Nuclear masses near the proton drip-line and their impact on nucleosynthesis in explosive stars

Abstract

The interplay of the fundamental forces (here mainly the strong force and electromagnetic force) holds nucleons together to form atomic nuclei. However, in nature only less than ten percent of the total number of nuclei is stable. The majority of nuclei are unstable; that is, after having lived for a certain time, they change into the daughter nuclei by radioactive decay. The familiar decay types that can be found in most parts of the chart of nuclide are α-decay and β-decay. There are other important processes in which unstable nuclei can change into other ones. These occur, for example, in very neutronrich or proton-rich regions of the chart of nuclide. There are boundaries called drip-lines, which are the lines on the Z (proton)-N (neutron) plane where the nucleon separation energy is zero. The nuclear binding becomes weaker and weaker when moving from the stable region towards the drip-lines, and eventually no nucleus can exist beyond the drip-lines. Taking the proton-rich region as an example, near the proton drip-line, protons are only weakly bound and a proton radioactivity can occur. Also because of the small binding, nuclei near the proton drip-line may capture additional protons and become new, heavier nuclides if the capture conditions are present. Detailed knowledge on the nucleon-capture processes lies at the heart of the understanding of nucleosynthesis in the Universe——a very fundamental but unanswered question about how the heavy elements (i.e. those heavier than iron) are created. In order for nuclei to capture protons, a high temperature environment (usually above 1×10 9 K) is needed so that they can overcome the large coulomb barrier for charged particle reactions. A hydrogen rich