Transcript Prezentacja programu PowerPoint

Ternary reactions in
197Au+197Au
collisions revisited
I. Skwira-Chalot, K. Siwek-Wilczyńska, J. Wilczyński
(for CHIMERA Collaboration)
1. Motivation
2. Energy and time calibration
3. Results
4. Summary
Motivation
Main goal:
To observe transition between two basic mechanisms of
energy dissipation:
one-body and two-body dissipation.
Very heavy system
Experiment at 10 – 20 MeV/nucleon
Kazimierz, 30.09.2006
Motivation
Los Alamos model of fission
N. Cârjan, A. Sierk, and J. R. Nix,
Nucl. Phys. A 452 (1986) 381
Kazimierz, 30.09.2006
Motivation
Best signatures of 1-BD  2-BD transition
for ternary division of very heavy systems
 formation of 3-rd fragment
instead of
2-BD
1-BD
 different Ekin (relative motion)
Ekin (2  BD )  Ekin (1  BD )
Kazimierz, 30.09.2006
Experiment
Heavy system:
197Au
+ 197Au
Beam energy:
15 AMeV
Charged Heavy Ion Mass and Energy Resolving Array
100  lab  860
beam
CsI(Tl)
target
Si
E
1192 telescopes
TOF
We detect fragments which stop in
silicon detector.
Kazimierz, 30.09.2006
Energy calibration
Reactions used for energy calibration
Elastic scattering
12C
+ 197Au
at 40 and 90 MeV
16O + 197Au
at 60 and 100 MeV
197Au + 197Au at 15 MeV/nucleon
separate
experiments
Inelastic scattering
197Au
+
197Au
at 15 MeV/nucleon
+
12C
at 15 MeV/nucleon
Fission fragments
197Au
Kazimierz, 30.09.2006
Time calibration
TOF calibration based on
• energy spectrum of projectile-like fragments of A 197
• fission fragments from the 197Au + 12C reaction
• energy spectrum of Li fragments stopped in Si detectors
Kinetic energy formula
M
D2
E 
2  2 t0  tch 2
FIND
M – mass
D – distance
- coefficient ns/channel
t0 – „time zero”
tch – time in channels
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Time calibration
t0  t0sat  a  exp(E  b )
Kazimierz, 30.09.2006
For the analysis we take information from
silicon detectors
in R5 to R16 (100  lab  860).
We disregard particles with A  6.
Kazimierz, 30.09.2006
Selection of „binary” events
We selected a class of
binary events
satisfying conditions:
the total mass:
325  A1  A2   400
the transversal
momentum:
 ptrans  0.04 p0
coplanarity with
beam direction:
1  2  1800  200
colinearity in the
C.M. system:
c1 .m .  c2.m .  180 0  50
Kazimierz, 30.09.2006
Results. Mass – angle distribution of binary events
Kazimierz, 30.09.2006
Results. Transversal vs. longitudinal velocity.
325  A1  A2  A3   400
p
trans
p
long
 0.04 p0
p0 corresponding to A
Kazimierz, 30.09.2006
Results
325  A1  A2  A3   400
p
trans
p
long
 0.04 p0
p0 corresponding to A
Kazimierz, 30.09.2006
Summary
Collisions of a very heavy 197Au+197Au system at 15 AMeV were
studied in an exclusive 4 detection experiment.
In the selected class of ternary events we observe clear evidence
for sequential fission processes. We are going to determine the
time scale of these reactions.
Events when three fragments of comparable masses are formed
simultaneously (massive middle fragment formation) are less
intensive than in the previous preliminary analysis based on
incomplete data.
The study of the dominating dissipation mechanism and
theoretical analysis of the 197Au+197Au reaction in terms of the
QMD model of Lukasik and stochastic BNV model of Di Toro et al.
are under way.
Kazimierz, 30.09.2006
INFN, Laboratori Nazionali del Sud e Dipartimento di Fisica e Astronomia,
Università di Catania
INFN, Sezione di Catania e Dipartimento di Fisica e Astronomia, Università
di Catania
INFN, Sezione di Milano Collaboration
e Dipartimento di Fisica, Università di Milano
INFN, Gruppo Collegato di Messina e Dipartimento di Fisica, Università di
Messina
Institute of Experimental Physics, Warsaw University, Warsaw
Soltan Institute for Nuclear Studies, Świerk/Warsaw
M. Smoluchowski Institute of Physics Jagiellonian University,Cracow
Institute of Physics, University of Silesia, Katowice
GANIL, CEA, IN2P3 - CNRS, Caen
Departament of Physics, University of Ioannina, Ioannina
Saha Institute Of Nuclear Physics, Kolkata
Zakopane 2006
Results
325  A1  A2  A3   400
p
trans
p
long
 0.04 p0
p0 corresponding to A
Kazimierz, 30.09.2006
100  lab  700
100  lab  860
Kazimierz, 30.09.2006
100  lab  700
100  lab  860
Kazimierz, 30.09.2006
Results. Selection of „ternary” events
100  lab  700
100  lab  860
We selected a class of ternary events satisfying nearly complete balance
of mass numbers:
AP
 AT   8%  AP  AT

Kazimierz, 30.09.2006
Results. Selection of „ternary” events
100  lab  700
100  lab  860
We selected events for which
ptransversa l
0.0 
 0.04
p0
Kazimierz, 30.09.2006
Results
325  A1  A2  A3   400
p
trans
p
long
 0.04 p0
p0 corresponding to A
Kazimierz, 30.09.2006
Kazimierz, 30.09.2006
Kazimierz, 30.09.2006