低能带电粒子聚变反应中的静电屏蔽效应

系统地评述了天体物理感兴趣能区带电粒子核反应中电子屏蔽效应的实验及理论研究的进展 ,简要地介绍了恒星热核反应中等离子体静电屏蔽效应理论探讨的概况 .着重说明深入研究天体物理环境对核过程的影响是核天体物理学的重要课题之一.     

Absolute cross sections for the 6Li(p, 3He)4He reaction at energies below 1 MeV

Total cross sections and angular distributions in the ⁶Li(p,³He)⁴He reaction have been measured over the energy range E_p = 100?700 keV. The extrapolation of the cross section to the energy region which is of interest in controlled thermonuclear reactors is given. The values of the “astrophysical S-function” are deduced from the cross sections.     

Experimental determination of the electron screening potential energy for the d(d, n)3He Reaction in ZrD2 and D2O in the ultralow energy region

This work is devoted to measuring of the values of the astrophysical S-factors and electron screening potential energy for a d(d,n)³He reaction occurring at ultralow energies in zirconium deuteride ZrD₂ (3.5–7.0 keV) and heavy water D₂O (2.2–6.0 keV). The experiment was performed on the Hall pulsed plasma accelerator at the TPU Nuclear Physics Institute (Tomsk) with ZrD₂ and D₂O targets produced by the magnetron sputtering of zirconium in a deuterium environment and heavy water freezing-out on a copper support, respectively. A χ ² analysis of the dependence of the neutron yields and astrophysical S-factors for the dd reaction on the deuteron collision energy E revealed that the upper bounds of the electron screening potential energy for interacting deuterons in ZrD₂ and D₂O and of the astrophysical S-factors at the deuteron collision energy E = 0 were U _e (ZrD₂) < 30 eV, U _e (D₂O) < 25 eV, S(0) = (57.2 ± 3.9) keV · b (ZrD₂), S(0) = (58.6 ± 3.6) keV · b (D₂O) at the 90% confidence level.     

Current status of the α + d → <Superscript>6</Superscript>Li + γ reaction

The current experimental and theoretical situation for the radiative capture reaction α + d → ⁶Li + γ is reviewed. Particular emphasis is placed upon the low-energy region important for astrophysical and thermonuclear applications.     

The 39(α, p)42Ca cross section and thermonuclear reaction rate

Excitation functions have been measured for the reaction ³⁹K(α, p)⁴²Ca over the energy range 4.5–9.0 MeV. Cross sections have been extracted from the data for individual proton groups and for aggregates of proton groups. These are compared with statistical-model calculations based on global optical model parameters. The overall agreement is good to within a factor of 1.5. The data and the statistical-model results are used in calculations of thermonuclear reaction rates for temperatures of astrophysical interest.     

Screening influence on the Stark effect of impurity states in strained wurtzite GaN/AlxGa1-xN heterojunctions under pressure

The screening effect of the random-phase-approximation on the states of shallow donor impurities in free strained wurtzite GaN/Al x Ga 1 x N heterojunctions under hydrostatic pressure and an external electric field is investigated by using a variational method and a simplified coherent potential approximation.The variations of Stark energy shift with electric field,impurity position,Al component and areal electron density are discussed.Our results show that the screening dramatically reduces both the blue and red shifts as well as the binding energies of impurity states.For a given impurity position,the change in binding energy is more sensitive to the increase in hydrostatic pressure in the presence of the screening effect than that in the absence of the screening effect.The weakening of the blue and red shifts,induced by the screening effect,strengthens gradually with the increase of electric field.Furthermore,the screening effect weakens the mixture crystal effect,thereby influencing the Stark effect.The screening effect strengthens the influence of energy band bending on binding energy due to the areal electron density.     

Thermonuclear fusion in a strong laser field

Thermonuclear fusion induced by the irradiation of solid deuterated cluster targets and foils with fields of strong femtosecond and picosecond laser pulses is discussed. The thermonuclear-fusion process D(d, n)³He in a collision of two deuterons at an energy of 50 to 100 keV in a deuterium cluster target irradiated with a strong laser pulse is discussed. A theory of thermonuclear fusion proceeding upon the irradiation of clusters formed by deuterium iodide (DI) molecules with the field of a superintense femtosecond laser pulse is developed. This theory is based on an above-barrier process in which the sequential multiple inner ionization of atomic ions within a cluster is accompanied by field-induced outer ionization. The yield of neutrons from thermonuclear fusion in a deuteron-deuteron collision after the completion of a laser pulse is calculated. The yield of neutrons is determined for the thermonuclear-fusion reaction proceeding in the interaction of an intense picosecond laser pulse with thin TiD₂ foils. A multiple ionization of titanium atoms at the front edge of the laser pulse is considered. The heating of free electron occurs in induced inverse bremsstrahlung in the process of electron scattering on multiply charged titanium ions. The yield of alpha particles in the thermonuclear-fusion reaction involving protons and ¹¹B nuclei that is induced in microdrops by a strong laser field is determined. Experimental data on laser-induced thermonuclear fusion are discussed.     

Screened Coulomb potentials for astrophysical nuclear fusion reactions

The electron-screening acceleration of laboratory fusion reactions at astrophysical energies is an unsolved problem of great importance to astrophysics. That effect is modeled here by considering the fusion of hydrogen-like atoms whose electron probability density is used in Poisson's equation in order to derive the corresponding screened Coulomb potential energy. That way atomic excitations and deformations of the fusing atoms can be taken into account. Those potentials are then treated semiclassically in order to obtain the screening (accelerating) factor of the reaction. By means of the proposed model the effect of a superstrong magnetic field on laboratory hydrogen fusion reactions is investigated here for the first time showing that, despite the considerable increase in the cross-section of the dd reaction, the pp reaction is still too slow to justify experimentation. The proposed model is finally applied on the H² d, pH³ fusion reaction describing satisfactorily the experimental data although some ambiguity remains regarding the molecular nature of the deuteron target. Notably, the present method gives a sufficiently high screening energy for hydrogen fusion reactions so that the take-away energy of the spectator nucleus can also be taken into account. Received: 19 May 2000 / Accepted: 4 September 2000     

Infrared wave interaction with an electron in the rectangular and circular plasma waveguide

In this article, the effect of the electron collision frequency with background ions on TM mode field components, the trajectory, and the electron energy gain in interaction infrared radiation with collisional plasma is studied. The field components of the TM mode in the rectangular and circular collisional plasma waveguides are obtained. The deflection angle and acceleration gradient of an electron in the fields associated with a transverse magnetic (TM) wave propagating inside a plasma waveguide for TM mode is studied. The relativistic momentum and energy equations for an electron are solved, which was injected initially along the propagation direction of the infrared. The results for collisionless and collisional plasma are graphically represented. Finally, the results for rectangular and circular waveguides are compared.     

Potential resonant screening effects on stellar 12C + 12C reaction rates

The ¹²C + ¹²C fusion cross-sections show a resonant behavior down to the lowest energies accessible so far in the laboratory. If this tendency continues into the astrophysical energy range, the stellar ¹²C + ¹²C reaction rates have to be corrected for resonant screening effects, in addition to the conventional screening corrections. We estimate the resonant screening effects in the weak electron screening limit for hydrostatic burning and white-dwarf environments. Received: 24 May 2002 / Accepted: 31 July 2002 / Published online: 7 November 2002 RID="a" ID="a"e-mail: langanke@ifa.au.dk Communicated by J. ?yst?     

Experimental observation of electron screening for the D(p, γ)3He nuclear reaction in titanium Deuteride TiD

Characteristics of the pd reaction (p + d → ³He + γ(5.5 MeV)) in titanium deuteride at astrophysical proton-deuteron collision energies ranging from 5.3 to 10.5 keV are investigated. Experiments are conducted on the pulsed plasma Hall accelerator at Tomsk Polytechnic University (Tomsk, Russia). The number of accelerated protons in a pulse 10 μs long is 5 × 10¹⁴ at a repetition rate of 7 × 10^?2 Hz. Gamma rays with an energy of 5.5 MeV are recorded by eight detectors based on NaI(Tl) crystals (100 × 100 × 400 mm) arranged around the TiD target. The dependence of the astrophysical S factor for the pd reaction on the proton-deuteron collision energy and the electron screening potential of protons interacting with deuterons in titanium deuteride are measured for the first time.     

Proton capture reaction of 33S in nova V1065 Centauri

Previous studies have shown that 33S（p,γ）34Cl is the most important reaction that affects the abundance of 33S in the product of nova nucleosynthesis. In this paper, a more accurate thermonuclear reaction rate of 33S（p, γ）34Cl in the nova is calculated based on the newly measured 34C1 nuclear resonance levels. The electron screening correction and the non-resonance and narrow-resonance contributions are considered. The calculations are also combined with the recent observational data of nova V1065 Centauri and show that the thermonuclear reaction rates of 33S（p, γ） 34C1 are significantly different in the improved method. Because these results can affect the isotopic ratio of sulfur in the nova ejecta significantly, we make an estimate of the values of 328/33S and 338/338Q, which can be used as a diagnostic tool for the novae.     

Long time properties of the evolution of an unstable state

An effect generated by the nonexponential behavior of the survival amplitude of an unstable state in the long time region is considered. In 1957 Khalfin proved that this amplitude tends to zero as t → ∞ more slowly than any exponential function of t. This can be described in terms of the time-dependent decay rate γ(t) which, when considered with the Khalfin result, means that this γ(t) is not a constant for large t but that it tends to zero as t → ∞. We find that a similar conclusion can be drawn for a large class of models of unstable states for a quantity, which can be interpreted as the “instantaneous energy” of the unstable state. This energy should be much smaller for suitably larger values of t than when t is of the order of the lifetime of the considered state. Within a given model we show that the energy corrections in the long (t → ∞) and relatively short (lifetime of the state) time regions, are different. This is a purely quantum mechanical effect. It is hypothesized that there is a possibility to detect this effect by analyzing the spectra of distant astrophysical objects. The above property of unstable states may influence the measured values of astrophysical and cosmological parameters.      

Plasma Diagnostics Using K‐Line Emission Profiles of Silicon

Modifications of K‐line profiles due to a warm dense plasma environment are a suitable tool for plasma diagnostics. We focus on Si K_α emissions due to an electron transfer from 2P to 1S shell. Besides 2P fine structure effects we also consider the influence of excited and higher ionized emitters. Generally spoken, a plasma of medium temperature and high density (warm dense matter) is created from bulk Si the greater part of atoms is ionized. The high energy of K_α x‐rays is necessary to penetrate and investigate the Si sample. The plasma effect influences the many‐particle system resulting in an energy shift due to electron‐ion and electron‐electron interaction. In our work we focus on pure Si using LS coupling. Non‐perturbative wave functions are calculated as well as ionization energies, binding energies and relevant emission energies using the chemical ab initio code Gaussian 03. The plasma effect is considered within a perturbative approach to the Hamiltonian. Using Roothaan‐Hartree‐Fock wave functions we calculate the screening effect within an ion‐sphere model. The different excitation and ionization probabilities of the electronic L‐shell and M‐shell lead to a charge state distribution. Using this distribution and a Lorentz profile convolution with a Gaussian instrument function we calculate spectral line profiles depending on the plasma parameters. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Astrophysical <Emphasis Type="Italic">S</Emphasis> factor for the radiative-capture reaction <Emphasis Type="Italic">p</Emphasis><Superscript>6</Superscript>Li → <Superscript>7</Superscript>Beγ

A new measurement of differential cross sections for elastic p ⁶Li scattering in the energy range 0.35–1.2 MeV was performed. A partial-wave analysis of the data obtained in this way was carried out, and potentials simulating the p ⁶Li interaction were constructed. Various experiments devoted to studying elastic p ⁶Li scattering over the broad energy range of 0.5–50 MeV were analyzed on the basis of the optical model. By using the potentials obtained from the partial-wave analysis, the possibility of describing the astrophysical S factor for radiative proton capture on ⁶Li at low energies was considered within the potential cluster model involving forbidden states.     

On the role of the Coulomb interaction in the mechanism of d-wave Cooper pairing of charge carriers in high-T c superconductors

The question of the effect of the structure of the anisotropic quasi-two-dimensional electron spectrum of high-T _c superconductors on the character of the screening of the Coulomb interaction and the symmetry of the superconducting order parameter is studied. Calculations of the polarization operator of electrons are performed on the basis of the single-particle band spectrum extracted from angle-resolved photoemission spectroscopy data. It is shown that the static screened Coulomb repulsion has a minimum at small momentum transfers. This corresponds to an effective electron-electron attraction in the -wave channel of Cooper pairing of the charge carriers on account of their interaction with the long-wavelength charge-density fluctuations. This attraction together with the anisotropic electron-phonon interaction increase the critical superconducting transition temperature T _c with increasing hole density and can give quite high values of T _c while at the same time suppressing the isotope effect, in qualitative agreement with the experimental data for underdoped hole-type cuprate metal-oxide compounds. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 10, 703–710 (25 May 1999)     

Plasmon excitations in homogeneous neutron-star matter

We study the possible collective plasma modes which can affect neutron-star thermodynamics and different elementary processes in the baryonic density range between nuclear saturation ρ ₀ and 3ρ ₀. In this region, the expected constituents of neutron-star matter are mainly neutrons, protons, electrons, and muons (npeμ matter), under the constraint of beta equilibrium. The elementary plasma excitations of the peμ three-fluid medium are studied in the RPA framework. We emphasize the relevance of the Coulomb interaction among the three species, in particular, the interplay of the electron and muon screening in suppressing the possible proton plasma mode, which is converted into a sound-like mode. The Coulomb interaction alone is able to produce a variety of excitation branches and the full spectral function shows a rich structure at different energy. The genuine plasmon mode is pushed at high energy and it contains mainly an electron component with a substantial muon component, which increases with density. The plasmon is undamped for not too large momentum and is expected to be hardly affected by the nuclear interaction. All the other branches, which fall below the plasmon, are damped or over-damped. The text was submitted by the authors in English.     

Effect of Debye plasma on compressed exotic atoms

The effect of plasma environment on the energy levels and structural properties of exotic atomic systems p⁺μ⁻ and μ⁺μ⁻ bound by Coulomb force and confined at the centre of an impenetrable spherical box has been thoroughly studied. The plasma environment is assumed to produce a Debye type of screening in the potential energy. Compression is generated by confining the exotic system in a spherical box. The effect of plasma and compression on system properties like orbital energies, excited states, dipole polarizabilities, oscillator strength and transition probabilities has been studied using time dependent variation perturbation theory. Ionisation pressures at different plasma screening have been estimated. The data obtained may be useful in the astrophysical context where different plasma environments exist.     

Binary and multiparticle electron-electron interaction on the surface

It is shown for the first time that electron-electron scattering of slow electrons with an energy of 10–50 eV at the surface of some metals is mainly an event of binary scattering of particles with conserved total momentum and energy, while analogous scattering at the surface of a semiconductor (n-Si) and an insulator (MgO) is a multiparticle event. A model is proposed, in which the electron subsystem of a solid is characterized by short-range order. Each electron is at the center of a spherical cell and surrounded by nearest neighbors (electrons) with a coordination number of 12. The overlap of the fields of charges gives rise to a negative potential U _c (r) ≈ U _c , which is virtually constant along the coordinate and contains spherical cells with a central field U(r) of individual charges. The value of constant negative potential U _c depends on the extent of electron screening, which is high for metals and low for semiconductors and insulators. In metals, scattering governed by the binary mechanism may take place (i.e., scattering of a primary electron in the central field of an electron of the metal); this is ensured by a relatively small value of constant potential U _c . The electron subsystem of the metal behaves as a Fermi gas of weakly interacting quasiparticles. Electron screening in semiconductors and insulators is insignificant, and constant negative potential U _c is an order of magnitude higher than the analogous potential in metals. Slow primary electrons are scattered in the total field of many charges before they reach the central field of an individual electron. The electron subsystem of a semiconductor and an insulator in the excitation range studied here behaves as an ensemble of strongly interacting particles.     

Enhanced electron screening in d (d, p)t for deuterated Ta*

The recent observation of a large electron screening effect in the d(d, p)t reaction using a deuterated Ta target has been confirmed using somewhat different experimental approaches: U _e = 309±12 eV for the electron screening potential energy. The high U _e value arises from the environment of the deuterons in the Ta matrix, but a quantitative explanation is missing. Received: 21 December 2001 / Accepted: 29 January 2002