In order to explain the formation of the elements in the universe, information about the reactions of light atomic nuclei is required. A team with leading participation from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now investigated one of the central reactions with unprecedented precision: the fusion of a hydrogen nucleus, the proton, with the nucleus of the hydrogen isotope deuterium. This key reaction of so-called primordial nucleosynthesis was studied at the Laboratory for Underground Nuclear Astrophysics (LUNA) at Gran Sasso d'Italia, where the cosmic radiation that interferes with measurements is efficiently shielded.
For this purpose, the nucleus of the hydrogen isotope deuterium was bombarded with a proton. This produces helium-3, a stable helium isotope, as well as a gamma quantum that can be detected with an ultra-pure germanium detector. The researchers were particularly interested in the so-called cross-section of the reaction, which provides information about the probability of its occurrence. They have now determined this parameter with unprecedented precision.
The results of the study make it possible to precisely determine the density of ordinary matter in space, which, according to current knowledge, makes up only five percent of the entire universe. The remaining 95% is attributed to invisible dark matter and dark energy. The density of this matter consisting of protons and neutrons determined using the theory of primordial nucleosynthesis agrees with values previously derived from other methods, such as the measurement of cosmic background radiation or the investigation of the deuterium abundance in certain hydrogen gas clouds. The team will continue its scientific work in the next decade with the LUNA-MV project, in which further key reactions of heavy element nucleosynthesis will be investigated.
