共查询到20条相似文献,搜索用时 15 毫秒
1.
F. F. Karpeshin 《Physics of Particles and Nuclei》2006,37(2):284-305
A theory of resonance conversion (RC) is presented. It is shown that by resonance conversion being a natural extension of traditional internal conversion, into the subthreshold domain, in a number of cases, it strongly affects nuclear de-excitation. Moreover, as it concentrates transition strength in narrow bands corresponding to atomic spectral lines, it is a unique tool for accelerating nuclear processes. Along with the wellknown process of non-radiative nuclear excitation through electron NEET transition and the inverse RC process, resonance conversion provides convenient mathematics for a number of crossing-invariant processes involving a nucleus and electrons, excitation and de-excitation of nuclei, by a hyperfine magnetic field, spin mixing of nuclear states via an electron shell, a hyperfine interaction and magnetic anomalies in an atomic spectra, and the excitation of nuclei in collisions accompanied by the ionization of an electron shell, in muon decay in the orbit, etc. Mechanisms of isomer pumping via a laser-radiation-induced RC and of isomer energy triggering in a resonance laser radiation field are considered. An especially strong effect can be obtained in hydrogen-like ions, with practically no RC damping. The theory is also generalized to the case of discrete Auger transitions. 相似文献
2.
S. A. Karamian 《Physics of Particles and Nuclei》2008,39(4):490-525
The state of experimental studies and promising proposals for the application of nuclear isomers presented as controlled energy or γ-ray sources are reviewed. The properties of isomeric states, methods of their production, and approaches to their efficient stimulation using various types of radiation are analyzed. The long-lived isomers, which can be accumulated in reactor irradiations or in other nuclear interactions with abundant yield, are listed. The isomers are estimated according to their specific energy accumulated per nucleus and the level of the cross section for their formation in reactions with neutrons. The nuclei are classified as promising either for obtaining controlled γ-ray pulses, for the enhanced release of the radioactive decay energy, or for experimental studies on detecting forbidden electromagnetic transitions from the ground to isomeric state. In all cases, the possibility of external-stimulus action on nuclear transitions has key significance, which should become the subject of investigations. The results of successful observation of stimulation of isomers are described at excitation energy E* > 1 MeV in the reactions with bremsstrahlung photons and Coulomb excitation in the ion beam. The essential increase in the K-hindered transitions with increasing energy and also the K-mixing at high rotational frequency for high-spin levels are discussed. The attention is focused on attempts to detect the triggering induced by the radiation in the x-ray range, in particular, that of the 178m2Hf isomer with the help of x-ray sources and the synchrotron radiation. Proposals for experiments with other isomers are considered. The possibility of affecting the nuclear states by means of ionization of electron shells of a corresponding atom is discussed as promising, and various schemes of similar experiments are proposed. The atomic cross sections are eight orders of magnitude higher than the nuclear ones; therefore, the stimulation of an isomer can occur even if the conversion from atomic excitations to nuclear ones has a low probability. 相似文献
3.
N. K. Skobelev V. Z. Maidikov N. T. Surovitskaya 《Zeitschrift für Physik A Hadrons and Nuclei》1983,314(1):5-7
The recoil-atom ionization of some isotopes from Sc to Po produced by heavy ioninduced nuclear reactions has been investigated. An analysis of the available data on the ionic charge distributions of nuclear reaction products has shown that atomic ionization in the mass range ofA~ 40–70 corresponds to the calculated values. It has been found that the contribution from additional ionization due to the formation of inner-shell vacancies as a result of the internal conversion of nuclear transitions grows as the atomic number and excitation energy of nuclei increase and reaches 90% for Po recoil atoms from fusion reactions. 相似文献
4.
J.-J. Shin D. R. Ermer S. C. Langford J. T. Dickinson 《Applied Physics A: Materials Science & Processing》1996,64(1):7-17
Visible fluorescent “plumes” are readily produced when nominally transparent ionic materials are exposed to pulsed UV laser
irradiation. Over a wide range of laser fluences where plumes are observed, however, the photon and electron densities are
inadequate to support multiphoton ionization and inverse bremsstrahlung, which are often used to explain plasma production
and excitation of atomic spectral lines. We present evidence that the great majority of charged particles (electrons and positive
ions) comprising the plume at the onset of formation in defect-laden NaNO3 are emitted directly from the surface. A model is described wherein the required electron energy to excite and eventually
ionize neutral atoms is provided by electrostatic interactions in the expanding plume. The time evolution of the “overlap”
between the expanding charge cloud and thermally emitted neutrals accounts for the time evolution of the atomic line emissions
after the laser pulse.
Received: 15 August 1996/Accepted: 16 August 1996 相似文献
5.
A scheme of nuclear excitation by the ionic X-ray lines in laser plasma using two femtosecond laser pulses is proposed. The first pulse produces plasma with a given degree of ionization, allowing the X-ray line energies of the target ions to be tuned to resonance with the nuclear transition, while the second pulse generates hot electrons that are necessary for X-ray generation. 相似文献
6.
The excitation spectra are measured for the atomic and the hot molecular self-trapped exciton (STE) luminescence in solid Ne. The atomic STE component is enhanced in comparison with the molecular STE at 17 and 19 eV of excitation energies, which are located at the low energy side of the bulk exciton transitions. On the other hand, the branching ratio into the atomic and the hot molecular STE's is almost constant at the other excitation energies. 相似文献
7.
The triggering of long-lived isomeric nuclei by non-radiative excitation to a relatively short-lived mediating state is considered.
Coulomb triggering in inelastic scattering of heavy ions, a transfer of triggering energy from resonant electron transitions
of atomic shell (NEET) and triggering by capture of a free electron into a bound atomic state (NEEC) are discussed. Cross
sections for the above processes of non-radiative triggering are presented and the relative efficiencies of these different
triggering mechanisms are discussed. Numerical estimates are presented for the selected isomers.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
V. P. Krainov 《Physics of Atomic Nuclei》2011,74(10):1410-1423
Investigation of nuclear reactions in a solid-state plasma generated by modern high-intensity sources of ultrashort-wavelength
laser radiation is undoubtedly of interest for establishing nuclear-reaction yields versus the intensity of laser radiation
and for efficiently exciting new nuclear and photonuclear reactions—in particular, in the resonance energy region. The present
article is devoted to describing, for laser plasmas, various mechanisms of electron acceleration, which triggers the acceleration
of atomic ions and the excitation of subsequent nuclear reactions. 相似文献
9.
Relative populations of the excited levels for Cr(I), Cr(II), Fe(I) and Fe(II) in the argon plasma flow of an arc two-jet
plasma generator used in spectrochemical analysis were measured. The range of the total energy E of excitation and ionization
was 4.5–8.0 and 12.5–16.0 eV, respectively. It is shown that the populations of atom and ion levels are linear with respect
to energy lower than E∼15 eV. For ionic lines with energy close to 15.5–16.0 eV the line intensities behave anomalously against
equilibrium values. This can be associated with charge transfer between the analyte and argon ions. Deviation of I from LTE
values increases in the plasma zones below and above the site of jet confluence, where the plasma temperature decreases.
A. P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1a Favorskii St., Irkutsk,
664033, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 575–581, September–October, 1997. 相似文献
10.
R. A. Lomsadze M. R. Gochitashvili R. V. Kvizhinadze N. O. Mosulishvili S. V. Bobashev 《Technical Physics》2007,52(11):1506-1510
The absolute values of cross sections of ionization, charge exchange, and excitation during Na+-Ar collisions are measured in the ion energy range 0.5–10.0 keV. Experiments are performed by a modified method of transverse electric field and by the optical spectrometry method. The mechanisms for realization of inelastic channels are explained qualitatively on the basis of a schematic correlation diagram of diabatic quasi-molecular energy levels of a system of colliding particles. The quasi-molecular nature of interaction is revealed for excitation processes. The excitation mechanisms of collision partners are established. A noticeable contribution to the excitation of the 4s state of the argon atom comes from the cascade transition from upper-lying 4p and 3d levels. An oscillatory structure is observed in the excitation functions of atomic lines of ArI (104.8 and 106.7 nm). The shape of the curve describing the dependence of the charge-exchange cross section on the collision energy is explained by the presence of two nonadiabaticity regions. In the low-energy region (up to E = 2 keV), charge exchange is due to electron capture to the ground state as a result of Σ–Σ transitions, while Σ–Π transitions associated with the rotation of internuclear axis play the leading role in charge exchange in the energy range E > 3 keV. The contribution of a number of inelastic channel is estimated for the ionization process. It is found that the main contribution to ionization is associated with the decay of self-ionization states in an isolated atom. 相似文献
11.
The electron and nuclear dynamics of C60 fullerenes
irradiated with femtosecond laser pulses are investigated with
photoelectron and photoion spectroscopy. The focus of this work is
the detailed exploration of the population mechanism of Rydberg
levels within the excitation process of neutral C60. The effect
of excitation wavelength, intensity, chirp, and polarization on the
kinetic energy distribution of photoelectrons in single-pulse
experiments gives first insight into the underlying processes. In
combination with time-resolved two-color pump-probe spectroscopy
depending on either pump, or probe pulse intensity, a more complete
picture of the interaction can be drawn. The results point towards a
very interesting but nevertheless complex behavior including four
steps: (i) non-adiabatic multielectron excitation of the HOMO
(hu) → LUMO+1 (t1g) transition; (ii)
thermalization within the hot electron cloud on a time scale below
100 fs, followed by a coupling of energy to vibrational modes of
the molecule via doorway state(s); (iii) population of
electronically excited Rydberg states by multiphoton absorption, and
(iv) single photon ionization from the excited Rydberg states. This
excitation process results in a characteristic sequence of
photoelectron lines in the photoemission spectra. The comparison of
the experimental results with recent theoretical work gives
convincing evidence that non-adiabatic multielectron dynamics (NMED)
plays a key role for the understanding of the response of C60
to short-pulse laser radiation. 相似文献
12.
《光谱学快报》2013,46(4-5):539-555
Abstract Low‐pressure laser‐induced plasmas generated with a pulsed Nd∶YAG laser have complicated structures both temporally and spatially. The emission characteristics of the plasma are investigated for optimizing the experimental parameters in atomic emission spectrometry. The emission intensities of copper emission lines, measured in a time‐resolved as well as a time‐integrated mode, are strongly dependent on the kind of copper lines, ionic or atomic line, and the excitation energy. Also, the pressure of argon gas is the most important parameter for determining the behavior of these emission lines, including argon lines. Generally, copper ionic lines are dominantly emitted from the initial breakdown zone, because the copper ions are produced mainly in the hot breakdown zone. However, the Cu II 229.44‐nm line is emitted also from the expansion zone of the plasma. It results from an additional excitation process through the charge‐transfer collision particularly effective for the corresponding excited level. In this work, the excitation mechanisms for Cu I, Ar I, and Ar II lines are also discussed. The excitations occurring in the laser‐induced plasma can be well understood by taking the temporal and spatial variations in their intensities into consideration. 相似文献
13.
L. P. Babich 《Journal of Experimental and Theoretical Physics》2004,98(4):707-718
The collision operator of relativistic electrons with a cold gas of atomic particles is derived consistently taking into account elastic interactions, excitation of electron shells, and ionization. The creation of secondary electrons is described accurately. In the range of energies exceeding the binding energy of atomic electrons, the operator implicates only the angular scattering by nuclei and the ionization integral that automatically allows for scattering by atomic electrons. The collision operator used earlier for studying the kinetics of avalanches of relativistic runaway electrons is analyzed. A more exact operator derived in the present study is simpler in form and saves time in computer calculations. 相似文献
14.
Adriana Pálffy 《Contemporary Physics》2013,54(6):471-496
Atomic electrons are sensitive to the properties of the nucleus they are bound to, such as nuclear mass, charge distribution, spin, magnetisation distribution, or even excited level scheme. These nuclear parameters are reflected in the atomic transition energies. A very precise determination of atomic spectra may thus reveal information about the nucleus, otherwise hardly accessible via nuclear physics experiments. This work reviews theoretical and experimental aspects of the nuclear effects that can be identified in atomic structure data. An introduction to the theory of isotope shifts and hyperfine splitting of atomic spectra is given, together with an overview of the typical experimental techniques used in high-precision atomic spectroscopy. More exotic effects at the borderline between atomic and nuclear physics, such as parity violation in atomic transitions due to the weak interaction, or nuclear polarisation and nuclear excitation by electron capture, are also addressed. 相似文献
15.
I. N. Izosimov V. G. Kalinnikov A. A. Solnyshkin 《Physics of Particles and Nuclei》2011,42(6):963-997
The β transition strength function S
β(E) is the nuclear excitation energy distribution of moduli squared of the β-decay-type matrix elements. The function S
β(E) determines the characteristics of β decay, the spectra of accompanying radiation, and the probabilities of delayed processes
following the β decay. Until recently, tools widely used for experimental investigation of the S
β(E) structure have been total absorption gamma spectrometers and total absorption gamma-ray spectroscopy (TAGS) which could
not provide high energy resolution. Development of experimental techniques allows nuclear spectroscopy methods with high energy
resolution to be used for studying the fine structure of S
β(E). A thorough investigation of this kind has been carried out for a number of nuclei produced at the YASNAPP-2 facility in
Dubna. In this review, studies involving works on measuring the fine structure of S
β(E) in spherical and deformed nuclei are analyzed. Modern nuclear spectroscopy methods made it possible to identify the splitting
of peaks from nuclear deformation in S
β(E) for Gamow-Teller (GT) transitions. The resonance nature of S
β(E) for first-forbidden (FF) transitions in both spherical and deformed nuclei is experimentally proven. It is shown that for
some nuclear excitation energies, FF transitions can be comparable in intensity with GT transitions. Criteria for verifying
the completeness of nuclear decay schemes are considered. The S
β(E) functions obtained by TAGS and by the high-resolution spectroscopy are compared. 相似文献
16.
E. A. Volkova A. M. Popov O. V. Tikhonova 《Journal of Experimental and Theoretical Physics》2011,113(3):394-406
The dynamics of a model silver atom in the strong radiation field of a Ti:sapphire laser is studied in the Keldysh parameter
regions γ ⩾ 1 and γ ⩽ 1. It is found that in the entire range of Keldysh parameter variations, along with ionization, the
efficient excitation of Rydberg states of the atom with principal quantum numbers n = 6−14 is observed. A Rydberg wavepacket appearing in this case proved stable with respect to ionization; i.e., the atomic
system in strong low-frequency electromagnetic fields becomes stable with respect to ionization. The physical reasons behind
the stabilization are discussed. 相似文献
17.
V. Yu. Bychenkov V. T. Tikhonchuk S. V. Tolokonnikov 《Journal of Experimental and Theoretical Physics》1999,88(6):1137-1142
A technique is suggested for triggering nuclear reactions by accelerating ions with a powerful ultrashort laser pulse in a
plasma. The underlying idea of the suggested compact “reactor” is utilization of high-energy ions accelerated by the charge-separation
electrostatic field in the direction perpendicular to the laser beam axis in a gas-filled capillary. Accelerated ions with
energies of several MeV penetrating the target from the inside surface of a channel give rise to nuclear reactions which can
be used to create a compact source of fast neutrons and neutrons of intermediate energies for generating various (short-and
long-lived, light and heavy) isotopes, for generating gamma radiation over a broad energy range, for making sources of light
ion and induced radioactivity. The yield of the corresponding nuclear reactions as a function of the laser beam parameters
has been investigated. The suggested technique for triggering nuclear reactions provides a practical tool for studies of nuclear
transformation on the pico-and nanosecond scales, which cannot be achieved using other methods.
Zh. éksp. Teor. Fiz. 115, 2080–2090 (June 1999) 相似文献
18.
Spectroscopic studies of the production of MgII ions from atomic metastable states by electron impact in crossed atomic and electron beams were made. Cross sections for excitation of the strongest spectral transitions and their energy dependences were determined. The maximum value of the cross section for ionization with excitation of the 32 S 1/2–32 P 3/2 transition reached 2.4×10?16 cm2. Possible mechanisms of production of excited ions from metastable states and their contribution to the total ionization process are discussed. 相似文献
19.
20.
We study the double ionization of the atomic K-shell by a single photon in the relativistic energy domain. The differential and total cross sections of the process are
calculated. It is shown that the ratio of the cross sections of double and single ionization increases with the photon energy,
tending to the limit 0.34/Z
2, where Z is the atomic number or the nuclear charge. The formulas are found to be valid for Z≫1 and αZ≪1, where α=1/137 is the fine-structure constant.
Zh. éksp. Teor. Fiz. 114, 1537–1554 (November 1998) 相似文献