The Sun's radiative zone is the thick shell of the solar interior between the core and the convective zone. In the radiative zone, energy created in the core as a result of nuclear fusion is transported by photons. These photons are repeatedly absorbed and re emitted, taking hundreds of thousands of years to reach the convective zone. The boundary between the radiative and convective zones is called the tachocline.
Many other stars also have radiative zones. The Sun's radiative zone extends from the core outward to about 70% of the Sun's radius. In a smaller cooler stars, the convective zone tends to be larger, extending further into the star's interior, and the radiative zone tends to be smaller.Very small stars may be entirely convective, and very large stars may be entirely radiative.