Transcript Document

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.
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)
EMPIRE II –
TALYS –
http://www.talys.eu/
http://www.nndc.bnl.gov/empire219/
http://www-nds.iaea.org/empire/
Two approaches to take into account all photonuclear reaction
exit channels to derive GDR parameters from experimental data
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
2. Fitting GDR parameters with condition
of
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…
________________________________________
Present report
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
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
• SLO - standard Lorenztian model
Brink D.M. //Ph. D. Thesis. Oxford University. 1955.
Axel P. //Phys. Rev. 1962. V.126, P.671.
f ( E )  8,674 10   R  R 
E  R
8
( E  E )  ( E  R )
2
2 2
R
2
, (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.


E  ( E , T )
f ( E )  8674 10   R   R  L ( E , T )   2
2 2
2
(
E

E
)

(
E


(
E
,
T
))
 

R


8
, (МеВ),
QRPA – microscopic approach: S.Goriely,E.Khan. Nucl. Phys. A, 2002, V.706, p.217
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 HauserFeshbach 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
Threshold (MeV)
Abundance (%)
64Zn
20.98
48.6
66Zn
19.04
27.9
68Zn
17.25
18.8
Nucleus
E1 ,
MeV
σ1,
mb
Γ1,
MeV
E2 ,
MeV
σ2,
mb
Γ2,
MeV
 n2
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
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
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
63Cu
60Ni
Stability of calculation results to variation of parameters (χ2 between experimental and calculated
data): 63Cu, reaction (,xn), LEVDEN = 2, parameter GSTRFN = 6 (model RSF SLO), χ2 =2,09; 60Ni,
reaction (,xn), LEVDEN = 0, parameter GSTRFN = 1 (model RSF MLO1), χ2 =2,76; 64Zn, reaction
(,xn), LEVDEN = 2, parameter GSTRFN = 6 (model RSF SLO), χ2 =2,19.
Conclusions
this paper the GDR parameters for medium mass nuclei 60Ni, 63Cu, 64Zn are
updated taking into account exit channels with emission of charged particles
• In
• 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