Electronic color centers in SrF2-Na crystals

It was shown that optical bleaching of M _A ⁺ color centers at 80 K in SrF₂-Na crystals causes the core of an M _A ⁺ -center to transform into the V _a ⁺ Me ⁺ V _a ⁺ configuration, in which all three point defects are arranged diagnonally in the cube cell. Reirradiation of an optically bleached crystal by x-rays generates F _D centers in it: V _a ⁺ Me ⁺ V _a ⁺ + e ^? → V _a ⁰ Me ⁺ V _a ⁺ ≡ F _D. The F _D → M _A ⁺ transformation in SrF₂-Na crystals proceeds at T = 135 K, in contrast to the F _A → M _A ⁺ transformations, which take place at T > 200 K.     

Mass spectrometer studies of the ion composition in the pink afterglow

The time dependences of the ion number densities in the pink afterglow of nitrogen, as represented by the ion wall currents, have been measured. The ions were extracted through an orifice from a flow system and analysed by a quadrupol mass spectrometer. It has been found thatN ₂ ⁺ ions are dominating in the early afterglow. With the beginning of the ionization processN ₃ ⁺ and at pressure >6 TorrN ₄ ⁺ become the majority ions. The ratio of the number densities(N ₃ ⁺ )/(N ₂ ⁺ ) reaches a maximum during the increase of the ionization processes before the maximum is reached. This behaviour suggestsN ₃ ⁺ ions to be the primary ions created by the ionization processes. The time dependences of the ion number densities (N ₂ ⁺ ), (N ₃ ⁺ ) and(N ₄ ⁺ ) are found to vary similar, showing that the ions are strongly coupled by conversion processes. The conversion processes are discussed. In the maximum of ionization at a total pressure of 4.4 Torr the ratios of the number densities of the afterglow ions (N ₂ ⁺ )∶(N ₃ ⁺ )∶(N ₄ ⁺) are 1∶1.9∶0.64.     

Electric properties of levels of 156Dy rotational bands

The nonadiabaticity of E0 transitions from 0 ₂ ⁺ states and 2 ₁ ⁺ bands in ¹⁵⁶Dy is examined within a phenomenological model that takes into account the mixing of K ^π = 0 ₁ ⁺ , 0 ₂ ⁺ , 0 ₃ ⁺ , 2 ₁ ⁺ states and 1⁺-bands. It is shown that the nonadiabaticity of E0 transitions is due primarily to the mixing of 0 ₂ ⁺ and 0 ₃ ⁺ bands.     

Color center production by femtosecond-pulse laser irradiation in fluoride crystals

Color centers are lattice vacancy defects trapping electrons or holes. They are easily created in single crystals by irradiation with ionizing radiation. We report the production of color centers in LiF and LiYF₄ single crystals by ultrashort high-intensity laser pulses (60 fs, 12.5 GW). An intensity threshold for color center creation of 1.9 and 2 TW/cm² was determined in YLF and LiF, respectively, which is slightly smaller than the continuum generation threshold. Due to the high energy density of the coherent radiation of the focused laser beam, we were able to identify a large amount of F centers, which gave rise to aggregates such as F₂, F ₂ ⁺ , and F ₃ ⁺ . The proposed mechanism of formation is based on multiphoton excitation, which also produces short-lived F ₂ ⁺ centers. It is also shown that it is possible to write tracks in the LiF crystals with dimensional control.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

Gyromagnetic ratios of excited states in186W

The gyromagnetic ratios of the 4 ₁ ⁺ , 6 ₁ ⁺ , and 2 ₂ ⁺ states in¹⁸⁶W were measured relative to that of the 2 ₁ ⁺ level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV⁶³Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 ₁ ⁺ )/g(2 ₁ ⁺ )=1.04±0.07,g(6 ₁ ⁺ )/g(2 ₁ ⁺ )=1.03 ±0.20 andg(2 ₂ ⁺ )/g(2 ₁ ⁺ )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.     

Radioluminescence of ionized electron color centers in LiF crystals

Photoluminescence (PL) and temporal variation of optical absorption and radioluminescence (RL) of LiF crystals after irradiation with an electron impulse are investigated by pulse spectrometry methods using different irradiation regimes and different degrees of initial radiation damage. The difference in the RL and PL characteristics of ionized F ₂ ⁺ and F ₃ ⁺ centers is revealed. Several mechanisms for inducing these centers by irradiation, which differ in energy and kinetic parameters and in temperature dependence, are proposed. It is established that the ionized centers in the radiation active state are created due to the interaction of the respective neutral centers with holes of different thermalization extent. A mechanism for the excitation of these radiation-active centers is proposed.     

E2 andE3 transition strengths in some rare-earth nuclei

Coulomb excitation byα-particles of vibrational-like states in even-mass rare-earth nuclei is used to determine the reduced transition probabilitiesB(E2; 0 _gs ⁺ →2 _γ ⁺ ),B(E2; 0 _gs ⁺ →2 _β ⁺ ),B(E2; 2 _gs ⁺ →0 _β ⁺ ) andB(E2; 0 _gs ⁺ →3 _oct ^? ) in¹⁵⁰Nd,^{152, 154}Sm,^{154, 158}Gd,¹⁶⁴Dy and¹⁶⁶Er. TheB(Eλ; 0 _gs ⁺ →I=λ)-values range from 2.4 to 6.5 single-particle units for transitions to the 2 _γ ⁺ -states, 0.8 single-particle units for the 2 _β ⁺ -states and from 14.1 to 21.7 single-particle units for the 3^?-states.     

Multiplicities of charged particles prior to fission

Electric monopole transitions between the 0 ₂ ⁺ , 0 ₁ ⁺ and 2 ₂ ⁺ , 2 ₁ ⁺ levels in⁷⁶Se, populated in the decay of⁷⁶Br, were investigated by means of conversion electrons and gammaray spectroscopy. TheK-electron intensity ratios ofE0 andE2 transitions connecting the 0 ₂ ⁺ level to the 0 ₁ ⁺ and 2 ₁ ⁺ levels and of theE0 andE2 components in the 2 ₂ ⁺ →2 ₁ ⁺ transition were determined. The ratioX(E0/E2) of theE0 toE2 reduced transition probabilities and, from the available lifetimes, theE0 strength parameters ρ(E0) were deduced for the two transitions. The results are compared with the predictions of current models.     

Microscopic foundation of the interacting boson model in thes d-shell nuclei

Starting from an isospin invariant shell-model hamiltonian, we describe a method for deriving microscopically the IBM-hamiltonian appropriate to lights d-shell nuclei. The key ingredients of our approach are:a) the Belyaev-Zelevinsky-Marshalek (BZM) bosonization procedure;b) two successive unitary transformations that extract the “maximally decoupled” collective bosons with angular momentaJ=0(s _ππ ⁺ ,s _νν ⁺ ,s _πν ⁺ ) andJ =2(d _ππ ⁺ ,d _νν ⁺ ,d _πν ⁺ (T=0),d _πν ⁺ (T=1)). The method is applied to obtain the low-energy spectra and the electron scattering form factors for the 0 ₁ ⁺ →2 ₁ ⁺ transitions in²⁰Ne and²⁴Mg. Good agreement with the exact shell-model results is achieved. The inclusion of proton-neutron bosons (s _πν ⁺ ,d _πν ⁺ (T=1),d _πν ⁺ (T=0)), as well as the renormalization of boson parameters due to the non-collective degrees of freedom, are shown to play a crucial role.     

Untersuchung des Zerfalls von134Cs durch γ-γ-Winkelkorrelationsmessungen

γ-γ-angular correlation measurements with Ge(Li) detectors and NaJ(Tl) detectors provided theE2/M1 mixing ratios of the following gamma transitions: 3 ₁ ⁺ →2 ₂ ⁺ (475.3 keV), 2 ₂ ⁺ →2 ₁ ⁺ (563.3 keV), 4 ₂ ⁺ →4 ₁ ⁺ (569.4 keV), 3 ₁ ⁺ →2 ₁ ⁺ (1,039 keV). The angular correlation measurements were only consistent with spin 3 of the 1,643 keV level. The half life of the 1,401 keV level was determined by delayed coincidence techniques to beT _1/2 (1,401 keV)≦30 ps.     

An ESR study of NH 3 + , al center and HO2 · radical in alkali feldspars

Paramagnetic centers of NH ₃ ⁺ , Al, and HO₂ · have been observed in alkali feldspars from Aichi prefecture, Japan. The quartet signal has been tentatively ascribed to NH ₃ ⁺ rather than to ·CH₃, although the hyperfine splitting by¹⁴N (I=1) was not observed. The averageg- andA-valuesg _av=2.0033 andA _av ^H =2.45 mT, respectively, were attributed to hydrogen. The powder spectra of Al centers stable up to 400 K were simulated by the anisotropicg factors ofg _zz =2.060,g _xx =2.0014,g _yy=2.0021 andA=0.9 mT. Newly discovered HO₂ · is stable up to 570 K. The intensities of the spectra from NH ₃ ⁺ and Al centers were enhanced by gamma-ray irradiation, while that of HO₂ · was not enhanced. Production efficiency,G-value (radical/100 eV) of NH ₃ ⁺ has been obtained to beG=0.01. These results suggest that ESR dating of feldspars is possible.     

g-factor of the second 4+ state in24Mg

The transient field technique has been used to determine theg-factor of the 4 ₂ ⁺ state at 6.010MeV excitation in²⁴Mg. The deduced value ofg=+0.5(4) is consistent with collective model expectations. Further, the equality within experimental accuracies, of the g-factors of the 2 ₁ ⁺ , 2 ₂ ⁺ , 4 ₁ ⁺ and 4 ₂ ⁺ states agrees with theoretical predictions for thisT=0 self-conjugate nucleus, in contrast to the results for²⁰Ne.     

Statistical mechanism of the formation of the energy spectra of sputtered molecular clusters

The energy spectra of Si _n O _m ^? clusters sputtered from Si targets by Xe⁺ ions with O₂ pumping onto a bombarded surface, as well as by O ₂ ⁺ ions, are studied. It is shown that the form of the Si _n O _2n+1 ^? energy distributions does not depend on the experimental conditions. Significant differences in the energy spectra of O and Si monomers as compared to Si _n O _2n+1 ^? clusters are revealed. The mentioned features of the energy distribution of Si _n O _m ^? clusters are explained within the framework of the statistical recombination mechanism of their formation in combinatorial synthesis processes.     

Form factor π0 → γ* + γ* at different photon virtualities

The π⁰ γγ vertex for virtual photons of squared masses q ₁ ² and q ₂ ² plays a vital rôle in several physical processes; for example for q ₁ ² < 0, q ₂ ² < 0, in the two-photon physics reaction e ⁺ e ^? → e ⁺ e ^?π⁰, and for q ₁ ² > 0, q ₂ ² > 0, in the annihilation process e ⁺ e ^? → π⁰ l ⁺l^?. It is also of interest because of its link to the axial anomaly. We suggest a new approach to this problem. We have obtained a closed analytic expression for the vertex in the limit in which at least one of ¦q ₁ ² ¦ and ¦q ₂ ² ¦ is large for arbitrary fixed values of the ratio q ₁ ² /q ₂ ² . We compare our results with those obtained previously by Brodsky and Lepage. It should be straightforward to test our predictions experimentally.     

Vacuum condensates in supersymmetric gluodynamics

We analyse the restrictions imposed by supersymmetric Ward identities on the dimension-six condensates in supersymmetric gluodynamics. It is shown that the system of the Ward identities admits a nonzero value for the four-fermion condensate \(\left\langle {\left( {\lambda \sigma _\mu T^a \bar \lambda } \right)^2 } \right\rangle _0 \) while 〈f ^abc F _μν ^a F _νρ ^b F _ρμ ^c 〉₀ must vanish.     

Confrontation between the quasiparticle-phonon nuclear model and the interacting boson model for deformed nuclei

TheK ^π=0⁺, 2⁺ and 4⁺ states are considered in doubly even deformed nuclei. It is shown that in the quasiparticle-phonon nuclear model (QPNM) and in the interacting boson model (IBM) a vibrational state has one dominating component. The states withK _n ^π =0 ₃ ⁺ , 0 ₄ ⁺ 0 ₅ ⁺ 2 ₂ ⁺ , 2 ₃ ⁺ , 4 ₁ ⁺ and 4 ₂ ⁺ have a dominating one-phonon component within the QPNM and a two- or three-boson component within the IBM. According to the QPNM the contribution of two-phonon components to the wave functions of these states is less than 10%, i.e. there is a qualitative discrepancy in describing the structure of these states within the QPNM and the IBM. The experimental data indicate the existence in these states of one-phonon or two-quasiparticle components. They are rather well described within the QPNM. These states cannot be described within the IBM. This is due to the fact that the IBM takes into account only a small part of the space of two-quasiparticle states, just the one entering intoΒ- andγ-vibrational states.     

Luminescence centers in silicate and germanate glasses activated by bismuth

Concentration series of silicate and germanate glasses activated by bismuth are studied. It is shown that luminescence in the IR region is controlled by several active centers related to bismuth. Based on a comparison of spectroscopic characteristics of the studied glasses with the data previously obtained for chloride glass, the observed centers were identified as Bi⁺, Bi ₂ ⁴⁺ , and Bi ₅ ³⁺ in germanate glass and Bi⁺, Bi ₂ ⁴⁺ in silicate glass.     

Description of the properties of the low-lying energy states in 100Mo with IBM2

The properties of the low-lying energy states for the 100Mo isotope is investigated within the framework of the proton-neutron interacting model IBM2.By considering the relative energy of the d proton boson to be diferent from that of the neutron boson and taking into account the dipole interacting among like-boson LπLπand LνLν,the low-lying energy spectrum is reproduced well.Particularly,the relative position of the energies for 2+1,0+2,2+2 and 4+1states shifted correctly fit the experimental data.The electromagnetic properties,including the key observable B(E2)reduced transition branching ratios and the E2 reduced matrix elements of the experimental data,are well described.Our calculations show possible shape coexistence in the 100Mo nucleus.