Isotopes: How did they all begin? Primordial nucleosynthesis: experimental study of the roles of neutrons

Light nuclei with mass number of below 8 are considered to be produced by the so-called the Big-bang nucleosynthesis (BBN) occurring in the early universe. Since BBN depends on various assumptions related to the origin of the universe and the laws of fundamental interactions and elementary particles, those assumptions can be verified by comparing the abundances of light isotopes calculated with BBN and the astronomically observed ones. Since the neutrons are the starting materials of BBN together with protons, and also they are electrically neutral, they play a unique and critical roles in BBN. In this paper status of the BBN analysis and experimental studies of the properties of neutrons relevant to BBN will be reviewed.