Heavy Projectiles Research Articles

Nanometric transformation of the matter by short and intense electronic excitation: Experimental data versus inelastic thermal spike model

Experimental investigations of ion tracks and sputtering phenomena with energetic heavy projectiles in the electronic energy loss regime are re-examined in metallic and insulating materials. An overview of track data such as the velocity dependence of the track size and the critical electronic energy loss for track formation is presented. Different physical characterizations of the material transformation are listed in order to deduce a track size which is independent of the observations. It will point out the differences of damage creation by electronic energy loss compared to nuclear energy loss. In the second part, we present a theoretical description of track formation based on the inelastic thermal spike model. This thermodynamic approach combines the initial size of the energy deposition with the subsequent diffusion process in the electronic and lattice subsystems of the target. The track size, resulting from the quench of a molten phase, is determined by the energy density deposited on the atoms around the ion path governed by the electron–phonon strength. Finally, we discuss the general validity of this model in metallic materials and its suitability to describe track formation in amorphizable and non-amorphizable insulators.

Introducing electron capture into the unitary-convolution-approximation energy-loss theory at low velocities

Recent developments in the theoretical treatment of electronic energy losses of bare and screened ions in gases are presented. Specifically, the unitary-convolution-approximation (UCA) stopping-power model has proven its strengths for the determination of nonequilibrium effects for light as well as heavy projectiles at intermediate to high projectile velocities. The focus of this contribution will be on the UCA and its extension to specific projectile energies far below 100 keV/u, by considering electron-capture contributions at charge-equilibrium conditions.

Relativistic Quantum Collision Theory for Many-particle Systems

Starting from the relativistic equation of motion governing quantum collision processes, we shall formulate the relativistic quantum collision theory in an ab-initio manner. Quantum electrodynamic effects are, however, incorporated perturbatively. Because heavy projectiles or ultra-high incident energies are considered, the recoil of the target is also treated. Electron-impact ionization of the uranium ion U and proton-impact ionization of hydrogen will be given as examples.

Simulation of GEM-TPC Prototype for the Super-FRS Beam Diagnostics System at FAIR

The Supercondacting Fragment Recoil Separator will be a key part of the experiments of the NuSTAR-collaboration. The beam of the separator will have heavy ion projectiles that are steered to experimental area. With the Time Projection Chambers with Gas Electron Multiplier amplification (GEM-TPC), diagnostics of the beam properties can be performed. The performance of the components of the design of a GEM-TPC prototype has been studied with Geant4 and Garfield simualtion tools.

Particle production in nucleus-nucleus collisions at the SPS and the QCD phase diagram

The ratios of particle multiplicities determined in central collisions of heavy nuclei fit well into the concept of statistical particle production. In fact, statistical model caculations using heavy ion data on particle multiplicities converge on an approximate universal line in the T-μB plane for the resulting values of temperature and baryochemical potential. We discuss whether variations of system size can lead to significant deviations from this universal interrelation. Previous analyses of data from C+C and Si+Si collisions have shown that small systems produce a higher chemical freeze-out temperature than central collisions of heavy projectiles, whereas the baryochemical potential seems to be independent of system size. These findings suggest that in small systems a departure from the universal freeze-out line towards higher temperatures is possible. Based on new data on the centrality dependence of proton and antiproton spectra from NA49, which await a dedicated statistical model analysis, we argue that in peripheral collisions both the freeze-out temperature and the baryochemical potential are lower than in central collisions, suggesting a departure from the universal freeze-out line towards the origin of the phase diagram.

SAMURAI Project at RIBF

SAMURAI project aims to open a new research field in nuclear physics by the use of a large acceptance spectrometer for kinematically complete measurements of multiple particles emitted in RI-beam induced reactions. The SAMURAI spectrometer consists of a large gap superconducting dipole magnet, heavy ion detectors, neutron detectors, and proton detectors. What is special about the SAMURAI system is that projectile-rapidity protons or neutrons are detected with large angular and momentum acceptance in coincidence with heavy projectile fragments. With an effective combination of these equipments, the SAMURAI system allows us to perform various experiments: electromagnetic dissociation, various direct reactions, polarized deuteron induced reactions, and EOS studies. SAMURAI project is currently underway at RIBF. The construction of the superconducting dipole magnet will start in autumn 2010 and finish in spring 2011. The detectors are also being constructed in parallel. The first commissioning run will be performed in early 2012.

Back Cover: Creation of colour centres in diamond by collimated ion‐implantation through nano‐channels in mica (Phys. Status Solidi A 9/2011)

The fabrication of scalable quantum devices in diamond relies on the ability to produce optical centres with a high spatial resolution. Ion implantation is the most powerful technique for placing impurity atoms in a diamond matrix. Pezzagna et al. (pp. 2017–2022) present a novel approach by implanting ions through a mask with high-aspect-ratio nano-channels and improve the collimation to below 50 nm. The mask contains parallel oriented channels of a few tens of nm in diameter. They are produced by exposing mica sheets to GeV heavy ion projectiles and subsequent track etching. The high-resolution creation of deep nitrogenvacancy centres in diamond by implanting nitrogen ions through the nano-channels is demonstrated.

Creation of colour centres in diamond by collimated ion‐implantation through nano‐channels in mica

AbstractThe fabrication of scalable quantum devices in diamond relies on the ability to produce optical centres with a high spatial resolution. Ion implantation is the most powerful technique for placing impurity atoms in a diamond matrix. Even though shallow optical centres can be produced with a resolution below 20 nm, deep centres may be preferred for generally better overall properties. However, the focusing of ion beams in the MeV range can hardly be achieved below 1 µm. We present here a novel approach by implanting ions through a mask with high‐aspect‐ratio nano‐channels and improve the collimation to below 50 nm. The mask contains parallel oriented channels of a few tens of nanometres in diameter. They are produced by exposing mica sheets to GeV heavy ion projectiles and subsequent track etching. We demonstrate the high‐resolution creation of deep nitrogen‐vacancy (NV) centres in diamond by implanting nitrogen ions through the nano‐channels. Transmission rates and energy distribution of the nitrogen ions transmitted through the nano‐channels were also analysed.

Au400 Sputtering of a Polymer with Adsorbed Metal Nanoparticles: A Molecular Dynamics Study

Using molecular dynamics simulations, this article investigates the interaction of 5―40 keV Au400 projectiles with polyethylene and with gold-adsorbed nanoparticles of ∼25 A in diameter. Impacts over the Au nanoparticles and on the polymer are compared in terms of sputtered quantities, projectile penetration, and energy deposition in the substrate, and connections with experiments are made. In the considered energy range, impacts over a nanoparticle emit 1 order of magnitude more organic material than impacts on the polymeric substrate. This is explained by the large range of the heavy Au400 projectile in the polymer and the increased stopping when it first encounters an adsorbed nanoparticle. As a result, we predict that organic material sputtering and analysis with Au400 should be favored by the presence of gold nanoparticles (metal-assisted secondary ion mass spectrometry). The simulations also indicate that the average depth of emission of organic material does not exceed 20 A, and it is much less for impacts on the nanoparticles. Finally, Au400 projectiles with >10 keV of energy are able to sputter entire nanoparticles via pressure wave development and collective molecular motions in the organic substrate.

Non-equilibrium processes in Heavy-ion induced Fission Reactions

Heavy ion induced reactions offer a wide range of possibilities in exploring the collective behavior of nuclei and nuclear processes. Recent years have seen a spurt in the experimental and theoretical studies to understand the mechanism of the fission process in heavy target projectile systems, arising from the interest to produce elements in the superheavy region. A number of new features are observed experimentally with respect to the kinetic energy, mass and angular distributions of fission fragments and their correlations, implying prevalence of non-equilibrium phenomena in the fission process in many target projectile systems. There are many theoretical attempts both in terms of static potential energy considerations and dynamics to understand the important degrees of freedom that govern the evolution of the nuclear system from initial interaction to the final fission stages. Depending on the degree and nature of equilibration, various processes such as fast-fission, quasi-fission and pre-equilibrium fission have been invoked that can compete with the fully equilibrated compound nuclear fission process. In what we call a C-T Fissility plot, we show the remarkable dependence of the onset of these non-equilibrium processes on the entrance channel parameters.

Convergent close-coupling approach to positron and antiproton collisions with atoms

Recent developments in application of the convergent close-coupling approach to antimatter-matter scattering are outlined. These include positron collisions with alkalis and helium, in the ground or metastable states, as well as extension of the method to heavy projectiles, such as antiprotons.

Evidence for quasifission in the sub-barrier reaction ofSi30+U238

Fragment mass distributions for fission after full momentum transfer were measured for the $^{30}\mathrm{Si}$$+$$^{238}\mathrm{U}$ reaction at bombarding energies around the Coulomb barrier. At energies above the Bass barrier, the mass distributions were Gaussian with mass symmetry. An asymmetric fission channel with mass ${A}_{\mathrm{L}}/{A}_{\mathrm{H}}$ $\ensuremath{\approx}$ $90/178$ emerged at the sub-barrier energies, where competition between fusion and quasifission was suggested from the evaporation residue (ER) cross section produced in the fusion $^{30}\mathrm{Si}$$+$$^{238}\mathrm{U}$. We thus conclude the asymmetric channel is attributed to quasifission. It was supported by a model calculation using the Langevin equation to give the fragment mass distribution, where fusion-fission and quasifission were separated. The observed mass asymmetry for quasifission as well as the calculation is significantly smaller than those observed in actinide targets bombarded with heavier projectiles, which suggests that the system $^{30}\mathrm{Si}$$+$$^{238}\mathrm{U}$ approaches the shape of the compound nucleus before disintegrating as quasifission.

Characteristics of alpha projectile fragments emission in interaction of nuclei with emulsion

The properties of the relativistic alpha fragments produced in interactions of 84^Kr at around 1 A GeV in nuclear emulsion are investigated. The experimental results are compared with the similar results obtained from various projectiles with emulsion interactions at different energies. The total, partial nuclear cross-sections and production rates of alpha fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass number and initial energy of the incident projectile nucleus are investigated. The yields of multiple alpha fragments emitted from the interactions of projectile nuclei with the nuclei of light, medium and heavy target groups of emulsion-detector are discussed and they indicate that the projectile-breakup mechanism seems to be free from the target mass number. It is found that the multiplicity distributions of alpha fragments are well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The mean multiplicities of the freshly produced newly created charged secondary particles, normally known as shower and secondary particles associated with target in the events where the emission of alpha fragments were accompanied by heavy projectile fragments having Z value larger than 4 seem to be constant as the alpha fragments multiplicity increases, and exhibit a behavior independent of the alpha fragments multiplicity.

Neutron dosimetry in the particle accelerator environment

Radiological safety aspects in general and neutron dosimetry in particular, around medium and high-energy particle accelerators pose some unique challenges to the practitioners of radiation protection. This is mainly because the source of radiations are directional, dynamic, pulsed and a mixture of different types. In conventional dosimetry, measurements are done in the units of the quantities in which the radiological protection limits are expressed. In the accelerator environment, measurement of energy and angular distribution of radiations is preferred instead. Research activities being carried out (particularly in India) in the field of neutron dosimetry are discussed. Measurements of neutron ambient dose equivalent directly using conventional rem-meters as well as neutron energy distributions using the time-of-flight technique employing proton recoil scintillators have been done at different directions with respect to light and heavy ion projectiles incident on various thick elemental targets. The observations and conclusions are summarized. Finally, a discussion on the concept of dose and radiological protection and operational quantities is done along with the recommendation of using Evidence theory instead of Bayesian probability in assessing radiological risk.

Electron capture in intermediate-to-fast heavy ion collisions with neutral atoms

Electron capture processes of heavy ions, like Ge q +, Xe q +, Pb q +, and U q +, respectively, with the charge q ≈ 10–40, occurring in collisions with gaseous targets are considered in the E = 0.1–100 MeV/u projectile energy range. Calculations of single-electron capture cross sections are performed using the CDW and the CAPTURE computer codes. These are compared with available experimental data and CTMC (Classical-Trajectory Monte Carlo) calculations. Although the overall agreement is found to be within a factor of two, in some cases of heavy many-electron projectiles, e.g., U 28+ + N 2, Ar collisions, experimental cross sections at high energies are far smaller than theoretical predictions. Moreover, for these collision systems the observed energy dependencies are quite different from each other. Possible reasons for this behavior and how the theoretical models can be improved are discussed.

Transient processes induced by heavy projectiles in silicon

Abstract The thermal spike model developed for the electronic stopping power regime is extended to consider both ionization and nuclear energy loss processes of the projectile as electronic and atomic heat distinct sources. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated and discussed for different ions in silicon, at room and cryogenic temperatures, taking into account the peculiarities of electron–phonon interaction in both domains. The model developed contributes to the understanding of transient microscopic processes immediately after the projectile interaction in the target.

Coincidence studies with antiprotons

We present a short overview of a new method for calculating fully differential cross sections that is able to describe any aspect of coincidence measurements involving heavy projectiles. The method is based upon impact parameter close coupling with pseudostates. Examples from antiproton impact ionization are shown.

Breakup of positronium in a collision with aLi+ion

Fragmentation of ground state ortho Positronium (Ps) in collision with Li ion (Li+) is studied in the framework of post collisional Coulomb distorted eikonal approximation (CDEA) for the target elastic case . The present model takes account of the two center effect on the ejected e which is crucial for a proper description of the projectile ionization involving an ionic target. Both the fully differential (TDCS) and the doubly differential (DDCS) cross sections (energy spectra) are investigated at intermediate and high incident energies. A broad distinct Electron loss peak (ELP) centered around v_e ~ v_p is noted in the e energy spectrum in contrast to the sharp ELP for a heavy projectile. Two salient features are noted in the present study: i) the shift of the e DDCS peak (summed over e+ angles) towards higher ejection energy with respect to half the residual energy of the system, ii) comparison of the e& e+ energy spectra reflect a strong e - e+ asymmetry with respect to the ratio v_e/v_p =1 >. Both these features could be attributed to the post collisional two center effect on the e due to its parent nucleus (e+) and the screened target ion . Two different wave functions of the Li ion are chosen in order to test the sensitivity of the present results with respect to the choice of the wave function.

Reliability of stopping power tables and codes for heavy ions (8 ≤ Z ≤ 92) in gases

A comparative study of various stopping power tables and codes for heavy ions in gases has been made through comparison of computed values and the corresponding experimental data. Ten gaseous media: five monatomic rare gases (He to Xe), two diatomic gases (H2, N2) and three polyatomic gaseous compounds (CH4, CF4 and CO2) have been chosen to study the stopping power investigations of heavy ions (8 ≤ Z ≤ 92) having energy ranges of ∼0.10–10.00 MeV/n and ∼20.00–57.00 MeV/n. We compare the experimental data of stopping power to values calculated using various tables and computer codes by ICRU-73, Ziegler et al (SRIM2003.26), Grande and Schiwietz (CasP3.1), Paul and Schinner (MSTAR3.12), and Bazin and Tarasov (LISE ++:2-ATIMA1.2). On the basis of statistical analysis, we estimate the reliability of these tables and codes. It has been observed that the MSTAR3.12 code shows the best agreement with the experimental data for projectile ions (8 ≤ Z ≤ 18) in the entire energy range. The SRIM2003.26 code provides good results except for some heavy projectiles (Xe, Pb and U). The values tabulated by CasP3.1 code underestimate especially at low energy region. No significant trend is observed in case of LISE++:2-ATIMA1.2 code and ICRU-73 report.

Electron loss of fast heavy projectiles in collision with neutral targets

The multiple electron loss of heavy projectiles in fast ion-atom collisions has been studied in the framework of the sudden perturbation approximation. Especially, a model is developed to calculate the cross sections for the loss of any number of electrons from the projectile ion, including the ionization of a single electron and up to the complete stripping of the projectile. For a given collision system, that is specified by the (type and charge state of the) projectile and target as well as the collision energy, in fact, the experimental cross sections for just three final states of the projectile are required by this model in order to predict the loss of any number, $N$, of electrons for the same collision system, or for any similar system that differs only in the energy or the initial charge state of the projectile ion. The model is simple and can be utilized for both, the projectile and target ionization, and without that large computer resources are requested. Detailed computation have been carried out for the multiple electron loss of Xe$^{18+}$ and U$^{6+,\, 10+,\, 28+}$ projectiles in collision with neutral Ar and Ne gas targets.