Relation of contact densities with Mössbauer isomer shifts for 35.46 keV M1 transition of125Te

The internal conversion electron and Mössbauer isomer shifts associated with the 35.46 keV M1 transition of¹²⁵Te were observed for different metal samples into which radioactive¹²⁵I as probe atoms were introduced by means of ion-implantation. From the correlation between the Mössbauer isomer shifts and intensity ratios of O shell to N_I shell conversion electrons, a relation between 5s-electron contact densityp _5s(0) in a.u. and isomer shift δ in mm/s was deduced to bep _5s(0)=106+30.3 δ±4.3[(δ?0.30)²+0.069]^1/2, where δ was measured relative to ZnTe in mm/s. The change of the nuclear charge radius in the 35.46 keV M1 transition of¹²⁵Te was found to be ΔR/R=(0.85±0.12)×10^?4 (corresponding to Δ<r ²>=(3.7±0.5)×10^?3 fm²) when a theoretical 4s-electron contact density of 928 a.u. was used.     

Calibration of the isomer shift of125Te from internal conversion and mössbauer measurement

Radioactive¹²⁵I was ion-implanted into 7 different metal matrices. Al, Au, In, Pt, Sn, Te and Zn, and internal conversion and Mössbauer spectra associated with the 35.46 keV M1 transition of¹²⁵Te were measured for the same samples. A value R/R=(0.853±0.115)×10^–4 was derived for the relative difference of the nuclear charge radius for the 35.46 keV M1 transition of¹²⁵Te.     

Lasers as a bridge between atomic and nuclear physics

This paper reviews the application of visible and ultraviolet laser radiation to several topics in low-energy nuclear physics. We consider laser-induced nuclear anti-Stokes transitions, laser-assisted and laser-induced internal conversion, and the electron bridge and inverse electron bridge mechanisms as tools for deexcitation and excitation of low-lying nuclear isomeric states. A study of the anomalously low-lying nuclear isomeric states (in the case of the ²²⁹Th nucleus) is presented in detail.     

Nuclear excitation by electron capture followed by fast x-ray emission

The resonance strength of the two-step process of nuclear excitation by electron capture followed by γ decay of the nucleus can be significantly increased in highly charged ions if the resonant capture proceeds via an excited electronic state with subsequent fast x-ray emission. For fully ionized ²³⁸₉₂U and ²³²₉₀Th, the x-ray decay stabilizes the system against internal conversion of the captured electron, with an increase of both nuclear lifetimes and resonance strengths of up to two orders of magnitude compared with the case when occupied atomic orbitals prevent the x-ray de-excitation. Applications of this effect to the measurement of the not yet experimentally observed nuclear excitation by electron capture and to dense astrophysical plasmas are discussed.     

Determination of the static quadrupole moment of the first 2+ states of 122Te, 124Te,and 130Te by heavy-ion coulomb excitation

A Coulomb excitation experiment has been performed on the first 2⁺ states of ¹²²Te, ¹²⁴Te and ¹³⁰Te. The relative excitation probabilities of the first 2⁺ states were measured at backward and forward projectile scattering angles. Particle-γ coincidences were used to identify the inelastic events. The data were analyzed with the aid of the Winther-deBoer multiple Coulomb excitation program. Separate γ-ray angular distribution measurements were made as a function of target recoil velocity to determine the influence of the deorientation effect. The projectile and bombarding energy were chosen to minimize the effect on the experiment of higher state interference due to Coulomb excitation of the first 2⁺ state via the second 2⁺ state. For positive higher state interference the extracted quadrupole moments of the first 2⁺ states are Q₂₊ = ?0.43 ± 0.08 b, ?0.49 ± 0.08 b and ?0.08 ± 0.08 b for ¹²²Te, ¹²⁴Te and ¹³⁰Te respectively. These results and other measurements of Q_2⁺ for the doubly even Te isotopes are used to discuss the model dependent calculations of Q_2⁺.     

Collision strengths for the N = 2 excitation of hydrogenic ions

An empirical formula is given for the estimation of the collision strengths for electron impact excitation of the 2s and 2p states of hydrogenic systems based on close coupling calculations. The coefficients in this formula are given as functions of the nuclear charge, Z, thereby making a possible estimation of the collision strength for any system between H and Fe²⁵⁺.     

Charge transition densities for the excitation and nucleon decay of the giant dipole resonance in16O

Predictions on charge transition densities in¹⁶O for the excitation of the giant dipole resonance are given within a continuum self-consistent RPA-SK3 theory. The nuclear states are allowed to decay with proton or neutron ejection. The discussion is focused on the analysis of the radial behaviour of transition densities in terms of their microscopic structure. The rôle of RPA ground state correlations is clarified. The surface properties of resonant nuclear states extracted from photonuclear and (e, e′ x) reactions at low momentum transfer are confronted with the full radial dependence of the resonant structure shown in charge transition densities.     

Ionization of iridium ions in the Dresden EBIT studied by X-ray spectroscopy of direct excitation and radiative recombination processes

Ir^q+ ( 41≤q≤64) ions with open-shell configurations have been produced in the electron beam of the room-temperature Dresden Electron Beam Ion Trap (Dresden EBIT) at electron excitation energies from 2 keV to 13 keV. X-ray emission from direct excitation processes and radiative capture in krypton-like to aluminium-like iridium ions is measured with an energy dispersive Si(Li) detector. The detected X-ray lines are analyzed and compared with results from multiconfigurational Dirac-Fock (MCDF) atomic structure calculations. This allows to determine dominant produced ion charge states at different electron energies. The analysis shows that at the realized working gas pressure of 5×10^-9mbar for higher charged ions the maximum ion charge state is not preferently determined by the chosen electron beam energy needed for ionization of certain atomic substates, but by the balance between ionization and charge state reducing processes as charge exchange and radiative recombination. This behaviour is also discussed on the basis of model calculations for the resulting ion charge state distribution. Received 12 July 2001 and Received in final form 10 September 2001     

Nuclear structure and chemical effects in internal conversion of the 35 keVM1+E2 transition in125Te

The relative conversion line intensities of the 35 keV transition in¹²⁵Te were measured using the 50 cm π√2 iron-yoke magnetic spectrometer. The transition was proved to be ofM1+(8.7±1.5)×10^?4 E2 multipolarity, the magnetic component being affected by the nuclear structure with λ=2.4±1.4. The conversion intensity ratio,0/N ₁ , was determined to be 0.115+0.005 for both Ag¹²⁵ I and Cu¹²⁵ I sources. It is in accordance with previous measurements for the Zn^125m Te and Pb^125m Te sources and differs from those for the^125mTeO₂ and Na₂H ₄ ^125m TeO₆ ones. The conversion coefficients were calculated for 32 configurations of the valence shell of free tellurium atom and ions and were compared with the experimental results.     

Beta decay of 125Sb and level structures in 125Te

The decay of 2.76y ¹²⁵Sb to levels of ¹²⁵Te has been studied using an HPGe detector for gamma-ray and a mini orange electron spectrometer for conversion electron measurements. We identify 38 transitions in this decay, including 13 gamma rays and 4 conversion electron lines being reported for the first time. New results also include E1 multipolarity assignments to 3 newly observed transitions and M-shell conversion coefficient for the 109 keV M4 transition. A revised ¹²⁵Te level scheme is constructed using Ritz combination principle. While confirming the existence of 10 well established levels below 700 keV excitation, we introduce 3 other levels at 402.0, 538.6 and 652.9 keV. Interpretation of the observed levels in terms of various theoretical approaches is briefly discussed. The newly introduced 538.6 keV (1/2⁺) and 652.9 keV (3/2⁺) levels are seen as the two missing members of the (s _1/2 ⊗ 2⁺) and (d _3/2 ⊗ 2⁺) sextuplet in the quasiparticle-phonon coupling scheme.     

Radiative recombination of ions and nuclei in electron cooling systems

Experimental data on rates for the radiative recombination of nuclei (from helium to uranium) and various ions in interaction with an electron beam in electron cooling systems are reviewed. An analysis of the experimental data has yielded the dependence of the radiative recombination rate on the relative electron energy appreciably differently than the theoretical models obtained earlier by H. Kramers and R. Schuch. In addition, it is shown that the radiative recombination rate of nuclei in the experiment depends on the transverse electron energy as T _?? ^?0.82 ,which is also different from the results of the calculations by the theoretical model proposed by M. Bell and J. Bell. Experimental data on the cooling of ions in intermediate charge states are analyzed and the dependence of the radiative recombination rate on the charge state of the ion (electron-shell configuration) is shown. For some ion charge states, the rate of the process is of a resonance character. Loss to radiative recombination in the electron cooling system of the NICA Booster is evaluated for the Au³²⁺, Au³³⁺, Au⁵⁰⁺, and Au⁵¹⁺ ion beams. Limitations imposed on the Au79+ beam lifetime by radiative recombination in the electron cooling system of the NICA Collider are analyzed. Possible ways to decrease the radiative recombination rate of nuclei by selecting the parameters of the electron cooling system for the NICA Collider are proposed.     

Local composition and carrier concentration in Pb0.7Ge0.3Te and Pb0.5Ge0.5Te alloys from Te NMR and microscopy

Pb_0.7Ge_0.3Te and Pb_0.5Ge_0.5Te alloys, (i) quenched from 923 K or (ii) quenched and annealed at 573 K for 2 h, have been studied by ¹²⁵Te NMR, X-ray diffraction, electron and optical microscopy, as well as energy dispersive spectroscopy. Depending on the composition and thermal treatment history, ¹²⁵Te NMR spectra exhibit different resonance frequencies and spin-lattice relaxation times, which can be assigned to different phases in the alloy. Quenched and annealed Pb_0.7Ge_0.3Te alloys can be considered as solid solutions but are shown by NMR to have components with various carrier concentrations. Quenched and annealed Pb_0.5Ge_0.5Te alloys contain GeTe- and PbTe-based phases with different compositions and charge carrier concentrations. Based on the analysis of non-exponential ¹²⁵Te NMR spin-lattice relaxation, the fractions and carrier concentrations of the various phases have been estimated. Our data show that alloying of PbTe with Ge results in the formation of chemically and electronically inhomogeneous systems. ¹²⁵Te NMR can be used as an efficient probe to detect the local composition in equilibrium as well as non-equilibrium states, and to determine the local carrier concentrations in complex multiphase tellurides.     

The ionic charge distribution of fission products and the influence of internal conversion on highly preionized heavy ions

At the mass spectrometer LOHENGRIN of the Institut Laue-Langevin the ionic charge state distributions of²³⁵U(n _th,f)-fission products separated according to their mass, nuclear charge and kinetic energy were determined. The mean values and the widths of the ionic charge state distributions are compared with semiempirical predictions. Deviations between the experimental data and the estimation of Nicolaev and Dmitriev are found. Furthermore, the influence of the internal conversion process on the ionic charge state distribution of highly ionized fission products was established. Internal conversion is observed mainly for odd-odd nuclei and nuclei with 59 neutrons. The Auger cascade following the internal conversion process shifts the ionic charge state distribution by about 3 charge units. The yield of conversion electrons per fragment was determined in the mass range 85≦A≦103.     

高电荷态离子引起的富勒烯离子的碎裂

离子在与富勒烯的相互作用过程中会导致C60分子的激发。处于低激发态的C60r+离子通过发射中性C2分子或带电的轻团簇碎片Cn+等非对称碎裂方式来耗散激发能,但如果激发能很高,笼形的C60r+离子可能会彻底崩溃,而发生多重碎裂。C60r+离子的碎裂过程与其电荷态r及分裂势垒密切相关。低电荷态的C60r+(r≤3)离子蒸发一个C2分子需要克服10.3 eV左右的势垒。随着电荷态的升高,发射带电的Cn+会变得越来越容易,并逐渐过渡到多重碎裂过程。另一方面,C60r+离子的碎裂机制还与激发方式有关,在直接正碰过程中,将C60分子当作固体薄靶来处理,通过分析不同价态的C60r+离子的碎片谱,发现母核的初始电荷态决定碎裂方式,由此获得一个可以表征激发能大小的可观测量——发射电子个数。     

Triggering of nuclear isomers via decay of autoionization states in electron shells (NEET)

Nuclear excitation by an electron transition (NEET) may be used for triggering the decay of nuclear isomers only when there are compensations between energies (ΔE) and multipolarities (ΔL) of the nuclear transition and the transition in an electron shell. It is shown that using the autoionization states (AS) allows one to compensate for the ΔE and ΔL differences. Laser radiation may be used for the excitation of AS with energies up to 10–15 eV and ^229m Th (3.5 eV) nuclear isomer excitation by NEET via AS decay. Ion beams, electron beams, and X rays may be used for the excitation of the trigger nuclear levels with energies up to 150 keV by NEET via AS and for the triggering of the nuclear isomer decay. For excitation of AS with the energies up to 150 keV, two or more hole states in deep inner electron shells must be excited. The cross section for such two-hole state excitation in electron shells by ion beams may be sufficiently high. The possibilities of NEET via AS for the triggering of nuclear isomer decay are discussed.     

Charge transfer effects in surface enhanced Raman scattering

Surface enhanced Raman scattering (SERS) due to charge transfer interactions between the adsorbed molecule and the metal surface is analyzed using the semiempirical Wolfsberg-Helmholz method¹ to relate the molecule-surface interactions and the resulting charge transfer states to the overlap integrals between the metal conduction-band orbitals and an acceptor or donor molecular orbital of the molecule. Calculations for the model system of ethylene adsorbed on silver (approximated as a simple cubic metal with tight binding wave functions constructed from Ag 5s valence orbitals), with charge-transfer excitation of an electron from the metal to the antibonding ethylene π orbital, show that charge-transfer Raman enhancements of the order of 10 to 1000 are possible if the charge-transfer band is partially resonant with the exciting radiation. The net enhancement is the product of the charge-transfer gain and the electrodynamic enhancement due to plasmon resonances at surface roughness elements. Symmetric vibrations usually will be enhanced substantially more than nonsymmetric ones by charge-transfer because, in contrast to non-resonant Raman scattering, the vibrational coupling is primarily Franck- Condon (due to differences in the equilibrium nuclear configurations of the ground and excited charge transfer states and the resulting nonorthogonality of different vibrational sublevels of these states) rather than Herzberg-Teller (due to vibrationally induced changes in the electronic wave functions). The charge-transfer mechanism is selective with the most enhanced vibrations involving those atoms which experience the greatest change in electron density between the ground and excited charge-transfer state. A recent report of SERS for benzene on platinum,² strongly suggests charge-transfer enhancement because the electromagnetic-field-enhancing plasmon resonances are strongly damped in this metal.The complete paper will be published in the December 1, 1982 issue of the Journal of Chemical Physics.     

Coulomb-nuclear interference in the scattering of 3He and α-particles by 122,124Te, 124Sn and 114Cd

Angular distributions and excitation functions of the elastic and inelastic scattering of ³He and α-particles by ^122,124Te, ¹²⁴Sn and ¹¹⁴Cd at incident energies around the Coulomb barrier were measured. The experimental results were analyzed in the framework of the optical model and DWBA taking into account the interference between nuclear and Coulomb excitation. Nuclear and charge deformation parameters were deduced.     

Local nuclear orientation of125I in tin and graphite using defect induced electric field gradients

Defect-induced field electric field gradients, generated by ion implantation of¹²⁵I in α- and β-Sn and in graphite, were used to obtain local nuclear orientation at low temperatures. The resulting nuclear orientation at the parent¹²⁵I state was detected by¹²⁵Te Mössbaner spectroscopy. From the measured nuclear quadrupole interaction strengths at the parent state, the electric field gradient and the cooling behavior of implanted atoms were studied.     

Meson-exchange contributions to the nuclear charge operator

The role of the meson-exchange current correction to the nuclear charge operator is studied in electron scattering processes involving the excitation of medium and heavy nuclei to energies up to the quasi-elastic peak. The effect of these contributions in the quasi-free electron scattering process is a reduction of at most a 3% in the longitudinal response at the energy of the peak, a value which is below the experimental error and must not be taken into account in calculations in this energy region. On the other hand, the excitation of low-lying nuclear levels of neutronic character shows, with respect to the protonic ones, a considerable effect due to the inclusion of the two-body term in the charge operator. More realistic calculations, such as those performed in the random-phase approximation framework, give rise to a mixing of one particle-one hole configurations of both kinds which reduce these effects. However, it has been found that the excitation of some of these levels is sizably affected by the meson-exchange contribution. More precise experimental data concerning some of these states, such as e.g. the high-spin states in ²⁰⁸Pb, could throw some light in the problem of a more feasible determination of these effects and, as a consequence, could provide an alternative procedure to determine the charge neutron form factor.     

Excited and ground state conformations of p-dimethylamino-benzaldehyde and p-dimethylaminoacetophenone

p-dimethylaminobenzaldehyde (DMABA) and p-dimethylaminoacetophenone (DMAA) were investigated in nonpolar and polar protic and aprotic solvents over a wide temperature range. The sequence of the lower lying excited states was established. The temperature dependence of the fluorescence yields was interpreted within the irreversible reaction kinetics scheme b¹→TICT (twisted internal charge transfer) state. The activation energies and the rate constants were evaluated. Differences between the low-temperature fluorescence or phosphorescence excitation spectra and the absorption spectrum were found to be due to the existence of different rotamers in the ground state. Quantum chemical (INDO) calculations of the energies of electronic transitions, oscillator strengths and dipole moments were performed for flat and twisted conformations of DMABA.