Working Level (WL) 4
Working Level (WL) 4 : Any combination of short-lived radon daughters (for radon-222, polonium-218, lead-214, bismuth-214, and polonium-214; and for radon -220: polonium-216, lead-212, bismuth-212, and polonium-212) in 1 liter of air that will result in the ultimate emission of 1.3 x 105 million electron volts of potential alpha particle energy