The cyclotron, enabling production of human-made radioactive tracers, was invented in which year?

• A. 1923
• B. 1931
• C. 1958
• D. Early 1960s

Answer: (B)

The main idea here is the historical origin of the cyclotron and its role in producing artificial radionuclides for tracers. The cyclotron was first built and demonstrated around 1931 by Ernest O. Lawrence and M. Stanley Livingston at UC Berkeley. It uses a strong magnetic field to bend charged particles into a spiral path while an alternating electric field accelerates them across gaps, energy increasing with each pass. When these fast particles strike target materials, new radioactive isotopes are created that can serve as tracers in medical imaging and research, such as isotopes used in PET scans. That’s why 1931 is the best answer. Dates like 1923 or the early 1960s don’t correspond to the invention or first demonstration of the cyclotron, and 1958 is also not the correct milestone for its invention.