Multineutron photodisintegration of the 197 Au nucleus behind the giant dipole resonance
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CLEI Experiment
Multineutron Photodisintegration of the 197Au Nucleus behind the Giant Dipole Resonance A. N. Ermakov, B. S. Ishkhanov, I. M. Kapitonov, Kyaw Kyaw Htun, I. V. Makarenko, V. N. Orlin, and V. I. Shvedunov Institute of Nuclear Physics, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia Received June 6, 2007
Abstract—An experiment in which the gold isotope 197 Au was irradiated with a beam of bremsstrahlung photons having an endpoint energy of Eγm = 67.7 MeV and originating from the RTM-70 racetrack microtron of the Institute of Nuclear Physics at Moscow State University was performed. The gammaray spectra of the residual beta activity of an irradiated sample were measured. Multinucleon photonuclear reactions on 197 Au nuclei were observed in the experiment. Photonuclear reactions on a 197 Au nucleus that involve the emission of up to seven neutrons were recorded for the first time. The experimental results in question suggest the important role of the quasideuteron photodisintegration mechanism in the energy region behind the giant dipole resonance. PACS numbers: 24.30.Cz, 25.20.-x, 13.40.-f DOI: 10.1134/S1063778808030010
INTRODUCTION Although mechanisms of photon–nucleus interaction have been investigated for the past few decades, many questions of paramount importance that concern the structure and dynamics of nuclei are still open. For example, the photon-energy range corresponding to the excitation of a giant dipole resonance (GDR) has been investigated quite comprehensively. Those investigations made it possible to reveal a number of new phenomena, such as the formation of collective states in nuclei, the configuration splitting of giant resonances, and manifestations of isospin symmetry in the excitation and decay of giant resonances. However, the region above GDR energies has received much less study. The main reason for this is that, in contrast to what we have in the region of giant resonances, whose decay is completed by the emission of one nucleon (more rarely, two of them), photodisintegration at energies of 20 to 100 MeV is accompanied by the emission of up to ten nucleons from the nucleus being considered. Methods traditionally used in the region of GDR energies to detect decay products can hardly be applied at higher energies because of a low efficiency in simultaneously detecting several finalstate particles. At the same time, investigations in this energy region are of particular interest, since the mechanism of photon–nucleus interaction changes there. While, in the region of giant-resonance energies, photons interact with a nucleus as a discrete
unit, in the region above GDR energies, a photon interacts with individual nuclear clusters—first of all, with quasideuterons. Problems associated with the dissipation of energy absorbed by individual nuclear fragments and energy transfer to other degrees of freedom have yet to be studied conclusively. The excitation of nucleons belonging to deep inner shells of the nucleus plays an important role in this energy region. The photodisin
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