Slides

Isospin dynamics in multifragmentation vs production
of exotic nuclei around 50 AMeV Dynamical emission of neutrons around Fermi energy (?)
Martin Veselsky
Institute of Physics, Slovak Academy of Sciences, Bratislava
G.A. Souliotis
University of Athens, Greece
S.J. Yennello, A. Keksis, S. Galanopoulos, D. Shetty et al.,
Cyclotron Institute, Texas A&M University, College Station, USA
Kun Wang, Yu-Gang Ma
SINAP Shanghai
Quasiprojectile calorimetry with 28Si beam (selected highlights)
Experiment performed at Texas A&M University
Reactions 28Si+112,124Sn at 30,50 AMeV
Forwards silicon detector array FAUST used
Charged particles isotopically resolved up to Z=5
Quasiprojectiles with Z=12-15 reconstructed
Mechanism of quasiprojectile formation and de-excitation
DIT+SMM simulation
M. Veselský et al., PRC 62(2000)64613
Left - Experimental (solid circles) and simulated (solid lines) mass change (neutron loss)
for the fully isotopically resolved quasiprojectiles with ZQP=14.
Right - Distributions of excitation energy of the quasiprojectiles. Symbols mean
experimental distributions of the set of isotopically resolved quasiprojectiles with ZQP=14
(solid circles) and ZQP=12-15 (solid squares). Solid histograms mean simulated distributions
using DIT+SMM.
DIT - L. Tassan-Got, C. Stefan, Nucl. Phys. A 524 (1991) 121.
SMM - J.P. Bondorf et al., Phys. Rep. 257 (1995) 133.
Yield ratios of mirror nuclei and temperature M. Veselsky et al., PLB 497 (2001) 1.
T(2,3H/3,4He)
T(3H/3He)
Yield ratios of mirror nuclei 3H/3He depend exponentially on N/Z of the quasiproectile,
slope evolves with excitation energy, no apparent effect of missing neutrons observed,
scaling used to estimate temperature (assuming constant chemical potential)
Correlated signals consistent with the 1. order phase transition ­ 28Si+112,124Sn at 30 and 50 AMeV, M. Veselsky et al., Nucl. Phys. A 749 (2005) 114c. Top left – Evolution of chemical potential (from isoscaling) – departure from the trend of homogeneous system, bottom left – correlated to “plateau” in the caloric curve, right ­ kinematic temperatures ­ signal of equilibration with nucleon gas
LCP
IMF
Distribution of isospin between “phases“ ( M. Veselský et al., PRC 62(2000)41605 )
Signals of criticality ?
M. Jandel et al., PRC 74(2006)54608. Can both types of phase transition
coexist ? Confusing situation !
Asymmetric nuclear matter
M. Veselsky, IJMPE 17 (2008) 1883; arXiv.org:nucl-th/0703077
Multifragmentation scenario
consistent with DIT+SMM:
- heated by the energy dissipated in
the initial ( dynamical ) stage
- isolated in the latter stages, no heat
transfer in/out of the system
- adiabatic expansion until the
spinodal region is entered
- during phase change enthalpy
conserved
Asymmetric system – significant part of
the system can transform into very
asymmetric gas phase => 1. order phase
transition, the remnants of liquid phase
T
will undergo percolation-like decay,
since
the
system
passed
the
fragmentation barrier
Symmetric system – only small part of
the system transforms into asymmetric
gas phase, the system will decay via
percolation - like decay => dominant
second order transition
Signal of Transition from
second to first order
phase transition
with increasing asymmetry ?
M. Jandel et al., PRC 74(2006)54608.
Excitation energies identical for two
systems, N/Z shift observed but
smaller than expected
Isotropic emission as expected from
the equilibrated source, no midvelocity tails
Recent experiment at FAUST:
Ca+27Al at 45 AMeV, selection of
projectile-like hot nuclei heavier than the beam, thus the incomplete fusion
mechanism contributes dominantly. Calorimetry of thermally equilibrated projectilelike nuclei ( except neutrons ).
40,48
Δμiv
Trend of chemical potential incompatible with the homogeneous system confirmed.
Left - double isotope ratio temperature d,t/3,4He observed for the reactions
40Ca+27Al ( squares ) and 48Ca+27Al ( triangles ) at 45 AMeV. Isotopicaly
resolved quasiprojectiles with Z>20 are selected. Excitation energy is reconstructed
using observed charged particles. Line shows theoretical dependence, obtained using
simple EoS for isolated system entering spinodal region, right – dependence of yield
ratios of mirror nuclei (Z=1-7) on quasi-projectile N/Z for48Ca+27Al .
Independence on neutron excess provides signal of dynamical emission of
neutrons ( prior to thermal equilibrium !!! ), neck emission ???.
Same bin “isoscaling“ – identical N/Z-bins compared, test of independence of
fragment observable on neutron excess of the quasiprojectile
Heavy residue (PLF) data : Pre-Eq + DIT/ICF + SMM simulation (M.
Veselsky, NPA 705(2002)193) works in most of the Fermi energy domain
M.Veselsky and G.A. Souliotis, Report for subtask 6 of task 11 of EU 6FP Eurisol DS project
Xe +
129
Al
27
K.A. Hanold et al.,
Phys. Rev. C 52 (1995) 1462.
Xe+27Al, 26 AMeV, 0 deg, PE+DIT/ICF+SMM
129
solid lines – filtered simulation
dashed lines – unfiltered simulation
Xe+90Zr,197Au, 44 AMeV, 0 deg also
reproduced by PE+DIT/ICF+SMM,
also for 124Sn+27Al, 20 AMeV, 0 deg
PE+DIT/ICF+SMM works well =>
behavior at 50 AMeV signals sudden
change in reaction dynamics, prior to
de-excitation
129
Xe+27Al, 50 AMeV, 0 deg, PE+DIT/ICF+SMM
129
experimental data become excessively proton-rich,
pure paticipant-spectator scenario ?
129
Xe+27Al, 50 AMeV, 0 deg, PE+Part/Spec+SMM(-6n)
pure participant-spectator scenario does not help alone,
emission of neutrons prior to statistical de-excitation ?
R. Pfaff et al., Phys. Rev. C 53 (1996) 1753.
Kr+58Ni, 75 AMeV, 0 deg, PE+Part/Spec+SMM
78
for proton-rich symmetric system pure participantspectator scenario fails
Kr+58Ni, 75 AMeV, 0 deg,
78
PE+DIT/ICF+SMM (dashed) and INC+SMM (solid line) very similar, better in magnitude but still too n-rich
Kr+58Ni, 75 AMeV, 0 deg, PE+DIT/ICF+SMM(-3n)
78
DIT/ICF is better after removal of 3n (solid), standard
DIT/ICF too n-rich (dashed), again neutron loss
(depending on centrality ?) !!!
86
Kr data
R. Pfaff et al., Phys. Rev. C 51 (1995) 1348.
M. Mocko et al.,
Phys. Rev. C 76 (2007) 014609
Kr+181Ta, 64 AMeV, 0 deg, PE+DIT/ICF+SMM
86
n-rich system, DIT/ICF without apparent
neutron loss
Kr+27Al, 70 AMeV, 0 deg, PE+DIT/ICF+SMM
86
for n-rich projectile no apparent neutron loss, pure
participant-spectator scenario (dashed) similar
to DIT/ICF (solid)
Neutron loss can be indistinguishable
from evaporation cascade dominated
by neutron emission
Dynamical neutron emission in the „fragmentation domain“
Seen at this conference
W. Lynch – unexpected behavior in p-p correlations in reactions
40Ca+40Ca, 48Ca+48Ca at 80 AMeV– radii of the 40,48Ca sources
similar, expected that for 48Ca source will be larger
Future experiments
- neutron ball gives multiplicity, can not select specific subset
- 4-pi neutron array, if any, will suffer from low detection efficiency and
other problems
- n-p, n-n correlations in coincidence with QP calorimetry?
Summary
1. 40,48Ca+27Al at 45 AMeV – observations from 28Si+112,124Sn verified
(chemical potential inconsistent with the trend of homogeneous system, mirror
nucleus ratios, isoscaling, caloric curve) – consistent results, increasing effect of
secondary decay for heavier systems
2. neutron loss - dynamical emission of neutrons ( in the neck region ? )
3. heavy residue data – available quasi-projectile data investigated systematically,
Pre-eq+DIT/ICF+SMM reproduces majority of cases
4. heavy residue data – apparent neutron loss in inverse kinematics above 50 AMeV
5. direct (correlation ?) measurement of coincident neutrons is needed !!!