Complex sentence: Physicist Raja Ramanna played an essential role in research into nuclear weapons technology; he expanded and supervised scientific research on nuclear weapons and was the first directing officer of the small team of scientists that supervised and carried out the test of the nuclear device.
Split into simpler sentences: Physicist Raja Ramanna played an essential role in research into nuclear weapons technology. He expanded and supervised scientific research on nuclear weapons and was the first directing officer of the small team of scientists that supervised and carried out the test of the nuclear device.