Abstract: With the deepening awareness of radon hazards, granite is a natural radiation source to which people are more often exposed in production and daily life. Granite's radon exhalation characteristics and its radiation impact on human settlements have been widely attention. In this paper, a literature review has been made for radon exhalation in granite from two aspects ofprimary properties and secondary changes of rocks. It is found that the radon exhalation of granite is relevant to the primary properties of rock chemical composition, rock mineral composition, and rock genetic type, as well as secondary factors caused by weathering and alteration such as the distribution of radionuclides, the size of mineral granules and rock micro-cracks. Researches show that there is a linear correlation between both uranium activity and radium activity and radon exhalation rate in granite, but this will be affected by the types of uranium-occurring minerals, the specific impact of mineral composition needs further study, which may be related to its structural background or material source. The effect of secondary changes on radon exhalation in granite is mainly manifested in weathering and alteration that cause radionuclides to migrate to the granule surface and rock fractures that are favorable for radon exhalation. Secondly, the granule size decreases and the specific surface area increases, and the internal surface area and pores of the rock also increase. These changes makes uranium and radium enrich and escape, which ultimately promotes the radon exhalation from the rock. Both the primary properties and secondary changes of rock play an important role in the radon exhalation in granite. Uranium and radium activity can be used as a predictor of the potential for radon exhalation rate in granite, while the mineral composition and the secondary changes of granite are important potential factors for the study of radon exhalation in granite. Therefore, it is necessary to systematically study and quantitatively describe chemical composition, mineral composition and these secondary changes, and establish a reasonable and effective rock radon exhalation model in the future, so as to more comprehensively grasp the rules of radon exhalation in the rocks, and provide a theoretical basis for radon exhalation in underground engineering and human settlements.

Key words: radon exhalation, granite, rock properties, weathering and alteration