Nucleosynthesis in First Stars

First stars have formed about 400 million years after the Big Bang by gravitational contraction of density inhomogeneities in the rapidly expanding primordial material. Model simulations suggest that first stars have masses between 10 and 150 solar masses and rapidly develop towards a core-collapse supernova, because of their insufficient nuclear energy production. First stars provide the conditions for the first step of the chemical evolution of our universe. They are essential for converting the primordial or Big Bang abundances of hydrogen, helium, and lithium isotopes, which have emerged in the first ten minutes of the universe, to more massive isotopes in the CNO to Ca range as observed in the eldest star generations. This step requires bridging the A=5 and A=8 mass gap through a series of nuclear reactions that are based on the cluster configuration of light lithium, beryllium, and boron isotopes. Alpha cluster configurations typically emerge near the alpha threshold in nuclear compound systems and enhance the reaction rate of alpha capture by orders of magnitude, therefore providing critical stepping stones for the production of CNO nuclei. The talk will present a number of underground studies to probe these cluster configurations and to investigate the impact on nucleosynthesis in a first star environment.