Final answer:
A stationary target in a particle accelerator is inefficient because it recoils upon particle strike, thus transferring much of the particle's energy into the target's motion and reducing the energy available to break the particle into its components. Colliding beams in accelerators allow for more efficient collisions with less energy loss, enabling the creation of more massive particles.
Step-by-step explanation:
A stationary target is considered inefficient in a particle accelerator for the reason that accelerated particles collide more effectively with moving targets (option d). When a particle collides with a stationary target, the target absorbs a significant fraction of the particle's energy as it recoils, which means less energy is available for breaking the particle into its constituent parts. Conversely, in accelerators using colliding beams, such as those at Fermilab or the LHC, head-on collisions between particles moving in opposite directions reduce energy loss, allowing for the creation of more massive particles.
Particle accelerators are designed to probe the fundamental components of matter by accelerating particles to extremely high speeds and then colliding them. The total energy of the beam in an accelerator can't create a single extremely massive particle simply because energy is distributed among many particles, and laws of physics, such as conservation of momentum, limit the conditions under which new particles can form. Particle accelerators also face limitations such as synchrotron radiation, which occurs when charged particles are accelerated and emit electromagnetic radiation, robbing the accelerator of energy. This is more severe for electron accelerators than for proton accelerators because electrons have much less mass and therefore emit more synchrotron radiation when accelerated.