Optimization of Actinides Trace Precipitation on Diamond/Si PIN Sensor for Alpha-Spectrometry in Aqueous Solution

We report here on a new approach for the detection and identification of actinides (²³⁹Pu, ²⁴¹Am, ²⁴⁴Cm, etc). This approach is based on the use of a novel device consisting of a boron doped nanocrystalline diamond film deposited onto a silicon PIN diode alpha particle sensor. The actinides concentration is probed in situ in the measuring solution using a method based on electro-precipitation that can be carried out via the use of a doped diamond electrode. The device allows probing directly both alpha-particles activity and energy in liquid solutions. In this work, we address the optimization of the actinides electro-precipitation step onto the sensor. The approach is based on fine tuning the pH of the electrolyte, the nature of the supporting electrolytes (Na₂SO₄ or NaNO₃), the electrochemical cell geometry, the current density value, the precipitation duration as well as the sensor surface area. The deposition efficiency was significantly improved with values reaching for instance up to 81.5% in the case of electro-precipitation of 5.96 Bq²⁴¹ Am on the sensor. The diamond/silicon sensor can be reused after measurement by performing a fast decontamination step at high yields ≥99%, where the ²⁴¹Am electro-precipitated layer is quickly removed by applying an anodic current (+2 mA · cm^-2 for 10 minutes) to the boron doped nanocrystalline diamond electrode in aqueous solution. This study demonstrated that alpha-particle spectroscopic measurements could be made feasible for the first time in aqueous solutions after an electrochemical deposition process, with theoretical detections thresholds as low as 0.24 Bq · L^-1. We believe that this approach can be of very high interest for alpha-particle spectroscopy in liquids for actinides trace detection.