1 R / 6.0 5.5 7 6 5.0 ℓ /cm R / 4.5 40.0 3.0 4.0 50.0 4.0 60.0 4.5 3.5 5 70.0 5.0 3.0 80.0 6.0 4 2.5 2.0 1.5 1.0 0.5 2 3 0 20 40 60 80 ℓ / cm 49