low-Z Targets Research Articles

Contrasting effect of high-Z coating on proton acceleration from thin transparent low-Z foil target

Abstract In the present work, we investigate the impact of a thin metallic coating on proton acceleration from transparent dielectric foils. A substantial difference in the experimental results is observed based on the placement of the thin metal coating - either on the front surface (the side facing the laser) or on the rear surface of the foil. In the former case, we observed an enhancement in both the energy and flux of the accelerated protons/ions. However, in the latter case, the thin metal coating was found to have a highly detrimental effect on the acceleration process. Measurements conducted on transmitted laser pulse signals confirm the crucial role of the intensity-dependent target material transparency and the laser pre-pulse playing vital roles in determining the proton/ion acceleration dynamics. Numerical simulations involving radiation hydrodynamics followed by two-dimensional particle-in-cell simulations confirm the experimental observations.

Lepton pair production in muon-nucleus scattering

The MUonE experiment aims at providing a novel determination of the leading hadronic contribution to the muon anomalous magnetic moment through the study of elastic muon-electron scattering. Since the initial-state electrons are bound in a low-Z atomic target, the interaction between the incoming muons and the nuclei is expected to be the main source of experimental background. In this article, we study the production of a real lepton pair from the muon-nucleus scattering, discussing its numerical impact in the MUonE kinematic configuration. The process is described as a scattering of a muon in an external Coulomb field with the addition of a form factor to describe the nuclear charge distribution. The calculation is implemented in the fully differential Monte Carlo event generator Mesmer, without introducing any approximation on the angular variables.

MUonE experiment

The anomalous magnetic moment of the muon has been a long stand ing issue in the field of particle physics. The recent results by Fermilab have pointed to a possible discrepancy of 4.2σ with respect to the Standard Model prediction. Although the future measurements will undoubtedly strengthen this result, the large uncertainty of the prediction, caused by a non-perturbative hadronic contribution, remains an issue. The MUonE experiment is designed to provide an independent, precise measurement of this contribution by employ ing a series of tracking stations and low-Z targets, to precisely determine the shape of differential cross-section of an elastic µ + e → µ + e scattering. It is expected to increase the result’s significance to at least 7σ, thus solidifying the discovery. The design of the detector allows also for New Physics searches with a signature of displaced vertices.

OLIMPO: A balloon-borne SZE imager to probe ICM dynamics and the WHIM

OLIMPO is a proposed Antarctic balloon-borne Sunyaev-Zel’dovich effect (SZE) imager to study gas dynamics associated with structure formation along with the properties of the warm-hot intergalactic medium (WHIM) residing in the connective filaments. During a 25 day flight OLIMPO will image a total of 10 z∼0.05 galaxy clusters and 8 bridges at 145, 250, 365, and 460 GHz at an angular resolution of 1.0′–3.3′. The maps will be significantly deeper than those planned from CMB-S4 and CCAT-P, and will have excellent fidelity to the large angular scales of our low-z targets, which are difficult to probe from the ground. In combination with X-ray data from eROSITA and XRISM we will transform our current static view of galaxy clusters into a full dynamic picture by measuring the internal intra-cluster medium (ICM) velocity structure with the kinematic SZE, X-ray spectroscopy, and the power spectrum of ICM fluctuations. Radio observations from ASKAP and MeerKAT will be used to better understand the connection between ICM turbulence and shocks with the relativistic plasma. Beyond the cluster boundary, we will combine thermal SZE maps from OLIMPO with X-ray imaging from eROSITA to measure the thermodynamics of the WHIM residing in filaments, providing a better understanding of its properties and its contribution to the total baryon budget.

Production of high-energy neutrons by interaction of a deuteron beam with matter

Experimental double differential cross section data for neutrons in the high-energy region are still scarce because of the difficulty of producing high-energy neutrons. The present work studies the possibility of producing high-energy neutrons by interaction of a deuteron beam with matter. The Geant4 toolkit is used to simulate the interaction between a deuteron beam and matter. An analytical method is also developed to calculate the neutron yields produced in the interaction of the deuteron beam with matter. The input cross section data are not only taken from the TEDNL-2017 library but are also calculated by the isospin-dependent quantum molecular dynamics model. It is shown that it is possible to produce high-energy neutrons by interaction of a deuteron beam with matter. If one wishes to produce high-energy neutrons, a low-Z target and a small emission angle may be considered. A thin target is a good choice if one wishes to produce neutrons with a smaller energy peak width.

Investigation of planar image quality for a novel 2.5MV diamond target beam from a radiotherapy linear accelerator.

Background and purposeA commercial 2.5 MV beam has been clinically available for beam’s-eye-view imaging in radiotherapy, offering improved contrast-to-noise ratio (CNR) compared to therapeutic beams, due to the softer spectrum. Previous research suggested that imaging performance could be improved using a low-Z diamond target to reduce the self-absorption of diagnostic energy photons. The aim of this study was to 1) investigate the feasibility of two 2.5 MV diamond target beamline configurations and 2) characterize the dosimetry and planar image quality of these novel low-Z beams.Materials and methodsThe commercial 2.5 MV beam was modified by replacing the copper target with sintered diamond. Two beamlines were investigated: a carousel-mounted diamond target beamline and a ‘conventional’ beamline, with the diamond target in the target arm. Planar image quality was assessed in terms of spatial resolution and CNR.ResultsDue to image artifacts, image quality could not be assessed for the carousel-mounted low-Z target beam. The ‘conventional’ 2.5 MV low-Z beam quality was softer by 2.7% compared to the commercial imaging beam, resulting in improved CNR by factors of up to 1.3 and 1.7 in thin and thick phantoms, respectively. In regard to spatial resolution, the ‘conventional’ 2.5 MV low-Z beam slightly outperformed the commercial imaging beam.ConclusionWith a simple modification to the 2.5 MV commercial beamline, we produced an improved energy spectrum for imaging. This 2.5 MV diamond target beam proved to be an advantageous alternative to the commercial target configuration, offering both superior resolution and CNR.

Thick target neutron yields from LiF, C, Si, Ni, Mo, and Ta bombarded by 6.7 MeV/u deuterons

Double-differential thick target neutron yields from the bombardment of LiF, C, Si, Ni, Mo, and Ta targets by 6.7 MeV/u deuterons were measured at forward angles using an EJ-301 liquid organic scintillator. The neutron energy spectra were derived via an unfolding method using the FORIST code with the detector response function calculated using the SCINFUL-QMD code. The neutron energy spectra and total neutron yields at 0∘ from the deuteron incidences were compared with the previous data of triton incidences on LiF, Si, Ni, Mo, and Ta targets measured at the same incident energy per nucleon. The comparison revealed that deuterons yield more neutrons for low-Z targets than tritons, and less neutrons for high-Z targets. The measured neutron energy spectra were compared with model calculations using the DEUteron-induced Reaction Analysis Code System (DEURACS). DEURACS successfully reproduced the neutron spectra from all the targets. For the triton incidence, some calculation codes were benchmarked, with JQMD/GEM and CCONE yielding good agreement with the measured neutron spectra at 0∘.

Depth profiling of ion-implanted samples by high-energy electron scattering

For heavy ions implanted in low-Z targets it is possible to determine the depth and concentration of introduced heavy impurities by studying the energy spectra of electrons scattered from the surface. Here, we demonstrate this for the case of 30 and 300 keV Au implantation in SiO2. For high-energy incoming electrons the elastic peak splits up in different components as the recoil losses depends on the mass of the scattering atom. Heavy impurities also affect the partial intensities and hence changes in the shape of the energy loss spectra are observed. These effects are reproduced by a simple model that uses sample composition, atomic elastic scattering cross sections and target dielectric function as input.

NEWS-G, a Spherical Proportional Counter with low-Z target to search for sub-GeV Weakly Interacting Particles

Despite several large-scale direct detection experiments operating worldwide, dark matter remains elusive. Not favoured by supersymmetric theories, the low Weakly Interacting Massive Particle (WIMP) mass regime (less than few GeV) has been largely ignored. The NEWS-G project builds on the experience gathered with the operation of the SEDINE detector at the Laboratoire Souterrain de Modane (France). The goal is to construct a 140cm diameter low-background Spherical Proportional Counter (SPC) capable of holding up to 10 bar of gas and to be operated at the SNOLAB underground facility (Canada). The use of low-Z target materials such as Ne, He and H, together with a strict selection of low activity materials will provide sensitivity to WIMP masses down to 0.1 GeV/c2. The detector is expected to be deployed in 2018.

Neutron production from thick LiF, C, Si, Ni, Mo, and Ta targets bombarded by 13.4-MeV deuterons

Double-differential thick target neutron yields from LiF, C, Si, Ni, Mo, and Ta targets bombarded by 13.4-MeV deuterons were measured by using an EJ-301 liquid organic scintillator at the Center for Accelerator and Beam Applied Science, Kyushu University. The measured (d, xn) spectra were compared with the (t, xn) spectra measured by the other group at the same incident energy per nucleon (6.7 MeV/u) and theoretical model calculations by Particle and Heavy Ion Transport code System (PHITS) and DEUteron-induced Reaction Analysis Code System (DEURACS). Some bumps are observed in the (d, xn) spectra for low-Z target elements, while no specific structure was seen in the (t, xn) spectra. The PHITS calculation, in which the intra-nuclear cascade of Liége (INCL) and generalized evaporation model (GEM) were used, generally overestimates neutron spectra while the DEURACS calculation agrees with experimental ones fairly well.

A feasibility test run for the MUonE project

The 3.4 σ discrepancy between the experimental value of the muon anomalous magnetic moment g-2 and the Standard Model prediction is one of the most intriguing indications of physics beyond the Standard Model. The MUonE project plans to measure the leading hadronic corrections to the muon g-2 by scattering high energy ( ∼ 150 GeV) muons off the atomic electrons of a low-Z target through the elastic process μ +e → μ +e. The angles of the incoming muons and the outcoming muons and electrons have to be measured precisely, to exploit the kinematical correlation of the μ -e collision. To reach this goal a modular target is foreseen, consisting of 60 low-Z (Be or C) elements, 1 cm thick, each sandwiched in layers of Si-microstrip detectors, organized in XY, XU and VY planes ( ± 45 °, to disentangle double tracks). In 2018, a feasibility test at the CERN North Area is foreseen, running parasitically on the beamline behind COMPASS. The setup consist of 16 layers with an area of 9.5 × 9.5 cm 2 , 410 μ m thick, single side AGILE silicon detectors, which have a readout pitch of 242 μ m and a floating strip scheme, resulting in a position resolution of the order of 40 μ m . The DAQ rate is of the order of a few kHz. The contribution will describe the setup, the DAQ system and the first data collected during the commissioning phase in April/May.

The MUonE experiment

The precision measurement of the anomalous magnetic moment g − 2 of the muon at present exhibits a 3.5 σ deviation between theory and experiments. In the next few years it will be measured to higher precisions at Fermilab and J-PARC. The theoretical prediction can be improved by reducing the uncertainty on the leading hadronic correction $ a_\mu ^{HLO} $ to the g − 2. Here we present a new approach to determine $ a_\mu ^{HLO} $ with space-like data, by means of a precise measurement of the hadronic contribution to the effective electromagnetic coupling α, exploiting the elastic scattering of 150 GeV muons (currently available at CERN North area) on atomic electrons of a low-Z target. The direct measurement of $ a_\mu ^{HLO} $ in the space-like region will provide a new independent determination and will consolidate the theoretical prediction of the muon g − 2 in the Standard Model. It will allow therefore a firmer interpretation of the measurements of the future muon g − 2 experiments at Fermilab and J-PARC.

Generation of GeV Electron Beam From a Laser-Plasma Accelerator and Its Prospect as a Desktop Source of Energetic Positrons and Gamma Rays For Applications

Laser wakefield acceleration (LWFA) is a plasma-based electron beam accelerator technology that can deliver electron beams with energies up to several GeVs, depending mainly on the power of the used laser system and the electron injection scheme. Here, we present the results from a GeV electron accelerator with a high reproducibility and a charge up to 30 pC using 110–120-TW laser pulses and by employing the well-established self-truncated ionization injection (STII) mechanism. These electron beams can be further used via bremsstrahlung in high-Z solid materials for the generation of gamma-rays and positron beams, therefore, composing a compact radiation source for various applications. Here, we use the Monte Carlo simulation code “Geant4” for studying the properties of those radiations. As expected, the characteristics of the generated gamma-rays and positron beams showed a strong dependence on the incident electron beam, target material, and thickness. The trend of positrons and gamma-rays energies and yield is shown for different high-Z to low-Z targets with the same areal mass density. Thicknesses of the target material in terms of its radiation length have been varied periodically in order to find the optimal thickness for obtaining the maximum energy and yield of the radiations. A trend can be seen in terms of energy spectra of the gamma-rays and positrons while increasing the thickness of the targets. The amount of radiation yields is also crucial to the choice of appropriate thickness of the target. In addition, this paper provides a brief description of the electrodynamics processes such as bremsstrahlung and electron–positron pair production initiated by LWFA electron beams.

Energy deposition of fast electrons in dense magnetized plasmas

Mechanisms of fast electron energy deposition in dense magnetized plasma are studied by hybrid particle-in-cell/fluid simulations. It is found that the energy deposition ratio of Ohmic heating and collisional heating can be enhanced significantly as an Al target is presented in a strongly axial magnetic field, attributed to the fast electrons rotating around the axial field. The weight of Ohmic heating is increased with laser intensity during ultraintense laser-driven fast electrons propagating both in magnetized and unmagnetized solid targets, which is the dominant heating mechanism as the laser intensity is greater than 1018 W/cm2 compared to the collisional heating. The degree of the axial magnetic field effect on the fast electron energy deposition mechanisms is dependent on target materials, which is much weaker for low-Z targets, such as CH2. The results here should be helpful for the target designing of fast electron applications.

Investigation of the use of external aluminium targets for portal imaging in a medical accelerator using Geant4 Monte Carlo simulation

To install a low-Z target on the wedge tray mount of a medical linear accelerator to create a new image beam and to confirm image contrast enhancement. Experimental low-energy photon beams were produced with the linac running in the 6 MeV electron mode and with a low-Z target installed on the wedge tray mount [denoted 6 MeV (low-Z target)]. Geant4 Monte Carlo simulation was performed to analyse the energy spectrum and image contrast of a 6 MeV (low-Z target) beam. This study modelled the 6 MeV (low-Z target) beam and the 6 MV (megavoltage) radiotherapy photon beam and verified model validity by measurement. In addition, a contrast phantom was modelled to quantitatively compare the image contrasts of the 6 MeV (low-Z target) beam and the 6 MV radiotherapy photon beam. A low-Z target was fabricated to generate low-energy photons (25-150 keV) from incident electrons, and a portal image of the Alderson RANDO phantom was acquired using a clinical linear accelerator for qualitative analysis. The measured and calculated percentage depth dose of the 6 MV photon and 6 MeV (Al) beams were consistent within 1.5 and 1.6%, respectively, and calculated lateral profiles of the 6 MV photon beam and the 6 MeV (Al) beam were consistent with the measured results within 1.5 and 1.9%, respectively. Although low-energy photons (25-150 keV) of the 6 MV photon beam were only 0.3%, the Be, C, and Al low-Z targets, but not the Ti target, generated 34.4 to 38.5% low-energy photons. In 5 to 20 cm water phantoms, contrast of the 6 MeV (Al) beam was approximately 1.16 times greater than that of the 6 MV beam. The contrasts of 6 MeV (Al) and 6 MV photon beams in the 20 cm water phantom were ~34% lower than those in the 5 cm water phantom. 6 MeV (Al)/CR (computed radiography) images of the human body phantom were more vivid and detailed than 6 MV/EPID (electronic portal imaging device) and 6 MeV (Al)/EPID images. The experimental beam with a low-Z target, which was simply installed on the wedge tray mount of the radiotherapy linear accelerator, generated significantly more low-energy photons than the 6 MV radiotherapy photon beam, and provided better quality portal images. Advances in knowledge: This study shows that, unlike the existing low-Z beam studies, a low-Z target can be installed outside the head of a linear accelerator to improve portal image quality.

Measuring the leading hadronic contribution to the muon g-2 via the -e elastic scattering.

The precision measurement of the anomalous magnetic moment g-2 of the muon presently exhibits a 3.5 σ deviation between theory and experiments. In the next few years the anomalous magnetic moment will be measured to higher precisions at Fermilab and J-PARC. The theoretical prediction can be improved by reducing the uncertainty on the leading hadronic correction HLO μ to the g-2. Here we present a novel approach to determine aHLO μ with space-like data, by means of precise measurement of the hadronic shift of the effective electromagnetic coupling α exploiting the elastic scattering of 150 GeV muons (currently available at CERN North area) on atomic electrons of a low-Z target. The direct measurement of aHLO μ in the space-like region will provide a new independent determination competitive with the time-like dispersive approach, and will consolidate the theoretical prediction of the muon g-2 in the Standard Model. It will allow therefore a firmer interpretation of the measurements of the future muon g-2 experiments at Fermilab and J-PARC

Comparison of Geant4 multiple Coulomb scattering models with theory for radiotherapy protons

Usually, Monte Carlo models are validated against experimental data. However, models of multiple Coulomb scattering (MCS) in the Gaussian approximation are exceptional in that we have theories which are probably more accurate than the experiments which have, so far, been done to test them. In problems directly sensitive to the distribution of angles leaving the target, the relevant theory is the Molière/Fano/Hanson variant of Molière theory (Gottschalk et al 1993 Nucl. Instrum. Methods Phys. Res. B 74 467–90). For transverse spreading of the beam in the target itself, the theory of Preston and Koehler (Gottschalk (2012 arXiv:1204.4470)) holds.Therefore, in this paper we compare Geant4 simulations, using the Urban and Wentzel models of MCS, with theory rather than experiment, revealing trends which would otherwise be obscured by experimental scatter. For medium-energy (radiotherapy) protons, and low-Z (water-like) target materials, Wentzel appears to be better than Urban in simulating the distribution of outgoing angles. For beam spreading in the target itself, the two models are essentially equal.

Applications of the pulsed gas stripper technique at the GSI UNILAC

In the frame of an upgrade program for the GSI UNILAC, preparing it for the use as an injector system for FAIR, a pulsed gas stripper cell was developed. It utilizes the required low duty cycle by applying a pulsed gas injection instead of a continuous gas inlet. The resulting lower gas consumption rate enables the use of low-Z gas targets over a wide range of stripper target thicknesses. The setup enables an increased flexibility for the accelerator by allowing the gas stripper to be used in time-sharing beam operation matching the capabilities of the GSI UNILAC like the acceleration of different ion beams in quasi-parallel operation. Measured charge state distributions of 238U, 50Ti, and CH3 beams on H2 and N2 gas highlight the benefits of the pulsed gas stripper cell for the accelerator operation and performance.

Measuring the leading hadronic contribution to the muon g-2 via mu e scattering

We propose a new experiment to measure the running of the electromagnetic coupling constant in the space-like region by scattering high-energy muons on atomic electrons of a low-Z target through the elastic process mu , e rightarrow mu , e. The differential cross section of this process, measured as a function of the squared momentum transfer t=q^2<0, provides direct sensitivity to the leading-order hadronic contribution to the muon anomaly a^mathrm{{HLO}}_{mu }. By using a muon beam of 150 GeV, with an average rate of sim 1.3 times 10^7 muon/s, currently available at the CERN North Area, a statistical uncertainty of sim 0.3% can be achieved on a^mathrm{{HLO}}_{mu } after two years of data taking. The direct measurement of a^mathrm{{HLO}}_{mu } via mu e scattering will provide an independent determination, competitive with the time-like dispersive approach, and consolidate the theoretical prediction for the muon g-2 in the Standard Model. It will allow therefore a firmer interpretation of the measurements of the future muon g-2 experiments at Fermilab and J-PARC.

Measuring the leading-order hadronic contribution to the muon g-2 in the space-like region

A new experiment is proposed to measure the running of the electromagnetic coupling constant in the space-like region by scattering high-energy muons on atomic electrons of a low-Z target. The differential cross section of the elastic process μe → μe provides direct sensitivity to the leading-order hadronic contribution to the muon anomaly aμ HLO . It is argued that by using the 150-GeV muon beam available at the CERN North Area, with an average rate of ~ 1.3 × 107 muon/s, a statistical uncertainty of ~ 0.3% can be achieved on aμ HLO after two years of data taking. The direct measurement of aμ HLO via μe scattering will provide an independent determination and consolidate the theoretical prediction for the muon g -2 in the Standard Model. It will allow therefore a firmer interpretation of the measurements of the future muon g -2 experiments at Fermilab and JPARC.