Large area isotopic silicon targets for astrophysical reaction rate studies in 26Si

Abstract

For measurements of stellar reaction rates of proton rich nuclei involving resonance levels just above threshold, targets of 28Si were used in studies of the 28Si(4He,6He)26Si reaction using the Research Center for Nuclear Physics (RCNP) Ring Cyclotron at Osaka University. Resonance structure observed in 26Si above the 5.5MeV proton threshold identified levels populated in the astrophysically important reaction 26Al(p,γ)26Si and help to determine the yield of 26Al γ-rays seen in Novae. A few isolated states were also observed above the 9.2MeV α threshold in the (4He,6He) reaction which can be used to improve the present stellar rate calculations. We describe here the involved preparation of large area 28Si metal targets used for these experiments produced by the method of electron beam evaporation. The parting agent used was betaine. To obtain the 0.7mg/cm228Si target thickness needed for the experiment, several mounted layers were assembled together by stacking. This formidable approach therefore required many foils. Two targets stacks of 0.7mg/cm2 and 0.5mg/cm228Si were delivered to Osaka for the run.