Experimental relative axial neutron-field mapping in the Argonauta research reactor using dysprosium activation and...

Knowledge of spatial variations in the neutron field is required for irradiation planning, reactor characterization, and experimental validation. This work determined the relative axial neutron-field response in fuel element No. 6 of the Argonauta Research Reactor using thirteen 10 wt% Dy-Al wires. The monitors were irradiated simultaneously in a single 30 min run at 340 W between fuel plates 2 and 3. The net areas of the 94.7 keV gamma-ray peak from ¹⁶⁵Dy were measured with an HPGe detector and corrected for decay during counting and between the end of irradiation and counting. End-of-irradiation activities were obtained using the full-energy peak efficiency and gamma-ray emission probability, and specific activities were calculated using the total Dy-Al wire mass. The specific activities ranged from 8.45 × 10⁷ to 1.51 × 10⁸ Bq g^-1, with the maximum response at 34 cm from the top of the fuel element. The normalized profile showed a broad central maximum and decreasing responses toward both ends. Comparison with an adjusted one-dimensional diffusion reference yielded R² = 0.960 and RMSE = 0.0298, whereas comparison with a published MCNPX thermal profile for the same fuel element yielded R² = 0.888 and RMSE = 0.0501. Because cadmium-covered monitors were not used, thermal and epithermal contributions could not be separated; therefore, the results are interpreted as a relative response to the incident neutron field rather than an absolute thermal-neutron flux measurement.