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Two-proton radioactivity an experimentalists
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
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Leaving the valley of stability.
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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

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Two-proton radioactivity
Sequential emission Three-body decay
2He emission
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Two-proton radioactivity
Sequential emission Three-body decay
2He emission
Measurement of protons and recoil
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• Two types of experiments
• long-lived nuclei (gt10ms) implantation and
  decay
• short-lived nuclei (lt1ps) complete kinematics
  experiments

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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

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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
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Experimental Procedure
24Mg fragmentation in SISSI at 95 MeV/u Selection
with Alpha spectrometer 17F, 18Ne,
20Mg Stripping reactions at entrance of SPEG
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Mass of 19Na
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
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First mass measurement of 18Na
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

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Theoretical calculation for 18Na

• Main shell-model components
• 18Na (1-) (p(d5/2)33/2np1/2)
• (p(d5/2)22ps1/2np1/2
  )
• 18Na (2-) (p(d5/2)35/2np1/2)
• (p(d5/2)22ps1/2np1/2
  )
• 17Ne (1/2-) (p(d5/2)20np1/2)
• 17Ne (3/2-) (p(d5/2)22np1/2)

Shell-model spectroscopic factors
Barrier-penetration predicts all excited states
to decay to 17Ne ground state
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2p emission from 17Ne
15Op
15O2p
Good agreement with known separation energies
and 16F
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Proton-proton angle distribution
Three-body center of mass frame 2p emission from
17Ne
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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..

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New search for 2p emission in 16,17Ne
MUST
p
Target 9Be
17Ne
VAMOS
14,15O
SPIRAL 24 MeV/u 2104pps
16,17Ne
p
MUST
Mass
15Fp
16Ne
23.99 MeV G 120 keV
23.89 MeV G 1.2 MeV
14O2p
19.31 MeV
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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

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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
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Two-proton emission from medium-mass
nuclei
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Two-proton emission from 45Fe ground state
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Decay scheme for 45Fe
?Possibly very rich decay pattern
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GANIL 1999

• The observation of doubly-magic 48Ni
• Study of 42Cr, 49Ni, and 45Fe

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Production of radioactive nuclei at GANIL

• 58Ni _at_ 75 MeV/A on nickel target
• High primary beam intensity 3-5?A

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Production and observation of 48Ni
10 parameters to identify 48Ni 4
counts 49Ni 106 counts 45Fe 53
counts 42Cr 287 counts
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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

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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

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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

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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)

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Two-proton decay of 45Fe GANIL data
J. Giovinazzo et al., PRL 89 (2002) 102501
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Two-proton radioactivity of 45Fe GANIL data
Identification of 45Fe
Identification of 22 45Fe implants
J. Giovinazzo et al., PRL 89 (2002) 102501
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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 bs in coincidence with 1.14 MeV peak

T1/2 16.77.0 ms
J. Giovinazzo et al., PRL89 (2002) 102501
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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
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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
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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
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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
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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.
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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

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First observation of 55Zn and 56Zn
Expected production rate for 54Zn 10-15 per
day
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New setup for 2p experiments on LISE3 TPC
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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
• ..

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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
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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