Fast-emitting scintillators are essential for advanced diagnostic techniques, yet many suffer from low radiation attenuation. This trade-off is particularly pronounced in polymer scintillators, which, despite their fast emission, exhibit low density and low atomic numbers, limiting the radiation attenuation factor, resulting in low detection efficiency. Here, we overcome this limitation by creating a heterostructure scintillator of alternating nanometric layers, combining fast light-emitting polymer scintillator layers and transparent stopping layers with a high radiation attenuation factor. The nanolayer thicknesses are tuned to optimize the penetration depth of recoil electrons in active emissive layers, maximizing the conversion of X-rays to visible light. This design increases light output by up to 1.5 times and enhances imaging resolution by a factor of 2 compared to homogeneous polymer scintillators due to the ability to use thinner samples. These results demonstrate the potential of heterostructure scintillators as next-generation detector materials, overcoming the limitations of homogeneous scintillators.