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In this work, the evolution of superparamagnetism (SPM) at room temperature is observed in the reactive magnetron sputter deposited amorphous Al-N-O alloy thin films after irradiation with oxygen ions (O−). Energy dispersive X-ray (EDX) analysis reveals the presence of notable Al-vacancy (V Al) in as-grown Al-N-O alloy thin film. X-ray photoelectron spectroscopy (XPS) confirms nitrogen trapping at V Al sites for thermodynamic stability, forming the Al(NO y) x phase. Upon the irradiation using O− at low fluence, i.e. 5 × 1013 ions/cm2, mainly V Al -O N complexes emerged. Here O N refers to nitrogen replaced by oxygen. Furthermore, an increase in oxygen fluence from 1 × 1015 to 2 × 1016 ions/cm2 yields the cross-over from V Al -O N complexes to mainly V Al , due to knocking off the trapped nitrogen atoms at V Al sites. From depth-resolved positron beam-based Doppler broadening measurements, the greater density of V Al sites is noticed in the film irradiated with the highest fluence of O− ion, i.e., 2 × 1016 ions/cm2. The correlation between the elevation of V Al sites with O− irradiation dose is in excellent agreement with the emergence of superparamagnetism (SPM) in the films. Hence, the emergence of SPM in the film after irradiation has been attributed to the creation of V Al sites, which leads to a localized magnetic moment. [ABSTRACT FROM AUTHOR]

We have proposed a compact scheme for generating high-density and high-energy positrons by irradiating different shaped targets with an ultra-intense laser pulse, using 2D particle-in-cell simulations and numerical analysis. Our simulations show that the Breit–Wheeler process dominates positron production during laser-target interaction when a laser with an intensity of 4 × 10 23 W cm − 2 is used. We obtain a positron beam with an energy of 2.5 GeV and a total number exceeding 109, which is an improvement by two orders of magnitude compared to previous work with the same laser intensity. By using different shaped targets, we are able to generate a high-energy positron beam with low divergence. The yield of positron pairs depends on both the target and the laser parameters, and we have investigated how the shape of the target can enhance pair production and reduce divergence. Both of our analytical and simulation results demonstrate that this high-flux and low-divergence positron beam has direct applications in the field of medical and astro-physics that can be explored in the upcoming high intensity laser facilities. [ABSTRACT FROM AUTHOR]

The space-based gamma-ray telescope must effectively separate photons from charged particles of instrumental background and cosmic rays. It requires that the anticoincidence system of the telescope must have high detection efficiency, large dynamic range and good enough energy and time resolution for charged particles. The main results obtained using 246 MeV secondary positron beam of synchrotron S-25R "PAKHRA" of Lebedev Physical Institute with prototype of system of anticoincidence detectors of space-based gamma-ray telescope GAMMA-400 are presented. The amplitude resolution, time resolution and charged particles detection efficiency are adduced. All measurements were performed using "fast" output of silicon photomultipliers of prototype scintillation detectors sensors. Fractal dimensions of temporal profiles registered during measurements using positron beam and atmospheric muons are discussed. [ABSTRACT FROM AUTHOR]

The results of Doppler broadening of the annihilation line spectroscopy obtained using a variable energy positron beam for the pure gold samples exposed to 100 keV self-implantation and 250 keV H+ implantation are reported. The annihilation characteristics of parameter S as a function of positron energy were determined. Irradiation-induced defects were confirmed in all measured profiles. However, the S parameter distributions were not typical for the ion-implanted materials. No significant changes in the shape of defect profiles for non-defected and self-implanted samples were found. The implanted Au+ ions fill the earlier produced vacancies and decrease the overall defect concentration. In the case of 100 keV H+ implantation, the distribution does not cover the area with higher S values pointing out the presence of defects. This is caused by the localization of H+ inside the produced vacancies. The thicknesses of the damaged layers are smaller compared to those numerically predicted by the SRIM implantation ranges. The long-range effect was not observed. [ABSTRACT FROM AUTHOR]

This paper reports experimental studies of silver after 167 MeV Xe26+ ions irradiation. Heavy ion implantation of samples with doses 2×1012, 5×1012, 1013, 5×1013 and 1014 was performed at IC-100 cyclotron at FLNR, JINR. Radiation damages were investigated with variable energy positron beam. Doppler broadening spectroscopy was applied and the line shape S parameter of annihilation line was extracted. The analysis of S parameter profiles gives information about the presence of open volume defects in irradiated samples. The positron diffusion length extracted from the profile decreases with the dose increase. It points out the increase of defects concentration. Probably, changes in the size or type of defects generated by various doses took place. [ABSTRACT FROM AUTHOR]

In this investigation, propagation properties of ion-acoustic shocks (IAShs) are studied in electron–ion plasma embedded with relativistic positron beam. Employing reductive perturbation technique, we have derived the Burgers’s equation. Further, by considering the higher order effects, inhomogeneous Burgers-type equation and its solution are derived. It is found that the inclusion of higher-order corrections, results in creating new type of shocks called humped IAShs. Behaviour of different types of IAShs is seen to be dependent on the ion temperature, beam density and kinematic viscosity of electrons. [ABSTRACT FROM AUTHOR]

Trapping technologies of positrons, the antimatter counterpart of electrons, are indispensable for various atomic, molecular, and optical experiments and for material analyses that use positron swarms. Efficient trapping of high-intensity positron beams generated by electron linear accelerators (LINACs) will improve the quality and throughput rate of experiments but have yet to be practically realized. In the present work, we demonstrate the efficient trapping and extraction of a LINAC-based positron beam by using a silicon carbide (SiC) remoderator with a center hole. The positron beam was remoderated by 4H-SiC wafers in the back-reflection geometry followed by accumulation in an electromagnetic trap with CF _4 cooling gas. A rotating electric field was driven to spatially compress the accumulated positrons, enabling the lossless extraction of the positrons through the SiC hole. A trapping efficiency in the higher 20% range was achieved. The proposed trapping scheme employing a center-hole SiC remoderator is thus a practical technique to accumulate and cool positron beams generated by LINACs.

We studied the propagation of small-amplitude dust ion acoustic (DIA) solitary waves in four-component relativistic plasma comprised of nonthermal electrons, mobile positively charged ions, positron beam and negatively charged massive dust particles. By using the reductive perturbation method, the Korteweg–de-Vries (KdV) nonlinear wave equation is derived numerically. In this work, we have elucidated the role of energetic positron beam in the relativistic plasma and analyzed the existence region for ion-acoustic (IA) solitary wave formation. It is found that for certain plasma parameters, the propagation of both compressive and rarefactive solitary waves is possible. Here, the injecting streaming positron beam in plasma gives rise to the increase in the phase velocity (Mach number) and reaches up to the hypersonic regime of flow velocity. It is observed that the initial increase in relativistic factor of positron beam , as well as temperature ratio of the positron beam to electrons decrease the characteristic features (the amplitude) of the compressive solitary wave potential profiles. On the other hand, on increasing dust grain charge , positron beam concentration ratio as well as nonthermal electrons concentration result in enhancement of the amplitudes of IA solitary wave potential profiles. The findings of this work can be more helpful in understanding the Earth's upper atmosphere (Aurora region of the ionosphere) as well as the space plasmas. [ABSTRACT FROM AUTHOR]

Positron beam measurements carried out on high temperature Ni+ implanted FeCrCoNi show no void formation but only presence of monovacancies. With thermal treatment, evidence for the formation of nano sized σ-CoCr are obtained from positron based ratio curve analysis in the temperature range 973–1123 K. Corroborative evidence for the presence of these precipitates are obtained from EBSD and GIXRD measurements. Further annealing beyond 1150 K leads to coarsening of these precipitates and they no longer trap the positrons. • First time study on the defect microstructure and its evolution in high temperature Ni+ implanted FeCrCoNi using the variable low energy positron beam. • Defect sensitive S-parameter reveals presence of monovacancies for the high temperature implanted condition. No presence of voids observed. • Positron beam based ratio curve analysis show formation of nano sized CoCr precipitates after annealing beyond 1023 K. [ABSTRACT FROM AUTHOR]

The influence of sandblasting on surface and subsurface of stainless steel is investigated using variable energy positron beam (VEP), positron annihilation spectroscopy (PAS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Samples of stainless steel were blasted using 110 μm particles of Al2O3 under different pressure and time duration. In the case of sandblasting for 90 s, the reduction of positron diffusion length depending on the applied pressure was observed. Sandblasting during 30 s leads only to the reduction of positron diffusion length to about 60 nm for all samples. Positron lifetimes close to 170 ps measured using positrons emitted directly from the source point to the presence of vacancies on the dislocation lines. SEM and AFM images show that surface roughness depends rather on pressure of sandblasting than time of exposition.

The Low Energy Positron Toroidal Accumulator (LEPTA) at the Joint Institute for Nuclear Research (JINR) proposed for generation of positronium in flight has been adopted for positron annihilation spectroscopy (PAS). The positron injector generates continuous slow positron beam with positron energy range between 50 eV and 35 keV. The radioactive 22Na isotope is used. In distinction to popular tungsten foil, here the solid neon is used as moderator. It allows to obtain the beam intensity of about 105 e+/s width energy spectrum characterized by full width at half maximum (FWHM) of 3.4 eV and a tail to lower energies of about 30 eV. The paper covers the characteristic of variable energy positron beam at the LEPTA facility: parameters, the rule of moderation, scheme of injector, and transportation of positrons into the sample chamber. Recent status of the project and its development in the field of PAS is discussed. As an example, the measurement of the positron diffusion length in pure iron is demonstrated.

A 4MV Van de Graaff accelerator was used to induce the nuclear reaction 12 C(d,n) 13 N in order to produce an intense beam of positrons. The graphite target was heated so the radioactive 13 N would desorb from the bulk into the vacuum. This radioactive gas is frozen onto a cryogenic freezer where it decays to produce an antiparticle beam of positrons. This high current beam is then guided into a superconducting magnet with field strength up to 7 Tesla where the positrons will be stored in a newly designed Micro-Penning-Malmberg trap. Several source geometries have been experimented on and found a maximum antimatter beam with a positron flux of greater than 0.55 ± 0.03 × 10 6 e + s −1 was achieved. This beam was produced using a solid rare gas moderator composed of krypton (Kr) at a temperature of 25 ± 5 K. Due to geometric restrictions on this set up and other loss mechanisms, 10 7 –10 8 e + s −1 of the total number of positrons are lost. Simulations and preliminary experiments suggest a new geometry, currently under testing, will produce a beam of 10 7 e + s −1 or more. The setup and preliminary results for the new geometry will be discussed as well. [ABSTRACT FROM AUTHOR]