Decreasing the detection limits to ppq levels for high purity silicon analysis by instrumental neutron activation analysis with kilogram sampling weight

The amount of silicon sample used in instrumental neutron activation analysis (INAA) is generally less than twenty grams and the detection limits are in the range of ppb to ppt. The detection limits can be decreased further in several ways. Increasing neutron flux density, extending irradiation period and/or using more effective detector can improve the detection limits to some extent. Increasing sample weight, however, is a more feasible way to decrease the detection limits by a factor of hundreds with no new investment in existing irradiation/counting systems. In this work, two 8-inch high-purity silicon samples were analyzed by INAA to evaluate the validity and limitations of this concept in respect to neutron flux inhomogeneity, neutron shielding and -ray counting efficiency.