Yields of photoneutron reactions on 197 Au nuclei in the giant-dipole-resonance region
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CLEI Experiment
Yields of Photoneutron Reactions on 197 Au Nuclei in the Giant-Dipole-Resonance Region S. S. Belyshev, A. N. Ermakov, B. S. Ishkhanov, A. A. Kuznetsov, A. S. Kurilik, K. A. Stopani, and S. Yu. Troschiev* Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia Received December 21, 2010; in final form, May 5, 2011
Abstract—Yields of photonuclear reactions on 197 Au nuclei were measured in a beam of bremsstrahlung photons, the endpoint energy of the bremsstrahlung spectrum being 29.1 MeV. These measurements were performed by means of the gamma-activation procedure. The results obtained in this way were compared with the results of earlier experiments and theoretical calculations. DOI: 10.1134/S1063778811110044
1. INTRODUCTION Experimental data on cross sections for photonuclear reactions in the giant-dipole-resonance (GDR) region form a basis for understanding special features of the structure of nuclei and for developing theoretical models that would describe giant dipole resonances [1]. In the present study, we explore photonuclear reactions on the 197 Au nucleus. Previously, cross sections for photoneutron reactions occurring on 197 Au nuclei were measured in three laboratories: in experiments with beams of quasimonochromatic gamma rays in Saclay (IRAMIS Saclay Institute of Matter and Radiation) [2], in Livermore (Lawrence Livermore National Laboratory) [3], and in a beam of bremsstrahlung photons in Moscow [4]. Although the measured cross sections display identical special features of the energy dependence, they differ substantially from one another. These distinctions are associated with the method for analyzing experimental data—in particular, with the separation of photonucleon-reaction channels in multiplicity [5]. A method for separating neutrons in multiplicity was proposed in [5] on the basis of an analysis of directly measurable cross sections σ(γ, xn) for the total-photoneutron-yield reaction. The gamma-activation method for an analysis of yields of photonuclear reactions makes it possible to contrast against one another reactions of different multiplicities; thereby, one compares (γ, 1n) and (γ, 2n) cross sections in an independent way and estimates the efficiency of the method proposed in [5]. *
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The objective of the present study was to measure, by the gamma-activation method, the yields of reactions on the 197 Au nucleus in the energy region of the giant dipole resonance that are characterized by various multiplicities, as well as to analyze the results obtained in this way and to compare them with data reported in [2–10]. 2. EXPERIMENTAL PROCEDURE A beam of electrons accelerated to an energy of 29.1 MeV in an RTM-70 racetrack microtron [11] was incident to a tungsten bremsstrahlung target 2.5 mm thick. A 197 Au sample 100 μm thick was arranged immediately downstream of the target on the beam axis. The irradiation time was three hours and twenty-three minutes. In the course of irradiation, photonuclear reactions acco
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