What we call radiation is actually the transfer of energy, either as a stream of particles or as electromagnetic waves (such as light). Radiation is classified according to the effect it has and is often divided into two categories: ionizing radiation and non-ionizing radiation.

During ionization, an electron is removed from a molecule or atom, which becomes electrically charged. Radiation is called ionizing when it has enough energy to change molecules in the body and can thus cause chemical changes in the body's cells, which can then have a harmful effect on the cell's function.

An example of this type of radiation is:

• x-rays

• gamma rays

Examples of radiation that is not ionizing, that is non-ionizing, are:

• microwaves, for example in a microwave oven,

• ultraviolet radiation, for example from the sun or tanning beds (ultraviolet rays)

• normal light

In addition, it is customary to mention ultrasound or resonance as part of the category of non-ionizing radiation, even though it does not use electromagnetic waves but sound waves for the energy transfer.

The effects of radiation on the human body can manifest in different ways, depending on how and how many cells are harmed. The damage caused by radiation can often be repaired by the body. In cells, it is mainly DNA, the nucleic acid molecules in the chromosomes, that are sensitive to damage. The effect of ionising radiation can be small or large, based on the degree of damage and where it occurs. The intensity of the effect depends on the type of radiation and the absorbed dose (issue dose).

Ionizing radiation affects matter in different ways depending on whether the radiation is charged with particles or uncharged. Charged particles are alpha and beta particles, whereas uncharged particles are X-ray and gamma rays. Charged particles continuously interact with their environments and lose some of their kinetic energy while moving around a material. Uncharged particles (fotons) interact with their environment to nothing except when they collide with electrons in a material. Therefore, phonons retain their intact energy and unchanged direction until it is involved in a collision. Therefore the energy loss of phonons is not continuous, but the energy loss of each phonon is random.

The effects can be divided into two categories, harm that is random or random and damage that is indicative or acute.

1. Chance encounters and delayed random injuries can occur with low radiation exposure

• The amount of radiation determines the likelihood of harm, not its amount.

• Higher radiation means a higher probability of causing cancer, but it is thought that one of them is enough to cause cancer.

• Random injuries have no theoretical threshold according to the current model.

• All radiation exposure thus has some probability of random damage.

This risk is always present (for example because of ), but in most cases it is negligible and much less than other environmental risks.

2. Indicators are harmful and acute by intense radiation exposure

• The damage is caused by the intense radiation that causes many cells damage such that they die and have a visible effect on the tissue or function of an organ.

• Indicator and acute damage only occur if the amount of radiation is above a certain level (threshold).

• For local radiation, the effects may be manifested as burns.

• If the organ is a fragile organ or if radiation has spread widely to the body, death can occur in the space of a few hours to weeks

• The amount of radiation determines the size of the injury, the damage is also a threshold and if the amount of radiation falls below certain thresholds, then no effect on the body's function will be visible.