2-proton emission experimental set-up decay results 2p emission from 45Fe perspectives

Jérôme Giovinazzo – CEN Bordeaux-Gradignan – France

PROCON’03 – Legnaro – Feb. 2003

« 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)

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

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

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.

54Zn49Ni

48Ni

45Fe

42Cr

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

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

projectile fragmentationnatural Nickel targetSISSI device(high acceptance)

LISE3 spectrometerBselectionachromatic degrader (Be)Wien filter

detection set-upions identificationdecay measurement

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 %

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 fli

ght

- micro-channelPLATES

- cyclotrons HF

- light particlesveto

- residualenergy

- energy loss

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

P

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-

comparison with theoretical predictions

shell model(nuclear structure, interactions)

less exotic higher production rate proton-gamma coincidences some identified transitions mass estimates (IMME)

EP ~ 1.9 MeV T1/2 ~ 10-12 smeasured half-life: 13.4 ms most likely decay

EP ~ 3.7 MeV T1/2 ~ 10-19 smeasured half-life: 12 ms most likely decay

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

comparison of 45Fe and 46Fe (p):same energy conditions:

close Q and same EP energy

coincidence efficiency: 30~35 %

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…

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 MeVmass models : 1.15 ± 0.09 MeV (Brown, 1991)

1.22 ± 0.05 MeV (Cole, 1996) 1.28 ± 0.18 MeV (Ormand, 1996)

Q2P

half-

life

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.

experiment42Cr, 49Ni most likely decay45Fe 2-proton emission from ground state

coherent 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 ?

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

?

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. fie

ld

Collaborations

GANIL: CENBG, GANIL, IAP Bucarest, Univ. Varsovie, NSCL / MSUGSI: 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