Complex sentence: While its half life of 28.8 years is much shorter than that of 238 Pu, it also has a much lower decay energy: thus its power density is only 0.46 kilowatts per kilogram.
Split into simpler sentences: While its half life of 28.8 years is much shorter than that of 238 Pu, it also has a much lower decay energy. Thus its power density is only 0.46 kilowatts per kilogram.