Complex sentence: In 1948, she became a naturalized U.S. citizen, and then in 1950, she began research work at the Oak Ridge Institute of Nuclear Studies as a chemist and senior scientist in nuclear studies.
Split into simpler sentences: In 1948, she became a naturalized U.S. citizen. In 1950, she began research work at the Oak Ridge Institute of Nuclear Studies as a chemist and senior scientist in nuclear studies.