For a 140 kVp x-ray beam, the secondary protective barrier should be made of a heavyweight material like lead or concrete that is capable of absorbing high-energy x-ray photons to protect against radiation exposure.
If the peak energy of the x-ray beam is 140 kVp, the secondary protective barrier should consist of a material capable of significantly reducing x-ray exposure, such as lead or concrete. The actual thickness required for the barrier will depend on factors such as the amount of use the x-ray machine gets, the distance from the source to the barrier, and the occupancy factors of adjacent areas. Lead is commonly used because it is highly effective at absorbing x-ray photons, which prevents them from reaching and potentially harming other areas and individuals.
X-ray photons have high energies that allow them to penetrate many materials that are opaque to visible light. The protective barrier's purpose is to absorb the x-rays and minimize exposure to patients and healthcare workers. The thickness of the lead or concrete used in the barrier is determined based on regulations that take into account the energy of the x-rays and the level of protection needed.
So, when using a 140 kVp x-ray beam, a secondary protective barrier made of a heavyweight and dense material like lead or concrete is essential for radiation protection.