2-proton emission experimental set-up decay results 2p emission from 45 fe perspectives jérôme...
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2-proton emission
experimental set-up
decay results
2p emission from 45Fe
perspectives
Jérôme Giovinazzo – CEN Bordeaux-Gradignan – France
PROCON’03 – Legnaro – Feb. 2003
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« classic » decay modesbeta minus, beta plusalpha emission, fission
at the proton drip-line:nuclear strong interaction is notable to bound last nucleons kept inside by Coulomb
barrier
1-proton radioactivity1981: discovered at GSI (Hoffmann et al.)~30 known emitters, Z = 53 à 83
2-proton radioactivitydue to pairingpredicted in the 60’s (Goldansky)
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from an excited state-2p decay:
22Al, 26P, 31Ar,…
other cases:14O, 17Ne, 18Ne(T. Zergueras et al.)
from the ground statein light nuclei
6Be, 12O, 16Ne, 19Mghalf-lives in the order ofreaction times(~10-20 s)
in the A~50 mass regionhalf-lives: ~ms45Fe, 48Ni, 54Zn, ?…
séquential emission
3 bodies break-up
2He radioactivity
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simple model:tunneling of an 2He particle through the Coulomb barrier
comparison mass modelspredictions
T1/2 = f(Q2P)
if Q2P too high not bound or too short T1/2
if Q2P too small tunneling too slow:
+ dominates the decay
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mass region A~50: Coulomb barrier high enough (Z = 20 ~ 30) half-life: 1 s ~ 10 ms
candidates: (mass models from Cole, Brown, Ormand)45Fe, 48Ni, 54Zn42Cr, 49Ni
accessible in projectile fragmentation exp.
54Zn
49Ni48Ni
45Fe
42Cr
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1996 GSI (Darmstadt - Germany)first observation of 42Cr, 45Fe, 49Ni
no information about decay modes
1998 GANIL (Caen - France)looking for 48Ni (not successful)
first observation of 55,56Zn
1999 GANILdiscovery of 48Ni
decay of 42Cr et 49Ni45Fe: very low statistics (elect. trigger problems)
48Ni: no decay data
2000 GANIL – 2001 GSI2-proton decay of 45Fe
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cross sections estimates (accessibility)low confidence… orders of magnitudes (from exp. 1999 à GANIL)
42Cr 20~200 pb45Fe ~0.8 pb49Ni ~1.3 pb48Ni ~0.04 pb
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projectile fragmentationnatural Nickel targetSISSI device(high acceptance)
projectile fragmentationnatural Nickel targetSISSI device(high acceptance)
LISE3 spectrometerBselectionachromatic degrader (Be)Wien filter
LISE3 spectrometerBselectionachromatic degrader (Be)Wien filter
detection set-upions identificationdecay measurement
detection set-upions identificationdecay measurement
primary beamCSS1 and CSS2 cyclotrons58Ni @ 75 MeV / Aintensity on target ~3 Ae
primary beamCSS1 and CSS2 cyclotrons58Ni @ 75 MeV / Aintensity on target ~3 Ae
105 p/s
1013 p/s
10-100 p/s
transmission efficiency: 1~10 %
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silicon telescopeion by ion identification of implantation events
implantation: double side silicon strip detector (X-Y) 16 x 3 mm
redundant measurements background reduction
time of fl
ight
- micro-channelPLATES
- cyclotrons HF
- light particlesveto
- residualenergy
- energy loss
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Blank et al. (2000)
Observation of 48Ni4 implanted nuclei
experiment at GANIL 200022 events of 45Fe implantation
identification conditions:8 à 10 parameters
almost no background
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PP
implantation decaypixel correlation of events
background reduction indecay energy / timedistributions
proton energystrip detector Є ~ 100 %
coincidence with particlesneighbour silicon Є ~ 30 %
germanium detectors arraydetailed spectroscopy-, -p-
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comparison with theoretical predictions
shell model(nuclear structure, interactions)
less exotic higher production rate proton-gamma coincidences some identified transitions mass estimates (IMME)
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EP ~ 1.9 MeV T1/2 ~ 10-12 s
measured half-life: 13.4 ms
most likely decay
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EP ~ 3.7 MeV T1/2 ~ 10-19 s
measured half-life: 12 ms
most likely decay
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transition assignment:
peak energy: 1.14 ± 0.05 MeVin the expected range for2p emission to beobservable
peak width: 60 keV30 % narrower than p no pile-up
half-life: 4.7 mscompatible with Q2P
filiation:in agreement with p decayof 43Crenergy and time
coherent picture of 2pemission from 45Feground state
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comparison of 45Fe and 46Fe (p):
same energy conditions:close Q and same EP energy
coincidence efficiency: 30~35 %
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22 implanted nuclei of 45Fe / 12 counts in the 2p peakshort half-life, acquisition dead-time 0.3~0.5 ms3 à 4 decay events may be lost
2p branching ratio: 70~80 %competition between p and 2p channelin agreement with GSI resultsvery low statistics…
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experiment:
simple tunneling model:
including spectroscopic factor:S ~ 0.20 shell model (B. Brown)
ms7.4T 4.34.12/1
ms024.0T 074.0017.02/1
ms12.0T 38.009.02/1
experiment: 1.14 ± 0.05 MeV
mass models : 1.15 ± 0.09 MeV (Brown, 1991) 1.22 ± 0.05 MeV (Cole, 1996) 1.28 ± 0.18 MeV (Ormand, 1996)
Q2
Ph
alf
-lif
e
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R-matrix: (Barker, Brown)with p+p interaction s-wave S = 0.20
3-body calculationp-p correlation (Jacobi T)
good agreement forp-wave correl.
from mirror nucleus: last twoprotons in f state
(Grigorenko et al.)sequential emission
intermediate state 44Mn Q1P = -24 à +10 keVT1/2 few hours ~ few days
ms41~4T 2/1
di-proton
3-body
indép.
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experiment
42Cr, 49Ni most likely decay
45Fe 2-proton emission from ground statecoherent full pictureincluding daughter decay (43Cr)
possible competition between 2p / p
data from GSI in good agreement with GANIL results
experiment
42Cr, 49Ni most likely decay
45Fe 2-proton emission from ground statecoherent full pictureincluding daughter decay (43Cr)
possible competition between 2p / p
data from GSI in good agreement with GANIL results
comparison avec les models
results depending on the model new calculations in progress
sequential emission seems excluded
still open question:3-body break-up or 2He radioactivity ?
comparison avec les models
results depending on the model new calculations in progress
sequential emission seems excluded
still open question:3-body break-up or 2He radioactivity ?
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experiment (GANIL)
45Fe confirm 2p emission(reproducibility) precise Q2P and T1/2
daughter decay, branch
48Ni observation 1999 good conditions
for 2p emission decay mode?
54Zn observation 55,56Zn 1998 10 à 15 nuclei 54Zn / day
experiment (GANIL)
45Fe confirm 2p emission(reproducibility) precise Q2P and T1/2
daughter decay, branch
48Ni observation 1999 good conditions
for 2p emission decay mode?
54Zn observation 55,56Zn 1998 10 à 15 nuclei 54Zn / day
?
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purposeangular correlation measurements of emitted protonsdiscrimination between 2He emission / other cases
TPC development
implantation in agas cell
3D tracking of protons X-Y detector Z time projection
MGWC technology(high energy physics)
M. Dracos et al.
integrated electronics(ASICs)
purposeangular correlation measurements of emitted protonsdiscrimination between 2He emission / other cases
TPC development
implantation in agas cell
3D tracking of protons X-Y detector Z time projection
MGWC technology(high energy physics)
M. Dracos et al.
integrated electronics(ASICs)
identification
drift of ionisation electrons
emitting nucleus
protons
X-Y detector
elec
t. f
ield
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Collaborations
GANIL: CENBG, GANIL, IAP Bucarest, Univ. Varsovie, NSCL / MSU
GSI: Univ. Varsovie, GSI, CENBG, GANIL, ORNL, Univ. Edimbourg
research program in a more general 2p emission context 2He radioactivity emission in light nuclei correlated component in the -2p decay
(mainly sequential) ...
Jérôme Giovinazzo – CEN Bordeaux-Gradignan – France
PROCON’03 – Legnaro – Feb. 2003