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CLOSED-FORM E1 RADIATIVE STRENGTH FUNCTIONS FOR PHOTOABSORPTION AND GAMMA-DECAY

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CLOSED-FORM E1 RADIATIVE STRENGTH FUNCTIONS FOR PHOTOABSORPTION AND GAMMA-DECAY V. A. Plujko Taras Shevchenko National University, Kyiv, Ukraine – PowerPoint PPT presentation

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Title: CLOSED-FORM E1 RADIATIVE STRENGTH FUNCTIONS FOR PHOTOABSORPTION AND GAMMA-DECAY


1
CLOSED-FORM E1 RADIATIVE STRENGTH FUNCTIONS FOR
PHOTOABSORPTION AND GAMMA-DECAY
  • V. A. Plujko
  • Taras Shevchenko National University, Kyiv,
    Ukraine

2
CONTENT
  • Introduction average description of the
    gamma-transitions by the use of radiative
    strength function (RSF).
  • 2. Closed-form description of the dipole RSF
  • SLO EGLO GFL MLO (SMLO).
  • 3. Determination of the RSF function parameters.
  • 4. Calculations and comparisons with experimental
    data.
  • 5. Conclusions.

3
INTRODUCTION
Gamma-emission is the most universal channel
of the nuclear decay, because it is, as a rule,
realized during emission of any particle or
cluster. The strengths of electromagnetic
transitions between nuclear states are much used
for investigations of nuclear models, mechanisms
of ?-decay, width of the collective excitations
and nuclear deformations. Average strengths
of ? - transitions are described by radiative
strength functions. It is very important for
decreasing in computing time to use simple
closed-form expressions for ?-ray strength
functions, since these functions in the most
cases are auxiliary quantities required for
calculations of other nuclear reaction
characteristics. The goal of this
contribution is to overview and test practical
methods for the calculation of E1 radiative
strength functions both for ?-decay and
photoabsorption.
4
Radiative strength functions
  • The photoexcitation strength function
  • The gamma-decay strength function

5
MAIN CLOSED-FORM MODELS OF E1 RSF
Standard Lorentzian (SLO)D.Brink. PhD
Thesis(1955) P. Axel. PR 126(1962)
Enhanced Generalized Lorentzian
(EGLO) J.Kopecky , M.Uhl, PRC47(1993) S.Kadmen
sky, V.Markushev, W.Furman, Sov.J.N.Phys
37(1983)  
Infinite fermi- liquid (two-body dissipation)


empirical factor from fitting exp. data
6
Generalized Fermi liquid (GFL) model (extended
to GDR energies of gamma- rays)
S. Mughabghab, C. Dunford PL B487(2000)
Ext.V.A. Plujko, O.O.Kavatsyuk, Proc. 11th Int.
Symp. Capture Gamma-Ray Spectr. and Related
Topics (CGS 11), 2002, 793.
- fragmentation component
7
  • The RSF within SLO, GFL and EGLO models for
    gamma-decay are not agree with general expression
    for radiative strengths in heated nuclei which
    corresponds to detailed balance principle with
    the canonical distribution for initial states.
  • In the EGLO expression for RSF includes an
    additional phenomenological contributions.
  • Gamma-ray energy dependence of widths in
    expressions within EGLO and GFL models is
    introduced formally by substitution of the
    gamma-ray energy instead of GDR energy.
  • T. Belgya, O. Bersillon, R. Capote, T.
    Fukahori, G. Zhigang, S. Goriely, M. Herman, A.V.
    Ignatyuk, S. Kailas. A. Koning, P. Oblozinsky, V.
    Plujko and P. Young. IAEA-TECDOC-1506 Handbook
    for calculations of nuclear reaction data
    Reference Input Parameter Library-2, IAEA,
    Vienna, 2005, Ch.7 http//www-nds.iaea.org/RIPL-2
    /

8
RSF within modified Lorentzian (MLO)
MLO is based on expression for average
gamma-width averaged on microcanonical
ensemble of initial states V.A.Plujko
(Plyuiko), Sov.J.Nucl.Phys. 52 (1990) 639 Proc.
9th Inter. Conf. Nucl. Reaction Mechanisms,
Varenna, June 5-9, 2000, edited by E. Gadioli,
(Universita degli Studi di Milano, Suppl. N.115,
2000),113
9
RSF for gamma-decay
V.A.Plujko, NPA649 (1999) Acta Phys. Pol. B31
(2000) 435. V.A. Plujko, S.N. Ezhov, M.O.
Kavatsyuk et al ,J.Nucl.Sci Techn. (2000) Plujko
V. A., Kadenko I. M., Kulich E. V., Goriely S. et
al Proc. of Workshop on photon strength functions
and related topics, Prague, June 17-20, 2007,
PSF07, 2008 http//arxiv.org/abs/0802.2183
Approximation of strong collective state for
response function
10
  • MLO1 - no restriction on multipolarity of the
    deformation of Fermi-surface

Doorway state approach for collisional relaxation
time
  • SMLO

At U0, width is similar to that proposed by
S.Coriely ( PhL. B436(1998) 10)
11
RSF for photoabsorption
Axially deformed nuclei - n2
12
GDR parameter determination
  • The adjustment is performed by the least square
    method with minimizing
  • Energy dependent errors are used for estimated
    data
  • Spherical nuclei
    Deformed nuclei

13
The E1 photoabsorption cross section on 144Nd
14
(a)
(b)
15
The E1 gamma-decay strength function on 144Nd
for UBn
Model EGLO SLO GFL MLO1 MLO2 MLO3 SMLO
2.2 22.9 2.6 6.47 6.52 7.16 6.06
16
(a)
(b)
17
(a)
(b)
18
(a)
(b)
19
(No Transcript)
20
(a)
(b)
21
(a)
(b)
22
Model EGLO SLO GFL MLO1 SMLO
5.0 105 5.27 7.55 2.0
23
Systematics of GDR energies and widths
  • Systematics are found on base of resonance
    parameters, that are obtained from fitting of
    experimental data

24
Comparison of systematics with fitting data
25
Conclusions
  • MLO approach with asymmetric shape of the RSF
    provide unified and rather reliable simple
    methods to estimate the dipole RSF both for
    gamma-decay and for photoabsorption over a
    relatively wide energy interval ranging from zero
    to slightly above the GDR peak EGLO approach is
    also rather reliable for description of
    gamma-decay RSF.
  • MLO approach is based on general relations
    between the RSF and the nuclear response
    function. Therefore it can potentially lead to
    more reliable predictions among other simple
    models.
  • The energy dependence of the width is governed
    by complex mechanisms of nuclear dissipation and
    is still an open problem.
  • Reliable experimental information is needed to
    better determine the temperature and energy
    dependence of the RSF, so that the contributions
    of the different mechanisms responsible for the
    damping of the collective states can be further
    investigated.
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