The predissociation of the 2σ u −1 (c 4Σ u − , v states of the oxygen molecular ion

The dynamics of predissociation of the 2σ _u ^?1 (c ⁴Σ _u ^? ), v vibrational states of the O ₂ ⁺ ion was studied theoretically using the method of coupled differential equations. The main equations describing the vibrational motions of nuclei in the adiabatic and diabatic approximations are given. The applicability scope of approximate methods for solving these equations was studied. The predissociation widths for the v = 0 and 1 vibrational levels were found to be Γ₀ = 0.054 meV and Γ₁ = 9.71 meV. This substantiated the results of recent observations of neutral fragments formed after the dissociation of the O₂ molecule. About 99% of the O ₂ ⁺ ions in the 2σ _u ^?1 (c ⁴Σ _u ^? ), v states were found to decompose to the O(¹ D) + O⁺(⁴ S) dissociation products.     

Disparity between the transient hyperfine fields for Pt and Os in Fe; an electron vacancy sharing interpretation

Precessions of the 2 ₁ ⁺ states in¹⁹⁸Pt and¹⁹²Os have been measured in the enhanced transient hyperfine magnetic field acting on these nuclei as they recoiled through thin polarized cobalt foils. Two separate targets consisting of contiguous layers of¹⁹⁸Pt and¹⁹²Os electrodeposited on ～1 μm and ～4 μm Co foils were employed. The levels of interest were Coulomb excited by 80 MeV³²S and 220 MeV⁵⁸Ni beams and the precessions of the 2 ₁ ⁺ →0 ₁ ⁺ γ-ray angular distributions in both nuclides were measured simultaneously. The results of these studies are compared with recently reported similar studies in which ions of¹⁸⁸Os and¹⁹⁴Pt recoiled through thin polarized Fe foils. It is concluded that (i) the transient field acting on Pt in Fe is singularly anomalous, and (ii) the recent contention that the g-factors of the 2 ₁ ⁺ states in the event Pt isotopes may be substantially lower than had been reported in the literature cannot be sustained. This transient field discontinuity is examined in terms of possible molecular orbital electron vacancy sharing between Pt and Fe.     

Investigation of N 2 + (C 2Σ u + → X 2Σ g + fluorescence excited through auger decay of the 1s −1π* resonance

A theoretical investigation of N ₂ ⁺ (C ²Σ _u ⁺ → X ²Σ _g ⁺ molecular fluorescence excited through the Auger decay of the 1s ^?1π* resonance is carried out. The fluorescence cross sections are calculated with due regard for the dependence of the matrix element of the C → X dipole transition on the internuclear distance, the interference between channels of excitation via different vibrational levels v _r of the 1s ^?1π* resonance, the rotational structure of the fluorescence band, and the predissociation of the N ₂ ⁺ C ²Σ _u ⁺ v′ ≥3) states. The calculated cross sections are in good agreement with the experimental results of recent measurements. The results of the calculations have demonstrated that the observed dependence of the cross section of the (C ²Σ _u ⁺ (v′) → X ²Σ _g ⁺ (v″) fluorescence on the excitation energy and the fluorescence wavelength for a group of bands with equal values of the difference Δv = v′ ? v″ is associated with transitions between the vibrational levels of the electronic states involved in the excitation and subsequent cascade decay of the 1s ^?1π* resonance: N₂ (v ₀ = 0) → N*₂(1s ^?1π*(v _r)) ? N ₂ ⁺ : (C ²Σ _u ⁺ (v′) → X ²Σ _g ⁺ (v″).     

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.     

New determination of the magnetic moment of the54Fe(2 1 + ) state at 1.408 MeV

Relative to the wellknowng-factor of⁵⁶Fe(2 ₁ ⁺ ) at 0.847 MeV, theg-factor of the⁵⁴Fe(2 ₁ ⁺ ) state at 1.408 MeV has been remeasured employing the technique of transient magnetic fields (TF) with the ions slowed down in ferromagnetic Gd host at initial velocities of 2.5 ν₀. Coulomb excitation on beams of^54,56Fe was accomplished with a Si target. The value obtained,g=1.05(17), is in excellent agreement with two previous results but disagrees with the value from a TF measurement where the ions passed through ferromagnetic Fe.     

A new many-body solution of the Friedel resonance problem

It is numerically shown that the groundstate of the Friedel problem (consisting of a conduction band and a dresonance), occupied with (n+ 1) electrons, can be written as Ψ = (A a ₀ ^* +Bd*) Π _v=1 ⁿ a _v ^* Φ₀, where a ₀ ^* represents a localized conduction electron state, d* is the Friedel resonance state and Π _v=1 ⁿ a _v ⁸ Φ₀ is a Slater determinant of n single electron states a _t ^* , (Φ₀ is the vacuum state). The a _i ^* together with a ₀ ^* are part of a full ortho-normalized basis of the conductions band.     

SIMS of silicon bombarded with Sb m + cluster ions

The emission of Si _n ⁺ (n = 1–11) cluster ions and Si _n X _m ⁺ (X stands for B or Sb) polyatomic ions when bombarding a single silicon crystal with Sb _m ⁺ (m = 1–4) cluster ions with energies E ₀ = 3–12 keV is studied. Considerable nonadditive enhancement of the yield of Si _n ⁺ cluster ions and most polyatomic ions is observed when the number of atoms in the bombarding cluster ions is increased. The sensitivity enhancement factor for detecting boron impurities is as high as 50 when the cluster-SIMS-molecule technique is applied.     

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 low-lying rotational states in156, 158, 160Gd

Transient-field precessions were measured simultaneously for levels in the ground-state bands of^{156, 158, 160}Gd as ions of these nuclei traversed a thin polarized Fe foil. Relative g-factors of levels up to 6 ₁ ⁺ were deduced, those of the 4 ₁ ⁺ levels being determined with greatest precision. In contrast with the conclusions of the recent report by Alzner et al. [1], our results are consistent with g(4 ₁ ⁺ ) having the same value in all three isotopes and imply g(2 ₁ ⁺ )=g(4 ₁ ⁺ ) in¹⁵⁶Gd, consistent with nuclear structure models.     

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.     

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.     

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.     

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.     

Disparity in transient field characteristics for Au ions traversing Fe and Gd hosts through measurements ofg-factors in197Au

Transient field precessions were measured for levels in the nuclides of^182,184,186W and¹⁹⁷Au as their ions simultaneously traversed polarized Fe and Gd hosts. Consistent sets of gyromagnetic ratios were inferred for the lowest 5/2⁺ and 7/2⁺ states in¹⁹⁷Au using these two ferromagnetic host media, provided that (i) the transient field for Au ions in Gd is calibrated using the W in Gd precessions (simultaneously measured) and, (ii) the transient field for Au in Fe is calibrated using the field strength and velocity dependence for Pt in Fe (previously measured). The presentg-factor results are: g(5/2 ₁ ⁺ ;¹⁹⁷Au)=0.296±0.023, g(7/2 ₁ ⁺ ;¹⁹⁷Au)=0.241±0.021, and g(5/2 ₁ ⁺ ;¹⁹⁷Au)=1.2±0.2.     

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.     

Conserved-vector-current hypothesis and the\bar v_e e^ - \to \pi ^ - \pi ^0 process

Based on the conserved-vector-current (CVC) hypothesis and a four-ρ-resonance unitary and analytic VMD model of the pion electromagnetic form factor, theσ _tot(E _v ^lab ) and dσdE _π ^lab of the weak \(\bar v_e e^ - \to \pi ^ - \pi ^0\) process are predicted theoretically for the first time. Their experimental approval could verify the CVC hypothesis for all energies above the two-pion threshold. Since, unlike the electromagnetic e⁺e^?→π⁺π^? process, there is no isoscalar vector-meson contribution to the weak \(\bar v_e e^ - \to \pi ^ - \pi ^0\) reaction, accurate measurements of theσ _tot(E _v ^lab ) that moreover is strengthened with energyE _v ^lab linearly could solve now a widely discussed problem of the mass specification of the first excited state of theρ(770) meson. As a by-product, an equality \(\sigma _{tot} (\bar v_e e^ - \to \pi ^ - \pi ^0 ) = \sigma _{tot} (e^ + e^ - \to \pi ^ - \pi ^0 )\) is predicted for \(\sqrt s \approx 70 GeV\) .     

Investigation of gamma-ray transitions in56Ni

Angular correlation measurements for the⁵⁴Fe(³He,n γ)⁵⁶Ni reaction were performed at \(E_{3_{He} } = 12.5\) MeV. Method II of Litherland and Ferguson was used to determine the multipole mixing ratio of theγ-radiation and the spins of the excited levels at 3925 and 3956 keV. As the most probable spin assignments we deduced 4⁺ (3925 keV) and 0⁺ (1,2) (3956 keV). The mixing ratio found for the 1225 keV transition from 4⁺→2 ₁ ⁺ isδ(M3/E2)=+0.21 _?0.16 ^+0.23 This result is compared with a shell model calculation.     

MeanM-subshell fluorescence yields atZ=88, 90, 92, and 94

M x-ray —L x-ray coincidence measurements with high resolution, cooled Si(Li) x-ray detectors were made on transitions following the alpha decays of²²⁸Th,²³²U,²³⁸Pu, and²⁴⁴Cm, in order to determine the meanM-subshell fluorescence yields. The values obtained are:v ₄ ^M =0.032±0.002, andv ₅ ^M =0.024±0.002 atZ=88;v ₁ ^M =0.038±0.003,v ₄ ^M =0.042±0.002, andv ₅ ^M =0.038±0.002 atZ=90;v ₁ ^M =0.047±0.002,v ₄ ^M =0.048±0.002, andv ₅ ^M =0.044±0.002 atZ=92;v ₁ ^M =0.066±0.002,v ₄ ^M =0.062±0.002, andv ₅ ^M =0.063±0.002 atZ=94. The quantityΩ ₁ ^M +f ₁₂ ^MΩ ₂ ^M was measured as (56±10)×10^?4, (62±12)×10^?4, (99±18) ×10^?4, and (93±15)×10^?4 forZ=88, 90, 92, and 94, respectively, which agree well with the calculations of McGuire. The radiativeL ₁-L ₃ transition intensity was measured for the four atomic numbers and found to be consistently less than the calculations of Scofield by about 45 percent.     

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.     

Electromagnetic transition probability from the ground to the first excited 2+ state in138ce

The ratio of the B(E2) values for the 0 ₁ ⁺ → 2 ₁ ⁺ transitions in¹³⁸Ce and¹⁴²Ce was measured by Coulomb excitation with α-particles. From the known value of the transition probability in¹⁴²Ce it results: B(E2,¹³⁸Ce, 0 ₁ ⁺ → 2 ₁ ⁺ =0.45 +/?0.03 e² b ²