[en] Radiocaesium Interception Potential (RIP) is the intrinsic soil parameter which is defined as the product of the distribution coefficients and the concentration of potassium of the outer solution on condition that Frayed Edge Sites (FES), which are adsorption sites with high selectivity for caesium, are saturated by potassium. Measuring RIP usually needs a lot of time, about 2 weeks. Besides, career-free radiocaesium is usually added in measuring RIP because the amount of adsorbed caesium must be slight. In this paper, at first, a rapid measurement method for RIP is suggested, and RIP values of some soils and clay minerals are measured by both the rapid method and the old one, using career-free radiocaesium. As a result, it is turned out that the new method for RIP leads to overestimate actual RIP values, which is because removal of organic matter by shaking is thought to make caesium to access FES more easily. Moreover, in measuring RIP by the rapid method using not career-free but stable caesium, RIP values when addition of stable caesium is about 1μg is almost as much as the values in addition of career-free caesium. (author)