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Partial level density of n-quasiparticle excitations, radiative strength functions and new experimental information on the dynamics of nuclear structure change in the B n range

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Abstract

The most reliable at present values of the level density in the fixed spin window and the sums of radiative strength functions of cascade gamma transitions are obtained from analysis of intensities of two-step cascades excited upon thermal neutron capture for approximately 40 nuclei in the mass range 40 ≤ A ≤ 200. The maximal reliability of these data is provided by the experimental conditions—minimum possible propagation error coefficients and practically unique solution of the problem of determination of gamma decay parameters from measured spectra. The experimental data are approximated by the sum of partial level densities corresponding to excitation of n quasiparticles. Steplike structures in the level density at excitation energies smaller than 3–4 MeV are described with good accuracy as the superposition of two-quasiparticle (three-quasiparticle in odd A nuclei) and vibrational excitations with the coefficient of collective density enhancement K coll ≈ 10−20. They correspond to excitation-energy-correlated maximum enhancement of the radiative strength functions of primary gamma transitions. The level density at larger excitation energies is well reproduced if the breakup of at least two more Cooper pairs of nucleons is taken into account. The increase in the number of excited quasiparticles in the nucleus corresponds to unconditional reduction of the radiative strength functions of primary gamma transitions of the compound state decay. However, the maximum possible value of partial widths of primary transitions increases regularly with decreasing energy. Some ambiguity in the results of approximation and divergence from existing theoretical ideas of the energy dependence of nucleon correlation functions in an excited nucleus point to the possibility of direct extraction from experiment of fundamentally new information on the structure of excited nuclear levels in the range of the neutron binding energy. These are, first of all, the parameters of dependence of nucleon correlation functions on the excitation energy of the nucleus.

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References

  1. Reference Input Parameter Library RIPL-2. Handbook for Calculations of Nuclear Reaction Data, IAEA-TECDOC, 2002; http://www-nds.iaea.org/RIPL-2; Handbook for Calculation of Nuclear Reactions Data, IAEA, Vienna, TECDOC-1034 (1998).

  2. V. M. Maslov, “Pairing Effects in 232Th Neutron-Induced Fission Cross Section,” Nucl. Phys. A 743, 236–255 (2004); V. M. Maslov, Yu. V. Porodzinskij, M. Baba, and A. Hasegawa, “Neutron Capture Cross Section of 232Th,” Nucl. Sci. Eng. 143, 1–11 (2003).

    Article  ADS  Google Scholar 

  3. O. T. Grudzevich et al., “Extraction of Level Density from Evaporative Spectra and Threshold Reaction Excitation Functions,” Yad. Fiz. 53, 143–150 (1991) [Sov. J. Nucl. Phys. 53, 92 (1991)]; V. V. Zhuravlev, “Structure in the Energy Dependence of 165Er Level Density at Low Excitation Energy,” Bull. Russ. Acad. Sci., Phys. 63, 123 (1999).

    Google Scholar 

  4. V. Bondarenko, J. Honzätko, I. Tomandl, et al., “Low-Spin Mixed Particle-Hole Structures in 185W,” Nucl. Phys. A 762, 167–215 (2005).

    Article  ADS  Google Scholar 

  5. S. F. Mughabghab, Neutron Cross Sections BNL-325, Ed. by S. F. Mughabghab, M. Divideenam, and N. E. Holden (Academic, New York, 1984), Vol. 1, Part A; S. F. Mughabghab, Neutron Cross Sections (Academic, New York, 1984), Vol. 1, Part B.

    Google Scholar 

  6. A. M. Sukhovoj and V. A. Khitrov, “Experimental Estimate of the Density of Levels in a Heavy Nucleus That Are Excited in (n, γ) Reactions at Excitation Energies Below 3–4 MeV,” Yad. Fiz. 62, 24–36 (1999) [Phys. At. Nucl. 62, 19 (1999)].

    Google Scholar 

  7. W. Dilg, W. Schantl, H. Vonach, and M. Uhl, “Level Density Parameters for the Back-Shifted Fermi Gas Model in the Mass Range 40 < A < 250,” Nucl. Phys. A 217, 269–298 (1973).

    Article  ADS  Google Scholar 

  8. V. A. Khitrov, Yu. P. Popov, A. M. Sukhovoj, and Yu. S. Yazvitsky, “Analysis of Fluctuations of Low-Lying State Populations in Radiation Neutron Capture,” in Proceedings of III International Symposium on Neutron Capture Gamma-Ray Spectroscopy, Ed. by R. E. Chrien and W. R. Kane (Plenum, New York, 1979), pp. 655–658.

    Google Scholar 

  9. S. T. Boneva, E. V. Vasil’eva, Yu. P. Popov, et al., “Two-Quantum Cascades of Radiative Capture of Neutrons 1. Spectroscopy of Exited States of Compound Nuclei in the Range of Neutron Binding Energy,” Fiz. Elem. Chastits At. Yadra 22, 479–511 (1991) [Sov. J. Part. Nucl. 22, 232 (1991)]; S. T. Boneva, E. V. Vasil’eva, V. D. Kulik, et al., “Two-Quantum Cascades of Radiative Capture of Neutrons 2. Basic Parameters and Features of Gamma-Decay of Compound States of Compound Nuclei,” Fiz. Elem. Chastits At. Yadra 22, 1433–1475 (1991) [Sov. J. Part. Nucl. 22, 698 (1991)].

    Google Scholar 

  10. S. T. Boneva, V. A. Khitrov, and A. M. Sukhovoj, “Excitation Study of High-Lying States of Differently Shaped Heavy Nuclei by the Method of Two-Step Cascades,” Nucl. Phys. A 589, 293–306 (1995).

    Article  ADS  Google Scholar 

  11. E. V. Vasilieva, A. M. Sukhovoj, and V. A. Khitrov, “Direct Experimental Estimate of Parameters That Determine the Cascade Gamma Decay of Compound States of Heavy Nuclei,” Phys. At. Nucl. 64, 153–168 (2001); http://arxiv.org/abs/nucl-ex/0110017; V. A. Khitrov and A. M. Sukhovoj, “New Technique for a Simultaneous Estimation of the Level Density and Radiative Strength Functions of Dipole Transitions at E ex < B n − 0.5 MeV,” INDC(CCP) (Vienna, 2002), Vol. 435, pp. 21–42.

    Article  Google Scholar 

  12. J. Kopecky, “Mass Dependence of the Giant Resonance Model,” in Proceedings of the Symposium on Neutron Capture Gamma-Ray Spectroscopy and Related Topics 1981, Ed by T. Von Egidy (Bristol-London, 1981), pp. 423–425.

  13. M. A. Lone, R. A. Leavitt, and D. A. Harrison, “Prompt Gamma Rays from Thermal Neutron Capture,” Nucl. Data Tables 26(6), 511–559 (1981).

    Article  ADS  Google Scholar 

  14. G. L. Molnar et al., “The New Prompt Gamma-Ray Catalogue for PGAA,” Appl. Radiat. Isot. 53, 527–533 (2000); http://ww-nds.iaea.org/pgaa/egaf.html.

    Article  Google Scholar 

  15. V. A. Khitrov, Chol Li, and A. M. Sukhovoj, “Estimation of the Value and Localization of Possible Systematic Errors in Determination of Level Density and Radiative Strength Functions from the (n, 2γ)-Reaction,” in Interaction of Neutrons with Nuclei, Proceedings of XI International Seminar, Dubna, 2003, E3-2004-9 (Dubna, 2004), pp. 98–106; http://arxiv.org/abs/nucl-ex/0404028.

  16. S. F. Mughabghab, “Thermal Neutron Capture Cross Sections, Resonance Integrals and g-Factors,” Report INDC(NDS)-440 (IAEA Vienna 2003).

  17. A. Voinov et al., “Determination of the Electromagnetic Character of Soft Dipole Modes Solely Based on Quasicontinuous Gamma Spectroscopy,” Nucl. Instrum. Methods Phys. Res. A. 497, 350–358 (2003); A. Voinov et al., “Nature of the Pygmy Resonance in Continuous Gamma-Spectra,” Yad. Fiz. 67, 1891–1897 (2004) [Phys. At. Nucl. 67, 1866 (2004)]; F. Bečvár et al., “E1 and M1 Strengths Studied from Two-Step Gamma Cascades Following Capture of Thermal Neutrons in 162Dy,” Phys. Rev. C 52, 1278–1294 (1995).

    Article  ADS  Google Scholar 

  18. A. M. Sukhovoj, V. A. Khitrov, and Chol Li, “On Correctness of Some Processing Operations for Two-Step Cascade Intensities Data from the (n th, 2γ) Reaction,” in Interaction of Neutrons with Nuclei, Proceedings of XII International Seminar, Dubna, 2004, E3-2004-169 (Dubna, 2004), pp. 438–449; http://arxiv.org/abs/nucl-ex/0409016.

  19. Yu. P. Popov, A. M. Sukhovoj, V. A. Khitrov, and Yu. S. Yazvitskii, “Investigation of Gamma-Decay 165Dy Using (n, 2γ) Reaction,” Izv. Akad. Nauk SSSR, Ser. Fiz. 48, 891 (1984).

    Google Scholar 

  20. http://www.nndc.bnl.gov/nndc/ensdf.

  21. V. A. Bondarenko et al., “Cascade Population of Levels and Probable Radical Change in Properties of Heavy Nucleus in the Region E ex = 0.5B n,” in Interaction of Neutrons with Nuclei, Proceedings of XII International Seminar, Dubna, 2004, E3-2004-169 (Dubna, 2004), pp. 38–50; http://arxiv.org/abs/nucl-ex/0406030.

  22. A. M. Sukhovoj and V. A. Khitrov, “Experimental Manifestations of the Effect of Assumed Breaking of Nucleon Cooper Pairs in Various Nuclei,” Fiz. Elem. Chastits At. Yadra 36, 697–731 (2005) [Phys. Part. Nucl. 36, 359 (2005)].

    Google Scholar 

  23. A. Schiller et al., “Extraction of Level Density and Gamma Strength Function from Primary Gamma Spectra,” Nucl. Instrum. Methods Phys. Res. A 447, 498–511 (2000).

    Article  ADS  Google Scholar 

  24. C. E. Porter and R. G. Thomas, “Fluctuations of Nuclear Reaction Widths,” Phys. Rev. 104, 483–491 (1956).

    Article  ADS  Google Scholar 

  25. A. M. Sukhovoj and V. A. Khitrov, “Method of Improvement of Resolution of Spectra of Cascades of Gamma-Transfer at Coincidence Codes Processing by Computer,” Prib. Tekh. Eksp. 5, 27–30 (1984).

    Google Scholar 

  26. V. A. Bondarenko, J. Honzatko, V. A. Khitrov, et al., “Two-Step Cascades of the 185W Compound Nucleus Gamma-Decay,” Fizika B (Zagreb) 11, 201–222 (2002).

    ADS  Google Scholar 

  27. S. T. Boneva, E. V. Vasil’eva, E. P. Grigor’ev, et al., “Possibility of Identification of Soft Initial γ-Transitions in (n, 2γ) Reaction,” Izv. Akad. Nauk SSSR, Ser. Fiz. 53, 882–887 (1989).

    Google Scholar 

  28. A. V. Ignatyuk, Statistical Properties of Exited Atomic Nuclei (Energoatomizdat, Moscow, 1983) [in Russian]; Report INDC-233(L) (IAEA, Vienna, 1985).

    Google Scholar 

  29. V. M. Strutinsky, “On the Nuclear Level Density in Case of an Energy Gap,” in Proceedings of the International Conference on Nuclear Physics, Paris, 1958, pp. 617–622.

  30. F. Rejmund, A. V. Ignatyuk, A. R. Junghans, and K.-H. Schmidt, “Pair Breaking and Even-Odd Structure in Fission-Fragment Yields,” Nucl. Phys. A 678, 215–234 (2000).

    Article  ADS  Google Scholar 

  31. A. M. Sukhovoj and V. A. Khitrov, Preprint JINR E3-2005-196 (Joint Institute for Nuclear Research, Dubna, 2005).

  32. H. Vonach, “Extraction of Level Density Information from Non-Resonant Reactions,” in Proceedings of IAEA Advisory Group Meeting on Basic and Applied Problems of Nuclear Level Densities, 1983 BNL-NCS-51694, Ed. by M. R. Bhat, pp. 247–290.

  33. A. I. Vdovin, V. V. Voronov, L. A. Malov, et al., “Semi-Microscopic Description of Density of Compound Nuclei States,” Fiz. Elem. Chastits At. Yadra 7, 952–988 (1976) [Sov. J. Part. Nucl. 7, 380 (1976)].

    Google Scholar 

  34. S. Harissopulos et al., “Cross Section Measurement of the 93Nb (p, γ) Reaction at E p = 1.4−4.9 MeV Relevant to the Nucleosynthetic p Process,” Phys. Rev. C 64, 55 804 (2001).

    Article  Google Scholar 

  35. V. A. Kravtsov, Atomic Masses and Binding Energies of Nuclei (Atomizdat, Moscow, 1974) [in Russian].

    Google Scholar 

  36. S. G. Kadmenskii, V. P. Markushev, and V. I. Furman, “Radiation Neutron Resonance Widths and Giant Dipole Resonances,” Yad. Fiz. 37, 277–283 (1983) [Sov. J. Nucl. Phys. 37, 165 (1983)].

    Google Scholar 

  37. P. Axel, “Electric Dipole Ground-State Transition Width Strength Function and 7 MeV Photon Interactions,” Phys. Rev. 126, 671–683 (1962).

    Article  ADS  Google Scholar 

  38. V. G. Soloviev, Theory of Atomic Nuclei: Quasiparticles and Phonons (Institute of Physics Publishing, Bristol, 1992); V. G. Soloviev, Theory of Complex Nuclei (Nauka, Moscow, 1971; Pergamon, Oxford, 1976).

    Google Scholar 

  39. A. M. Sukhovoj et al., nucl-ex/0511016.

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  1. Joint Institute for Nuclear Research, Dubna, Russia

    A. M. Sukhovoj & V. A. Khitrov

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Original Russian Text © A.M. Sukhovoj, V.A. Khitrov, 2006, published in Fizika Elementarnykh Chastits i Atomnogo Yadra, 2006, Vol. 37, No. 6.

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Sukhovoj, A.M., Khitrov, V.A. Partial level density of n-quasiparticle excitations, radiative strength functions and new experimental information on the dynamics of nuclear structure change in the B n range. Phys. Part. Nuclei 37, 899–922 (2006). https://doi.org/10.1134/S1063779606060049

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