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Two-proton radioactivity: an experimentalist’s view. Catalin Borcea CEN Bordeaux-Gradignan and IFIN-HH. Two proton radioactivity – a new decay mode Two-proton emission from light nuclei Decay of 42 Cr and 49 Ni Two-proton radioactivity of 45 Fe

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Two-proton radioactivity:

an experimentalist’s view

Catalin Borcea

CEN Bordeaux-Gradignan and

IFIN-HH

  • Two proton radioactivity – a new decay mode

  • Two-proton emission from light nuclei

  • Decay of 42Cr and 49Ni

  • Two-proton radioactivity of 45Fe

  • Future perspectives and developments

NANUF03, Bucharest September 7-12, 2003


Stable and b-unstable nuclei

Stable nuclei

Leaving the valley of stability….


One-proton radioactivity

Model calculations

to determine single-

particle level sequence

  • Physics topics:

  • test of nuclear mass models

  • nuclear structure beyond stability

  • - single particle ordering and energy

  • - j content of wavefunction

  • - shape of mean-field potential

  • quantum tunneling through 3D barrier


Two types of 2p emission:

- ground-state emission

• long lived: 45Fe, 48Ni, 54Zn

• short lived: 6Be, 12O, 16Ne, 19Mg

- emission from excited states

• β delayed: 22Al, 31Ar, …

• others: 14O, 18Ne, 17Ne

To be measured:

• proton energies

• proton-proton angle

Two-proton radioactivity

Sequential emission:

Three-body decay:

2He emission:


Two-proton radioactivity

Sequential emission:

Three-body decay:

2He emission:

Measurement of protons

and recoil


  • Two types of experiments:

  • long-lived nuclei (>10ms): implantation and decay

  • short-lived nuclei (<1ps) : complete kinematics experiments


Two proton emission

from light nuclei

  • Mass: A = 6 – 20

  • Z = 4 – 12

  • low Coulomb (+ centrifugal) barrier

  • broad states - short half-lives

    T1/2 = 10-21s – 10-12s

     decay already in the target

    complete-kinematics measurements

    behind production target


seq. decay

2He decay

2p emission from 12O

Proton-proton angle:

Total decay energy:

Proton-proton energy:

 Data consistent with 3-body

or sequential decay

R.A. Kryger et al., Phys. Rev. Lett. 74 (1995) 860


GANIL

Experimental Procedure

24Mg fragmentation in SISSI at 95 MeV/u

Selection with Alpha spectrometer : 17F, 18Ne, 20Mg

Stripping reactions at entrance of SPEG


19Na

18Ne + p

MUST

p

Target

9Be

20Mg

SPEG

18Ne

19Na

MUST

Mass of19Na

J. Cerny et al.:

W. Benenson et al.:

Garvey-Kelson:

Pape-Antony:

12.97(7) MeV

12.93(1) MeV

12.88(20) MeV

13.30(20) MeV

Mass excess: 13.09(5) MeV

Reasonable agreement with

experiment and predictions


18Na

17Ne + p

Audi-Wapstra:

Garvey-Kelson:

Pape-Antony:

25.3(4) MeV

25.4(2) MeV

25.7(2) MeV

First mass measurement of18Na

MUST

Target

9Be

p

20Mg

SPEG

17Ne

18Na

MUST

Mass excess: 24.19(5) MeV

  • If assumed to be ground state:

  • huge Thomas-Ehrman shift

  • 1. peak: 18Na* 17Ne*

  • 2. peak: 18Na  17Ne: 25.04(12)MeV

  • problems with theoretical calculations


Theoretical calculation for18Na

  • Main shell-model components:

  • 18Na (1-): ([p(d5/2)3]3/2+[np1/2])

  • ([p(d5/2)2]2+[ps1/2][np1/2])

  • 18Na (2-): ([p(d5/2)3]5/2+[np1/2])

  • ([p(d5/2)2]2+[ps1/2][np1/2])

  • 17Ne (1/2-): ([p(d5/2)2]0+[np1/2])

  • 17Ne (3/2-): ([p(d5/2)2]2+[np1/2])

Shell-model spectroscopic factors:

Barrier-penetration predicts all excited states to decay to 17Ne ground state


17Ne*

16F + p

15O + 2p

MUST

Target

9Be

p

18Ne

SPEG

15O

p

17Ne*

MUST

18.689

18.398

18.392

18.254

18.161

17.968

17.778

17.431

16.490

17Ne

16F+p

15O+2p

2p emission from 17Ne

15O+p

15O+2p

Good agreement with known

separation energies and 16F


2He

2He (» 53%)

Sequential / 3-body

Sequential (» 47%)

Sum

Proton-proton angle distribution

Three-body center of mass frame: 2p emission from 17Ne*


Proton-proton angle distribution

Three-body center of mass frame: 2p emission from 17Ne*

  • Agreement with MSU data : no angular correlation for Q2p =0.9 MeV states

  • Indication of angular correlation for higher lying states…..


New search for 2p emission in 16,17Ne

MUST

p

Target

9Be

17Ne

VAMOS

14,15O

SPIRAL

24 MeV/u

2*104pps

16,17Ne

p

MUST

Mass

15F+p

16Ne

23.99 MeV

Γ = 120 keV

23.89 MeV

Γ = 1.2 MeV

14O+2p

19.31 MeV


Conclusion:

  • 2p emission from 19Mg

  •  19Mg seems to be a good candidate

  • unexpected effect for 17Ne …. to be checked

  • determined masses of intermediate nucleus 18Na for

  • study of one- and two-proton emission from light proton-rich nuclei


Collaborators:

T. Zerguerras, Y. Blumenfeld, T. Suomijärvi, D. Beaumel, M. Fallot,

I. Lhenry-Yvon, J.A. Scarpaci, A. Shrivastava

IPN Orsay

B. Blank, M. Chartier, J. Giovinazzo

CEN Bordeaux-Gradignan

W. Mittig, P. Roussel-Chomaz, H. Savajols

GANIL Caen

C. Jouanne, V. Lapoux

DAPNIA Saclay

M. Thoennessen

Michigan State University


Two-proton emission

from medium-mass nuclei


X

Two-proton emission from 45Fe ground state


Decay scheme for 45Fe

Possibly very rich decay pattern


GANIL 1999

  • The observation of doubly-magic 48Ni

  • Study of 42Cr, 49Ni, and 45Fe


Production of radioactive nuclei at GANIL

  • 58Ni @ 75 MeV/A on nickel target

  • High primary beam intensity: 3-5A


Production and observation of 48Ni

10 parameters to identify:

48Ni: 4 counts

49Ni: 106 counts

45Fe: 53 counts

42Cr: 287 counts


Spectroscopic studies of 42Cr: a 2p candidate

Charged-particle spectrum:

Two-proton ground-state emitter?

Decay-time spectrum:

  • -decay half-life

  • 1.9 MeV peak too high in energy

  •  Most likely -delayed decay


Spectroscopic studies of 49Ni: a 2p candidate

Charged-particle spectrum:

Decay-time spectrum:

  • -decay half-life predictions:

  • Möller et al.: 5.0 ms

  • Hirsch et al.: (7.3-20.4) ms

  • -decay half-life

  • 3.8 MeV peak too high in energy

  •  Most likely -delayed decay


Spectroscopic studies of 45Fe: a 2p candidate

Charged-particle spectrum:

Decay-time spectrum:

-decay half-life predictions:

Brown: 15.5 ms

Ormand: 7 ms

Hirsch et al.: (3 - 7) ms

Tachibana et al.: 12 ms

  • Too low statistics to decide

    between 2p emission and

     decay


Two-proton decay of 45Fe

  • Two experiments:

  • GANIL in July 2000

  • GSI in July 2001

  • GSI:

  • low production rate: 6 45Fe implantations in 6 days

  • fast data acquisition based on XIA modules

  • GANIL:

  • high production rate: 15 45Fe per day

  • standard data acquisition (CAMAC – VME)


Detection setup:

Si(Li)

  • 58Ni @ 75 MeV/A on nickel target

  • High primary beam intensity: 3-5A

Two-proton decay of 45Fe: GANIL data

J. Giovinazzo et al., PRL 89 (2002) 102501


Two-proton radioactivity of 45Fe: GANIL data

Identification of 45Fe:

Identification of

22 45Fe implants

J. Giovinazzo et al., PRL 89 (2002) 102501


1.14 MeV peak

Two-proton radioactivity of 45Fe: GANIL data

Decay-energy spectrum:

 spectrum:

Decay-time spectrum:

  • Q value in agreement with predictions

  • no b pile up for peak

  • half-life short enough for 2p emission

  • data in agreement with daughter decay

  • no b’s in coincidence with 1.14 MeV peak

T1/2 = 16.7±7.0 ms

J. Giovinazzo et al., PRL89 (2002) 102501


IDENTIFICATION IN FLIGHT

Br2 p/Z

TOF 1,2,3 v

DE  Z

}  A/Z

Two-proton decay of 45Fe: GSI data

The FRS:

Target

4 g/cm2 Be

Beam current

(SEETRAM)

TOF 1, 2, 3

(scintillators)

Implantation

set-up

Br1

Primary beam

650 MeV/u 58Ni

Br4

Br3

DE

(MUSIC)

Br2

S1 degrader

3.2 g/cm2 Al

S2 degrader

3.6 g/cm2 Al

NaI barrel

511 keV

Identified ions

511 keV

Trigger, DE

300 mm Si

Stack of Si detectors

7 x 300 mm

M. Pfützner et al., EPJA 14 (2002) 279


A/Z

0

0 1 2 3 4 5 6

Energy (MeV)

Two-proton decay of 45Fe: GSI data

  • 5 correlated decay events:

  • four 2p decays

  • one b-delayed decay

6 implantation

events identified

M. Pfützner et al., EPJA14 (2002) 279


~80%

~20%

Q2p = 1.14 MeV

T1/2 = 3.8 ms

Two-proton radioactivity of 45Fe

Clear evidence of 2p radioactivity

No coincident beta or gamma ray with

the 1.14 MeV peak

Peak width: no  pile-up

Observed energy in agreement with

predictions

Observation of daughter decays


2.0

0.8

Experimental half-life: T1/2 = 3.8± ms

Two-proton radioactivity of 45Fe: di-proton model

Di-proton model half-life:

0.02 ms

+ SM spectroscopic factors:

0.12 ms

+ preformation factor ?

+ resonance energy ?

 Lower limit for the half-life

R-matrix model (Brown-Barker):

S-wave p-p interaction : 4-40 ms


Two-proton radioactivity of 45Fe

Nice agreement between exp. data and predictions for p wave protons

but: f-wave protons expected…..

L.V. Grigorenko et al.


Conclusions

  • clear evidence for 2p radioactivity of 45Fe:

  • a new radioactivity

Future studies

  • other candidates: 48Ni, 54Zn

  • decay mechanism: 2He or 3-body

  • setup to measure p – p angle and individual energies

  • g TPC


First observation of 55Zn and 56Zn

Expected production rate for 54Zn:

10-15 per day


identification

emitter

Electric field

protons

Drift of ionisation

electrons

X-Y detector

New setup for 2p experiments on LISE3: TPC


Physics case

  • What information can bring the two-proton radioactivity:

  • masses of nuclei beyond drip line

  • pairing in nuclei

  • sequence of single-particle levels

  • j content of wavefunctions

  • deformation

  • complex tunneling process

  • …..


Collaborators

GSI:

M. Pfützner, R. Grzywacz, Z. Janas, J. Kurcewicz

University of Warsaw

B. Blank, M. Chartier, J. Giovinazzo, A.-S. Lalleman, J.-C. Thomas

CEN Bordeaux-Gradignan

E. Badura, H. Geissel, L.V. Grigorenko, M. Hellström, C. Mazzocchi, I. Mukha,

G. Münzenberg, C. Plettner, E. Roeckl, R.S. Simon

GSI Darmstadt

M. Stanoiu

GANIL Caen

C. Bingham, K.P. Rycaczewski

Oak Ridge National Laboratory

K. Schmidt

University Of Edinburgh

GSI:


Collaborators

GANIL:

GANIL:

J. Giovinazzo, B. Blank, M. Chartier, S. Czajkowski, A. Fleury,

M.J. Lopez Jimenez, M.S. Pravikoff, J.-C. Thomas

CEN Bordeaux-Gradignan

G. de France, F. de Oliveira Santos, M. Lewitowicz, V. Maslov, M. Stanoiu

GANIL Caen

C. Borcea

IAP Bucharest

R. Grzywacz, Z. Janas, M. Pfützner

University of Warsaw

B.A. Brown

NSCL, MSU East Lansing


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