Radiochemical neutron activation analysis (RNAA) was applied to geochemical and cosmochemical samples to determine trace amounts
of Mo and W. To determine the Mo concentration by NAA accurately, the contribution of the fission products of U should be
corrected. For that reason, we developed a simple and effective method, where a contribution of fissiogenic 99Mo was estimated by monitoring the ratio of uranium fission-product 99Mo to 133I. Mo concentrations corrected for fission with the W concentrations were consistent with the literature values, showing that
133I was found to be an effective monitor for fission correction. Detection limits are estimated to be 10 ppb for Mo and W and
30 ppb for U under the present experimental conditions.