summary of experimental results on collinear cluster tri-partition studies d. kamanin for the cct...
TRANSCRIPT
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.