High-spin states in 84 Rb have been studied by using the 70Zn(18O, p3n)84Rb reaction at beam energy of 75MeV. Three regular magnetic dipole bands including strong M1 and weak E2 transitions have been observed in this nucleus which shows the characteristic feature of magnetic rotation. These bands are interpreted in the projected shell model for the first time on the basis of the four-quasiparticle configuration of the type π(fp)π(g29/2)v(g9/2). It is shown that the calculated sequence lies roughly in the same energy range as the experimental one but the interval between neighboring levels is larger than the corresponding experimental value. We believe that a 4-quasiparticle band crossing with the 2-quasiparticle band will depress the energies of the states.
In view of the important application of GaAs and GaN photocathodes in electron sources,differences in photoemission behaviour,namely the activation process and quantum yield decay,between the two typical types of Ⅲ-V compound photocathodes have been investigated using a multi-information measurement system. The activation experiment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs-O two-step activation and by Cs activation alone for the GaN photocathode. In addition,a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes.
Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response,one has a gradient-doping structure and the other has a uniform-doping structure.The experimental results show that the gradient-doping photocathode can obtain a higher photoemission capability than the uniform-doping one.As a result of the downward graded band-bending structure,the cathode performance parameters,such as the electron average diffusion length and the surface electron escape probability obtained by fitting quantum yield curves,are greater for the gradient-doping photocathode.The electron diffusion length is within a range of from 2.0 to 5.4μm for doping concentration varying from 1019 to 1018 cm-3 and the electron average diffusion length of the gradient-doping photocathode achieves 3.2μm.
