Recent and prospective studies of three-body decays and related phenomena at GSI

L. Grigorenko

FLNR, JINR, Dubna GSI, Darmstadt

Kurchatov Institute, Moscow

pictures by I. Mukha, J. Marganiec

θp1 -14

O (mrad)

θ p2

-14O

(mra

d)

16Ne

19Mg

17Ne

Two-proton radioactivity

Bound orbita l

Unbound orbital

No bound orbitals !

Classical case: one

particle emission

is always possible

Quantum mechanical case:

it could be that both

particles should be

emitted simultaneouslyBorromean three-body ground state

0Core-n n-n

Three-body Core-n-n

0Three-body Core-p p-p Core-p-p

True three-body decay

Predicted by V.I. Goldansky in 1960Discovered at GSI in 2002

True 2p decay has different energy systematic compared to 1p Specific correlations among decay products True two-proton radioactivity is a "substitute" for Borromean halo nuclei when

we move from neutron to proton dripline:

6He 6Be

9Be 9B

12Be 12O

Related phenomena

True two-neutron decay exists. What about two-neutron radioactivity? Efimov states? Three-body virtual states? Reactions with few particles in the final states Exotic excitation modes. Soft dipole mode of the GDR Decays into few particles True five-body decay (4-neutron/4-proton emission)

Dynamics of the processes can not be reduced to the two-body dynamicsand studies should be done using methods of the few-body theory

Two-proton radioactivity and three-body decay

Theoretical dreams. What about reality?

What is known beyond the driplines? Red – true 2p/2n emitters studied Green – halo systems Black – nothing is known

7H and 8C are four neutron emitters. The candidates are 28O and 29Si. Two-neutron g.s. emission in 10He and 13Li studied recently at GSI True 2p emitters: 6Be, 12O, 16Ne, 19Mg, 45Fe, 54Zn. Discovery of 19Mg and most recent data on 16Ne are from GSI

It is probable that in the first instance the 2p decays of 26S, 30Ar and maybe 34Ca will be studied

Every second nucleus beyond the proton dripline is true 2p emitter

Pretending to understand asymmetric nuclear matter EOS one need to extend our knowledge as

far as possible beyond the driplines.

Instrument: three-body cluster model Schoedinger equation with complex energy

Hyperspherical Harmonic method

Approximate boundary conditions of the three-body Coulomb problem

“Natural” definition of width

Adopted to radioactive decay studies

max

( )† 5/ 2 5/ 2 ( )

max

25 ( )

0

Im( )( ) box

box

dddj

NM d d

( )ˆ / 2 ( , ) 0TH E i

Typical precision: stable solution for /ET > 1030

L.V. Grigorenko, R.C. Johnson, I.G. Mukha, I.J. Thompson, M.V. Zhukov, PRL 85 (2000) 22.

Coulomb three-body problem is not tractable in general case: the exact analytical boundary conditions are not known

News: 48Ni and 54Zn

True 2p character of decay is directly confirmed for 54Zn

2p radioactivity is discovered in 48Ni

Predictions: Grigorenko et al. (2003)

19Mg: decay in flight experiment

Idea of decay-in-flight experiment (GSI S271):I. Mukha and G. Schrieder, NPA 690 (2001) 280c.

Structure and decays of 19Mg: L. Grigorenko, I. Mukha, M. Zhukov, NPA 713 (2003) 372.

Dependence of the predicted lifetime on the structure. “Belt” of posible lifetimes defined by calculations with pure configuration

trackingTwo-proton events:

Coordinate along trajectory

2) exponential "tail" due to decay in the flight

1) Fragmentation in the target

AZXA+1

Z X

decaypoint

p

p

A-2Z-2X core

0.5 1.0

10-14

10-12

10-10

10-8 19 Mg

ET (MeV)

(MeV

)

Descouvemont: ET = 1.5 0.5 MeV

Audi-Wapstra:ET = 0.9 ± 0.3 MeV

d-wave p1

s-wave p2

Grigorenko,Mukha, Zhukov

10-8

10-10

10-12

10-14

Fran

k

T1/

2 (s

)

Chu

lkov

19Mg: vertex distribution and angular correlations

Analogy tracking approach in high energy physics. However. Charges of decay products are too different: very specific setups

19Mg: vertex distribution and angular correlations FRS, fragmentation of the secondary 20Mg beam at S2 Microstrip detectors tracking system Very thick target – efficient experiments for low intensity exotic beams

Kinematical enhancement

close to a maximum angle:

precise energy measurements

without invariant mass reconstruction

Predicted p-17Ne correlations from 19Mg,

L.V.Grigorenko, I.G.Mukha, M.V.Zhukov, Nucl.Phys. A 713 (2003)

19Mg: angular distribution of fragments and decay energy

Angular p-17Ne correlationsfrom 17Ne+p+p eventsselected inside the target

Angular p-17Ne correlationsfrom 17Ne+p+p eventsselected after target

Angular p-17Ne correlationsfrom 17Ne+p+p eventsselected before the target

Continuation?

Experiment S388 “Two-proton decay of 30Ar and one-proton decays of 69Br, 73Rb” is preliminary

scheduled for January 2012

New ideas?

What about doing the same with neutrons?

High granularity neutron detector:Resolution aim: ~1 mrad

Actual plans include studies of

Two- and four-neutron radioactivity search prospects

Two-proton radioactivity is the long awaited and the most recently found mode of the radioactive decay. Can neutron radioactivity exist? Estimates: one-neutron radioactivity is highly unlikely. There are additional effective few-body “centrifugal” barriers making few-body emission relatively slower. Long-living Two-neutron decay and moreover four-neutron decay states are reasonably probable.

It is proposed at GSI to develop neutron tracking technique (in analogy with microstrip proton tracking) having in mind narrow neutron resonances and 2n radioactivity search.

Two- and four-neutron decay studies with HGND

Angular distributions between heavy fragment and one of the neutrons for true 2n decay

of 26O (decay energy 20 and 300 keV). True 4n decay of 28O (decay energy 300 keV) and sequential decay via 26O g.s. (the latter has decay energy 20 keV).

Prediction: distinctive correlation patterns allows to work with 2n

emission down to very low energies. For 4n emission they allow to

distinguish different decay modes .

Features of possible experiments to be understood prior the construction.

Modes of two-proton radiative capture

A

A

A1

Directnonresonant capture

E

W(E)

Sequentialnonresonant capture

Directresonant capture

A1A1

AA

AA

A

A1

E

W(E)

AProton threshold

Sequential resonant capture

rp-process at high temperature and density. Could be important in the regions of nuclear chart, where there are “ridges” connected with paring and intermediate system is not nuclear stable. Analogy with true 2p emission. 15O, 18Ne, 38Ca : J.Gorres, M.Wiescher, and F.-K.Thielemann, PRC 51 (1995) 392. 68Se, 72Kr, … ,96Cd : H.Schatz et al., Phys. Rep. 294 (1998) 167. Famous aaa →12C+ capture process belongs to this class also.

p

p

2p

p

13O

16Ne

19Mg 21Mg

19Na19Ne

16F15O14O 16O

17Ne 18Ne17F

20Na

20Mg2p

“Soft E1” mode in proton dripline nuclei Soft dipole mode: fragmentation of the GDR in systems with spatially

extended density (haloes, skins). Existence of “soft E1” mode now established in neutron-rich nuclei

(“pigmy” dipole resonance in heavy systems). L.V.Grigorenko, K.Langanke, N.B.Shul’gina, M.V.Zhukov, Phys. Lett.

B641 (2006) 254. Possibility of “soft E1” in proton-dripline nuclei: predict a strong and

narrow E1 peak in 17Ne. The 2p capture rate is dominated by the nonresonant E1 capture

connected with SDM for T < 0.05-0.08 GK and T > 0.4-1.0 GK.

0.1 1 1010-50

10-40

10-30

10-20

10-10

Gorres et al. total Gorres et al. resonant

upper, median, lower rates total from Grigorenko and Zhukov nonresonnat E1 "OFSI" model

0.02

N 2 A

v (

cm6 /s

)

T (GK)

15O (2p,)17Ne

0 2 4 6 8 10 120.00

0.25

0.50

0.75

1.00

Grigorenko and Zhukov, NPA 713 (2003) 372.

W(s2) = 50 %

W(s2) = 93 % W(s2) = 25 % W(s2) = 5 %

dBE1

(E)/d

E (e

2 fm

2 MeV

1)

E (MeV)

Competition between a and 2p capture

15O(2p,)17Ne versus 15O(a,)19Ne

Densities (in g/ccm) at which the production rate of 17Ne by 2p-capture on 15O equals the production rate of 19Ne by α capture as function of temperature and α-particle

mass abundance Xa = 4 Ya.

1E21E4

1E6

1E8

1E10

1E12

1E14

1E41E6

1E8

1E10

0.0 0.2 0.4 0.6

T (G

K)

Xa

Upper

(a)

0.0 0.2 0.4 0.6

(c)

Gorres, et al.

Xa

0.0 0.2 0.4 0.6

(b)

Median

10.07.05.04.03.02.01.51.00.80.60.40.30.20.150.1

Xa

Status of 17Ne S318 experiment

“Study of the Borromean dripline nucleus 17Ne”.

17Ne beam, Pb/C/CH2 target. Very pronounced and narrow E1

peak in 17Ne.

Data below 2.5 MeV

E2 Coulex contribution dominated.

Strong deep at CM angle 11 mrad.

Different angular correlations for CM angle larger and smaller 11 mrad – different reaction mechanisms.

Classical interpretation: 11 mrad = 16 fm of impact parameter. Touching distance for 17Ne on Pb target is ~10 fm.

To be understood.

Data between 2.5 and 7 MeV

E1 Coulex contribution dominated. NEW cluster sum rule exhausted by 10-

13 MeV. Nice agreement with theoretical

predictions. First observation of the soft dipole mode

in 2p halo nucleus. Predicted for 2p halo in 17Ne. Implementations for astrophysics.

Data above 7 MeV

Broad angular distribution – different reaction mechanism. Strange events: protons emitted together or back to back in

a narrow cone (~30 dgr) No theoretical explanation so far.

2.5 < E < 7

7 < E

cos(qpp)

distribution

Red: cos(qpp) < - 0.85

Blue: cos(qpp) < 0.75

Role of theory in these studies

Extremely detailed and high quality data. Qualitative simplistic treatment “not possible”.

Quantitative results not possible without complete MC studies.

Four different theoretical problems to consider: coulomb/nuclear interference, coulex E2, coulex E1, unusual “cones emission” events.

Example of recent 6Be decay data from Dubna: 6Be(p,n) 6Be reaction at 30 A MeV.

0 4 8 12 16 E (MeV)

Active tasks and prospects

Practical task: preparation of S388 experiment (microstrip tracking, new 1p and 2p emitters).

Practical task: MC “event generator” development for reaction studies of three-body systems (for 17Ne S318 experiment data treatment).

Practical task: theoretical modeling of the reaction mechanisms (input for MC “event generator”)

Last two points to be seen in poster by I. Egorova.

Prospective studies: substantiation of plans the 2n-4n emission studies.

Prospective studies: applicability of high granularity neutron detector for research with the neutron dripline nuclei.

Rapidly developing field. Changing situation.Changes in the working plans.

Findings: two-proton halo in 17Ne seem to exist. Findings: soft dipole mode in 17Ne seem to exist. Findings: unusual correlation mode “cones emission” found in 17Ne excitation spectrum above 7 MeV.

0.1 1 1010-50

10-40

10-30

10-20

10-10

Gorres et al. total Gorres et al. resonant

upper, median, lower rates total from Grigorenko and Zhukov nonresonnat E1 "OFSI" model

0.02

N 2 A

v (

cm6 /s

)

T (GK)

15O (2p,)17Ne