In order to extend the available experimental database for the astrophysical $\gamma$-process, the cross
section measurements of the ${}^{130}$Ba($\alpha, \gamma$)${}^{134}$Ce and ${}^{130}$Ba($\alpha, n$)${}^{133}$Ce reactions are in progress. The measurements are carried out using thin layers of evaporated BaCO$_3$ as target. Since the target thickness enters directly into the calculation of the cross sections, the reliability of its determination is of crucial importance. Three different methods have been used to determine the target thickness. Details of these experiments and the obtained results are presented.