Radiation can ionize matter caused by the high energy which displaces electrons during interactions with atoms. In the electromagnetic spectrum higher frequency ultraviolet radiation begins to have enough energy to ionize matter.
Examples of ionizing radiation include alpha particles, beta particles, gamma rays, x-rays, neutrons, high-speed electrons, high-speed protons, and other particles capable of producing ions by direct or secondary processes in passage through tissues.
Damage of living tissue results from the transfer of energy to atoms and molecules in the cellular structure. Ionized cells have to repair themselves to remain alive. Generally, healthy cells have a higher capability to repair themselves than cancer cells.

Biological effects of ionizing radiation exposure:
Ionizing radiation are used in a wide range of facilities, including health care, research institutions, nuclear reactors and their support facilities, and other manufacturing settings. These radiation sources can pose a serious hazard to affected people and environment if not properly controlled.

See also Radiation Safety, Controlled Area, Radiotoxicity and As Low As Reasonably Achievable.

(NAA) Neutron activation analysis is a very sensitive analytical technique to determine even very low concentration of chemical elements, trace elements for example, in small biological samples.
NAA becomes commercial available in the USA in 1960.
In the activation process stable nuclides in the sample, which is placed in a neutron beam (neutron flux, 90-95% are thermal neutron with low energy levels under 0.5 eV), will change to radioactive nuclides through neutron capture (artificial radioactivity). These radioactive nuclides decay by emitting alpha-, beta-particles and gamma-rays with a unique half-life. Qualitative and quantitative analysis of the sample is done with a high-resolution gamma-ray spectrometer.
NAA is subdivided into the following techniques:

Radiation shielding is the process of limiting the penetration of radiation into the environment, by blocking with a barrier made of impermeable material. This protective barrier is usually formed of a material with high density, for example lead that absorbs the radiation.
Radiation sources are self-shielded with absorbing material incorporated into the equipment, adjacent to the source to reduce stray radiation to the surrounding area below dose limits.
Rooms with x-ray or other radiation equipment are additionally shielded with lead-lined walls to reduce the radiation exposure to humans within the facility. The amount of shielding required to protect against different kinds of radiation depends on how much energy they have. The shielding calculations are based on the half value layer of the primary radiation beam. Sufficient half value layers of shielding are calculated to reduce the radiation exposure outside the room to reasonable levels.
Personal shielding requirements depending on the type of radiation:
See also Radiation Safety.

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.

An antiparticle is a subatomic particle similar in mass but with opposite electromagnetic properties. Most particles have their antiparticles, electron - positron, etc. Antimatter is composed of antiparticles. Colliding of a particle with its respective antiparticle leads in case of low-energy particles mostly to photon production, in case of high-energy particles to exotic heavy particles.