Improvements in Depth Selective Electron Mössbauer Spectroscopy

The conditions for achievement of high resolving power of depth selective conversion electron Mössbauer spectroscopy method at a combined installation ‘electron spectrometer–nuclear gamma-resonance spectrometer’ have been obtained. There has been made a considerable step in development of the method at its realization at a magnetic sector electron spectrometer with double focusing, equipped with electron source (a sample under investigation) of large-area and position-sensitive detector. The paper presents a prospective symmetrical version of a magnetic sector electron spectrometer that allows realizing more completely possibilities of the method. It is noted that the proposed method is particularly valuable for investigations of nanosystems, nanostrutures that contain Mössbauer nuclei.     

Conversion electron spectroscopy at IGISOL

Conversion elecron spectroscopy has been an important part of the nuclear spectrocopy research at the Department of Physics of the University of Jyväskylä since the commissioning of the first cyclotron in the mid 1970s. At the IGISOL facility a specialiced conversion electron spectrometer ELLI was developed in the late 1980s. The first results with ELLI were obtained using the beams from the old MC-20 cyclotron to study newly discovered isotopes of refractory fission products. In the present K130 cyclotron laboratory ELLI has been utilized in many decay-spectroscopy experiments both neutron-deficient and neutron-rich side of the valley of stability. In the early 2000s the new JYFLTRAP ion trap system overthrew ELLI from its permanent place in the IGISOL beamline. Conversion electron spectroscopy has continued with the new Penning trap that has been used in in-trap electron spectroscopy tests and post-trap electron spectroscopy is foreseen.     

Resonance internal conversion as a way of accelerating nuclear processes

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.     

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.     

Gamma and electron spectroscopy of transfermium isotopes at Dubna: Results and plans

Detailed spectroscopic information of excited nuclear states in deformed transfermium nuclei is scarce. Most of the information available today has been obtained from investigations of fine-structure α-decay. Although α decay gives access to hindrance factors and lifetimes which are strongly correlated to shell/subshell closures and the presence of isomers, only the combined use of γ and conversion electron spectroscopy allows the precise determination of excitation energy, spin and parity of nuclear levels.     

Studies on Synthesis,Characterization, and Luminescence Properties of A Novel Light Conversion Agent of Eu (III) and Compatibility with PE

A novel light conversion agent (NLCA) has been synthesized that is applicable to polyethylene (PE) film. The composition and structure of the NLCA was characterized by elemental analysis, Fourier transform infrared (FT‐IR) spectroscopy, and nuclear magnetic resonance (NMR) spectrometry. The morphology, particulate dimensions, dispersion property and compatibility of the NLCA were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicate that the average particulate dimension was about 60–100 nm and they were dispersed well in the PE film. The luminescence property of the NLCA was studied via fluorescent spectrometry. The fluorescence spectra of the NLCA show that the NLCA has a highly efficient luminescence.     

A rare nuclear decay process: The internal conversion between bound atomic states

We shall report on the recently observed dependence of the lifetime of the first excited state in ¹²⁵Te on the ionic charge state. Then we shall give an interpretation of the dependence of the half-life in terms of a new type of nuclear internal conversion without emission of the electron into the continuum of electron energies. We have named this process internal conversion between bound atomic states or BIC. The resonant character of the BIC will be established and the main parameters governing the decay process will be discussed [1–3]. Finally the results of a recent experiment performed at the GANIL accelerator attempting to measure directly the value of the internal conversion coefficient associated with BIC in ¹²⁵Te ions with charge states ranging between 44+ and 48+ will be given. In conclusion we shall discuss the relation between the BIC and nuclear excitation by electron transition, NEET, in the excitation of some nuclear isomeric states.     

Inner conversion process of electric dipole transitions in180Hf and182W

The conversion electron process of the retarded electric dipole transitions of 58keV in¹⁸⁰Hf and 67, 116, 152, 156 and 222 keV in¹⁸²W have been studied by means of high resolution double focusing beta-ray spectrometers. No penetration effects were found in the conversion process of the retarded 58 keV and 67, 116 and 222 keV E1 transitions. While the retarded 152 and 156 keV transitions in¹⁸²W show an anomalous internal conversion ratios compared with theoretical values. Implications of the results for current nuclear theories are discussed.     

Internal conversion of the 6.2 keV transition in181Ta

The total conversion coefficient of the 6.2 keV Mössbauer transition in¹⁸¹Ta was measured by X- and gamma-ray spectroscopy. The result of 86 ± 20 disagrees with the literature value of 46, but agrees with theory if a nuclear penetration parameter deduced from relative conversion electron intensities is taken into account. The weak 6.2 keV gamma ray has intensity per decay that is less than the previous value by a factor of 8.5.     

Internal conversion of the 6.2 keV transition in181Ta

The total conversion coefficient of the 6.2 keV Mössbauer transition in¹⁸¹Ta was measured by X- and gamma-ray spectroscopy. The result of 86 ± 20 disagrees with the literature value of 46, but agrees with theory if a nuclear penetration parameter deduced from relative conversion electron intensities is taken into account. The weak 6.2 keV gamma ray has intensity per decay that is less than the previous value by a factor of 8.5.     

Controlled optimization of mode conversion from electron Bernstein waves to extraordinary mode in magnetized plasma

In the CDX-U spherical torus, agreement between radiation temperature and Thomson scattering electron temperature profiles indicates approximately 100% conversion of thermally emitted electron Bernstein waves to the X mode. This has been achieved by controlling the electron density scale length (L(n)) in the conversion region with a local limiter outside the last closed flux surface, shortening L(n) to the theoretically required value for optimal conversion. From symmetry of the conversion process, prospects for efficient coupling in heating and current drive scenarios are strongly supported.     

Pair creation by internal conversion

In this report we describe the general theory of internal electron-positron pair conversion. Within the point nucleus approximation we derive analytical formulae for the differential pair conversion coefficient using Coulomb wave functions for the electron. Numerical calculations of the pair conversion coefficient for pointlike and extended nuclei for various multipolarities, transition energies and nuclear charges are presented and compared with Born approximation results and experimental data.     

核衰变产生的X射线和俄歇电子数据计算

核衰变过程中,内转换电子发射和电子俘获能在原子电子壳层内留下空穴.其他原子电子壳层的电子将填补这些空穴,其原子电子位置将重排,并发射X射线和俄歇电子.X射线和俄歇电子的能量由原子电子结合能计算得到,X射线和俄歇电子的强度分别由内转换电子发射和电子俘获在原子电子壳层内留下的空穴数,X射线荧光产额,和空穴转移系数计算得到.本文简要介绍核衰变产生的X射线和俄歇电子数据的计算方法、计算程序与工作流程,并以核衰变为例说明其具体应用和简要讨论与总结.     

Diagnostics of the electron scattering in metals in terms of a terahertz response to femtosecond laser pulse

A new method for the experimental determination of the characteristics of the electron scattering in a metal on the basis of optical-to-terahertz conversion has been proposed. It has been shown that the measurement of the characteristics of a low-frequency signal generated at the reflection of a femtosecond laser pulse from the surface of the metal makes it possible to determine the temperature dependence of the electron collision frequency and to reconstruct the dynamics of heating and heat transfer. The existing experimental data on the optical-to-terahertz conversion on the surface of the metal have been analyzed in terms of diagnostics.     

Delayed autoionization of recoil ions by the decay of high-spin isomeric states

The time dependence of the ionization for isotopically different heavy ion fusion recoil ions has been observed. Delayed nuclear-induced autoionization of recoil ions caused by the decay of high-spin nuclear isomeric states by internal conversion was established. Internal conversion in isolated recoil atoms results in a drastic rearrangement in the atomic cloud with a loss of a great number of orbital electrons. Possibilities for the use of the observed phenomena in atomic and nuclear physics are discussed.     

Can the observed structures in positron spectra be caused by internal conversion?

The energy distribution of positrons emitted in quasimolecular collisions of Uranium on Uranium and Uranium on Curium has been measured by several groups. Peak structures in the positron spectra were observed. We discuss the possibility that these structures originate from internal conversion processes following nuclear Coulomb excitation or transfer reactions. Consequences for the nuclear photon spectra and theδ-ray distribution are pointed out and experimental procedures for an unambiguous determination of the significance of conversion processes are discussed.     

<Superscript>29</Superscript>Si nuclear spin relaxation in microcrystals of plastically deformed Si: B samples

Single crystals and microcrystals Si: B enriched with ²⁹Si isotopes have been studied using nuclear magnetic resonance and electron paramagnetic resonance (EPR) in the temperature range from 300 to 800 K. It has been found that an increase in the temperature from 300 to 500 K leads to a change in the kinetics of the relaxation of the saturated nuclear spin system. At 300 K, the relaxation kinetics corresponds to direct electron–nuclear interaction with inhomogeneously distributed paramagnetic centers introduced by the plastic deformation of the crystals. At 500 K, the spin relaxation occurs through the nuclear spin diffusion and electron–nuclear interaction with an acceptor impurity. It has been revealed that the plastic deformation affects the EPR spectra at 9 K.     

Resonance internal conversion in hydrogen-like ions

The resonance internal conversion effect in hydrogen-like ions is considered. For the M1 transition with an energy of 70.6 keV in ¹⁷¹Yb, the lifetime of this nucleus in the excited state decreases by five orders of magnitude as a result of deexcitation via a new channel—the resonance conversion—provided that the nuclear transition energy is equal to the energy of transition of a single 1s electron to a higher ns state. Observation of the resonance conversion in hydrogen-like ions is a powerful method for investigating their nuclear structure.     

Some features of the ionization of nuclear reaction products

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.     

Spectrum of velocities and dynamics of electron beams in divergent magnetic fields

The dynamics of an electron beam in divergent magnetic fields has been studied. The changes in the longitudinal and transverse electron velocities in the beam and the effect of the magnetic field parameters on the dispersion of longitudinal electron velocities have been analyzed. A possibility of high-efficiency conversion modes in divergent magnetic fields has been established by methods of numerical simulation.