Efficiency calibration of the BRIKEN detector: the world largest counter for beta-delayed neutrons

Beta-delayed neutron emission plays a fundamental role in the explosive nucleosynthesis of elements heavier than iron by the rapid neutron capture (r-process). The most ambitious project related to beta-delayed neutron detection of very exotic nuclei is carried out by the BRIKEN collaboration at RIKEN Nishima Center. In this work, a brief description of the BRIKEN project is presented. A methodology for the precise characterization of the BRIKEN neutron counter efficiency, for fast neutrons, using an uncalibrated 252Cf neutron source is described. The method relies on the well-known neutron multiplicity distribution of such source and correlation counting method. A detailed experimental study with the BRIKEN neutron counter and a 252 Cf neutron source at the RIKEN Nishina center is presented. The result of this work is the determination of the neutron detection efficiency of the BRIKEN neutron counter with high accuracy.