Nuclear data for nuclear installations: Radiochemistry improves the precision of the cross-section data of long-lived radionuclides

Matter and Material

Proton irradiations of lead, tantalum, and tungsten targets were performed twenty years ago at the SATURNE II synchrotron of the Laboratorie National Saturne (LNS) at Saclay. Due to a long time after irradiation, the short lived reaction products had already decayed. These targets were used to determine the production cross sections of long-lived α-emitting radionuclides (¹⁴⁸Gd (T_1/2 = 74.6 y), ¹⁵⁴Dy (3 × 10⁶ y)) and the long-lived β-emitting radionuclides (³⁶Cl (T_1/2 = 3.01 × 10⁵ y) and ¹²⁹I (T_1/2 = 0.57 × 10⁷ y)).

As a first step, radiochemical separation methods were developed to isolate these radionuclides. After separation, the measurements of ¹²⁹I/¹²⁷I and ³⁶Cl/³⁵Cl ratios were performed with accelerator mass spectrometry in collaboration with the Laboratory of Ion Beam Physics, ETH Zurich. Molecular plating technique was used to prepare thin and homogeneous lanthanides samples to obtain a good quality α-spectrum with high resolution and small low energy tail contribution. Autoradiography and focused ion beam/scanning electron microscopy techniques were used for the characterization of the lanthanide deposited layer.

The experimental results were compared with the theoretical calculations obtained with the combination of Liège intra-nuclear cascade (INCL++) and de-excitation phase (ABLA07) codes in collaboration with CEA/Saclay. The comparisons showed a satisfactory agreement for the ¹⁴⁸Gd, ¹²⁹I, and ³⁶Cl cross-section results. In our work, it is clearly shown that radiochemical separation has a high impact for improving the accuracy of the results. However, theoretical ¹⁵⁴Dy cross sections data were underestimated, which could be due to the high uncertainty of the accepted half-life value of ¹⁵⁴Dy (3±1.5 My). Therefore, to increase the accuracy of the experimental cross-section data more precise half-life measurements are required. Corresponding measurements are currently ongoing in the frame of the ERAWAST project.