**7. Conclusions**

In this study, we use the Tikhonov method to regularize the inverse problem to determine an unknown source term in a space-time-fractional diffusion equation. By an example, we prove that this problem is ill-posed in the sense of Hadamard. Under *a priori* and *a posteriori* parameter choice rules, we show the results about the convergen<sup>t</sup> estimate between the exact solution and the regularized solution. In addition, we show an example to illustrate our proposed regularization.

**Author Contributions:** Project administration, Y.Z.; Resources, L.D.L.; Methodology, N.H.L.; Writing—review, editing and software, C.N.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
