How is a sealed source constructed in nuclear gauges?

The construction of a sealed source in nuclear gauges typically involves a meticulous design for safety and efficacy. The correct option describes the process as involving a pellet of radioactive material enclosed within an inner capsule, which is further protected by a welded outer capsule. This two-layer containment system is crucial because it ensures that the radioactive material is effectively isolated from the environment, minimizing any risk of exposure to radiation outside the source.

The inner capsule acts as the first line of defense, securely holding the radioactive material and preventing any leakage. The outer capsule adds an additional layer of protection, which is welded to maintain a robust seal. This design is essential to comply with safety regulations and to ensure that the gauge operates safely throughout its lifespan.

In contrast, other options would not provide adequate safety. Utilizing only non-radioactive materials would not serve the purpose of a nuclear gauge, which inherently relies on radioactive sources for functionality. An open container without sealing would expose the radioactive material, posing significant safety hazards, and enclosing the material in a single capsule does not offer the redundancy that the inner and outer capsule system provides. Thus, the design described in the correct option is critical for ensuring the safe use of nuclear gauges in various applications.