  The model of three-body Borromean halo nuclei breakup was described by using
standard phase space distributions and the Monte Carlo simulation method was
established to resolve the detection problem of two neutrons produced from
breakup reaction on the neutron wall detector. For $^{6}$He case, overall
resolution $\sigma_{E_{k}}$ for the Gaussian part of the detector response and
the detection efficiency including solid angle acceptance with regard to the
excitation energy $E_{k}$ are obtained by the simulation of two neutrons from
$^{6}$He breakup into the neutron wall. The effects of the algorithm on the
angular and energy correlations of the fragments are briefly discussed.
