context: He demonstrated that the emission is mostly concentrated in the microwave spectral range.
source: By 1950, Prokhorov was assistant chief of the oscillation laboratory.
reference_original: Até 1950, Prokhorov era [o] assistente-chefe do laboratório de oscilação.
reference_flipped: Até 1950, Prokhorov era [a] assistente-chefe do laboratório de oscilação.