Introduction Both ~(159)Tb and ~(169)Tm are rare-earth elements. Their activation cross sections are a good indicator for nuclear science and technology applications. Precise values of the neutron capture cross section of terbium and thulium also are of practical importance in relation to reactor design since they are the fission product poisons. Introduction Both ~ (159) Tb and ~ (169) Tm are rare-earth elements. Their activation cross sections are a good indicator for nuclear science and technology applications. Precise values ​​of the neutron capture cross section of terbium and thulium also are of practical importance in relation to reactor design since they are the fission product poisons