## 3 Results and Discussion  
### Preparation of the Alpha-Particle Solid Source onto BDD Substrates  
#### 3.1.1 Uniformity of Solid Sources  
The \({}^{241}\)Am compound was used as a typical radioactive source for regarding how \({}^{241}\)Am layers were deposited onto BDD substrates and the effect of either Na\({}_{2}\)SO\({}_{4}\) or NaNO\({}_{3}\) electrolyte solution was also regarded. First, in the Na\({}_{2}\)SO\({}_{4}\) electrolyte, the autoradiography image demonstrated that the deposition of the \({}^{241}\)Am was coated onto the entire BDD substrate (in Figure 2A). The alpha-activity derived from autoradiographs exhibited that \({}^{241}\)Am was deposited on the whole substrates in whichradioactivity in the center is slightly more concentrated than at the border of substrates. Such a result could be explained by the fact that the mechanical stirring system representing an oval shape produces a higher mass transport of the center than the border and thus making \({}^{241}\)Am layer thicker. A very similar quality of the \({}^{241}\)Am layer could be achieved on stainless steel substrates, here used as a comparison (Figure 2B). Such a result demonstrated that a radioactive layer deposited BDD substrate has a good uniformity and same quality as stainless steel.  
Secondly, electro-precipitation in the NaNO\({}_{3}\) electrolyte enables the production of high-quality sources representing a high homogeneity for both BDD and stainless steel substrates (Figure 3A,B). In this case, it should be noted that the alpha-activity distribution is more homogenized with respect to that prepared in Na\({}_{2}\)SO\({}_{4}\) solution. It was proposed that in Na\({}_{2}\)SO\({}_{4}\), the electrolysis of water generates hydroxyl ions with more hydrogen gas while in NaNO\({}_{3}\) electrolysis of nitrate is preferential and thus does not form hydrogen gas. Such bubbling of the hydrogen gas could be the origin of the effect of the radioactive distribution.  
Figure 3: Autoradiographs (left) and profile of radioactivity distributions (right) of the \({}^{241}\)Am alpha sources: (**A**) diamond and (**B**) stainless steel substrates. Electro-precipitation conditions: 0.3 M Na\({}_{2}\)SO\({}_{4}\) pH 3.0 electrolyte + 5.96 Bq \({}^{241}\)Am, current density = 3.3 mA.cm\({}^{-2}\), t = 90 min.  
Figure 2: Autoradiographs (left) and profile of radioactivity distributions (right) of the \({}^{241}\)Am alpha sources: (**A**) diamond and (**B**) stainless steel substrates. Electro-precipitation conditions: 0.3 M Na\({}_{2}\)SO\({}_{4}\) pH 3.97 electrolyte + 5.96 Bq \({}^{241}\)Am, current density = 8 mA.cm\({}^{-2}\), t = 90 min.  
Furthermore, we also investigated how the radioactive source has grown during the electro-precipitation onto the BDD substrate. At this state, electro-precipitation for mixtures of \({}^{239}\)Pu, \({}^{241}\)Am, and \({}^{244}\)Cm were also carried out in Na\({}_{2}\)SO\({}_{4}\) as well as NaNO\({}_{3}\) electrolyte solutions. First, an autoradiograph displays that the precipitation in Na\({}_{2}\)SO\({}_{4}\) solution is preferentially deposited in the center and then extended to the border of BDD substrate following precipitation duration from 15-120 min (see in Figure 4). It was assumed that the radioactivity was first deposited in the center due to higher mass transport and then extended to the near region onto a BDD substrate that has a more conductive layer than actinide oxides layer. This observation explained the radioactive distribution as mentioned above. It should be noted that the radioactive source layers in NaNO\({}_{3}\) electrolyte were grown in the same way as that in Na\({}_{2}\)SO\({}_{4}\) electrolyte (Figure 5).