Which of the following is NOT a type of ionizing radiation?

Ionizing radiation refers to radiation that carries enough energy to liberate electrons from atoms or molecules, thereby ionizing them. This type of radiation can cause significant changes in matter, especially biological tissues, which can lead to various health effects.

Alpha radiation consists of helium nuclei (two protons and two neutrons) emitted from certain radioactive materials. Beta radiation involves the emission of electrons or positrons and is also a form of ionizing radiation. Neutrons are uncharged particles that can also ionize materials by causing secondary reactions within the target substance.

Photons, however, are a type of electromagnetic radiation, which includes X-rays and gamma rays. While photons themselves do not have mass and are not particles in the same sense as alpha or beta particles, X-rays and gamma rays (types of photons) are potent forms of ionizing radiation capable of damaging biological tissues.

Therefore, the correct answer relates to the conceptual understanding that while photons are part of the electromagnetic spectrum, the question pertains specifically to forms of radiation associated with particle emissions typically classified as ionizing radiation.