A Significant Contribution of INAA in Autoradiography for Elemental Profile Construction

Autoradiography has been carried out occasionally at the out-of-pool neutron radiography (NR) facility of the Thai Research Reactor-1/M1 for more than a decade. Because of low and uncertain neutron flux at exposure position, the technique is not well recognized. The first attempt to conduct neutron activation autoradiography (NAAR) using in-pool irradiation facility was initiated in Thailand in early 2014. The technique combines fundamental concepts of instrumental neutron activation analysis (INAA) and autoradiography to fulfil their limitations. The elemental composition obtained from INAA, however, is for the whole sample and it is not possible to map specific location of particular elements. Autoradiography, on the other hand, provides visual images without elemental information. Here, a near triangle of 1.5 cm x 3.0 cm metal Buddha image was irradiated using the in-pool dry irradiation facility. Irradiation times were 10 seconds and 15 minutes and decay times were varied. In parallel to elemental analysis, the irradiated sample was placed in good contact with an imaging plate to record self- emitting radiation. At a condition of irradiation, autoradiographic image and elemental appearances in INAA spectrum were compared. The structural profile in complementary with elemental information will help address questions regarding provenance, manufacturing technology, traditional beliefs which can be further applied to conservation methodology and authenticity approval.