velocity range.

A novel experimental setup for energy loss and charge state measurements in dense moderately coupled plasma using laser-heated hohlraum targets

We report on a new experimental setup for ion energy loss measurements in dense moderately coupled plasma which has recently been developed and tested at GSI Darmstadt. A partially ionized, moderately coupled carbon plasma (ne ≤ 0.8• 1022 cm-3, Te = 15 eV, z = 2.5, Γ = 0.5) is generated by volumetrical heating of two thin carbon foils with soft X-rays. This plasma is then probed by a bunched heavy ion beam. For that purpose, a special double gold hohlraum target of sub-millimeter size has been developed which efficiently converts intense laser light into thermal radiation and guarantees a gold-free interaction path for the ion beam traversing the carbon plasma. This setup allows to do precise energy loss measurements in non-ideal plasma at the level of 10 percent solid-state density.

Traceable stopping cross sections of Al and Mo elemental targets for 0.9–3.6-MeV protons

Accurate knowledge about the energy loss of ions in matter is essential in many problems, ranging from fundamental to applied nuclear physics. Indeed, there is a recent and increasing demand for new data on stopping cross sections measured with high accuracy and with a rigorous budget of their uncertainty sources. In the present paper we describe an accurate and traceable approach to determine the stopping cross sections in pure elemental materials---aluminum and molybdenum---for protons in the energy range of 0.9--3.6 MeV by the transmission method. The main sources of uncertainties here considered are (i) (random) the uncertainty in the peak positions and in the Gaussian fits and (ii) (systematic) the presence of thickness nonuniformity (a special procedure has been developed to correct it as far as possible). The accuracy in the final stopping cross section is $0.63%$ ($0.32%$ random and $0.54%$ systematic) for Al and $1.5%$ ($0.44%$ random and $1.4%$ systematic) for Mo, both mainly limited by the quality and homogeneity of the foils. For Al, this high accuracy represents an improvement compared to previous publications and serves as a benchmark for our procedure. For Mo, even though the uncertainty is somewhat higher, our results will help in improving the few data currently available in the energy range here considered. The data were also compared to the most commonly employed theoretical models (srim 1985, srim 2013, pstar, and casp 5.2) and Monte Carlo codes (geant 3 and geant 4). The experimental results are electronically available as supplemental material.