  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.
