Stable elements get activated by neutrons.

An accelerator uses electrostatic or electromagnetic fields to increase the kinetic energy of charged particles (see alpha particle, beta particle) in order to produce ionization or a nuclear reaction in a target.
Accelerators (see cyclotron, linear accelerator) are used for the production of radionuclides (see Fluorine-18, Molybdenum, Technetium-99m) or directly for radiation therapy. Accelerator-produced radioactive material (ARM) is any radioactive substance that is produced by a particle accelerator. The accelerators used for radiation therapy generate gamma rays (also called Bremsstrahlung) with continuous energy by collision of high energy electrons on materials with high density (also referred as 'high z' - chemical elements with a high atomic number (Z)).
Electron accelerators with energies above 10 MeV can also produce neutrons induced by photons in the accelerator head material (mainly caused by photo nuclear reaction).

The x-ray absorption is the uptake of energy or the decrease of the number of photons by the tissue or matter through which the radiation travels.
Absorption in nuclear reactions and particulate radiation is a process of taking up kinetic energy of particles or the combination of particles with an atom, a nucleus, or another particle.
Absorption characteristics of imaged tissues are represented by their linear attenuation coefficients.

See also Absorber.

Actinides are elements in the periodic table with an equal or higher atomic number than actinium, which has an atomic number of 89 and up to 103 lawrencium, including plutonium, curium, and californium). Actinides are also called 'rare earth metals'.
Actinides include most of the well-known elements found in nuclear reactions with atomic numbers higher than 92. These elements do not occur naturally but are produced by bombarding other elements with particles in an accelerator.

The nuclide produced by radioactive decay or nuclear reaction (e.g. in a generator) of the parent nuclide. The daughter nuclide becomes, if not stable, the unstable parent in the next decay.

See also Decay, Decay Chain and Generator.