The unit determined by the frequency of radiation given off by cesium-133 is the second.

Here's why:

* Atomic Clocks: Cesium-133 atoms have a specific, very stable frequency at which they transition between energy levels. This frequency is incredibly precise and consistent.

* Definition of the Second: The second is defined as the duration of 9,192,631,770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.

* International Standard: This definition was adopted by the International Bureau of Weights and Measures (BIPM) in 1967, making the second the most accurate and precise unit of time available.

So, cesium-133 atoms are the basis of atomic clocks, which are used to define the second, the fundamental unit of time.