Trace element analysis:

It may be mentioned that IDA is another ideal technique for trace element analysis though it has limitations of being unielemental and destructive. On the contrary INAA is essentially nondestructive as integrity of the sample is not changed in any manner by prechemistry or the addition of any foreign material before irradiation. Thus the problem of contaminants due to reagents introduced unlike AAS or ICP is completely avoided. The analytical approach of NAA for most of the elements of interest is primarily an instrumental technique. In some cases though, post irradiation chemistry may be required. Thus the technician time per sample analysis is low, producing an efficient, low cost analytical approach. NAA is a multi-element technique in that many elements can be analyzed simultaneously in a given sample by recording γ spectrum without changing or altering the apparatus as is necessary in AAS. NAA is fast in that for many elements, several samples can be irradiated at a given time and counted later on following a given decay schedule. A significant advantage of NAA is its sensitivity to trace elements. The sensitivity obtained by NAA is a function of the neutron absorption cross section (σ in cm²) of the element in question, available neutron flux (? in n cm^-2 s^-1), irradiation time, resolution and efficiency of the detector, matrix composition, and the total sample size. Hence, increasing neutron flux and irradiation time, and the major advances in detector technology especially with regard to increased efficiency and resolution have pushed the detection limits of most elements of interest to the very low levels (10^-12 g). It is observed that NAA shows much lower detection limits for most of the elements compared to AAS and XRF. With the availability of research reactors, NAA is now a more acceptable technique to the scientific community and industry. This is evident from the fact that more research papers have been published on trace element analysis using NAA during last decade compared to any other instrumental technique mentioned above.