Lifetimes of high-spin levels in39Ar

The high-spin states in³⁹Ar at 2651, 3992, 4543, and 5536 keV were excited in oxygen-induced fusion-evaporation reactions. Mean lifetimes ofτ _m =1.0±0.2, 1.2±0.3, 1.6±0.3, and <1 ps were determined for these levels, respectively, by means of the recoil distance Doppler shift technique. The transition rates are discussed in terms of the Bansal-French weak-coupling model.     

Coulomb excitation and lifetime measurements of the 21+ states in 76, 82, 84Kr

A mean lifetime of τ = 35 ± 3 ps of the 2⁺₁ state in ⁷⁶Kr has been measured with the recoil distance method via the reaction ⁶³Cu(¹⁹F, α2n)⁷⁶Kr. The B(E2; 0⁺₁ → 2⁺₁) values and lifetimes of the 2⁺₁ states in ^{82, 84}Kr have been measured via Coulomb excitation using the 1.4 MeV/A UNILAC krypton beams. The intensities of the γ-rays from the Coulomb excited levels of ^{82, 84}Kr were interrelated with those of the target nuclei ²⁷Al, ^{64, 66}Zn and ^{70, 72, 74, 76}Ge and yielded the values $\text{B(}\text{E}\text{2; 0}{}^{\mathrm{+}}{}_1\text{→ 2}{}^{\mathrm{+}}{}_1\text{= 0.255±0.009}\text{and}\text{0.122 ± 0.005}\text{e}\text{2 ·}\text{b}\text{2}\text{for}{}^{\mathrm{82,\; 84}}\text{Kr}$, respectively. In turn, these B(E2) values and the (E2; 0⁺₁ → 2⁺₁ values of the even Ge and Zn isotopes from the literature were used in a Doppler-shift attenuation analysis to obtain experimentally lacking electronic stopping power for Kr ions slowing down in Al, Zn and Ge. for Ge ions in Ge and for Zn ions in Zn.     

Study of electromagnetic transition strengths in 81Rb

High-spin states in ⁸¹Rb were excited in the fusion-evaporation reaction ⁶⁵Cu(¹⁹F, p2n)⁸¹Rb. Their lifetimes were determined by means of the recoil distance and Doppler-shift attenuation techniques. Deduced B(E2) and B(M1) transition strengths are discussed in the framework of the asymmetric rotor-plus-particle model.     

Nuclear structure studies of high-spin states in 79Rb and 79Kr

Fluorine and carbon induced fusion-evaporation reactions were used to excite high-spin states in ⁷⁹Rb and ⁷⁹Kr. The level scheme of ⁷⁹Rb was established on the basis of neutron multiplicity measurements, γγ coincidence data and excitation functions. From recoil distance and Doppler shift attenuation lifetime measurements, E2 strengths of the positive-parity yrast states in ${}^{79}\text{Kr}\text{(}\text{up to}\text{I}{}^{\mathrm{\pi }}\text{=}\text{21}\text{2}{}^{\mathrm{+}}$) and the favored and unfavored states in ${}^{79}\text{Rb}\text{(}\text{up to}\text{I}{}^{\mathrm{\pi }}\text{=}\text{25}\text{2}{}^{\mathrm{+}}$) were derived. An interpretation of these data in terms of the asymmetric rotor-plus-particle model and the interacting boson fermion model (with or without separate proton and neutron bosons) is proposed. Energies and lifetimes of a second stretched band in ⁷⁹Rb (probably with negative parity) were also measured.     

Statistical model calculations of continuum feeding times in heavy-ion fusion reactions

The time development of oxygen-induced compound reactions on ²⁷Al and ⁵⁸Ni targets at 30–70 MeV beam energy has been calculated in the framework of the statistical model. Feeding times associated with the population of yrast states in the evaporation residues have been estimated. It is shown that the experimental feeding times τ₁ < 0.2 ps, when combined with measured evaporation residue cross sections and/or absolute γ-ray yields, put restrictions on the spin dependence of the level density. Furthermore, it has been found that the dipole strength of continuum transitions between high-spin states is of the same order of magnitude as that obtained in radiative neutron capture reactions.     

Evidence of boson cut-off in the aligned g92 band in 79Rb

Electronic timing, recoil distance and DSA lifetime measurements were performed for the states of the decoupled$\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton band in ⁷⁹Rb, up to $\text{29}\text{2}{}^{\mathrm{+}}$, by means of the reactions ⁷⁰Ge(¹²C, p2n) and ⁶³C(¹⁹F, p2n). It was found that the B(E2) values of the higher in-band transitions are reduced with respect to the predictions of the rotational alignment model, but agree well with the interacting boson fermion model. This effect is attributed to the finite boson number N = 8 of the ⁷⁸Kr core.     

Electronic excitations during grazing scattering of hydrogen atoms on KI(001) and LiF(001) surfaces

The energy loss of hydrogen atoms with energies of 400 eV and 1 keV is studied in coincidence with the number of emitted electrons during grazing scattering from atomically clean and flat KI(001) and LiF(001) surfaces. The energy loss spectra for specific numbers of emitted electrons are analyzed in terms of a binary interaction model based on the formation of transient negative ions via local capture of valence band electrons from anion sites. Based on computer simulations we derive for this interaction scenario probabilities for the production of surface excitons, for electron loss to the conduction band of KI, for emission of electrons, and for formation of negative hydrogen ions. The pronounced differences of data obtained for the two surfaces are attributed to the different electronic structures of KI and LiF.     

14.5GHz紧凑型、低成本、全永磁ECR离子源

A compact 14.5GHz electron cyclotron resonance (ECR) ion source for the production of slow, multiply charged ions has been constructed,with the plasma-confining magnetic field produced exclusively by permanent magnets.Microwave power of up to 175W in the frequency range from 12.75 to 14.SGHz is transmitted from ground potential via a PTFE window into the water-cooled plasma chamber which can be equipped with an aluminum liner.The waveguide coupling system serves also as biased electrode,and two remotely-controlled gas inlet valves connected via an insulating break permit plasma operation in the gas- mixing mode.A triode extraction system sustains ion acceleration voltages between 1kV and 10kV.The ECR ion source is fully computer-controlled and can be remotely operated from any desired location via Ethernet.