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 activation analysis is attractive for trace-element determinations in large samples. Facilities for reactor irradiation and -ray spectrometry of kilogram-size cylindrical samples are described. The thermal neutron flux is ca. 5·1012m–2·s–1 with ath/epi>104, so neutron self-thermalization can be neglected. The correction for the neutron attenuation within the sample is derived from measurement of the neutron flux depression just outside the sample. Correction for -attenuation in the sample is performed via linear attenuation coefficients derived via transmission measurements. Also the natural radioactivity in the sample is taken into account. Examples are given of materials to which large sample INAA has been applied successfully, and further lines of development and exploration are indicated.