Answer the following question given this paragraph: 

The type of radiation, which dictates how far it can penetrate into matter 2. The energy of the individual particles or photons 3. The number of particles or photons that strike a given area per unit time 4. The chemical nature of the substance exposed to the radiation The relative abilities of the various forms of ionizing radiation to penetrate biological tissues are illustrated inFigure 20.12 "Depth of Penetration of Ionizing Radiation". Because of its high charge and mass, α radiation interacts strongly with matter. Consequently, it does not penetrate deeply into an object, and it can be stopped by a piece of paper, clothing, or skin. In contrast, γ rays, with no charge and essentially no mass, do not interact strongly with matter and penetrate deeply into most objects, including the human body. Several inches of lead or more than 12 inches of special concrete are needed to completely stop γ rays. Because β particles are intermediate in mass and charge between α particles and γ.


Q: The type of what dictates how far it can penetrate into matter, such as lead or human flesh?

 Choices:

- insulation

- evaporation

- specific gravity

- radiation

A:
radiation
