Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics

1. Lomonosov Moscow State University,Skobeltsyn Institute of Nuclear Physics Multi-particle photodisintegration of heavy nuclei A.N. Ermakov, B.S. Ishkhanov, I.M. Kapitonov, I.V. Makarenko, V.N. Orlin irina@depni.sinp.msu.ru

3. GDR QD

4. Experimental complex A compact accelerator with maximum electron energy of 70 MeV, built with the use of permanent magnets based on rare-earth magnetic materials. It can be used as a source of bremsstrahlung with maximum γ-quanta energy of up to 70 MeV. • Electron accelerator microtron RTM-70 • Canberra HPGe detector with efficiency of 30% • Automated system for collecting and analysis of γ-spectra • Nuclear data bases • GEANT Monte-Carlo simulation • Theoretical models of multi-particle photonuclear reactions Electron racetrack microtron RTM-70 Skobeltsyn Institute of Nuclear Physics, Moscow State University

5. CDFE The Centre for Photonuclear Experiments Data of the Moscow Lomonosov State University http://www.cdfe.sinp.msu.ru CDFE is the member of the Nuclear Reaction Data Centres Network (NRDCNW), a world-wide cooperation of nuclear data centers from various countries under the auspices of the International Atomic Energy Agency (IAEA). The CDFE is responsible for compilation, analysis and evaluation of photonuclear data and dissemination of nuclear data

6. 209Bi(γ,4n)205Bi • Channel identification: • γ-transition energy Eγ • γ-transition relative intensity Iγ • half-life T1/2 • These quantities were compared to tabular ones • This method allows to determine photonuclear reaction channels definitely

7. MicrotronRTM-70 Electron energy 67.7 MeV Current: 4-5 mA Pulse duration: 4 μs Pulse frequency: 10 Hz HPGedetectorCanberra GC3019 Resolution: 0.9keV (122 keV), 1.9keV (1332 keV). Comparing of irradiated 209Bi sample residual activity spectrum (curve 1) and background spectrum (curve 2). Spectra were measured during 2 h

8. Relative method Use of relative methods is the most effective when investigated and monitor reactions cross sections are measured in the same target and at the same geometry. The method allows to investigate up to 10 reactions simultaneously at the same experimental conditions. This increases relative accuracy of reactions yields determination.

9. Bremsstrahlung γ-spectrum for the max electron energy Еe = 67.7 MeV.Reaction thresholds in 209Bi nucleus Irradiation duration: 4.3 h. 314 series of γ-spectra measurement were made Sample exposition: 245 d

10. Reaction yield (E)reaction cross section W(E,Em) number of bremsstrahlung photons with energy E in elementary energetic interval that are produced by monochromatic electrons ЕеЕт Ет–γ-quanta max energy M – total number of scattering centers in the irradiated part of the target • The following factors are taken into account: • detector efficiency energy dependence • self-absorption in investigated sample • time factors (dependence on irradiation, decay, and measurement time) Sγ–γ-peak area εγ –HPGedetector efficiency Iγ–γ-transition relative intensity λ – decay constant of final nucleus ti,td,tm– irradiation, decay, and measurement time relatively

11. Photonuclear reactions yields in 209Bi

12. Photonuclear reactions yields in 203,205Tl

13. Levinger J.S. // Phys. Rev. 84, 43 (1951) • Chadwick M.B. et al. // Phys. Rev. C 44, 814 (1991) • Ishkhanov B.S., Orlin V.N. // ЭЧАЯ, 38, 84 (2007) • Ishkhanov B.S., Orlin V.N. // Phys. At. Nucl., 71, 517 (2008)

14. 209Bi Solid curves – reactions cross sections dashed curves – QD cross sections.

15. Photonuclear reactions yields in 203,205Tl

16. Photonuclear reactions yields in 209Bi

17. Photonuclear reactions yields in 197Au

18. Conclusions • A research complex for multiparticle photonuclear reactions investigation is used in Skobeltsyn Institute of Nuclear Physics of Moscow State University • New experimental data on the multinucleon photodisintegration of heavy nuclei in the energy region behind the maximum of the giant dipole resonance up to a photon energy of 67.7 MeV have been obtained by the method of gamma spectroscopy of residual beta-active nuclei. • This method has made it possible to observe, for the first time, the entire set of multineutron photonuclear reactions (γ, in) in heavy nuclei, where i ranges between one and seven. • It has been established that the data obtained in our experiment can be described only by simultaneously taking into account both photodisintegration mechanisms—that of the excitation (and decay) of a giant dipole resonance and that of quasideuteron photodisintegration. As the photon energy and the neutron multiplicity increase, the contribution of quasideuteron photodisintegration grows, becoming dominant for reactions involving the emission of not less than four neutrons.