[en] Chemical trapping method for radon (Rn) gas utilizing a chemical reaction between Rn and fluorine was developed. By the corona discharge treatment of an air including Rn and CF4 gas of maximum 7.5 vol%, it is assumed that non-volatile and chemically stable radon difluoride (RnF2) suitable for trapping can be generated by combining excited Rn with radical fluorine. The reaction between Rn and radical fluorine may be proceeded by Rn + CF4 -- discharge --> excited Rn and radical-F --> RnF2 (trapped in charcoal) under the conditions of ambient temperature and atmospheric pressure. We tested to confirm the reaction and measured the trapping efficiency of Rn generated from the developed radium (²²⁶Ra) source with a high release efficiency of Rn. From the results, Rn concentration of about 1,000 Bq/m³ in a normal air was reduced to background level (10-20 Bq/m³) after trapped by a small charcoal filter at room temperature. The newly developed method of chemical trapping for Rn can make a trap or adsorbent to a small size, and does not need a cooling system of adsorbent in a general and a current charcoal adsorption system. Furthermore, the chemical trapping method can convert directly radioactive noble gases (eg. Rn, Xe, Kr) to solid wastes. For trapping radioactive noble gases of Rn, Xe and Kr, we are developing a chemical trapping method except introducing fluoric-compound gas, and are examining to apply it as a new trapping method instead of an usual gas treatment system of nuclear sites. (author)