def partial_cross_section_nm2(beam_energy: float, energy_loss_start_eV:
    float, energy_loss_end_eV: float, convergence_angle: float,
    collection_angle: float, atomic_number: int, shell_number: int,
    subshell_index: int) ->float:
    """Returns the partial cross section.

    Uses generalized oscillator strength function.

    beam_energy is in eV.
    energy_start, energy_end are in eV.
    convergence_angle is in radians.
    collection_angle is in radians.

    The return value units are nm * nm.
    """
    pass
