Original sentence: Calculations show that the critical mass is between 50 and 60 kg.Neptunium accumulates in commercial household ionization-chamber smoke detectors from decay of the (typically) 0.2 microgram) of americium-241 initially present as a source of ionizing radiation
Edited sentence: Calculations show that the critical mass is between 50 and 60 kg.Neptunium accumulates in commercial household ionization-chamber smoke detectors from decay of the (typically) 0.2 microgram of americium-241 initially present as a source of ionizing radiation