Collisions Of Alpha Particles Research Articles

Multi-method treatment of elastic scattering of alpha particles from atomic hydrogen over a wide impact energy range

Multiple theoretical methods are used to calculate the elastic scattering cross section for collisions of alpha particles with atomic hydrogen in the center-of-mass energy range of 10−4–108 eV. At the lowest energies where elastic scattering greatly dominates other reaction channels, a single-channel quasi-molecular-orbital approach is used. With the opening of inelastic channels at higher energies the multi-channel atomic-orbital, close-coupling method is applied, and at the highest energies considered perturbation theory (the Born approximation) is used. The results are compared with other data available in the literature and from preliminary multi-channel molecular-orbital, close-coupling calculations in order to assess the accuracy of the results and to create a recommended set of data spanning the entire energy range. The data is made available for use in astrophysical modeling and other plasma science applications online.

Various mechanisms for double capture from helium targets by alpha particles

An analysis is presented using six quantum-mechanical four-body distorted wave (DW) theories for double capture (DC) in ion-atom collisions at intermediate and high energies. They all satisfy the correct boundary conditions in the entrance and exit channels. This implies the usage of short-range perturbation potentials in compliance with the exact behaviors of scattering wave functions at infinitely large separations of particles. Specifically, total cross sections Q are analyzed for collisions of alpha particles with helium targets. Regarding the relative quantitative performance of the studied DW theories at different impact energies E, our main focus is on the sensitivity of Q to various collisional mechanisms. The usual mechanism in most DW theories assumes that both electrons undergo the same type of collisions with nuclei. These are either single or double collisions in one or two steps, respectively, per channel, but without their mixture in either channel. The signatures of double collisions in differential cross sections are the Thomas peaks. By definition, these cannot be produced by single collisions. There is another DC pathway, which is actually favored by the existing experimental data. It is a hybrid, two-center mechanism which, in each channel separately, combines a single collision for one electron with a double collision for the other electron. The ensuing DW theory is called the four-body single-double scattering (SDS-4B) method. It appears that this mechanism in the SDS-4B method is more probable than double collisions for each electron in both channels predicted by the four-body continuum distorted wave (CDW-4B) method. This is presently demonstrated for Q at energies E=[200,8000] keV in DC exemplified by alpha particles colliding with helium targets.

Indication of strong interatomic Coulombic decay in slow He2+ –Ne2 collisions

Electron removal in collisions of alpha particles with neon dimers is studied using an independent-atom-independent-electron model based on the semiclassical approximation of heavy-particle collision physics. The dimer is assumed to be frozen at its equilibrium bond length and collision events for the two ion–atom subsystems are combined in an impact parameter by impact parameter fashion for three mutually perpendicular orientations. Both frozen atomic target and dynamic response model calculations are carried out using the coupled-channel two-center basis generator method. We pay particular attention to inner-valence Ne(2s) electron removal, which is associated with interatomic Coulombic decay (ICD), resulting in low-energy electron emission and dimer fragmentation. Our calculations confirm a previous experimental result at 150 keV/amu impact energy regarding the relative strength of ICD compared to direct electron emission. They further indicate that ICD is the dominant Ne+ + Ne+ fragmentation process below 10 keV/amu, suggesting that a strong low-energy electron yield will be observed in the ion–dimer system in a regime in which the creation of continuum electrons is a rare event in the ion–atom problem.

Comment on “Avalanche proton-boron fusion based on elastic nuclear collisions” [Phys. Plasmas 23, 050704 (2016)

It is shown that collisions of alpha particles with protons could not result in the physically important manifestation of avalanche proton-boron fusion in experiments at Prague Asterix Laser System.

Invariant exchange perturbation theory for multicenter systems: Time-dependent perturbations

A formalism of exchange perturbation theory (EPT) is developed for the case of interactions that explicitly depend on time. Corrections to the wave function obtained in any order of perturbation theory and represented in an invariant form include exchange contributions due to intercenter electron permutations in complex multicenter systems. For collisions of atomic systems with an arbitrary type of interaction, general expressions are obtained for the transfer (T) and scattering (S) matrices in which intercenter electron permutations between overlapping nonorthogonal states belonging to different centers (atoms) are consistently taken into account. The problem of collision of alpha particles with lithium atoms accompanied by the redistribution of electrons between centers is considered. The differential and total charge-exchange cross sections of lithium are calculated.

Atomic Charge-Changing Processes in Plasmas

Properties of various kinds of plasmas are determined by atomic radiation and collision processes occurring between plasma particles, therefore, the detailed knowledge of the effective cross sections and rate coefficients for these processes is highly required. In this work, charge-changing processes, mainly for heavy-particle collisions, including impurity ions, are considered using available computer codes, and the background physics is discussed. Besides general features, the role of metastable states of plasma atoms and ions, which are often observed in most of plasmas and play a key role in plasma formation, is considered. The non-linear effects observed for heavy particle collisions, such as the density effect and multiple-electron ionization, are also considered. In addition, the isotope effects are briefly discussed related with electron capture in collisions of alpha particles with hydrogen and its isotopes (D and T). c

Transfer ionization and double capture of helium dimers

We employed the COLTRIMS (cold target recoil ion momentum spectroscopy) technique to investigate the collision of alpha particles with an energy of 150kev/u and he lium dimers (He2).

Charge exchange and excitation cross sections at collisions of alpha particles with be-like impurity oxygen ions in a plasma

The charge exchange and excitation cross sections at collisions of alphas with O4+(1s 22s 2) impurity atoms in a hot plasma for striking energies E c varying from 20 keV to 2 MeV are determined for the first time. The cross sections are calculated using the method of close-coupling equations with 13 singlet four-electron quasi-molecular states taken as a basis. The partial cross sections of charge transfer to the 1s, 2s, and 2p states of a He+ ion and for O4+(1s 22s 2) → O4+(1s 22lnl’) (n = 2, 3) electronic excitation of an oxygen ion are found. The maximal value of the charge exchange total cross section roughly equals 2.2 × 10−16 cm2 at E c ≈ 0.7 MeV. The excitation total cross section has a maximum of ≈ 7.7 × 10−16 cm2 at E c ≈ 80 keV for single-electron excitation and ≈6.5 × 10−16 cm2 at E c ≈ 0.7 MeV for two-electron excitation.

Single charge exchange in fast collisions of alpha particles with helium

A new second-order theory termed the Born distorted wave (BDW) approximation isintroduced within the framework of the four-body scattering theory and appliedto single charge exchange in fast symmetric collisions between alpha particles andhelium. The present formulation allows us to isolate the role of intermediateelectron continuum states. At the intermediate projectile energies, thepresent BDW approximation represents a substantial improvement over thecontinuum distorted-wave four-body formulation, thus illustrating a remarkablesensitivity of second-order theories for single charge exchange to the treatmentof electronic ionization continua. Numerical results for the total crosssections show a good agreement with the available experimental data.

Nonlocal interaction of fast magnetosonic waves with alpha-particles in tokamaks

Effects of nonlocal coupling between the fusion alpha particle current density and the fast magnetosonic wave electric field on cyclotron absorption of these waves by alphas are investigated. Such a nonlocality being due to the alpha particle motion along magnetic field lines is very strong because the alpha particle collisions with electrons and bulk ions are very rare and the collisional decorrelation of the wave-particle phase is weak. An alpha particle performs dozens of revolutions around the torus before the dephasing occurs. The expressions for the alpha particle current density and RF power absorbed by alphas in a tokamak are obtained and analysed. They account for the collisional decorrelation, finite Larmor radius and the magnetic drift of a phase.

A study of charge transfer and excitation processes in collisions of alpha particles with sodium atoms

The coupled state impact parameter model has been used to study collisions of alpha particles with sodium atoms. Straight-line trajectories are employed. The charge exchange and excitation cross sections are computed for impact energies in the range 10.0-270.0 keV. The calculated total charge exchange cross sections are found to be in good agreement with the recent experimental data of Dubois and Toburen (1985) in the energy range 10.0<or=Elab<or=100.0 keV. It is predicted that above this energy electron capture from the L shell starts to compete with electron capture from the M shell which is considered. The authors find that, for impact energies below 30.0 keV, the electrons are preferentially captured in the He+ (3l) state. This leads to a distinct possibility of population inversion and emission of Lyman- alpha (304 AA) and Lyman- beta (256 AA) soft X-ray photons.

Inclusion of deuteron and alpha-particle collisions in intranuclear cascade calculations

An intranuclear cascade model generalized to allow deuteron and alpha-particle collisions during the cascade is discussed. A comparison of calculations is presented for nucleon-induced cascades with and without clusters present in the target nucleus and the effects of clustering are inferred. Alpha-particle-induced collisions are studied in detail and compared with experimental data. It is found that many features of alpha-particle-induced reactions can be well understood with this model. Possible shortcomings and directions of future improvements in the code are highlighted.NUCLEAR REACTIONS Intranuclear cascade models; effects of including $d$ and $\ensuremath{\alpha}$ as incident projectiles or preformed clusters.

L-Shell Ionization in Proton and Alpha Particle Collisions with Argon

We report results of coupled-state calculations of argon L-shell ionization by proton and alpha particle collisions in the 100 to 500 kev/amu energy range. Our target-centered basis includes up through f-states. We have explored the angular momentum convergence and ability of our pseudostates to describe the ionization continuum by comparing to the Born calculations of Choi; excellent agreement is obtained. In the Born we have shown the effect of using different independent-particle target potentials; these effects are large, particularly at low energy. We propose a modification of the Hartree-Fock potential that leaves all the wavefunctions and the bound orbital energies unaltered, but that lowers the continuum by an amount that brings the L-shell ionization potentials roughly into agreement with experiment. Our coupled-states calculations show deviations from the 1st Born approximation, and are in fair agreement with experiment. A complete comparison to experiment will require the calculation of the charge transfer channel contribution to the vacancy production.

The evaluation of generator coordinate amplitudes

A method is outlined which enables one to calculate generator coordinate amplitudes using a series expansion that employs spherical Bessel functions. The method is illustrated for the case of the collision of alpha particles with 6Li nuclei.

The effect of concentration upon helium precipitation in irradiated copper boron alloys

The lattice parameter of copper is proportional to the concentration of dissolved interstitial helium up to approximately 0.03 at %. When the concentration of helium is increased to 0.08–0.1 at %, the gas precipitates to form bubbles during irradiation at temperatures in the range 75° C–100° C. During annealing at 500° C, the lattice parameter contracts owing to the formation of helium-vacancy complexes, at a rate which is proportional to the concentration of helium. Subsequent expansion of the lattice, caused by the precipitation of these complexes to form bubbles, also occurs at a rate which is proportional to helium concentration. The total time required for gas precipitation is inversely proportional to the helium content and this behaviour is associated with an increasingly fine scale of gas bubble nucleation. The average size and spacing of bubbles formed during the complete precipitation of helium increase with decreasing gas concentration. The bubble density is related to the number of dislocations generated by the annealing of displacement defects caused by fast neutron and alpha particle collisions. However, some homogeneous nucleation may also occur in materials with a high gas concentration. As the gas concentration of helium increases, a rapid initial contraction of the lattice develops during the first two minutes of annealing at 500° C. It is suspected that many of the helium atoms formed during irradiation are closely associated with potential vacancy sources such as jogs on dislocations, or clusters of vacancies caused by displacement collisions. At temperatures above those at which the vacancies become mobile, a proportion of these helium atoms enter substitutional solution very rapidly because the diffusion distances are short.

Nuclear Interactions and Mean Free Paths of Protons, Neutrons, and Alpha Particles at Energies Around 250 Bev/Nucleon

Nuclear interactions of protons, neutrons, $\ensuremath{\alpha}$ particles, and heavier nuclei of average energy 250 Bev/nuc were studied in nuclear emulsion. The source of these particles were fragmentations of heavy primary nuclei of the cosmic radiation. Their energy was determined from multiple scattering measurements. The interaction mean free path for protons is 41\ifmmode\pm\else\textpm\fi{}10 cm, for $\ensuremath{\alpha}$ particles 27\ifmmode\pm\else\textpm\fi{}7 cm. The mean free path shows no significant change compared with measurements at lower energies. The mean number of shower particles $〈{n}_{s}〉$ depends appreciably on the mass of the target nucleus. Our best estimate for nucleon-nucleon collisions at 250 Bev is $〈{n}_{s}〉=8.8\ifmmode\pm\else\textpm\fi{}1.9$. A detailed comparison of the estimate of the primary energy obtained from the angular distribution of shower particles with the true primary energy is carried out. The angular distribution of the shower particles will, in an individual case, give a quite unreliable value for the primary energy. In the average, the angular distribution method will over-estimate the true primary energy by a factor of 1.3 for interactions with a number of heavy prongs ${N}_{h}\ensuremath{\le}5$. If ${N}_{h}g5$, the angular distribution will underestimate the true energy in the average by a factor of 1.8. The angular distributions can be transformed into a system in which they are symmetric. This is even true for collisions with heavy target nuclei (${N}_{h}g5$). The results for alpha particle and heavy nucleus collisions are quite similar.The inelasticity for the proton and neutron interactions shows large fluctuations for individual events. It depends weakly on the number of shower particles and on the mass of the target nucleus. Its mean value is 50%. The mean value for the alpha-particle collisions is 22%.

Collisions of Alpha-Particles with Carbon Nuclei

More than 750,000 thorium (C+C\ensuremath{'}) alpha-particle cloud tracks have been photographed with a stereoscopic camera using a cloud chamber filled in one series with methyl-chloride and helium, and in another with acetylene and helium. For each series a range-velocity curve for carbon has been constructed by plotting the measured ranges, reduced to standard air values, against the calculated velocities for a total of 55 selected alpha-particle-carbon collisions. These curves are used for testing the validity of the method of reducing the ranges of heavy recoil nuclei in any gas to standard air values. Partial validity of the method has been observed in the present instance. An empirical relationship between the total mean straggling (in range), the atomic numbers of the atoms comprising the absorbing medium, and the atomic number of the recoil nucleus is presented. A brief analysis of the effectiveness of certain errors on the range-velocity results is given.

Collisions of Alpha-Particles with Chlorine Nuclei

Collisions of Alpha-Particles with Chlorine Nuclei

Collisions of Alpha-Particles with Neon and Deuterium Nuclei

The tracks of about 600,000 Th C and C' alpha-particle tracks were photographed in a Wilson cloud chamber filled with a mixture of neon and deuterium. An analysis of the elastic collisions with neon atoms gave points on a range-velocity diagram which fitted Eaton's curve fairly well except at the lower end. Reasons are given for thinking that this curve should be lowered slightly in the region of small velocities. A range-velocity curve is obtained from the collisions with deuterons. On the very reasonable assumption that, for a given velocity, the ranges of two isotopes are proportional to their masses, this curve indicates that Mano's calculations for protons are correct even for small velocities. It is shown that these collisions are elastic even when a high energy alpha-particle imparts considerable energy to a deuteron. No sign of inelastic collisions with either deuterons or neon atoms was obtained, although some were expected for the latter. The possible reasons for their nonappearance are discussed.

Collisions of Alpha-Particles with Sulphur Nuclei

More than 700,000 thorium C and C\ensuremath{'} alpha-particle tracks have been photographed with a stereoscopic camera in a Wilson chamber filled with a mixture of hydrogen sulphide and hydrogen. A range-velocity curve for sulphur recoil atoms has been constructed by plotting the measured ranges (reduced to standard air) against the calculated velocities for 60 selected alpha-particle sulphur collisions. This curve is discussed and compared with the results of other workers. A possible relationship has been noted between the range-velocity curves of atoms having similar electronic configurations. No collisions indicating possible sulphur disintegrations were observed. Several low energy collisions were noted which were apparently lacking in coplanarity, but this effect is explained as being due to small deflections suffered by the recoil nucleus shortly after the collision. The calculated distances of closest approach are compared with the radius of the sulphur nucleus as given by Pollard and Brasefield. The methods of measurement and calculation employed have been checked by applying them to collisions with protons.