def METHOD_NAME(self):
    """ detect the nearest neutrino in the decay branch
        return this neutrino and its level compare to this particle """
    analyse_list=list(self.des)
    level_list=[1,1]
    while analyse_list:
        particle=analyse_list.pop(0)
        level=level_list.pop(0)
        if particle.neutrino:
            return particle,level
        elif particle.external==0:
            analyse_list.append(particle.des)
            level_list.append(level+1)
            level_list.append(level+1)
    return 0,0 #no neutrino detected