A Pair Spectrometer for Nuclear Astrophysics Applications

A spectrometer using two fully depleted silicon detectors (in a configuration) has been realized with the goal of directly measuring the production rate of the e+e− pairs emitted in E0 transition of the 12C 16O reaction. This is a key reaction in nuclear astrophysics, which takes place during the He burning stage of red giant stars and thus regulates the carbon/oxygen abundance in the Universe. In particular, we are interested to determine the e+e− pair cross section at energies below 2 MeV, where theoretical estimate is possible by using the R- matrix extrapolation. Experimental e+e− pair emission data at this energy thus provides a valuable tool to validate such analytical approximate scheme. Resolution and efficiency measurements have been carried out using 241Am +239 Pu source, the α source, 32P,207 Bi β sources and the 19F(p, α)16O fusion evaporation reaction below 1 MeV on beam reaction at CIRCE tandem accelerator (Caserta, Italy). The results obtained approve to be in good agreement with our GEANT4 simulation.