**Core Concept**
Linear accelerators are high-energy particle accelerators that accelerate charged particles, typically electrons, to nearly the speed of light. This process results in the production of high-energy electromagnetic radiation, which is used in various medical and industrial applications.

**Why the Correct Answer is Right**
Linear accelerators produce X-rays by accelerating electrons to high energies and then decelerating them upon collision with a metal target, such as tungsten or copper. This collision produces X-rays through the process of bremsstrahlung, where the rapid deceleration of the electrons results in the emission of electromagnetic radiation across a wide range of energies. The energy of the X-rays produced depends on the energy of the electrons accelerated by the linear accelerator.

**Why Each Wrong Option is Incorrect**
**Option B:** Beta rays are produced when a nucleus undergoes beta decay, resulting in the emission of electrons or positrons. Linear accelerators do not produce beta rays as a direct result of accelerating charged particles.
**Option C:** Gamma rays are high-energy electromagnetic radiation produced by radioactive decay or other nuclear reactions. While linear accelerators can produce gamma rays indirectly through the interaction of X-rays with matter, they do not directly produce gamma rays.
**Option D:** Neutrons are subatomic particles produced through various nuclear reactions, such as nuclear fission or neutron scattering. Linear accelerators do not produce neutrons as a direct result of accelerating charged particles.

**Clinical Pearl / High-Yield Fact**
Linear accelerators are widely used in radiation therapy for cancer treatment, as they can produce high-energy X-rays that are focused on specific tumor sites, minimizing damage to surrounding healthy tissue.

**✓ Correct Answer: A. X rays**