def nDotRecMHR(z, clump_fact=1.0):
    """Recombination rate density from Madau, Haardt, & Rees 1999.

    Assumes hydrogen is fully ionized.
    
    Units are s^-1 coMpc^-3.

    """
    return 1e50 * clump_fact * ((1. + z)/7.)**3