Fabrication of [formula omitted]As targets for heavy ion nuclear reactions

Abstract

Thin uniform targets of 75As isotope with Pb/Au backing layer were fabricated for nuclear structure studies and sub-picosecond lifetime measurements of nuclear excited states using the Doppler shift attenuation method (DSAM) for nuclei populated in the heavy-ion induced fusion-evaporation reactions. The 75As targets of thickness 2.8–4.0 mg/cm2 (4.9–7.0μm) were prepared by in-vacuo sublimation of the As metal powder on to the backing (∼10 mg/cm2) of Pb (9.4μm) or Au (5.2μm), which were prepared by rolling method. The prepared targets were further rolled to improve their uniformity and avoid any interlayer gaps. The amount 75As material required for target preparation could be significantly reduced to ∼80 mg by increasing vapour flux by replacing the open dimpled tantalum boat with the pinhole tubular form. The uniformity, purity and thickness of As and Pb layers in the fabricated targets were assessed using a non-destructive Energy dispersive X-ray fluorescence (EDXRF) technique set-up. The measured thickness values of As and Pb/Au layers were found to agree within ∼3% with those deduced from the weighing method. The prepared targets have been successfully used with 28Si and 31P ion beams and the in-beam γ-ray spectroscopic studies in excited nuclear states in 98,99Rh, 99,100,101Pd and 102Ag isotopes.