Heavy Targets Research Articles

Impact ionization of highly charged ion-atom collisions considering strong magnetic field and plasma screening effect

The impact ionization process of target is a crucial issue in the study of Heavy Ion Beam (HIB)-driven Magnetized Inertial Fusion (MIF). The collision systems between heavy projectile ions (Xeq+, Biq+, Uq+) and light target atoms/ions (H, D, T, 3He, 3He+, 11B) are promising candidate reactions for fusion power. In this study, the impact ionization process in medium-energy (ranges 1–100 MeV/u) is studied numerically based on the extended Classical-trajectory Monte Carlo (CTMC) method, where the effects of projectile charge state, external magnetic field and plasma screening on the single ionization process are considered. The results show that the existed external magnetic field results in a decrease of the yield of ionized high-energy electrons, whereas the yield of backward emitted electrons is increased. The effect of plasma screening on the ionization process is shown to be determined by the competition between the screening charge of projectile ion and the target nucleus. Thus, a significant decrease of ionization cross section is found in the low energy region since the screening charge of projectile ion is dominant. However, the screening effect of target nucleus charge is dominant in high energy region, where a significant increase of ionization cross sections is found.

A reconsideration of photoneutron production through a 5 MeV electron LINAC using MCNP and FLUKA

In the present study, photoneutron production using a 5 MeV electron linear accelerator (LINAC) was investigated based on new photoneutron cross-sections (IAEA/PD-2019.2) from the International Atomic Energy Agency (IAEA). A detailed reconsideration of a past study has been done in order to make a photoneutron source based on a heavy water target. In this regard, new cross-sections of deuterium and beryllium were added to the library of the MCNP6.1 Monte Carlo code for the simulation of photoneutron production. In addition, the FLUKA4-3.0 Monte Carlo code was employed for comparison and data validation. Moreover, the obtained results from those two codes (MCNP and FLUKA) were compared and discussed with the theory and the previous study. Finally, it is concluded that the simulation of photoneutron production through an electron LINAC can have relatively different results based on the photoneutron cross-sections and even on the Monte Carlo code used. Therefore, a special attention should be paid to the difference between photoneutron cross-sections as well as the difference in Monte Carlo codes to maintain reliability.

Fusion reactions in collisions of neutron halo nuclei with heavy targets

Fusion reactions in collisions of neutron halo nuclei with heavy targets

Testing the ϕ-nuclear potential in pion-induced ϕ meson production on nuclei near threshold

The near-threshold pion-induced ϕ production off nuclei has been studied in the kinematical conditions of the HADES experiment using a collision model based on the nuclear spectral function. Starting from the elementary reaction π−p→ϕn, absolute differential and integral cross sections for the production of ϕ mesons off a light carbon and a heavy tungsten target have been calculated and compared to the recently reported experimental cross sections. The absolute cross section values are shown to be sensitive to the effective nuclear scalar ϕ and neutron potentials while the transparency ratio is governed by the ϕN absorption cross section. The experimental data are found to be consistent with an attractive ϕ-nucleus potential of ≈ -(50–100) MeV at normal nuclear matter density ρ0 and an effective ϕN absorption cross section of ≈ 12–25 mb. The extracted ϕ-nucleus potential is deeper than previous theoretical and experimental findings as well as those obtained in the present work within the (tρ) approximation with accounting for Pauli correlations from the spin-averaged ϕ-p scattering length reported in a recent ALICE experiment.

Analysis of elastic scattering angular distributions and fusion excitation functions of reactions induced by 9Be on 27Al, 28Si, 144Sm and 208Pb targets at near barrier energies

The elastic scattering angular distributions and the fusion excitation function data for the reactions induced by the loosely bound projectile 9Be on [Formula: see text]Al, [Formula: see text]Si, [Formula: see text]Sm and [Formula: see text]Pb targets at near and above barrier energies have been analyzed with a motive to investigate the importance of breakup couplings within the framework of continuum discretized coupled channels approach. It is found that at energies much higher than Coulomb barrier, the breakup effects are insignificant for light targets while for heavy targets, the breakup effects play a dominant role at these energies. But at energies comparable to the barrier height, the role of breakup becomes crucial for light mass targets also.

Neutrino physics and dark matter search with SHiP at CERN

SHiP (Search for Hidden Particles) is a new general purpose fixed target facility, proposed at the CERN SPS accelerator. In its initial phase the 400 GeV protons beam will be dumped on a heavy target with the aim of integrating [Formula: see text] pot in five years. A dedicated detector downstream the target will allow to probe a variety of models with the light long-lived exotic particles and masses below O(10) GeV/c2. The beam dump is also a copious source of neutrinos and in particular it is an ideal source of tau neutrinos, the less known particle in the Standard Model. We report the physics potential of such an experiment. We also describe an ancillary measurement of the charm cross-section carried out in July 2018.

Searching for an Enhanced Signal of the Onset of Color Transparency in Baryons with D(e,e′p)n Scattering

Observation of the onset of color transparency in baryons would provide a new means of studying the nuclear strong force and would be the first clear evidence of baryons transforming into a color-neutral point-like size in the nucleus as predicted by quantum chromodynamics. Recent C(e,e′p) results from electron-scattering did not observe the onset of color transparency (CT) in protons up to spacelike four-momentum transfers squared, Q2=14.2 GeV2. The traditional methods of searching for CT in (e,e′p) scattering use heavy targets favoring kinematics with already initially reduced final state interactions (FSIs) such that any CT effect that further reduces FSIs will be small. The reasoning behind this choice is the difficulty in accounting for all FSIs. D(e,e′p)n, on the other hand, has well-understood FSI contributions from double scattering with a known dependence on the kinematics and can show an increased sensitivity to hadrons in point-like configurations. Double scattering is the square of the re-scattering amplitude in which the knocked-out nucleon interacts with the spectator nucleon, a process that is suppressed in the presence of point-like configurations and is particularly well-studied for the deuteron. This suppression yields a quadratic sensitivity to CT effects and is strongly dependent on the choice of kinematics. Here, we describe a possible Jefferson National Accelerator Facility (JLab) electron-scattering experiment that utilizes these kinematics and explores the potential signal for the onset of CT with enhanced sensitivity as compared to recent experiments.

Uncertainties in neutrino oscillation parameter sensitivity due to resonance processes at NOνA

The long baseline (LBL) neutrino experiments use heavy nuclear targets for neutrino scattering in which nuclear effects give rise to complications in measuring the neutrino oscillation parameters up to high precision. These nuclear effects are not yet fully understood and therefore need to be quantified as they contribute to the systematic uncertainties. Precision reconstruction of neutrino energy is one of the main components in measuring the oscillation parameters, and it is required that the neutrino energy is reconstructed with very high precision. In this work, we investigate the effects of the resonance (RES) interaction process using two models for carbon target for [Formula: see text] disappearance channel of the NO[Formula: see text]A experiment, on neutrino-nucleus scattering cross-section, events, and neutrino oscillation parameter sensitivity. We also incorporate the realistic detector specifications of NO[Formula: see text]A. To quantify the systematic uncertainties due to RES interactions, we compare the cross-sections, events, and sensitivity analysis for two models of RES processes—Rein–Sehgal (RS) and Berger–Sehgal (BS), and comment on which model produces more precision. We observe that RES processes contribute significantly, and should be included carefully in models while extracting neutrino oscillation parameters.

Isotopic production cross sections in proton-16O and proton-12C interactions for energies from 10 MeV/u to 100 GeV/u

Proton interactions with16O or 12C nuclei are frequent nuclear interaction leading to secondary radiation in tissues for space radiationandcancer therapy with protons or ion beams. The fragmentation of these ionsby protons produces a large number of heavy ion (A > 4) target or projectile fragments often with high ionization density. Here we develop an analytical model of energy dependent proton-16O and proton-12C cross sections for isotopic nuclei production. Using experimental data and a 2nd order optical modelan accurate formula for the absorption cross section from <10 MeV/u to >10 GeV/u is obtained. The energy dependence of theelemental and isotopiccross sections is modeled as multiplicities scaled toabsorption cross section with average isotopic fractions estimated from experimental data. We show that this approach results in accurateanalytic formulae for isotopic fragmentation cross sections over the full energy range in hadron therapy and space radiation protection studies.

Global approach for the reactions Be7+Si28 and Be7+Pb208 at near- and sub-barrier energies

Elastic scattering, total reaction, and fusion cross section measurements for the radioactive $^{7}\mathrm{Be}$ nucleus on a light and a heavy target, are treated in a global approach at near and sub-barrier energies for probing the optical potential and describing fusion at low energies. Elastic scattering data of $^{7}\mathrm{Li}$ on the same target were analyzed under the same context to support this analysis. It is found that for low mass targets, dispersion relations are not adequate for describing the potential or the fusion. On the contrary this is possible for heavy targets, where the standard potential threshold anomaly and fusion enhancement is observed. The consequences of the above on fusion hindrance at deep sub-barrier energies is discussed.

Be10 -nucleus optical potentials developed from chiral effective field theory NN interactions

We present a determination of optical potentials for $^{10}\mathrm{Be}$-nucleus collisions using the double-folding method to compute the real part and Kramers-Kronig dispersion relations to derive the imaginary part. As microscopic inputs we use chiral effective field theory nucleon-nucleon interactions at next-to-next-to-leading order combined with state-of-the-art nucleonic densities. With these potentials, we compute elastic-scattering cross sections for the exotic nucleus $^{10}\mathrm{Be}$ off various targets, and compare them to experiment. Without any fitting parameter, we obtain good agreement with data. For collisions on light targets, we observe significant uncertainty related to the short-range physics, whereas for heavy targets that uncertainty remains small.

Cascade Models in Simulation of Extended Heavy Targets Irradiated by Accelerated Proton and Deuteron Beams

The paper presents a survey of the main numerical models used for simulation of interaction of accelerated particle beams with target nuclei. These models form the core of the software for simulation of various experiments and experimental facilities both for scientific and applied purposes. The beam and target parameters considered in detail in this study (protons and deuterons with energies from 0.66 to 4 AGeV and bulk U targets) cover the range of interest in development of new concepts of nuclear power production aided by accelerated particle beams.

Production of neutron-rich heavy nuclei around $$N = 162$$ in multinucleon transfer reactions

Within the framework of the dinuclear system model, the production mechanism of neutron-rich heavy nuclei around \(N = 162\) has been investigated systematically. The isotopic yields in the multinucleon transfer reaction of \(^{238}\)U + \(^{248}\)Cm are analyzed and compared with the available experimental data at GSI. Systematics on the production of superheavy nuclei via the collisions of \(^{238}\)U on actinide nuclides \(^{252,254}\)Cf, \(^{254}\)Es and \(^{257}\)Fm is investigated thoroughly. It is found that the shell effect is of importance in the formation of neutron-rich nuclei around \(N~=~162\) owing to the enhancement of fission barrier and neutron separation energy. The fragments in the multinucleon transfer reactions manifest the broad isotopic distribution and are dependent on the beam energy. The polar angles of the fragments tend to the forward emission with increasing the beam energy. The production cross sections of new isotopes are estimated and the heavier targets are available for the neutron-rich superheavy nucleus formation. The optimal reaction system and beam energy are proposed for the future experimental measurements.

DNA damage by radiation as a function of electron energy and interaction at the atomic level with Monte Carlo simulation

In radiotherapy, X-ray or heavy ion beams target tumors to cause damage to their cell DNA. This damage is mainly induced by secondary low energy electrons. In this paper, we report the DNA molecular breaks at the atomic level as a function of electron energy and types of electron interactions using of Monte Carlo simulation. The number of DNA single and double strand breaks are compared to those from experimental results based on electron energies. In recent years, DNA atomistic models were introduced but still the simulations consider energy deposition in volumes of DNA or water equivalent material. We simulated a model of atomistic B-DNA in vacuum, forming 1122 base pairs of 30 nm in length. Each atom has been represented by a sphere whose radius equals the radius of van der Waals. We repeatedly simulated 10 million electrons for each energy from 4 eV to 500 eV and counted each interaction type with its position x, y, z in the volume of DNA. Based on the number and types of interactions at the atomic level, the number of DNA single and double strand breaks were calculated. We found that the dissociative electron attachment has the dominant effect on DNA strand breaks at energies below 10 eV compared to excitation and ionization. In addition, it is straightforward with our simulation to discriminate the strand and base breaks as a function of radiation interaction type and energy. In conclusion, the knowledge of DNA damage at the atomic level helps design direct internal therapeutic agents of cancer treatment.

Electron and Positron Scattering from Precious Metal Atoms in the eV to MeV Energy Range

This article reports on the scattering of unpolarized and spin polarized electrons and positrons from 28Ni58,29Cu63,46Pd108, and 78Pt196, covering light to heavy precious metal targets. To cover the wide energy domain of 1 eV ≤Ei≤300 MeV, Dirac partial-wave phase-shift analysis is employed, using a complex optical potential for Ei≤1 MeV and a potential derived from the nuclear charge distribution for Ei&gt;1 MeV. Results are presented for the differential and integral cross-sections, including elastic, momentum transfer, and viscosity cross-sections. In addition, the inelastic, ionization, and total (elastic + inelastic) cross-section results are provided, together with mean free path estimates. Moreover, the polarization correlations S,T, and U, which are sensitive to phase-dependent interference effects, are considered. Scaling laws with respect to collision energy, scattering angle, and nuclear charge number at ultrahigh energies are derived using the equivalence between elastic scattering and tip bremsstrahlung emission. In addition, a systematic analysis of the critical minima in the differential cross-section and the corresponding total polarization points in the Sherman function S is carried out. A comparison with existing experimental data and other theoretical findings is made in order to test the merit of the present approach in explaining details of the measurements.

Stopping-power calculations and the Levine-Mermin dielectric function for inner shells

The contribution of bound electrons to the electronic stopping power is modeled by using the shellwise local plasma approximation (SLPA). An improvement to this formalism is proposed by including the Levine-Mermin dielectric function (SLPA-LM). This approach considers a more realistic description of the bound electron response by facing the problem of the damping in the collective excitations. We introduce a local damping that depends on the density of electrons of each shell, keeping the full-theoretical characteristic of the SLPA. We implement the present model to obtain the stopping power for metal targets of period-6 elements of the periodic table (Hf, Ta, W, Os, and Pt) and we analyze the importance of the SLPA-LM description of heavy multielectronic targets. Furthermore, we investigated metal targets of group VI of the periodic table (Cr, Mo, and W) to inspect the dependence of the SLPA-LM with the number of subshells.

Fusion processes in collisions of Li6 beams on heavy targets

We discuss a recently introduced model to evaluate complete and incomplete fusion in collisions of weakly bound nuclei. We propose a modification of the imaginary potential to deal with cross sections at energies well below the Coulomb barrier, and discuss the relation between the cross sections provided by a continuum discretized coupled-channel calculation and the ones measured in actual experiments. The new version of the model is used to make predictions of fusion cross sections in collisions of $^{6}\mathrm{Li}$ with a few heavy targets, and the results are compared to the available data. The overall agreement between theory and experiment is quite good.

Fusion cross section of α -induced reactions for heavy target nuclei

The fusion reactions induced by $^{4}\mathrm{He}$ projectiles on heavy target nuclei provide the reference to study the reaction dynamics of exotic halo nuclei. The present analysis aims to probe the effects of different nuclear density distributions and the effective nucleon-nucleon ($NN$) interaction potentials on the fusion cross section of $^{4}\mathrm{He}$-induced reactions for heavy target nuclei. The nuclear densities for the heavy nuclei are obtained within the well-known Skyrme-Hartree-Fock model and the relativistic mean-field (RMF) approach for the $\mathrm{NL}{3}^{*}$ parameter set. These densities are integrated with the density-dependent M3Y and the relativistic R3Y nucleon-nucleon ($NN$) potentials to obtain the nuclear interaction potential. The fusion cross section and the astrophysical $S$ factor are obtained for $^{4}\mathrm{He}+^{208}\mathrm{Pb}, ^{4}\mathrm{He}+^{209}\mathrm{Bi}, ^{4}\mathrm{He}+^{235}\mathrm{U}$, and $^{4}\mathrm{He}+^{238}\mathrm{U}$ systems within the $\ensuremath{\ell}$-summed Wong model. The relativistic R3Y $NN$ potential folded with RMF densities are observed to give a better fit to the available experimental data. Furthermore, a comparison is made for the results obtained using Hill-Wheeler and Wentzel-Kramers-Brillouin transmission coefficients for $^{4}\mathrm{He}+^{208}\mathrm{Pb}$ system. We found a reasonable fit in the cross section at around the Coulomb-barrier energies for both the approximations and also similar predictions can be drawn for all considered systems.

Break-up effect of the weakly bound 6Li nuclei scattered by 208Pb target

Using different potentials based on phenomenological, semi microscopic, and microscopic models, we investigated the reaction dynamics induced by the weakly bound 6Li ions on a heavy mass target 208Pb at sixteen energy sets ranging from 25 MeV to 210 MeV. The 6Li cluster nature and its dissociation into a core (α-particle) and a valence particle (deuteron) orbiting this core was taken into consideration using the cluster folding model (CFM). The new version of Sao Paulo potential (SPP2) is also used to investigate 6Li+208Pb data. In order to reproduce the experimental data, the strength of real part of potential created using SPP and CFM should be reduced by ~ 49 % and 62 %, respectively. The data could be well reproduced using non-renormalized real cluster folding potential, if an additional dynamical polarization potential (DPP) of repulsive real surface form is introduced. The observed reduction in the strength of the real double folded and cluster folding potentials is due to the break-up effect of 6Li.

Systematical Analysis on angular Distribution of Bremsstrahlung radiation in microtron MT-22

The systematic analysis has been made the measurement results of the relative angular distribution of gamma quantium with 11-22 MeV energy which is induced by bremsstrahlung within 2-3 g/cm optimal geometrical region of target nucleus. We are shown that relative intensity distribution of gamma radiation with energy 11-22 MeV, induced by stopped electrons with various thicknesses at heavy and lighter target nucleus as an exponential form within angular region 0°-14o