Complex sentence: Frederick Hallam, a scientist of limited ability but with a fiercely protective ego, discovers that an old test tube containing tungsten has been transformed into something that turns out to be plutonium 186--an isotope that cannot occur naturally in our universe.
Split into simpler sentences: Frederick Hallam, a scientist of limited ability but with a fiercely protective ego, discovers that an old container's contents seem to have been altered. Hallam responds with a furious effort and eventually finds that the sample, originally tungsten has been transformed into something that turns out to be plutonium 186--an isotope that cannot occur naturally in our universe.