SUMMARY OF EXPERIMENTAL SUMMARY OF EXPERIMENTAL RESULTS ON COLLINEAR CLUSTER RESULTS ON COLLINEAR CLUSTER

TRI-PARTITION STUDIESTRI-PARTITION STUDIESD. Kamanin for the CCT teamD. Kamanin for the CCT team

3636thth meeting of the PAC for Nuclear Physics 21-22 June 2012 meeting of the PAC for Nuclear Physics 21-22 June 2012

Basic support JINR Topic 03-5-1094-2010/2014 “Synthesis and Properties of Nuclei at the Stability Limits”This work also was supported supported by the grants

Germany (BMBF)

Kazakhastan (Plenipotentiary)

Romania (Plenipotentiary)

Russia (RFBR)

South Africa (DST)

ISINN 2002-2012

1996, 2001, 2006, 2011

Regular discussions

Collaboration in experiments and analysis

JINR (Dubna), MEPhI (Moscow), ATOMKI (Debrecen), JYFL (Yuväskylä), HMI (Berlin), MSU (Moscow), SUN (Stellenbosch), INR RAS (Moscow)

with support of INP (Kiev), KRI (St-Peterburg), …

Conventionalternary fission

Collinear Cluster Tripartition ( Multy-Cluster Decay )

Positive theory background

Nucl. Phys. 46 (1963) 639

two-neck and three-neck shapes

H. Diehl & W. Greiner, Nuclear Physics A229 (1974)

Yu.V. Pyatkov, V.V. Pashkevich, A.V. Unzhakova et al., Physics of Atomic Nuclei 66 (2003) 1631

Aligned and compact configurationsfor α-accompanied and α+6He+10Beaccompanied cold fission of 252CfD.N. Poenaru et al., Phys. Rev. C 59 (1999) 3457

The two-center shell model (TCSM)

is used.

“For a given nuclear configuration (R, η, δ1,,

δ2 ) we may unambiguously determine the two deformed cores a1 and a2 surrounded with a certain number of shared nucleons ΔA”

---- ---- ----

“However, there is a chance for these extra nucleons ΔA to concentrate in the neck region between the two cores and finally form the third fission fragment.”

ΔA

actually 3-body chain of cold

spherical nuclei is under analysis as well

Conventionalternary fission ~10-3/bin.fiss.

“Polar emission”

~10-5/bin. fiss.

F. Gönnenwein, Nucl. Phys. A 734 (2004) 213

(4He…)

Ternary fission of low excited nuclear systems - status

quo at the start:

?

True ternary fission - contradictory results:

M.L. Muga et al., (1967) - Y3 ~10- 6/bin. fiss.,

but it was strongly criticized ;

P. Schall, P. Heeg,

M. Mutterer, J.P. Theobald (1987) - Y3 <10- 8/bin.fiss.

Inspiration

FOBOS FOBOS 1996 1996

Measurement of the TOF - E and Z-sensitive variables (dE and Tdrift)for each correlated fragment enabled the multi-body research

Separation of the correlated pair by the grid

Al2O3

252Cf

“Start” PAC with source inside

“Stop” PSAC Ionization chamber

50 cm

Ma+M

b=constMa,b=const

Major trajectories in the missing mass plots

Experimental steps: FOBOS modified FOBOS mini-FOBOS

missing mass approach, Z -sensitive variables &

experimental neutron multiplicity νexp for selection of the CCT events

Start AC with 235U inside

MiniFOBOS in the cave 6b of the reactor IBR-2

The main results: Ni-bump in Mass1-Mass2 plots & its internal structure

Additional bumps based on deformed magic clusters

YMo~1% / bin.fiss.

Selection of the CCT events using drift-time “missing charge” picture

CCT

Yu.V. Pyatkov et al., Bulletin of the Russian Academy of Sciences. Physics, 75 (2011) 949

13

Neutron gated data, n=2

Start detector (252Cf +PAC)

neutron counters

Standard FOBOS modules

(PSAC + BIC)

128Sn 144Ba

68, 72Ni

94Kr

- nonrandom natureof the structuresobserved;- bright manifestationof clustering

2% of random realization

Only 4 discreet

directions

Selection of symmetric decays

V1≈ V2

P1 ≈ P2

V1≈ V2

P1 ≈ P2

Z1 ≈ Z2

Each point:

6 independent

experimental

parameters

236U*

252Cf

Experiments in JYFL 252Cf(sf) and 236U+(eV)

Preliminary results on observation of collinear cluster tripartition in 232Th +d (10 MeV) reaction.

190 200 210 220 230 240 250 260 270 280

0

2

4

6

8

co

un

ts/2

am

u

Ms(amu)

Ms_cor Ms

slow fast

Physics of Particles and Nuclei Letters. 2010. V. 7, No. 2. pp. 122–126.

3 particles are registered

Background

Cluster radioactivity 222-226Ra 14C H.J. Rose and G.A. Jones, Nature 307 (1984) 245

Cold fission “Tin radioactivity” ... Light α – cluster nuclei “Ikeda et al. [Suppl. Prog. Phys. (Japan) Extra (1969) 464] speculated a rang of different cluster structures might occur in 24Mg nucleus: α + 20Ne, 8Be + 16O, 12C + 12C, 12C + 12Cchain and a 6α chain state. There is now evidence for all these different structures [B.R. Fulton, Z. Phys A349 (1994) 227]”

Yu.V. Pyatkov, D.V. Kamanin et al., EPJ A 45 (2010) 29

CCT – as a new kind of cluster decay (radioactivity)

COMETA

COrrelation Mosaic E-T Array

&M2=60-74amu

COMETA data: Ni-bump & Ge-bump without any gating

128Sn

68Ni

72Ni

144Ba

80Ge

134Te

68Ni/128Sn68Ni/134Te

Third group (w3): V3<V2, V1 ~ VH_bin, TKEexp=178MeV

Q4~216MeV; Eint~188MeV;

Eint ~TKEexp

V(Ni)=1.73 ~ Vexp(Ni)=1.62cm/ns

good agreement

(the same partners as in w2)

After full acceleration

After full acceleration

1-st2-nd3-rd

Quaternary decay is expected

21

Neutron gated data, n=3 & V-E gate

Rectangular structure

similar to these observed

earlier but:

based on deformed

magic clusters

prescission neutrons?

dm=4

1. Neutron source being at rest;

2. Low missing mass;

prescission neutrons?

22

Ternary decays, all 3 fragments were detected

&Ms12<258dM12s ~ 40amu

By definition:

m1>m2>m3Bright manifestation of clustering

COMETA-2 setup, time-of-flight part

PIN-diodes 120˚& MCP

neutron belt 28 3He counters

What are the ways forward?

Coincidence experiment. Check for the total mass, linear momentumconservation, energy balance. Compromise between:

High granularity High complexity, expensive

Long arms Low efficiency

Intensive source Pile-ups processing

Alternatively

EM separation Low acceptance, unknown ionic charge,of the collinear pairs unusual velocities

0

500

1000

1500

2000

2500

0.17 0.51 0.85 1.20 1.54 1.88 2.22 2.56 2.90 3.25

Ca-Ni distance on detector,cm

N

Realistic calculations at 20 cm

Y, c

m

Ni

Ca

The known referencesA.A. Alexandrov et al., NIM A303 (1991) 323.N.C. Oakey, P.D. McFarlane NIM 49(1967) 220.

The parameters used for the calculations: High voltage 10 kV wire diameter 0.1 mm, channel diameter 56 mm, length of one guide arm 5 m target diameter 5 mm

Reactorcore

Experimental area

3D trajectories of the initially collinear ions of 52Ca+4 (1.46 cm/ns) and 72Ni+12 (0.75 cm/n)

Ion guide system for transportation and “de-collinearization” of the fission products

Δt=5x200ps

Flash- technique for resolving the double-hits from CCT

Velocities in “Ni”-bump

Independent measuring of V& E for both

~15 ns

R.B. Tashkhodjaev, A.K. Nasirov, and W. Sheid, Eur. Phys. J. A. 47, 136 (2011).

K.R. Vijayaraghavan, W. von Oertzen, and M. Balasubramaniam, Eur. Phys. J. A. 48, 27 (2012).

A scheme for the ternary collinear breakup of a parent nucleus into three fragments in two steps.

Awakening the theory

Conclusions• New multi-body, at least ternary, decay (CCT) of the low excited heavy

nuclei is observed in the frame of the different experimental approaches used. The total yield of the effect ~1% per binary fission i.e. even larger than the yield of the known conventional ternary fission with emission of the light charge particles.

• One of the CCT mode can be treated as new - ternary - cluster decay with extremely high yield. Physically it is due to the replacing of the doubly magic lead cluster giving rise to known heavy ion radioactivity by the chain of two magic clusters (for instance, 132Sn+68Ni) with drastic decreasing of the decay barrier.

• The effect observed is a bright manifestation of clustering in heavy and likely super-heavy nuclei to be studied in more details.

  We are grateful to the FLNR directorate for the support of our work.