This study established a method for easily and quickly estimating the specific activity produced in the concrete walls and floors of accelerator rooms during long-term operation of accelerator, for advanced zoning of activated/non-activated areas in planning the decommissioning of an accelerator. We propose a new, highly sensitive method for nondestructively estimating the specific activity in concrete that can be applied to activation zoning. In this method, instead of direct determination of the specific activities of important long-half-life radionuclides for decommissioning, such as 152Eu and 60Co, we determine the specific activities of short-half-life radionuclides, 24Na and 56Mn, in situ to obtain neutron flux. The obtained neutron flux and accelerator operation history yield the specific activities of 152Eu and 60Co for the advance zoning of activated/non-activated concrete. This method is a powerful long-term prediction tool for concrete activation.