determination of the photon strength function...

Centre for Energy Research,Hungarian Academy of Sciences

T. Belgya 1st ERINDA Progress Meeting and Scientific Workshop January 16-18, 2012 Villa Lana, Prague, Czech Republic 11

Determination of the photon strength function in 114Cd

Tamás BelgyaNuclear Analysis and Radiography Department



Radiative neutron capture

Targetnucleus

Compoundnucleus

neutron

Radiative capture (n, )AZ X 1 *A

Z X

Elastic scattering (n, n)

Other particle emitting reactionsn’, p, , f,…

Always present

Threshold reactions

There is always a competition between the reaction channels that depends on the nuclear structure thus the knowledge of radiative decay probability is important.



Radiative decay probability

<(Ec )> average decay width described by the photon strength function (f

(Eg ))

k is fluctuating widely (follows the Porter- Thomas distribution)

k () depends on the multipolarity

The most important is the electric dipole (E1)

113Cd 1/2+

Capture state

g.s.

1 2 3 …c-1 <(Ec )>

1 2 3 …m-1 <(Em )>

0+

2+

0+, 1+

n

2E1,M1,EX

),,D()(f),( 12Xλ

iiii JEEEEE

Gamma decay probability P for level m

1

1, /

m

iikkmP



Resonance fluorescence and absorption

Elastic and inelastic scattering

Absorption above Sn or Sp , GDR, GQR

The most important is the electric dipole (E1)

Resonant state

g.s.

1 2 3 …c-1 <(Ec )>

1 2 3 …m-1 <(Em )>

0+

2+

0+, 1+

2E1,M1,EXλ

)12()(f 12Xλ

EE

RSF for E1 TLO*

RSF for M1 and E2 from RIPL-II

*A.R. Junghans et. al. Physics Letters B 670 (2008) 200–204



EGDR strength functions (analytical forms)Axel-Brink hypothesis (GDR builds on all of the excited states) There are many different EGDR strength functions listed in RIPL-3

Standard Lorentzian Model (SLO) T independentEnhanced Generalized Lorentzian Model (EGLO)Kadmenskij-Markushev-Furman Model (KMF)Generalized Fermi Liquid model (GFL)Modified Lorentzian model (MLO) Recommended

R. Capote et al. Nuclear Data Sheets 110 (2009) 3107–3214



Problems with EGDR strength functions RIPL-3There are many different EGDR strength functions listed in RIPL-3

Difficult to determine when to use deformed RSF (with two humps)In case for transitional nuclei no good fit of EGDR can be obtainedLow amount of experimental data exists on low energy strengthThere exists some contradiction between RSF deduced from (, ’) and (n, ) data

1E-13

1E-12

1E-11

1E-10

1E-09

1E-08

1E-07

1E-06

0 5 10 15 20E (MeV)

RS

F S

e-78 MLO E1

M1E2TLO E1

E. Grosse et al. EPJ Web of Conferences 8, 02006 (2010)

TLOEGLOMicroscopic



Collaboration for research of RSFTo resolve these problems the HZD ELBE, EK NAL (IKI) and Charles Univ. groups initiated a collaboration in the framework of EFNUDAT and ERINDA to perform (n, ) experiments on 1/2-

ground state nuclei with mass A and (, ’) experiments on A+1In this case the capture state has 1- and 0- spin(, ’) can excite mainly 1- statesUnfortunately there are only two stable nuclei pairs with this feature 77-78Se and 195-196PtThere is another not so favored case for which the ground sate spin is 1/2+

This is the 113-114Cd pair, which is the subject of this talk

The analysis of the first set of data on 77-78Se has been finished and is submitted to PRC We concluded that it is possible to simulate the (n, ) and (, ’) experimental spectra with the same experimental RSFThe TLO based RSF description successfully joins to the EGDR tail

G. Schramm et al. PRC in print details in talk of Eckart Grosse



Experiments on 113Cd (n,) BudapestIt was decided to use the Budapest detector system for these experimentsThis decision had the following consequences:

The Budapest detector transfer function have to be created, this require a careful Monte Carlo simulationsDecay Scheme simulation program have also to be developed to have full handle on the evaluation

The experiments were done Oct. 2010, at the end of the EFNUDAT project Measurements on 113Cd using 1 mm2 pencil beam

99.99% pure, natural Cd foil 2.5x2.5x0.005 cm3 from Goodfellow90% enriced 113Cd metal, 100 mgbackgroundsample holderefficiency

We recorded both the Compton-suppresed and normal spectra



Compton-suppressed 113Cd (n,) spectra



Analysis of 113Cd (n,) spectrumThe spectrum was fit with Hypermet PC

This resulted in about 1200 resolved gamma peaksThe partial gamma-ray production Xsections were determined

0

5000

10000

15000

20000

0 2000 4000 6000 8000 10000

E (keV)

*E

/Bn (

b)

Thermal neutron capture cross section (20600 b) 40% is

missing



Preparation for decay scheme modeling EGDR for Cd-114 region

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15 20 25E (MeV)

( ,n

) bar

n

Cd-114TLOIn-115



1E-12

1E-11

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

0 5 10 15 20

E (MeV)

f(E)

MeV

-(2L+

1)

MLO E1M1E2TLO E1

Preparation for decay scheme modeling RSF for Cd-114 region



Preparation for response function modeling 27% detector X-ray radiograph



Preparation for response function modeling 27% detector GEANT4 response function for Co-60



Preparation for response function modeling 27% detector GEANT4 efficiency (Livermore data library)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2000 4000 6000 8000 10000 12000

E (KeV)

effic

ienc

y Measured/calculatedefficiency



Measurement at ELBE

Planned experiment on enriched Cd-114 sampleTime end of March – beginning of April 2012

Combined evaluation have to be doneBoth modeling needs more work (on side of EK NAL IKI)Expected outcome is better understanding of the role of M1 transitions

Sofar the experiments are very successful



Thank you Thank you for your attentionfor your attention!!

determination of the photon strength function...

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