Productions of heavy neutron-rich nuclei around neutron shell

closure N=126 in the reaction 136Xe+208Pb

Oleg Rudakov

Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research,

Dubna

JYFL User Meeting in Jyväskylä, Finland 7-8 March 2012

Chart of the nuclides

Top part of the nuclear map. The three problems are indicated: How to reach the island of stability, how to fill the gap and how to explore the blank spot of the nuclear map?

Nuclide map demonstrating the possibility of proton transfer in the reaction 136Xe+208Pb at energy closed to the Coulomb barrier.

North east area of the nuclides chart

Target208Pb

F1

F2

solid angle – 0.3 sr

angular resolution – 0.30

TOF-start detector

Beam136 Xe

position sensitivestop detectorx, y, TOF

TOF-start detector

the two-armed time-of-flight reaction product spectrometer CORSET composed of microchannel plates •Time resolution t 150 ps•Mass resolution / 7 amu•Angular resolution , 0.3•Solid angle of each arm 150 msr•Range of measured angles: 25 -70

Basic characteristics of the CORSET spectrometer

Mass-energy distributions of binary fragments for the reaction 136Xe+208Pb

Mass-energy distributions of the primary binary fragments obtained in the reaction 136Xe+208Pb at c.m. energies of 423, 526 and 617 MeV.

• The Q-value (Q = MTLF+MPLF-MT-MP) is not very large for this reaction (10÷5 MeV). The difference between the center-of-mass kinetic energies in the entrance and exit channels is manly transformed into internal energy and in a first approximation equals to the excitation energy for both fragments.

• The mass distributions for fragments with energy-losses greater than 40 MeV are shown in the right panel. The red points correspond to the mass distribution after de-excitation process, the black ones are mass distribution before de-excitation.

Mass-energy distributions of binary fragments for the reaction 136Xe+208Pb

Mass-energy distributions of binary fragments for the reaction 136Xe+208Pb

10-4

10-3

10-2

10-1

100

101

102

40MeV÷100MeV; 100MeV÷150MeV 150MeV÷200MeV; 200MeV÷250MeV

Eloss

>250MeV

Ec.m. = 617 MeV

Yie

ld (%

)

100 120 140 160 180 200 220 24010-4

10-3

10-2

10-1

100

101

Ec.m. = 526 MeV

Mass (u)

Yie

ld (%

)

Production cross section for the heavy nuclei (A>200 u) in the reaction 136Xe+208Pb at Elab=870MeV

200 205 210 215 220 225 230 23510-3

10-2

10-1

100

101

102

103

104

calculated by Zagrebaev (all events) E losses > 40MeV

experimental

Y

ield

(mb)

Mass (u)

Angular distributions of binary fragments for the reaction 136Xe+208Pb

a) Laboratory angular distributions of the Xe-like reaction products; b) laboratory angular distributions of the Pb-like reaction products for the mass region 200-216 u.

Elab, MeV exp, b

700±14 0.2±0.1

870±17 1.1±0.4

1020±20 1.3±0.4

Activation analysis

Laboratory angular distributionsLaboratory angular distributions of the Pb-like reaction products.of the Pb-like reaction products.

Irradiation time 3.07 d

Beam intensity 9 nA

Solid angles 4 ×23 mstr

Detection efficiency 9%

30 35 40 45 50 55 60 65 700.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6 136Xe+208Pb Elab=1020 MeV Elab=870 MeV Elab=700 MeV

d/d

(b/s

r)

lab

(deg)

• 224Ra(3.66d α)220Rn(55.6s α)216Po(145ms α) 212Pb(10.64h -)212Bi(1.01h

-)212Po(299ns α) 208Pb(st)

• 222Rn(3.82d α)218Po(3.10m α) 214Pb(26.8m -)214Bi(19.9m -)214Po(164.3µs α) 210Pb(22.3 a -) 210Bi(5.01d

-)210Po(138.38 α) 206Pb(st)

012345

214 Po

212 Po

0.2 d

0.0

0.3

0.6

0.9

Cou

nts

(Hz)

214 Po

212 Po

1.3 d

216 Po

220 R

n

218 Po

212 B

i

222 R

n22

4 Ra

0.00.10.20.30.4

214 Po

212 Po

5.6 d

216 Po

220 R

n

218 Po 21

2 Bi

222 R

n22

4 Ra21

0 Po

4000 5000 6000 7000 8000 9000 100000.000.010.020.030.04 bkg

E (keV)

214 Po

212 Po21

6 Po

220 R

n

218 Po

222 R

n22

4 Ra

210 Po

Alpha spectra obtained in activation analysis

The calculated production cross section for primary (dash lines) and survived (solid lines) isotopes of Po and Rn. The points correspond to the estimated cross sections for 210Po, 222Rn and 224Ra.

Daughter nuclei produced by successive β decay of Os parent isotopes. In red unknown isotopes, in green β unstable nuclei, in white stable nuclei.

Decays of osmium isotopes

Detection system with

cooled surface of deposition

Beta detector

Gamma detector

Detectors

Gas mixture Beam 136Xe

820 MeV

Rotating target 208Pb

Gas catcher

Reaction chamber

Electric furnace (8500)

Aerosol filter

Basement MAP cave

General layoutProduction of osmium isotopes

Summary The mass-energy and angular distributions of binary

fragments produced in the reaction 136Xe+208Pb have been

measured in the energy range close to the Coulomb barrier.

The obtained results demonstrate the following.

● Low-energy collisions of 136Xe with 208Pb can be really used for

the production of new neutron-rich heavy nuclei located along the

closed neutron shell N=126 (the last astrophysical waiting point).

● The yield of nuclei with masses heavier than target mass was found

to be larger than predicted by the theoretical model. This makes even

more promising the production of new neutron-rich SH nuclei in the

multi-nucleon transfer process at low-energy collisions of heavy

actinide nuclei.

Summary

Multi-nucleon transfer reactions are to be used for synthesis of neutron enriched long-living SH nuclei close to beta-stability line. 48Ca and 136Xe beams are insufficient. Uranium-like beam is needed !

O.Rudakov1, S Dmitriev1, P. Greenlees2, F. Hannape3, I.M. Itkis1, M.G.Itkis1, S. Khlebnikov4, A. Knyazev1, G. Knyazheva1, E.Kozulin1, T.Loktev1, A. Di Nitto5,

K. Novikov1, O.Petrushkin1, E. Rasinkov1, S.Smirnov1, W.H.Trzaska2, E. Vardaci5, V.Zagrebaev1

1Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, (FLNR JINR) Dubna, Russia

2Accelerator Laboratory of University of Jyväskylä (JYFL), Jyväskylä3Universite Libre de Bruxelles (ULB), Bruxelles, Belgium

4Khlopin Radium Institute(KRI), St. Petersburg, Russia5Dipartamento di Scienze Fisiche and INFN (INFN-Na), Napoli, Italy

18

Production of Os

136Xe + 208Pb

Figure 3. (Left panel) – total cross section of the formation of heavy fragments d2у/dZdN (mb), the number of the contour lines) in the reaction 136Xe+208Pb at energy Ecm=450MeV. (Right panel) – formation cross section of heavy neutron-rich nuclei in the same reaction, red lines are the yield of primary fragments, the blue – survived fragments after evaporation, open circles are unknown isotopes. (Bottom panel) – the yield of nuclei with N=126 (open circles – unknown isotopes).

197Os 198Os 199Os 200Os

197Os

201Os 202Os

203Pt 204Pt

200Ir 201Ir 202Ir 203Ir

194Re 195Re 196Re 197Re 198Re 199Re 200Re 201Re

Astrophysical r-process and heavy neutron rich nucleiAstrophysical r-process and heavy neutron rich nuclei

26

Use of low-energy Radioactive Ion Beams Use of low-energy Radioactive Ion Beams for production of neutron rich superheavy nuclei ?for production of neutron rich superheavy nuclei ?

No chances today. But in future ?

27

Formation of SH elements in astrophysical r-processFormation of SH elements in astrophysical r-processStrong neutron fluxes are expected to be generated by neutrino-driven proto-neutron star winds which follow core-collapse supernova explosions or by the mergers of neutron stars.

The question: How large is the neutron flux?

O.Rudakov1, S Dmitriev1, P. Greenlees2, F. Hannape3, I.M. Itkis1, M.G.Itkis1, S. Khlebnikov4, A. Knyazev1, G. Knyazheva1, E.Kozulin1, T.Loktev1, A. Di Nitto5,

K. Novikov1, O.Petrushkin1, E. Rasinkov1, S.Smirnov1, W.H.Trzaska2, E. Vardaci5, V.Zagrebaev1

1Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, (FLNR JINR) Dubna, Russia

2Accelerator Laboratory of University of Jyväskylä (JYFL), Jyväskylä3Universite Libre de Bruxelles (ULB), Bruxelles, Belgium

4Khlopin Radium Institute(KRI), St. Petersburg, Russia5Dipartamento di Scienze Fisiche and INFN (INFN-Na), Napoli, Italy

Activation analysis

Laboratory angular distributionsLaboratory angular distributions of the Pb-like reaction products.of the Pb-like reaction products.

Irradiation time 3.07 d

Beam intensity 9 nA

Solid angles 4 ×23 mstr

Detection efficiency 9%

30 35 40 45 50 55 60 65 700.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6 136Xe+208Pb Elab=1020 MeV Elab=870 MeV Elab=700 MeV

d/d

(b/s

r)

lab

(deg)