What stops 99% of Cs137 gamma radiation in terms of lead thickness?

The thick lead that effectively stops 99% of gamma radiation emitted by cesium-137 (Cs137) provides a practical understanding of gamma radiation shielding. Gamma rays are highly penetrating forms of radiation, necessitating materials with high atomic numbers—like lead—to attenuate their intensity.

The answer indicates that 2 inches of lead is sufficient to reduce the intensity of Cs137 gamma radiation by 99%. This is well-illustrated in radiation protection principles, where the attenuation of gamma radiation is measured and analyzed in terms of half-value layers. For Cs137, the half-value layer typically suggests that approximately 1 inch of lead reduces the intensity by half, so two inches would provide adequate shielding to reach a 99% reduction in exposure.

In the context of the other thicknesses listed, options like 1 inch or less would not provide the necessary attenuation to achieve the 99% threshold. Similarly, 3 inches, while it would certainly exceed the requirement, does not represent the optimal thickness when considering just enough material to achieve that specific level of protection. Therefore, 2 inches is the practical benchmark for this particular isotope's gamma radiation.