Speaker
Description
Neutron-induced reaction cross sections of short-lived nuclei are essential inputs to the astrophysical processes that produce elements heavier than iron. However, these cross sections are very difficult or impossible to measure due to the difficulty of producing and handling the necessary radioactive targets. The NECTAR project at the Experimental Storage Ring in GSI, Darmstadt demonstrates, for the first time, surrogate reactions in inverse kinematics at a heavy-ion storage ring. The method allows us to measure all the de-excitation probabilities of the same compound nucleus that is formed in the neutron-induced reaction, as a function of the excitation energy, and indirectly determine the aforementioned cross sections.
In this contribution, I will present results from our first two demonstration experiments where we investigated the ($p,p'$), ($d,p$) and ($d,d'$) surrogate reactions on $^{208}$Pb and $^{238}$U beams. In these experiments, we 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 competing decay channels enables the precise determination of fundamental quantities, including fission barriers, particle transmission coefficients, $\gamma$-ray strength functions, and nuclear level densities that allow us to infer ($n,f$), ($n,\gamma$), ($n,n'$), ($n,2n$), and ($n,3n$) cross sections. I will also describe our future plans to use the storage ring to perform surrogate reactions on radioactive beams.