At the Interfaculty Reactor Institute the development of large sample INAA has been started. A facility is being installed in the reactor's thermal column for irradiation of samples with, sizes up to 100 cm in length, and 15 cm in diameter and weights up to 50 kg. A gamma-ray spectrometer with a very large semiconductor detector and sample scanning options will be used for measurement of the induced radioactivity. Algorithms are being developed to correct for the neutron self-shielding and gamma-ray attenuation problems.
Neutron activated reference materials have been analyzed using a standard Ge(Li)-detector with 17% relative efficiency, a very large Ge-detector with 96% relative efficiency, and a well-type Ge detector. Sensitivities are presented, and usefulness of these systems for NAA is compared on the basis of performance, economics and complexity.
Contamination of rabbits with activities induced in the metal parts live of an irradiation facility constitute a major source of problems for INAA using short-lived nuclides. If the half life of the nuclides of interest is longer than about 10 sec, it is possible to unpack the sample without appreciable loss of information. But for shorter half lives, automatic unloading devices for rabbits have to be used. Such systems are complicated and can not be used for cyclic activation procedures. At IRI, a fast rabbit system is being installed consisting of polyethylene tubing and a carbonfiber end point at the core position. Carbonfiber combines a good mechanical stability under in-core conditions with a very high purity. It can be expected that as a result of the use of this material, contamination by the rabbit will become negligible, so that samples can be counted directly without unpacking. Results obtained with this new system are presented, and compared with results obtained with an aluminium rabbit system used until now.
Rare-earth elements are increasingly applied in advanced materials to be used, e.g., in electronic industry, automobile catalysts, or lamps and optical devices. Trace element analysis of these materials might be an interesting niche for NAA because of the intrinsic high accuracy of this technique, and the shortage of matrix matching reference materials with other methods for elemental analysis. The carbon composite materials form another category of advanced materials, where sometimes a very high degree of purity is required. Also for these materials, NAA has favorable analytical characteristics. Examples are given of the use of NAA in the analysis of both categories of materials.
An inventory study was carried out of the trace element distribution in plastic products, made of new raw materials, and products made of recycled plastic scrap. Both normal and large sample INAA have been used. The uncertainty introduced by sampling a product made of new plastic pellets was found to be 1.3% for analytical portions of 200 mg, the extreme concentrations being 5% apart. In the end product of the recycling of scrap plastic this sampling uncertainty reflects the variation of trace element levels in the semi-manufactured product, and variations up to 200–300% may occur. Even larger variations can be expected between products, produced within a batch.
At the laboratory for INAA in Delft, the final approval of the analysis' report partly depends on the quality of the results of simultaneously processed reference materials (RM's). An extensive databank exists holding the information on RM type and analysis conditions. This information can be convented into control charts. The control charts can display (1) an element concentration in one RM as a function of moment of analysis, (2) an element concentrations in one RM as a function of the concentration of an interfering element, (3) an element concentration in all RM's, and (4) the nomalized concentrations of all elements in one RM. The inspection of the various chats facilitates the decision on, e.g., the need for renewed standardization, the fitness-for-use of a RM, any analyst-dependent results, rigidity of the spectrum analysis software etc.
Contamination of rabbits during transfer in a fast irradiation facility has been reduced by development of a rabbit system containing no metal parts, and only plastic and carbonfiber. As a result, this system could be automated and has been equipped with a sample changer. Flexibility and versatility in the operation of this new system was attained by a combination of software and hardware control. With this new system, large-scale analysis can be performed with a considerable saving in man-power of the users.
The organization of the INAA laboratory at the Interfaculty Reactor Institute at Delft, The Netherlands, has been brought in accordance with the requirements of Euronorm EN45001 and ISO guide 25 for quality systems. Procedures, techniques and instructions involved in routine INAA have been fully described and documented, and compiled in a quality manual. The implementation of such a quality system and of its accreditation for an INAA laboratory in a university environment are discussed.
The needs of continuation and extension of nuclear knowledge and expertise for science, technology, and the society as a whole are emphasized. Varios aspects of education and research in the nuclear field at the universities are discussed, as well as associated research facilities and expertise continuity measures.
The laboratory for INAA in Delft processes several thousands of samples per year for multielement determinations in a variety
of matrices. Samples are measured on different spectrometers (using well-type and coaxial detectors), by different persons
and using many different analytical protocols. All these results should be consistent with each other with respect to the
degree of accuracy, i.e., the combination of trueness and precision. A rigorous internal quality control program has been
implemented with automatic on-line evaluation. Annually an additional evaluation of the internal quality control results is
carried out using statistical techniques. The Naji-plot approach has proven to be an important graphical tool since it provides
direct insight in both trueness and precision. It is demonstrated that the degree of accuracy of the results obtained under
the large variety of operational parameters is under constant improvement.