Electron Capture Cross Sections Research Articles

Effect of nuclear deformation on electron capture cross-section on chromium isotopes

The electron capture plays significant role in the presupernova and supernova evolutions of massive stars which in turn are of great importance in synthesizing heavy elements beyond iron. In this paper, we study the effect of nuclear deformation on the computed electron capture cross-section on selected even–even chromium isotopes ([Formula: see text]Cr). The nuclear deformation parameters were computed using two different theoretical models: Interacting Boson Model (IBM-1) and Macroscopic (Yukawa-plus-exponential)–microscopic (Folded–Yukawa) model (Mac–mic model). A third value of deformation parameter was adopted from experimental data. We chose the pn-QRPA model to perform our calculations. The predictive power of the chosen model was first tested by calculating Gamow–Teller (GT) strength distributions of selected [Formula: see text]-shell nuclei where measured GT data was available. The calculated GT strength distributions were well-fragmented over the energy range 0–12[Formula: see text]MeV and were noted to be in decent agreement with experimental data. The total GT strength was found to increase (decrease) with decrease (increase) in the value of deformation parameter for the three chromium isotopes. The computed GT strength distributions satisfied the model-independent Ikeda sum rule. The ECC were calculated as a function of the deformation parameter at core temperature 1.0[Formula: see text]MeV. Our results show that the calculated ECC increased with increasing value of nuclear deformation.

Solar wind charge exchange in cometary atmospheres

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary. Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas. Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions. Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

Vibrational Autodetachment from Anionic Nitroalkane Chains: From Molecular Signatures to Thermionic Emission.

We report the kinetic energy distributions in electron autodetachment from nitroethane, 1-nitropropane, and 1-nitrobutane anions upon laser excitation of CH stretching modes measured using velocity map electron imaging. In striking contrast to the case of nitromethane, the kinetic energy distributions show almost no distinct vibrational features, and they can be described by thermionic emission, relating the shape of the distributions to the electron capture cross section of the neutral molecule. The data suggest that a classical description is warranted above ca. 20 meV electron kinetic energy. At lower energies, quantum effects suppress the attachment cross section.

Excitation, ionization, neutralization and anionic production in collisions of C+, N+ and CnN+ (n = 1–3) with He atoms at 2.2 a.u. velocity; cross sections and dissociation branching ratios

We present measurements of absolute cross sections for projectile ionization and electron capture for C+, N+ and CnN+ (n = 1–3) projectiles impinging on He atoms with velocity v = 2.2 a.u. Single and multiple electron processes are considered, as well as projectile dissociative excitation in the case of incident molecular cations. The measurements are compared to Classical Trajectory Monte Carlo (CTMC) calculations for C+, N+ + He collisions in the framework of the independent electron approximation. CnN+ + He systems are described by means of the independent atom and electron (IAE) model which represents the molecule as a set of independent atoms. The impact parameter probabilities for excitation, ionization and electron transfer in C, C+, N–He collisions, underlying the IAE calculations, are also obtained by means of CTMC computations. A good agreement is generally found between measured and calculated cross sections, except for anionic production of C− and CnN−. The internal energy deposit due to electron excitation in CnN+ is also calculated with the IAE/CTMC model and compared to semi-empirical estimates based on either measured dissociation branching ratios for C2N+ and C3N+ (IdBarkach et al 2018 Mol. Astrophys. 12 25) or measured fragments kinetic energy release for CN+. Finally, measured dissociation branching ratios of excited CnN− and CnNQ+ species, with 1 ≤ n ≤3 and 0 ≤ Q ≤ 4, are reported.

Ionization and electron capture for H+ collisions at low keV energy with a water-vapor target

We have investigated the total relative ionization and dissociative electron capture cross section for proton collisions with water-vapor molecules within the energy range of 2.5–10 keV. Time of flight mass spectroscopy was employed in the measurements of the atomic and molecular singly charged particles H+, H2+, O+, OH+ and H2O+ as well as the doubly charged particles O++, H2O++, OH++, and the contribution of the different channels was evaluated. Ionization was found to be the dominant reaction channel as expected. The contribution of the singly charged particles was found to be one order of magnitude higher than that of the doubly charged particles.

Dynamics of Charge States of Relativistic Gold Ion Beams Passing through Cu and Au Foils in the NICA Project

In order to study the properties of dense baryonic matter, an accelerator complex is under development at the Joint Institute for Nuclear Research (Dubna, Russia) within the new NICA project. The NICA project assumes the use of accelerated ion beams ranging from protons to gold ions with relativistic energies up to 4.5 GeV/nucleon. To design experiments, it is necessary to have information on the efficiency of the yield of bare gold nuclei formed at the passage of a gold ion beam with energies of about several hundreds of MeV per nucleon through a foil of a specialized stripping station at the output of the booster of the accelerator. In this work, the optimal conditions (material and thickness of the foil and the energy of the ion) for the formation of fractions of bare gold nuclei with a probability of 80–90% have been determined by calculating electron loss and capture cross sections, as well as the dynamics of charge states of gold ions colliding with copper and gold foils at energies of 400 and 600 MeV/nucleon,

Electron capture, excitation and ionization in H+–Be+ collisions

State-selective single electron capture, excitation and ionization processes in proton collisions with Be+(1s22s) and Be+(1s22p) ions are studied by using the quantum-mechanical molecular orbital (QMOCC) and the two-center atomic orbital close-coupling (TC-AOCC) methods in the combined energy range 0.01–300 keV/u. In the QMOCC calculations six 2Σ+ and three 2Π states are included in the expansion basis. The TC-AOCC expansion basis includes 35 discrete states centered on the proton and 182 states on Be2+ out of which 88 are continuum pseudostates. The atomic states on Be2+ are generated by a one-electron model potential for the electron interaction with Be2+ ion core that reproduces the exact energies with accuracy better than 0.5%. Total and state-selective electron capture and excitation cross sections to final states with n ≤ 4 are presented. The sum of the cross sections for the transitions to continuum pseudostates (ionization cross section) is also reported for both initial target states. The physical mechanisms involved in the dynamics of considered processes are discussed in detail at both low and high energies. The reported cross sections should be useful in the kinetic modeling and diagnostics of edge plasmas in present magnetic fusion experiments, as well as in the current ITER design, in which beryllium is used as first wall material.

Thermal quasiparticle random-phase approximation calculations of stellar electron capture rates with the Skyrme effective interaction

A microscopic thermodynamically consistent approach is applied to compute electron capture (EC) rates and cross sections on nuclei in hot stellar environments. The cross section calculations are based on the Donnelly-Walecka multipole expansion method for treatment of semi-leptonic processes in nuclei. To take into account thermal effects, we express the electron capture cross section in terms of temperature- and momentum-dependent spectral functions for respective multipole charge-changing operators. The spectral functions are computed by employing the self-consistent thermal quasiparticle RPA (TQRPA) with the Skyrme effective interaction. Three different Skyrme parametrizations (SkM$^*$, SGII and SLy4) are used to investigate thermal effects on EC for $^{56}$Fe and $^{78}$Ni. For $^{56}$Fe, the impact of thermally unblocked GT$_+$ transitions on EC is discussed and the results are compared with those from shell-model calculations. In particular, it is shown that for some temperature and density regimes the TQRPA rates exceed the shell-model rates due to violation of the Brink-Axel hypothesis within the TQRPA. For neutron-rich $^{78}$Ni the full momentum-dependence of multipole transition operators is considered and it is found that not only thermally unblocked allowed $1^+$ transitions but also thermally unblocked first-forbidden $1^-$ and $2^-$ transitions favour EC.

The Study of Deep Level Traps and Their Influence on Current Characteristics of InP/InGaAs Heterostructures

The damage mechanism of proton irradiation in InP/InGaAs heterostructures was studied. The deep level traps were investigated in detail by deep level transient spectroscopy (DLTS), capacitance–voltage (C–V) measurements and SRIM (the stopping and range of ions in matter, Monte Carlo code) simulation for non-irradiated and 3 MeV proton-irradiated samples at a fluence of 5 × 1012 p/cm2. Compared with non-irradiated samples, a new electron trap at EC-0.37 eV was measured by DLTS in post-irradiated samples and was found to be closer to the center of the forbidden band. The trap concentration in bulk, the interface trap charge density and the electron capture cross-section were 4 × 1015 cm−3, 1.8 × 1012 cm−2, and 9.61 × 10−15 cm2, respectively. The deep level trap, acting as a recombination center, resulted in a large recombination current at a lower forward bias and made the forward current increase in InP/InGaAs heterostructures for post-irradiated samples. When the deep level trap parameters were added into the technology computer-aided design (TCAD) simulation tool, the simulation results matched the current–voltage measurements data well, which verifies the validity of the damage mechanism of proton irradiation.

Collision dynamics of proton to water dimer at 250 eV

Applying a real-space, real-time implementation of time-dependent density functional theory coupled to molecular dynamics (TDDFT-MD) non-adiabatically, we study the ionization and fragmentation of water dimer in collision with a proton at 250 eV. Four different incident orientations with various impact parameters are employed to account for orientation effects. The reaction channels, electronic density evolution, scattering pattern and energy loss of proton are obtained. We find that proton is scattered away for all impact parameters and the head-on collision effects the energy loss of proton dominantly as well as the scattering angle. The locations of peaks of the scattering angles are similar to those corresponding to the energy loss. The single-electron capture, the double-electron capture as well as the total electron capture cross-sections are obtained. We find that the single-electron capture cross-section contributes most to the total electron capture cross-section and the calculated total electron capture cross-section is in reasonable agreement with experimental and other theoretical results with respect to water gas and liquid water.

Electron capture and excitation in H+ − Li+ collisions

The processes of state-selective electron capture and excitation in proton collisions with Li+(1s2 1S) and Li+(1s2s 1,3S) ions are studied by using the two-center atomic orbital close-coupling (TC-AOCC) methods in the energy range 2.5–800 keV. The interaction of the active electron with the Li2+ ion core is represented by model potentials that reproduce the energies of excited singlet and triplet states of Li+ with accuracy better than 2%. The expansion basis in the coupled state calculations includes all states with n ≤ 8 (in total 120 states) centered on each of the colliding centers. Total and state-selective electron capture and excitation cross sections to final states with n ≤ 4 are presented. The physical mechanisms involved in the dynamics of considered processes are discussed in detail. The reported cross sections should be useful in the kinetic modeling and diagnostics of fusion reactor plasmas with liquid lithium divertors.

Electron capture, excitation and ionization in He2+–H and H+–He+ collisions

The wave-packet convergent close-coupling method has been applied to model electron capture, excitation and ionization processes in He2+–H and H+–He+ collisions. These processes constitute all possible reactions taking place in a three-body system of an α particle, a proton and an electron but corresponding to two different initial states. We present systematic and convergent calculations of nl-resolved cross sections required for plasma modeling and diagnostics. The presented results are largest and most accurate to date. The integrated cross sections for electron capture, excitation and ionization show generally good agreement with experimental measurements and previous close-coupling calculations where available, however the calculated cross section for Balmer-α emission in He2+–H collisions significantly disagree with experiment. We also present the fully differential, as well as various doubly and singly differential cross sections for ionization in He2+–H collisions at an incident energy of 200 keV amu−1.

Electron capture cross sections and nuclear partition functions for fp-shell nuclei

We present calculation of electron capture cross sections (ECC), in the limit of zero momentum transfer, using the pn-QRPA model in stellar matter. Towards this aim we make use of our recently introduced recipe for estimation of nuclear partition functions. For low momentum transfer (), the nuclear matrix elements of the operator provide the leading contribution to the total cross section which we estimate using the pn-QRPA model in a multi-shell single-particle space with a schematic interaction. Key fp-shell nuclei (odd-A, even–even and odd–odd) bearing astrophysical importance were selected for the calculation of ECC in stellar environment. These fp-shell nuclei play a crucial role in presupernova evolution of massive stars and core collapse. We further present microscopic calculation of ground and excited states Gamow–Teller strength distributions and stellar electron capture rates on these suite of nuclei. We used two different sets of empirically determined pairing gaps to calculate the ECC and electron capture rates. Results are compared with experimental data and previous computations. Our calculated ECC are systematically smaller at low electron incident energies as compared to the shell-model results.

Electron capture and loss of O+ projectile in collision with water near the Bragg Peak Energies

The combined experimental and theoretical works of the study of the absolute single and double electron loss (stripping) and single and double electron capture cross sections for 0.2–1.2 MeV O+ projectiles colliding with water molecule are presented. In order to mimic the experimental observation we performed three, four and five-body classical trajectory Monte Carlo calculations. In our model the O+ projectile is either one, (two or three) particle(s) depending on the model used (3, 4 or 5 body model, respectively) and the water target is taken into account as two virtual particles. We found that the calculated cross sections are in agreement with the present experimental data. Moreover, the similarity of the present data with an isoelectronic system, the methane molecule allows us to draw a common curve through both data sets.

State-selective and total cross sections for electron capture from the K-shell of multi-electron atoms by fully stripped projectiles

Capture of a K-shell electron by bare fast ions H+, He2+ and Li3+ from multi-electron atomic targets (carbon, nitrogen, oxygen, neon and argon) is theoretically studied by means of the four-body boundary-corrected first Born approximation. In a wide impact energy interval ranging from 100 to 40 000 keV/amu, extensive tables of the obtained state-selective cross sections Qnlm are presented for each individual final hydrogen-like state described by the usual quantum numbers {n,l,m}. The total cross sections Qnl, Qn and Qtot for capture summed over the quantum numbers m, {l,m} and {n,l,m}, respectively, are also reported. Theoretical cross sections Qtot are found to compare favorably with the corresponding experimental data. The maximal value of the principal quantum number n has been taken to be n=4, which satisfies the relationship n≥ZP, where ZP is the nuclear charge of the projectile. The tabulated state-selective cross sections Qnlm for single-electron capture by swift nuclei from multi-electron atoms are the first results in the literature on the theory of four-body collisions. The present data for the examined capture processes are of notable interest for many fundamental and applied problems in various interdisciplinary fields ranging from fusion research, plasma physics, astrophysics to radiotherapy.

Simulation of TiO2/CuO solar cells with SCAPS-1D software

TiO2/CuO and TiO2/Cu2O solar cells are promising devices for photovoltaic applications. The power conversion efficiency of these cells, however, remains low. We used the SCAPS-1D program to perform simulations of n-TiO2/p-Cu2O and n-TiO2/p-CuO thin-film solar cells. The short circuit current and efficiency were 13.3 mA cm−2, 28.4 mA cm−2 and 13.7% 22.4%, respectively, Furthermore, we evaluated some specific parameters of n-TiO2/p-CuO heterostructure, such as the influence of temperature, interface state density, metal work function, electron and hole capture cross-section, shallow uniform donor density (ND) for TiO2 with constant uniform acceptor doping density (NA) in CuO and shallow uniform acceptor density (NA) for CuO with constant (ND) in TiO2. Our findings revealed that the efficiency of n-TiO2/p-CuO solar cells can be improved by increasing metal work function of the contact and by decreasing defects and the electron and hole capture cross-section.

Electron capture, ionization and excitation cross sections for keV collisions between fully stripped ions and atomic hydrogen in ground and excited states

Using a semiclassical close-coupling approach, we have calculated electron capture, excitation and ionization cross sections for collisions of fully stripped hydrogen, helium and lithium ions with atomic hydrogen in the ground state and in all excited states up to n=3. The cross sections for collision energies between 1 and 100 keV/u are given in table form. Furthermore, we provide estimates of the accuracy of the cross sections. The set of data presented in this work represent the first complete and consistent quantum study of these collision systems and will find use in the modeling and diagnosis of thermonuclear fusion plasma reactors.

Construction of a table-top ion storage ring and its application to cross section measurements

A table-top electrostatic ion storage ring was constructed, and an argon ion (Arn+, n = 1, 2) beam was successfully stored. As an application of the storage ring, the electron capture cross section for a neutral Ar target was measured.

Wave-packet continuum-discretization approach to proton collisions with helium

We extend the two-center wave-packet convergent close-coupling method to proton collisions with helium. The target is treated as a three-body system, where correlations between the electrons are taken into account. We apply a frozen-core approximation, where one of the electrons is described by the He+1s orbital, and obtain the helium singlet wave functions as well as the energy levels using a numerical approach. The wave-packet approach is used to discretize the continuum of the target and the hydrogen atom formed after electron capture by the projectile. Convergence of the results is studied in terms of the included projectile- and target-centered states. We present electron-capture and single- and double-ionization cross sections for protons incident on He in the ground state in the energy range from 15 keV to 1 MeV. We also provide partial cross sections for electron capture and direct excitation into the n=2 shell states of hydrogen and helium, respectively. Our results are in good agreement with available experimental data and other calculations, where available.

Single-Capture Cross Sections from Biological Molecules and Noble Gases by Bare Ion Impact

In this work, we report theoretical electron capture cross sections for single-electron removal from molecules of biological interest and noble gases by bare ion (H+ and He2+) impact at energies ranging from 25 to 10,000 keV/amu. We use a distorted wave (DW) method where the intermediate continuum state of the active electron with the target ion has been taken into account. This method is developed within the framework of the independent electron model taking particular care of the representation of the bound continuum target states. Two different approximations have been considered for molecular targets: molecular representation of the bound-state target wavefunction and Bragg’s additivity rule. The molecular orbital for targets are described within the framework of the complete neglect of differential overlap (CNDO) method based on the linear combination of atomic orbital (LCAO) approximation. Using the DW method, we have also calculated the K-, L- and M- shell electron capture in collisions of bare ions with three noble gases He, Ne, and Ar respectively. Contributions from different molecular orbitals and different shells to the total cross sections (TCS) are studied. The preference of electron capture occurs in accordance as the binding energy of the active electron in molecular orbital and atomic shell. The maximum contributions to TCS for SC comes from the less bound electrons in repetitive orbitals, whereas the tightly bound electrons dominate the TCS at higher projectile energy regime. Variation of TCS with impact energy are compared with the available experimental observation and other theoretical findings. We find that the present theoretical method is satisfactory in both intermediate and high-energy region for molecules as well as noble gas targets to give reliable outcomes compared to other theoretical methods.