Complex sentence: The government was experimenting with the effects of atomic energy on an alien metal they had taken from a crashed spaceship to determine the full protective abilities of the metal, such as protecting a human being from a nuclear blast.
Split into simpler sentences: The government was experimenting with the effects of atomic energy on an alien metal they had taken from a crashed spaceship. They wanted to determine the full protective abilities of the metal, such as protecting a human being from a nuclear blast.