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Two-proton radioactivity
Marek Pfützner
Lecture 1
Faculty of Physics, University of Warsaw
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 1
Goldansky
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 2
Vitaly Iosifovich Goldansky18.06.1923 (Witebsk) – 14.01.2001 (Moscow)
Nuclear Physics 19 (1960) 482
Outline
� Basic introduction
� The story of 45Fe
� mass predictions
� production method
� discovery of 2p decay
� Quest for p-p correlations
� OTPC detector� OTPC detector
� images of 45Fe decay
� Introduction to theory
� Jacobi coordinates
� Simplified models
� Momentum correlations
� Decays of 6Be, 19Mg, 48Ni and 54Zn
� Predictions of heavier emitters
and the full 2p landscape
� Summary
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 3
What is radioactive?
� What is plotted on the chart? Present practice: all systems we know something about.
� Should they plot only those which exist? But what does exist?
Radioactivity
� Slow enough to form neutral atoms
� Characteristic time measured directly
� Independent of formation mechanism
Reactions/Resonances
� Fast on atomic scale
� Characteristic width measured directly
� Influenced by reaction mechanism
141 2 10 sT −≥ 1 meVΓ ≥
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 4
Mass parabola
Q ≅ 19 MeV
Q ≅ 14 MeV
Q ≅ 12 MeV
Q ≅ 7 MeV
Q ≅ 2 MeV
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 5
β-delayed particle emission
� When the decay energy is large, many exotic decay channels open
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Blank and Borge, Progress in Part. Nucl. Phys. 60 (2008) 403
6
Beyond the proton drip-line
r
V(r)
Competition between two decay modes
� The β+ decay
Probability of transition:
5Qλ ∼
� The emission of particles
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
rDecay energy may be large,
but the weak interaction
is really weak
�
∼
1 2 1 msT >
� To find where the drip-line actually is and to predict which decay will happen,
precise estimates of atomic masses are required!
� To study particle radioactivity fast techniques are needed!
There is a potential barrier which hampers
emission of an unbound proton (α, 2p, 14C,..)
2exp 2 [ ( ) ]
out
in
r
prV r Q drλ µ − ⋅ − ⋅
∫∼
ℏ
7
Why particle radioactivity?
� Charged particles (p, α, 2p,…) are much easier to detect than γ or electrons
� They provide information about very exotic nuclear systems, beyond drip-line
� Allow to determine masses
� Provide a tool to investigate quantum tunneling process
� Test nuclear structure models (single particle levels)
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 8
� Test nuclear structure models (single particle levels)
� Probe details of nuclear wave function
� Help to understand decay dynamics
� Yield information about proton pairing
� …
Two protons can be unbound!
� It is possible that pair of protons is
unbound while each of individual
proton is bound!
(Z,N)
Sp
ΓΓΓΓ2222
ΓΓΓΓ1111
20 21 22 23 24
-3
-2
-1
0
1
2
3
4
5
Sep
arat
ion
ener
gy [M
eV]
Z = 27
1pS
2 pS
Goldansky, Nucl. Phys. 19 (1960) 482Goldansky, Nucl. Phys. 27 (1961) 648Goldansky, Nuovo Cimento 25, Suppl. 2 (1962) 123
(Z-2,N)
(Z,N)
2p
Sp > ΓΓΓΓ1111 + Γ+ Γ+ Γ+ Γ2222
18 19 20 21 22
-4
-3
-2
-1
0
1
2
3
4
Sep
arat
ion
ener
gy [M
eV]
Neutron number, N
Z = 26
1pS
2 pS
20 21 22 23 24 Neutron number
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 9
Early considerations
Baz, Goldansky, Goldberg, Zeldovich,„Light and medium nuclei at the limits of stability, Moscov 1972
10M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Two-proton emission
Energy conditions for different modes of the 2p emission
true
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
democratic
a) 18Ne* b) 14O* , 17Ne* c) 19Mg , 45Fe, 48Ni, 54Zn,…
d,e) 6Be , 12O(?)
11
� True 2p decay is an essentially three-body phenomenon
Pfutzner, Karny, Grigorenko, Riisager, Rev. Mod. Phys. 84 (2012) 567
Predicting masses
Cu
Zn54
� Global mass models are not precise enough to determine the decay mode.
However, there is a trick based on the Isobaric Multiplet Mass Equation (IMME):
( ) ( ) ( ) ( ) 2, , , , ,z z zBE A T T a A T b A T T c A T T= + + ( ) 2zT N Z= −
( ) ( ) 2z zBE T T BE T T bT= − = = −
28
20
28
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
20
45
48� To get the mass (binding energy) of the
neutron-deficient nuclide, we need the
measured mass of its neutron-rich
analogue and the value of the
coefficient b from the theory
(shell-model, systematics…)
48
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 12
First 2p candidates
Predicted 1p and 2p separation energies
-0.5
0.0
0.5
1.0
1pS
MeV
-0.5
0.0
0.5
1.0
Brown, PRC 43 (91) R1513
Ormand, PRC 55 (97) 2407
Cole, PRC 54 (96) 1240
Brown et al., PRC 65 (02) 045802
-2.0
-1.5
-1.0
2 pS
45Fe 48Ni 54Zn-2.0
-1.5
-1.0
45Fe 48Ni 54Zn
� Exp
13M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Production methods
● Fusion-evaporationreactions between heavy-ionsGSI, Argonne, Oak Ridge, Jyväskylä,...
recoil separators
� To produce short-lived and very proton-rich radioactive nuclei
in-flight techniques proved advantageous.
● Fragmentationof relativistic heavy-ionsGSI, NSCL, GANIL, RIKEN,…
fragment separators
� large beam intensity
� thin target
identification by decays
� lower beam intensity
� thick target
identification in-flight
single ion sensitivity
Low energy: ≈ Coulomb barrier High energy: ≈ above Fermi energy
p and α radioactivity,(also superheavy elements)
2p radioactivity
14M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Fragment separator
1 GeV/nucleon
Example: FRS at GSI Darmstadt
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
3-20 MeV/nucleon
15
FRS – ion optics and particle ID
Beam
different emission angles
ions ofdifferent A/q
target
� Standard, achromatic mode
energy loss
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
wedge-shapeddegrader
ions ofdifferent Z
time of flight (s = 36 m)
Time-of-flight � v
Positions + B field � Bρ
Energy loss ∆E � Z
� Full in-flight identification of each ion� A/q ≈ A/Z}
Geissel et al., NIM B70 (1992) 286
16
by Bordeaux-GANIL-GSI-Warsaw collaboration
• GSI 1992 : first experiment, determination of x-sections, 50Ni
• GANIL 1999 : discovery of 48Ni , 53 ions of 45Fe
• GSI 1996 : first observation of 45Fe (3 ions!), 49Ni and 42Cr
• GANIL VII 2000 : next attempt of 45Fe spectroscopy : 22 ions of 45Fe
• GSI VII 2001 : new approach to 45Fe studies : focus on µs lifetimes
A long way to discovery
28
20
28
Ca
Sc
TiV
Cr
MnFeCo
Ni
20
Tz=-7/2
48
42
45
49
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 17
Example of identification
� First observation of three new nuclides : 42Cr, 45Fe i 49Ni
FRS, GSI, 1996
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 18
Decay of 45Fe studied at GSI
Target4 g/cm2 Be
TOF 1, 2, 3(scintillators)
Bρρρρ2 Bρρρρ3DE
(MUSIC)
Degrader 13.2 g/cm2 Al
Bρρρρ1
Bρρρρ4
58Ni, 650 A MeV4×108 ions/s
Implantationand decay
spectroscopy
� FRS @ GSI July 2001
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 19
Two TOFs allowed redundant
in-flight identification by the
Bρρρρ – TOF – ∆∆∆∆E method
Degrader 23.6 g/cm2 Al
3.2 g/cm Al
Dead-time free recording of all
events following the implantation
due to digital electronics (XIA)
� great sensitivity!
Si telescope7 x 300 mm ∅ 60 mm
511 keVIdentified
ions
511 keVTrigger, DE300 µm Si
NaI barrel :∅< = 8 cm,∅> = 40 cm,L = 30 cm
FRS Messhütte, 27 July, 2001
On-line joke ?
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 20
Z 45Fe
44V
M. P. et al., EPJ A 14 (2002) 279M. P. et al., NIM A 493 (2002) 155
Results from the GSI experimentC
ount
s 1
900 1000 1100 1200 13000
1
6 × 45Fe
Events correlated with the stopped ions :implantation and decay in the same detector
no γ + γ
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 21
A/q� emission of 2p is the dominant(80%) decay mode of 45Fe :
E2p = 1.1(1) MeVT1/2 = 3.2+2.6 ms
-1.0
0 1000 2000 3000 4000 5000 60000
1
Energy [keV]
0
Cou
nts
664 other ions44V
+ γ
J. Giovinazzo et al., PRL 89 (2002) 102501
58Ni @ 75 MeV/A on nickel targetHigh primary beam intensity: 3-5µA
Results from the GANIL experiment
� LISE @ GANIL July 2000
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 22
� 22 ions of 45Fe implanted � 12 counts in a narrow peak� no ββββ and no γγγγ in coincidence� no ββββp pile-up
E2p = 1.14(5) MeVT1/2 = 4.7+3.4 ms - 1.4
�
45Fe: decay energy and time
� The decay energy and the lifetime are enough to establish the 2p decay.
Brown and Barker, PRC 67 (2003) 041304(R)
Rotureau, Okołowicz, and Płoszajczak, Nucl. Phys. A767 (2006) 13
Grigorenko and Zhukov, Phys. Rev. C 68 (2003) 054005
23M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Other 2p candidates
2p decay event candidate48Ni @ GANIL
Zn5430
ms 321 ≅T
54Zn @ GANIL
GANIL: fragmentation of 58Ni beam @ 75 MeV/u
4 48Ni ions implanted in a Si strip detector
C. Dossat et al., PRC 72 (05) 054315
GANIL: fragmentation of 58Ni beam @ 75 MeV/u
8 54Zn ions implanted in a Si strip detector
B. Blank et al., PRL 94 (05) 232501
24M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
� Total decay energy and half-life can be precisely measured after implantation
into a thick Si detector. Then, however, information on individual proton’s momenta is lost!
The experimental challenge of 2p decay
� The goal: detect both protons separately, measure their energies,
and determine their angular distribution
� To explore fully the physics of the process, the correlations between
proton’s momenta must be determined!
� The three-body model by Grigorenko and Zhukov is the only one which
predicts these correlations.
L. Grigorenko : simulation for 200 events
Predicted 2p opening angle for 45Fe
and determine their angular distribution
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 25
Solution: a TPC detector
A „classical” Time Projection Chamber (TPC) constructed at CEN Bordeaux.
It has fully electronic readout. The position on the x-y plane is detected by two
ortogonal sets of 768 strips readout by ASIC-type electronics.
J. Giovinazzo et al., PRL 99 (2007) 102501
Expensive and difficult to handle. Problems with information on z coordinate
A decay event of 45Fe
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 26
Novel idea: optical readout
p
pe
E�
ionizationHV electrodes
counting gas at atmospheric pressure
incomingidentified
ion gating
� OTPC: Optical Time Projection Chamber
Gas mixture:He + Ar + N2 (≈1%)
Vdrift ≈ 1 cm/µs
Trigger
Recordingsystem
charge amplification zone
eionizationelectrons
light
ion gating electrode
CCD PMT
M. Ćwiok et al., IEEE TNS, 52 (2005) 2895 K. Miernik et al., NIM A581 (2007) 194
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 27
CCD 2/3’’
• 1000 × 1000 pix.• 12-bits• image ampl. (×2000)(1÷3) ×
15 cm
OTPC data acquisition
LabViewHVOTPC
HI
20 cm
Digitizer
FrameGrabber
PXI
PC
TOF∆E
Cam
era
PM
Trigger logic
100 MHz
HVOTPC
HI identification& selection
trigger
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 28
OTPC
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 29
Principle of operation
HI implantation decay
decay time
CCD image
ion
decay
PMT signal sampled
tracks of the ion and emitted particle(s) time sequence of events
decay
or only emitted particle(s)
decay details
30M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
θ
φ
Z
X
Y
Event reconstruction
t
PM
LPM = vd t
∆t = 5 µs
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
XY
Camera
Lo
Lxy=115 mm
MeV8.7
mm125)105(115 22
=⇔=⋅+=
αE
L
238U
214Bi(19.9 mn)
210Tl(1.3 mn)
214Po
210Pb22.3 y0.
021%
ββββα 7.7 α 7.7 α 7.7 α 7.7 MeV
(164 µµµµs)
� 214Po α decay
31
ACCULINNA @ FLNR, Dubna
Primary beam
TOF
∆∆∆∆E
13O
12N
20Ne @ 50 MeV/u + Be
� Low-energy fragment separator, full identification
of selected ions by TOF-∆E method
32M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Testing with decays of implanted ions
13O
p
Acculinna separator, JINR, Dubna, 2006 20Ne (50 MeV/u) + Be �...
12N13O8Li
βp emission from 13O
pCNO *
ms 8+→→ 121313
β
β2α decay of 8Li
12N
β3α decay of 12N
αβ
31212 →→ *
ms 11CO α
β288 →→ *
ms 840BeLi
K. Miernik et al., NIM A581 (2007) 194
33M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Experiment at NSCL/MSU
February 2007
Separation and in-flight identification (∆E + TOF)
in A1900 with two-wedge system
Reaction: 58Ni at 161 MeV/u + natNi � 45Fe
Gas mixture:
66% He + 32% Ar + 1% N2 + 1% CH4
� range of 550 keV proton ≈ 2.3 cm
� range spread of 45Fe ion ≈ 50 cm
Active volume: 20×20×42 cm3
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 34
A1900 separator
S1 vault
Wedges at I1 and/or I2
Ion identification in-flight : ∆E + TOF
Reaction: 58Ni at 161 MeV/u + natNi � 45Fe
35M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
Ion identification
All ions coming to OTPC (A1900 identification)
45Fe: 2 /h
43Cr: 8 /min.
41Ti
10000 11000 12000 13000 14000
17500
20000
22500
25000
27500
30000
dE
TOF
Ions which triggered
(OTPC identification)
43Cr
45Fe
trigger
36M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
2p events from 45Fe
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 37
β delayed protons from 45Fe
2.74 2.75 2.76 2.77 2.78
0.0
0.1
0.2
Time after implantation [ms]
β2p
2.57 2.58 2.59
0.0
0.2
0.4
0.6
Time after implantation [ms]
β3p
3.28 3.29 3.30 3.31
0.0
0.1
Time after implantation [ms]
βp
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 38
Decays of 45Fe and 43Cr
2p43Cr+2p
QEC = 18.7 MeVT1/2 = 7 ms
β+ β+
44Mn+p 45Fe
β2p
β3p 0.08%
β3p 11%
2pNSCL/MSU, 2007
IASIAS
βp
42Ti+p 43V45Mn
44Cr+p
βp β2p
β4pβpα
43V+2p42Ti+3p
41Sc+4p40Ti+pα
≈ 70% ≈ 30%
β2p
41Sc+2p
K. Miernik et al., Eur. Phys. J. A 42 (2009) 431
40Ca+3p
M. Pomorski et al., Phys. Rev. 83 (2011) 014306
βp
β2p
βp
β2p
β3p
β3p
K. Miernik et al., PRL 99 (07) 192501
39M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
3D reconstruction
0
1
ϑ
50_463� Full p-p corellation pattern could be
established
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2
PMT -1
0
1
-1
0
1
-1
∆φ
ϑ1 = (104 ± 2)°, ϑ1 = (70 ± 3)°
∆φ = (142 ± 3)º � θpp = (143 ± 5)º
0.534 0.536 0.538
0
2
4
6
Time after implantation [ms]
Lig
ht in
tens
ity [a
.u.]
K. Miernik et al., PRL 99 (07) 192501
40
☺
� More information on the OTPC and more decay images can be found at
http://www.fuw.edu.pl/~pfutzner/Research/OTPC/OTPC.html
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 41
Radioactive decays
Z = 82
β+ /EC decay
Fissionα α α α decay
p emission
2p emission
Cluster (14C)emission
N = 126„Classical” era
αααα, ββββ – Rutherford, 1899
ββββ+ – Curie & Joliot, 1934
EC – Alvarez, 1937
SF – Flerov & Petrzhak, 1940
N = 28
Z = 2
Z = 8
Z = 20
Z = 28
Z = 50
N = 2N = 8
N = 20
N = 50
N = 82
β- decay
2p emission
n, 2n emission
?
Modern times
p – Hofmann / Klepper, 1982
14C – Rose & Jones, 1984
2p – M.P. / Giovinazzo 2002
n, 2n – ?
M. Pfützner, Euroschool on Exotic Beams, Dubna 2013, Lecture 1/2 42