Final answer:
Neutron capture is not commonly used as an alternative to fission due to its inefficiency in generating energy, production of unstable isotopes that decay rapidly, and the difficulty in achieving a high neutron flux.
Step-by-step explanation:
Neutron capture is not commonly used as an alternative to fission due to several reasons. First, neutron capture is less efficient in generating energy compared to fission, as it requires more energy to initiate the capture process. Second, neutron capture produces unstable isotopes that undergo rapid decay, which makes it difficult to sustain a controlled chain reaction. Lastly, neutron capture requires a high neutron flux, which is difficult to achieve.