Calculation of GDR Parameters Using All Exit Channels of Photonuclear Reactions

1. Calculation of GDR Parameters Using All Exit Channels of Photonuclear Reactions O.Bezshyyko, L. Golinka-Bezshyyko, I. Kadenko, Nuclear Physics Department, Taras Shevchenko National University, Kyiv, Ukraine Giant Dipole Resonance (GDR) parameters are being calculated often using only experimental data from photoneutron reactions. Comparison of theoretical calculations with experimental data is quite complicated in the energy region where multiple neutron escape is possible, but this information is essential to get correct values of GDR parameters. Also one has to take into account that a competition between neutron emission and escape of charged particles (mainly protons and sometimes alpha particles) exist in the exit channel and complex theoretical calculations with incorporated detailed mechanism of multiple escape of neutrons and protons are needed. In this work we used the codes EMPIRE II and TALYS to evaluate GDR parameters for some medium mass nuclei 60Ni, 63Cu, 64Zn and others) with all photonuclear reaction exit channels considered. This information is useful for extending databases containing input parameters for theoretical calculations of nuclear reaction characteristics.

2. EMPIRE II – http://www.nndc.bnl.gov/empire219/ http://www-nds.iaea.org/empire/ TALYS – http://www.talys.eu/ Handbook on photonuclear data for applications. IAEA, 2000 ↓ (,sn) = (,n) + (,np) + (,n2p) + (,2n) + (,2np) + (,3n) +… (,xn) = (,n) + (,np) + (,n2p) +2(,2n) + 2(,2np) + 3(,3n) +… (,abs) = (,sn) + (,p) + (,2p) + (,d) + (,dp) + (,) +… (,sn) – total photoneutron cross section (,xn) – photoneutron yield cross section (,abs) – total photoabsorption cross section (,abs)  (,sn)  S.S.Dietrich and B.L.Berman, Atomic Data and Nuclear Data Tables 38, 199(1988)

3. Two approaches to take into account all photonuclear reaction exit channels to derive GDR parameters from experimental data 2. Fitting GDR parameters with condition of simultaneousaccordance to experimental data of maximum number of available independent sets for partial cross sections - (,abs), (,sn),(,xn), (,n), (,2n), (,np), (,p), (,2p), (,α) and other… ________________________________________ Present report 1. Compilation of experimental(,abs) cross section using experimental data for various partial cross sections _________________________________________ Moscow State University group (SINP) -V.Varlamov with colleagues http://cdfe.sinp.msu.ru/team.ru.html V.V. Varlamov, M. Stepanov, V.Chesnokov // Izv. RAN. Ser. Phys. 2006.,V. 67. № 5. P. 694. These methods are mutually complementary and their combined using may provide rather good reliability of fitting for GDR parameters

4. 1 approach - Compilation of experimental(,abs) cross section using experimental data for various partial cross sections • Advantages: • Absence of model approximations and fitted parameters • Shortcomings: • There is little or no of experimental data for photonuclear reactions with charged particles in the exit channel • Complicated fitting procedure for GDR parameters due not smooth behavior of photoproton cross sections and therefore complex shape of (,abs) cross section

5. SLO - standard Lorenztian model • Brink D.M. //Ph. D. Thesis. Oxford University. 1955. • Axel P. //Phys. Rev. 1962. V.126, P.671. • , (МеВ), • MLO1 - modified Lorentzian model • Plujko V.A., et al //J. Nucl. Sci. Technol. Suppl.2. 2002. P. 811. • Plujko V.A. // Nucl. Phys. A. 1999. V.649. P.209с. • , (МеВ),

11. QRPA – microscopic approach: S.Goriely,E.Khan. Nucl. Phys. A, 2002, V.706, p.217

13. 2 approach - Fitting of GDR parameters with condition of simultaneous accordance to experimental data of maximum number of available independent sets for partial cross sections • Shortcomings: • Influence of model parameters and competition between emission one neutron, two neutron and proton (level density, transmission coefficients – optical model parameters, RSF models and other) on derived GDR parameters. Decision of this problem – restraining of these degrees of freedom by requirement of simultaneous satisfactory description for many various partial cross sections • Advantages: • Such approach allows to perform GDR fitting without photoproton experimental data (using only optical model parameters, derived from inverse reactions accordingly Hauser-Feshbach statistical model) • Additional precise analysis is possible not only for GDR parameters but for other nuclear structure and reaction mechanism parameters, for example optical model parameters

18. Threshold (MeV) Abundance (%) 64Zn 20.98 48.6 66Zn 19.04 27.9 68Zn 17.25 18.8

21. Nucleus E1, MeV σ1, mb Γ1, MeV E2, MeV σ2, mb Γ2, MeV Comments 64Zn 16,23 41,40 3,27 19,19 56,10 5,98 61,1 RIPL2 16,67 95,10 3,11 19,49 121,1 8,15 1,3 Present work 63Cu 16,72 66,10 4,19 19,10 30,10 3,56 29,3 RIPL2 16,52 81,10 4,79 21,50 28,50 5,76 1,7 Present work 60Ni 16,30 34,10 2,44 18,51 55,20 6,37 27,9 RIPL2 17,00 51,10 3,45 19,40 54,20 8,90 1,4 Present work Stability of calculation results to variation of parameters (χ2 between experimental and calculated data):63Cu, reaction (,xn), LEVDEN =2, parameter GSTRFN = 6 (modelRSFSLO), χ2 =2,09; 60Ni, reaction (,xn), LEVDEN =0, parameter GSTRFN = 1 (modelRSFMLO1), χ2 =2,76; 64Zn, reaction (,xn), LEVDEN =2, parameter GSTRFN = 6 (model RSFSLO), χ2 =2,19.

22. Conclusions • In this paper the GDR parameters for medium mass nuclei 60Ni, 63Cu, 64Zn are updated taking into account exit channels with emission of charged particles • The code Empire II was used for fitting of GDR parameters and code Talys was applied to check the results obtained • During fitting of GDR parameters the constraint condition was used - simultaneous accordance to experimental data of maximum number of available independent sets for partial cross sections - (,abs), (,sn), (,xn), (,n), (,2n), (,np), (,p), (,2p), (,α) and other… • This approach allows to improve the applicability of photonuclear reactions as precise tool for deriving not only GDR parameters but and other nuclear structure parameters, to study competition of various neutron and proton exit channels • Potential power of photonuclear reactions for study of reaction mechanisms and nuclear structure is restricted hardly by insufficient amount of precise experimental data, especially for various photoproton and (,α) reactions