Production and half lives of heavy neutron-rich nuclei approaching the r-process path at N=126...

Production and half lives of heavy neutron-rich

nuclei approaching the r-process path at N=126

José BenlliureUniversidad of Santiago de Compostela

Spain

Pre-SPEC decay physics workshopBrighton, January 12-13, 2011

Nuclear data for the r process

Ground state properties of nuclei involved in the r pocess such us half lives or masses are required for the full understanding of this nucleoshynthesis mechanism.

Present RIB facilities made possible to producelight and medium-mass neutron-rich nuclei at the r-process path. However, the region around the A~195 waiting point is out of our reach.

The waiting point at A~195 defines the abundance of the heaviest elements in the Universe. But this is also an interesting region for nuclear structure because of the interplay between shell closure and deformation effects.

Brighton (UK), January 2011José Benlliure, Pre-SPEC decay physics workshop

Nucler data for the r process

The half lives of r-process nuclei along the N=126 shell define the role of the A~195 waiting point in the r process:

Matter flow through the N=126 bottleneck region fixing the abundance pattern of the heaviest elements in the Universe.

The velocity of synthesis of these heavy elements: r-process end point, r-process cycling.

It is our goal to investigate:- the production of heavy neutron-rich nuclei- determine their half lives

Present theoretical predictions of the half lives of r process nuclei close or at N=126 are rather discordant.

K.L. Kratz

[1] P. Möller, et al. PRC 67, 055802 (2003)[2] I. N. Borzov PRC 67, 025802 (2003)

José Benlliure, Pre-SPEC decay physics workshop Brighton (UK), January 2011

Pre-RISING S227 (2001-2003):

- production of heavy neutron-rich nuclei in fragmentation reactions induced by 238U and 208Pb projectiles

- first half-lives measurements using ion- position-time correlations with an active stopper

RISING S312 (2007):

- half-lives measurements using ion- position-time correlations with an active stopper+RISING

- low lying excited states

Pre-SPEC:

- few ideas on new half lives measurements and characterization of -decays.

Outline

José Benlliure, Pre-SPEC decay physics workshop Brighton (UK), January 2011

_

One of the challenges ofthe experiment was the iden-tification of charge states Beam energy (< 700 A MeV)

FRS+energy degrader

Experimental technique: SIS18+FRS (GSI)238U, 208Pb(1 A GeV)+Be (107 ions/s)

208Pb(1 A GeV)+Be

Production of heavy neutron-rich nuclei



75 heavy neutron-rich nuclei have been identified for the first time.


H. Alvarez-Pol et al.., PRC 82, 041602 (2010)

_


EPAX

COFRA

RIBF


www.usc.es/genp/cofra

half lives

_

Experimental technique: ion – (– ) correlations

Active stopper: highly segmented DSSSDion- time-position correlation

RISING -ray spectrometer prompt correlation


half lives

Time correlations evaluationStandard exponential fits of time correlations are not applicable in general

pulsed beam: time-modulated -electron background

half lives (~ 10 s) are longer than the production/implantation rate: multiple implantations

New proposed method:

prompt correlations: -electron suppresion

backward-time ion- correlations: remaining background evaluation numerical fitting fuction based on Monte Carlo simulations of the implantation-decay process including experimental implantation rates and having as free parameters the decay half life and the detection efficiencyT. Kurtukian-Nieto et al.., NIMA 67, 055802 (2008)


half lives

Time correlations evaluation


Brighton (UK), January 2011

half lives

Results

[1] P. Möller, et al. PRC 67, 055802 (2003)[2] I. N. Borzov PRC 67, 025802 (2003)

12.7 s654.0 s

1.4 s3.6 s

8.5 s3.3 s

25.0 s124.1 s

46.7 s370.6 s

6.9 s187.1 s

6.6 s106.8 s

7.4 s321.8 s

9.8 s68.4 s

28.4 s130.0 s

19.1 s377.1 s

2.1 s70.8 s

DF3+ QRPA[2]

FRDM+QRPA[1]

The half lives of 13 heavy neutron-rich nuclei have been determined, 11 of them for the first time.

203Pt

204Au

other works

196Re195Re

200Ir199Ir

200Os199Os

204Pt

202Ir201Ir

198Ir

194Re

withw/o Nuclei

s 546

s 2 8

s 436

s 425

s 123

s 5.01

s 311

s 6543

s 521

s 315

s 422

s 6516

s 8.037 s 9.08.39

s 1 6

s 1 8

José Benlliure, Pre-SPEC decay physics workshop

half lives

Results

The half lives of 13 heavy neutron-rich nuclei have been determined, 11 of them for the first time.


half lives

Results

FRDM calculations overestimate the measured half lives

DF3 calculations provides a better description of the data: role of first forbidden transitions

These results may suggest that the r process matter flow to the heavier fissioning nuclei could be faster than expected


T. Kurtukian et al., submitted to PLB

half lives

Role of first forbidden transitions

According to I. Borzov calculations, in this region of the chart of nuclides FF transitions appear at lower excitation energies than GT transitions. Because of the larger phase space, FF decays are then favored.

Borzov calculations do not include deformation effects


-delayed gamma spectroscopy

Characterization of low-lying excited states


The production/implantation technique at RISING produces rather complex gamma spectra

204Au




Selecting areas in the DSSSD detectors where different contaminants are preferably implated and determining uncorrelated decays from backward-time -ion correlations, the gamma spectra can be cleaned.

204Au




The feading of the lowest lying excited states together with spin-parity values based on shell model calculations would support the role of FF transitions in this decay.

OXBASH calculations by M. Gorska and H. Grawe




The interpretation of these level schemes based on shell model calculations is more difficult because of the valence space configuration and possible deformation effects.

Calculations are in progress.

Future measurements


Complete the systematics close to N=126

Accurate half lives for nuclei approaching the deformation region

Combined measurements with fast timing arrays

Complementary measurements of the strength with TAS

Key issues:- role of first forbidden transitions- role of deformation

Summary

We can not yet produce r-process nuclei at the N=126 shell, but. Tremendous progress has been done at the FRS expanding the north-est frontier of the chart of nuclides

Present (GSI) and future (FAIR) production rates can be reliably estimated

half lives were determined using ion – (-) correlations A new method to determine half lives under complex background conditions was introduced

The half lives of 13 heavy neutron-rich nuclei were determined.

The measured half lives better describe when FF transitions are considered.

The confirmation of this result for r process nuclei would indicate a faster r process matter flow towards the heavier fissioning nuclei.


Future possibilities are: Complete the systematics close to N=126

Investigate the role of FF transitions and deformation

Collaborators

S227H. Alvarez-Pol1, J. Benlliure1, T. Kurtukian-Nieto1, I.N. Borzov2, L. Audouin3, B. Blank4, F. Becker2,E. Casarejos1, D. Cortina-Gil1, T. Enqvist2,b, B. Fernández5, M. Fernández-Ordóñez1,c, J. Giovinazzo4, D. Henzlova2,d, A.R. Junghans6, B. Jurado4, K. Langanke2, G. Martinez-Pinedo2, P. Napolitani3, J. Pereira1,d, F. Rejmund5, K.-H. Schmidt2, O. Yordanov2,e

1U. Santiago, 2GSI, 3IPN-Orsay, 4CEN-Bordeaux, 5GANIL, 6FZ Dresden-Rossendorf

S312A.I. Morales1, J. Benlliure1, M. Gorska2, P. Regan3, Z. Podolyak3, N. Alkomashi3, A. Algora4,H. Alvarez-Pol1, G. Benzoni5, A. Blazhev6, P. Boutachkov2, A.M. Bruce7, L.S. Caceres2, E. Casarejos1, I.J. Cullen3, A.M. Denis7, P. Doornenbal2, M.E. Estevez4, G. Farrelly3, Y. Fujita8, A.B. Garnsworthy3,W. Gelletly3, J. Gerl2, J. Grebosz2, R. Hoischen9, I. Kojouharov2, N. Kurz2, S. Lalkovski9, Z. Liu10, C. Mihai9, F. Molina4, D. Mucher6, D.Perez1, S. Pietri2, W. Prokopowicz2, B. Rubio4, H. Shaffner2, S.J. Steer3, A Tamii11, S. Tashenov2, J.J. Valiente12, S. Verma1, P. Walker3, H.J. Wollersheim2, P.J. Woods10

1U. Santiago, 2GSI, 3U. Surrey, 4IFIC-Valencia, 5INFN-Milano, 6U. Cologne, 7U. Brighton,8U. Osaka, 9U. Lund, 10U. Edimburg, 11RCNP-Osaka, 12INFN-Legnaro


Production and half lives of heavy neutron-rich nuclei approaching the r-process path at N=126...

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