Which of the following types of radiation is not commonly recognized?

Gamma rays are a well-acknowledged form of radiation, often studied extensively in various fields, including medical imaging, cancer treatment, and nuclear physics. They are high-energy electromagnetic radiation emitted from radioactive materials and are known for their penetrating power and ability to ionize atoms.

In contrast, X-rays, alpha particles, and neutrons also hold significant recognition in scientific and medical communities. X-rays are frequently used in medical diagnostics, alpha particles are a form of particle radiation that is emitted by some radioactive substances, and neutrons are widely discussed in the context of nuclear reactions and some forms of radiation therapy.

The perception of gamma rays as commonly recognized may stem from their vast applications and the public awareness of radiation in contexts such as cancer therapy or environmental monitoring. Thus, while gamma rays are indeed a major type of radiation, they do not fit the intended context of "not commonly recognized" when placed beside the other options, which are also notable but perhaps not as universally known outside specialized fields.