Transcript Document

SUMMARY OF EXPERIMENTAL
RESULTS ON COLLINEAR CLUSTER
TRI-PARTITION STUDIES
D. Kamanin for the CCT team
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), …
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)
Regular discussions
Kazakhastan (Plenipotentiary)
Romania (Plenipotentiary)
ISINN 2002-2012
Russia (RFBR)
South Africa (DST)
1996, 2001, 2006, 2011
36th meeting of the PAC for Nuclear Physics 21-22 June 2012
Collinear Cluster Tripartition
( Multy-Cluster Decay )
Conventional
ternary fission
Positive theory background
Nucl. Phys. 46 (1963) 639
two-neck and three-neck shapes
H. Diehl & W. Greiner,
Nuclear Physics A229 (1974)
Aligned and compact configurations
for α-accompanied and α+6He+10Be
accompanied cold fission of 252Cf
D.N. Poenaru et al.,
Phys. Rev. C 59 (1999) 3457
Yu.V. Pyatkov, V.V. Pashkevich, A.V.
Unzhakova et al., Physics of Atomic
Nuclei 66 (2003) 1631
ΔA
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”
---- ---- ----
actually 3-body chain of cold
spherical nuclei is under
analysis as well
“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.”
Ternary fission of low excited
nuclear systems - status
quo at the start:
Conventional
ternary fission
~10-3/bin.fiss.
?
(4He…)
F. Gönnenwein, Nucl.
Phys. A 734 (2004) 213
True ternary fission - contradictory results:
“Polar emission”
M.L. Muga et al., (1967)
- Y3 ~10- 6/bin. fiss.,
but it was strongly criticized ;
~10-5/bin. fiss.
P. Schall, P. Heeg,
M. Mutterer, J.P. Theobald (1987) - Y3 <10- 8/bin.fiss.
Inspiration
FOBOS
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
“Start” PAC
with source inside
“Stop” PSAC
Al2O3
50 cm
252Cf
Major trajectories in the missing mass plots
Ma,b=const
Ionization chamber
Experimental steps:
FOBOS modified FOBOS mini-FOBOS
missing mass approach, Z -sensitive variables &
experimental neutron multiplicity
νexp for selection of the CCT events
MiniFOBOS in the cave 6b
of the reactor IBR-2
Start AC with 235U inside
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
neutron counters
Neutron gated data, n=2
Standard
FOBOS
modules
(PSAC + BIC)
Start detector
(252Cf +PAC)
94Kr
68, 72Ni
2% of random
realization
- nonrandom nature
of the structures
observed;
- bright manifestation
of clustering
Only 4 discreet
128Sn
144Ba
directions
13
Selection of symmetric decays
236U*
252Cf
Each point:
V1≈ V2
P1 ≈ P2
V1≈ V2
6
independent
P1 ≈ P2
experimental
Z1 ≈ Z2
parameters
Experiments in JYFL 252Cf(sf) and 236U+a (40 MeV)
Preliminary results
on observation
of collinear cluster tripartition
in 232Th +d (10 MeV) reaction.
Physics of Particles and Nuclei Letters.
2010. V. 7, No. 2. pp. 122–126.
8
3 particles are registered
Ms_cor
Ms
counts/2amu
6
4
2
slow
0
190
200
210
220
230
240
Ms(amu)
250
260
270
280
fast
Background
CCT – as a new kind of cluster decay (radioactivity)
Cluster radioactivity
221
Ra  C
Fr ÷ 242Cm  14C ÷
34
Yu.V.
H.J. Rose and G.A.
Si Pyatkov, D.V.
-10
Kamanin
EPJ
Jones, Nature 307 (1984) (10
÷ 10-17et
) Pal.,
α
A 45 (2010)
29
245
“Lead
radioactivity”
222-226
14
Binary
decays
Cold fission
“Tin radioactivity” ...
Light α
“Ikeda et al. [Suppl. Prog. Phys. (Japan) Extra (1969)
464] speculated a rang of different cluster structures Multicomponent
might occur in 24Mg nucleus: α + 20Ne, 8Be + 16O,
nuclear
12
12
12
12
C + C, C + Cchain and a 6α chain state. There molecules
is now evidence for all these different structures
[B.R. Fulton, Z. Phys A349 (1994) 227]”
–
c
l
u
s
t
e
r
n
u
c
l
e
i
COMETA
COrrelation Mosaic E-T Array
COMETA data: Ni-bump & Ge-bump without any gating
134Te
80Ge
144Ba
&M2=60-74amu
72Ni
68Ni
128Sn
68Ni/128Sn
68Ni/134Te
Third group (w3): V3<V2, V1 ~ VH_bin,
TKEexp=178MeV
(the same partners as in w2)
After full acceleration
Q4~216MeV; Eint~188MeV;
Eint ~TKEexp
V(Ni)=1.73 ~ Vexp(Ni)=1.62cm/ns
good agreement
3-rd
2-nd
1-st
After full acceleration
Quaternary decay is expected
Neutron gated data, n=3 & V-E gate
prescission neutrons?
dm=4
Rectangular structure
similar to these observed
earlier but:
based on deformed
magic clusters
1. Neutron source
being at rest;
2. Low missing mass;
prescission
neutrons?
21
Ternary decays, all 3 fragments were detected
By definition:
m1>m2>m3
Bright
manifestation of
clustering
dM12s ~ 40amu
&Ms12<258
22
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 momentum
conservation, energy balance. Compromise between:
 High granularity
High complexity, expensive
 Long arms
Low efficiency
 Intensive source
Pile-ups processing
Alternatively
 EM separation
of the collinear pairs
Low acceptance, unknown ionic charge,
unusual velocities
Ion guide system
for transportation and “de-collinearization” of the fission products
Experimental
area
The known references
A.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
5m
target diameter
5 mm
3D trajectories
of the initially collinear ions
of 52Ca+4 (1.46 cm/ns)
and 72Ni+12 (0.75 cm/n)
2500
Realistic calculations at 20 cm
2000
1500
N
Reactor
core
1000
500
0
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
Flash- technique for resolving the double-hits from CCT
Velocities in “Ni”-bump
Δt=5x200ps
~15 ns
Independent measuring of V& E for both
Awakening the theory
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.
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.