The neutrons have been captured by Erbium nuclei which were received by using clinical electron linear accelerator. In this experiment, the possibility of the neutron capture process has been observed because of emitted neutrons appearing in the experimental area. In particular, neutron capture of Er-170 nucleus has been observed. After the neutron capture of Er-170 nucleus, the unstable Er-171 has been formed and decayed into the Tm-171. By using this reaction path, some transition energies of Tm-171 obtained from the residual activity measurements and the half-life of Er-171 have been determined, and they are in agreement with adopted values in the literature.