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Working Area 3:
Nucleosynthesis of
heavy elements

The rapid neutron capture process can be understood as a (n,γ)-(γ,n) equilibrium interrupted by Beta-decays until most of the neutrons are captured and matter decays to stability. During this phase, properties of  the fission process of exotic nuclei have a strong impact.

The nucleosynthesis during the r-process is dominated by (n,γ)-(γ,n) reactions around b-unstable nuclei. As soon as the next element is reached via beta-decay, neutron captures will take over until the next waiting point is reached.

When the (n,γ)-(γ,n) equilibrium breaks, also called freeze out, there is a competition between neutron captures and beta decays. The neutron captures rates during the decay to stability are critical to determine the final abundance pattern that can be compared to observations from our Sun and from the oldest stars.

We will address the need for improved fission models with precision experiments at the S-DALINAC in Darmstadt. The electron beam from S-DALINAC will be used to trigger fission and the fission products will be detected with high angular resolution.

S-DALINAC at TU-Darmstadt
source: TU-Darmstadt (IKP)
The (e,e‘f) setup at S-DALINAC
source: Pietralla / Reifarth

Improvements of the freeze-out scenario requires improved neutron capture cross sections of short-lived isotopes. Here we will use a new technique – surrogate reactions in combination with a storage ring in inverse kinematics.

Schematics of the surrogate technique – we will investigate
e.g.135I(d,p) instead of 135I(n,γ) source: Reifarth
source: Reifarth

The experiments will be performed in inverse kinematics with the light reaction partner as a gas at rest and the ions revolving in a storage ring.

PIs in this work area include:  A. Arcones, M. Arnold, M. Block, T. Galatyuk, Y. Litvinov, G. Martínez-Pinedo, N. Pietralla