A new Rule of Thumb to evaluate alpha sources prepared by electro precipitation using X-ray Fluorescence

Highlights

• XRF is a suitable technique for the characterization of alpha sources in a short time.

• A Rule of Thumb allows rapid evaluation of alpha-particle sources.

• Small laboratories will benefit from this method, as the analysis can be performed even with portable devices.

Abstract

This report studies the feasibility of using X-ray Fluorescence for the characterization of alpha sources in a short time and proposes a new Rule of Thumb for the sake of simplicity. An uranium deposit of 0.012 $\pm$ 0.001 mg cm⁻² which XRF spectrum shows a low intensity U-L$\alpha$ peak at 13.61 keV, provides good resolution in alpha spectrometry. By this method, long data acquisition times in alpha spectrometry of poorly prepared sources are avoided without the need for expensive equipment.

Introduction

X-ray Fluorescence (XRF) is a non-destructive multi-elemental technique widely used in the study of the composition of feedstock, rocks, soils, clays, cement, cultural heritage objects and in the analysis of biological materials. Thanks to the speed with which an analysis can be performed, quality control of some goods can be carried out in many applications, where immediate results are required.

This study aims to introduce XRF for the evaluation of alpha sources prepared by electro precipitation. In order to obtain good resolution in alpha spectrometry, it is required that just a thin and homogeneous layer of uranium is deposited onto the plate, ideally a thickness of a few atoms, in this way avoiding the interaction between the alpha particles and other materials that leads to energy losses. Many variables are involved in the electro precipitation process, such as the pH of the electrolyte, the salt concentration, the anode shape, the cathode material, the anode rotation, the current density and the deposition time. The discussion about the influence of each variable on the electroplating process is out of the scope of this work, but it can be easily found in literature (Dimitru et al., 2013). Although these parameters can be optimized, the electro precipitation process of uranium from slightly acidic solutions (pH $>$ 2.5) on discs is considered erratic (Saliba-Silva et al., 2014) due to the generation of hydrogen bubbles on the cathode surface that need to be removed in order to form the hydroxyl layer that makes uranium hydroxide and uranium oxide precipitate (Crespo, 2012) . Many investigations are being carried out for improving electro precipitation, including the replacement of metallic substrates by boron-doped diamond, which aims at better peak resolution (Tran et al., 2019). Characterization of alpha sources is extremely helpful for sample preparation, as it allows to accept or reject sources before they go to alpha counting, which usually may take a long time. Several techniques are currently used in the sources characterization, like autoradiography (Jobbagy et al., 2013), Scanning Electron Microscopy/ Energy Dispersive X-ray Spectrometry (SEM/EDS), X-ray Diffraction (XRD), and Raman Spectroscopy (Wilbraham et al., 2015). In this work, we determined that XRF is suitable for the characterization of alpha sources. Over other techniques, it is more accessible, faster and users do not need much training. Furthermore, we have established a smart Rule of Thumb, that allows to make the evaluation of the alpha sources by just taking a glance at the XRF spectrum.