Speaker
Description
One of the most important fission quantities is the fission barrier as it defines the fission cross sections. The most direct (and often the only) way to obtain fission barriers is to measure the fission probability as a function of the excitation energy of nuclei formed by transfer and inelastic scattering reactions. The measurement of the fission probability together with the probabilities for the de-excitation channels that compete with fission (e.g. gamma or multiple neutron emission) sets strong constraints on the description of the de-excitation process and can lead to a significant reduction of the uncertainty of the fission barrier parameters. However, the measurement of gamma or neutron-emission probabilities in standard experiments is very difficult due to the very low detection efficiencies for gamma rays and low-energy neutrons, and the intense background of gamma rays and neutrons emitted by the fission fragments. Moreover, so far, the decay probabilities have only been measured for nuclei close to the valley of stability due to the difficulty to produce and handle radioactive targets.
We are developing a project that studies for the first time fission in inverse kinematics at a heavy-ion storage ring. This allows one to measure with unrivalled precision the fission probability and the probabilities for all the de-excitation modes competing with fission of nuclei located far from stability.
In this talk, I will present our new methodology and the results of the first two experiments that we have successfully performed at the ESR storage ring of the GSI/FAIR facility in Darmstadt, Germany. In these experiments, we have achieved a significant breakthrough by measuring for the first time the fission, gamma-ray, neutron and even two- and three-neutron emission probabilities simultaneously. The measurement of all these probabilities enables the precise determination of fission barriers and other fundamental quantities, including particle transmission coefficients, gamma-ray strength functions, and nuclear level densities. All these quantities will be employed to infer (n,f), (n,gamma), (n,n'), (n,2n), and (n,3n) cross sections.