Abstract

Purpose. To determine the isomeric yield ratios for the heavy cerium isotopes and their dependences on the gamma-quanta energy in the (γ,n) reactions.
Methods. An activation method is used to measure the isomeric ratios.
Results. Present paper presents the method and the results of measuring the isomeric yield ratios d obtained in the (γ,n)^m reaction for the ¹³⁷Ce and ¹³⁹Ce isotopes in the region of the maximal energies of the Bremsstrahlung gamma spectrum E_γmax=11-18 MeV. The Boltzmann curve parameters approximating the d=f(E_γmax) curves as well as the thresholds for the ¹³⁷Ce(γ,n)^137mCe and ¹⁴⁰Ce(γ,n)^139mCe reactions have been obtained.
Conclusion. The analysis of the isomeric ratios d obtained for the ¹³⁷Ce and ¹³⁹Ce nuclei shows that, given the general similarity of their dependences d=f(E_γmax), the isomeric ratios for the cerium-139 are ~20% less than those for the cerium-137. This effect should be related to the influence of the closeness of the 1h_11/2 shell of the ¹⁴⁰Ce nucleus on the isomeric ratio formation for the ¹³⁹Ce nucleus

Keywords: nuclear reaction, isomeric yield ratio, giant dipole resonance, Bremsstrahlung gamma-spectrum

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