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Formation and Decay of Highly Excited Nuclear Matter in Intermediate Energy Heavy-Ion Collisions. S. Hudan , R. Yanez , B. Davin , R. Alfaro, H. Xu, L. Beaulieu, Y. Larochelle, T. Lefort, V. Viola and R.T. de Souza Department of Chemistry and Indiana University Cyclotron Facility, - PowerPoint PPT Presentation
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Formation and Decay of Highly Excited Nuclear Matter in Intermediate Energy Heavy-Ion Collisions
S. Hudan , R. Yanez, B. Davin, R. Alfaro, H. Xu, L. Beaulieu, Y. Larochelle, T. Lefort, V. Viola and R.T. de
Souza
Department of Chemistry and Indiana University Cyclotron Facility, Indiana University, Bloomington, Indiana 47405
R. J. Charity and L. G. Sobotka
Department of Chemistry, Washington University, St. Louis, Missouri 63130
T.X. Liu, X.D. Liu, W.G. Lynch, R. Shomin, W.P. Tan,M.B. Tsang, A. Vander Molen, A. Wagner, H.F. Xi,
and C.K. Gelbke
National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824
Nucleosynthesis, Terra Incognita, and the EOS
Radioactive beams (e.g. at RIA) will allow us to probe the N/Z degree-of-freedom
Neutrons
Pro
tons
Stable Nuclei
Known Nuclei
Terra Incognita
N/Z(isospin)
Nuclei are two-component systems (neutrons and protons), the N/Z of the system affects the phase diagram.
Need to know not just ground-state of unstable nuclei (masses,
shapes, etc) but also excited states, level densities, etc.
H. Müller and B.D. SerotPhys. Rev. C 52, 2072 (1995)
Phase transitions for finite systems
Transition from one phase to an other at constant T
Constant PInfinite matterClosed system
“Caloric curve” for nuclear matter
Liquid phase
Gas phase
Liquid-gas coexistenceBOILING
J. Pochodzalla et al., PRL 75, 1040
(1995)1. Why do we observe a caloric curve for a
system which is not infinite, not closed, and not isobaric?
2. If in the plateau region the liquid and the gas are in coexistence, what is the liquid and what is the gas?
Tc = CT(K/m*)ρs-1/3
•Tc = critical temperature• K = nuclear compressibility• m* = effective nucleon mass• ρs = saturation density• CT = constant
Liquid phase
Gas phase?
The system is boiling at a constant T
J. Natowitz et al., PRC65, 034618 (2002)
P. Bonche et al., NP A436, 265 (1985)
J. Natowitz et al., PRC 65, 034618 (2002)PRL 89, 212701 (2002)
Differences in caloric measurements may be related to differences in size of fragmenting system (different finite size, Coulomb energy, isospin ) Limiting temperature
50 100 150 200 250A
Limiting temperature for A=90 system is 6-7 MeV
Caloric curves
Tc
How do we create highly excited nuclear matter?
BUU collision
Method A: Multi-GeV p, - collisions with a nucleus.
C. Mader, Hope CollegeBUU: 5 GeV p + Pb
• , N*•
b=1fm
Stage 1: Excitation of target nucleus by excitation of resonance.
Heating with minimal compression
Stage 2: Disassembly of excited nucleus into light charged particles (LCP:Z ≤2) and intermediate mass fragments (IMF:3 ≤ Z ≤20)
Ejection of fast pre-equilibrium particles
BUU = two-body collisions within a mean fieldNo inherent fluctuations in the field
Interaction stage Equilibrium?
Description of the reaction process
t = 0 t = 100-150 fm/c t =
time//
ThermodynamicsDynamics LINK?
Collision of a nucleus with a light-ion (Z<3) or a heavy-ion (Z>2) converts kinetic energy of relative motion into intrinsic excitation i.e. heats the
nucleus.
From the debris – the fragmentation pattern we need to determine what happened
• identity of all the particles
• number of clusters (Z>2)
• number of light particles Z=1,2
• energy of all the particles
• angles of all the particles V.E. Viola and K. Kwiatkowski, American Scientist 86,449 (1998)
Reconstructing a collision
E detector
Incident particle with
(Z,A,E)dx
E detector
dE = Z2A
dx E
Identifying the reaction products
• 162 individual telescopes covering 74% of 4
• Gas Ionization chamber/500 µm Si(IP)/CsI(Tl(PD)
• Each telescope measures Z,A, E, and
• Identification of Z for 0.6≤E/A≤96 MeV
• Identification of A for E/A ≥ 8 MeV for Z≤4
ISiS: Indiana Silicon Sphere
Probability for emitting one or more IMF exceeds probability for emitting none.
Charge distribution (Z) becomes flat.
Onset of an expansion
IMF Emission time becomes very
short
“If we were at equilibrium we would not only be dead, we would be homogenous”
S. Nagel, FermiNews and Physics Today (September 2002)
L. Beaulieu et al., PRL 84 5971 (2000)
Several quantities tell us that something unusual happens at E*/A=4-6 MeV for a Au nucleus
Liquid-gas Phase transition?
How do we create highly excited Nuclear matter?
Method B: Intermediate (20 ≤ E/A ≤ 200 MeV) energy heavy-ion collisions
1 fragment
vH>vL vL>vH
2 fragments fragmentation
E*, J
PLF*
TLF*
► Central collisions (head-on collisions)► Peripheral collisions (glancing collisions)
PLF* ≡ excited projectile-like fragment
TLF* ≡ excited target-like fragment
Ring Counter :Si (300 m) – CsI(Tl) (2cm)2.1 lab 4.21 unit Z resolutionMass deduced†
Beam
LASSA : 0.8Mass resolution up to Z=97 lab 58
114Cd + 92Mo at 50 A.MeV
Detection of charged particles in 4
† : Modified EPAX K. Sümmerer et al., PRC 42, 2546 (1990) Projectile
48
Experimental details
How do we create highly excited Nuclear matter?
Method B: Intermediate (20 ≤ E/A ≤ 200 MeV) energy heavy-ion collisions
Different reaction types as a function of centrality
: Charged Particles: Z and A; Neutrons; Gammas
P
T
bRP+RT
PLF
TLF
PeripheralCentral Mid-Peripheral
PLF
TLF
Degrees of freedom : E*, J, density, shape, N/Z
Multifragmentation (most excited systems)
Binary exit channel + statistical decay (relatively
gentle collisions)
Neck fragmentation (shape instability)
Conventional wisdom
Chemical equilibrium: different partitions are
populated according to their statistical weights.
Kinetic energy spectra fit Maxwell-Bolztman distribution: P(E) exp(-E/Tslope)
Angular distribution emission time as compared to rotation time
Kinetic equilibrium: motion of all
particles reflects a common temperature
Thermometers
F. Zhu et al., PRC52, 784 (1995)
Emitting system
10B
6Li
Relative energy spectrum of daughters reflects internal quantum levels of parent
Pm = (2Jm+1)e-(E*-Em/T)
Pm/Pn = (2Jm+1)/(2Jn+1)e-(En-Em)/T
Extract temperature T
114Cd
92Mo
Participant (Overlap zone) is highly
excited
1. Projectile and target-like nuclei are relatively unexcited
2. Velocity of PLF* nearly unchanged from beam velocity
3. Overlap of projectile and target is the key quantity in the reaction
Conventional wisdom (participant-spectator model)PLF*
TLF*Shearing
mechanism
Select fragments at very forward angles 2.1 lab 4.2
spectator
spectator
PLF* decay following a peripheral collision
PLF* = good case: (as compared to central collisions)System size (Z,A) is well -defined Normal densityLarge cross-section (high probability process) 0
Circular ridge PLF* emission“Isotropic” component
Projectile velocity
Other emission(mid-rapidity, ...)
KE spectra in PLF* frame selected on VPLF*
Decreasing VPLF*,
increasing dissipation, increasing excitation
• Decay of PLF* dominated by a single exponential (statistical evaporation).
• Pre-equilibrium emissions comprise at most 2% of the yield.
• Systematic increase of exponential slope with decreasing VPLF*
• 6He exhibit systematically higher
slope parameters (temperatures) emission from hotter sources possibly earlier in the de-excitation cascade.
Multiplicities increase with velocity damping
Tslope increases with velocity damping “Linear” trend for both observables
Evaporation and velocity damping
# emitted from the PLF* in a given
collision
(Linear) dependence of E* with velocity damping
High E* is reached (6 MeV/n), consistent with the beginning of the plateau
in the caloric curve.
Velocity damping and excitation energy
Reconstruct excitation of PLF* by doing calorimetry: particle multiplicity, kinetic energies, and binding energies.
Good agreement with GEMINI Some sensitivity of M to J, level density
“Statistical model code” supports E*/A scaleR.J. Charity et al., PRC63, 024611 (2001)
• Select PLF* size by selecting residue Z.
• Select excitation by selecting VPLF*
• Vary N/Z by changing (N/Z)proj.,tgt.
To study N/Z dependence of EOS:
Total excitation of PLF* depends on velocity damping and is relatively independent of PLF size.
Results are consistent with following scenario:
1. For each impact parameter a distribution of contact times exists.
2. While impact parameter determines the size of the PLF*, it is contact time that determines the velocity dissipation and excitation of the PLF*.
What causes the distribution of contact times? Mean field fluctuations?
Thermodynamic SummaryWe can create highly excited nuclear systems by:
High energy p, + A collisions
Central collisions of two heavy-ions at intermediate energies
Peripheral collisions of two heavy-ions at intermediate
energies (Excitation connected with velocity dissipation not
overlap!)
PLF* decay Access to highly excited well-defined system Explore same E* for different system size Radioactive beams
Exploration of EOS (mass and N/Z)
Dynamics: The two fragment case
1 fragment
vH>vL vL>vH
2 fragments fragmentation
E*, J
PLF*
TLF*
Binary breakup: PLF* reconstruction
ZH
ZL
ZHZL
PLF*
vL > vH
vH > vL
LH*PLF ZZZ )f(ZAA *PLFL*PLF HA
*PLF
LLHH*PLF
A
vAvAv
If the PLF*, subsequent to the collision process, decays statistically we expect both cases to be the same.
6 NC 10
Different charge correlation
Different alignments
Different relative velocities
B. Davin et al., PRC 65, 064614 (2002)
*PLFvrelv
Process characterization
Dynamical process appears at higher velocity lower damping lower excitation Up to 10% of the cross-section in binary breakup
1 fragment (x 0.1)
dynamical
statistical
Process probability : channel opening
More kinetic energy in the fragments for the dynamical caseFor a given velocity damping, difference of 20-30 MeV
statistical
dynamical
(L)E(H)ETKE PLF*k
PLF*k
Energy transferred to the fragments
A picture of the process
TimeSaddle-point Scission-
point
TKE
Q
Coulomb
Collective
Initial kinetic energy?
Deviation of TKE from (Q+Coulomb)
“Extra” energy
Time scale?
Dynamics : a new process?
As compared to standard fission, the dynamical process has :
Large asymmetry
Strong alignment
Lower E* threshold
Large kinetic energy in the 2 fragments, for all E*
Same dependence of TKE with E*
Do we have a new process?
Process with a large cross-section
E432@GANIL Caen, France
50 neutron TOF detectors (DEMON) to measure neutrons (KE spectra, multiplicities, free n/p at mid-rapidity)`
FIRST and LASSA are highly segmented 600 Si channels together with ISiS 1000 channels
Measure Z,A,E,
ISiS
LASSA
FIRST
124,136Xe + 112,124Sn at E/A=50 MeV
FIRST :Forward Indiana Ring Silicon
Telescopes
T1 : 200 m Si(IP), S2/ 1mm Si(IP), S2/ 2-3cm CsI(Tl)At 28 cm, = 2.25-7.05 with = 0.1
T2 : 300 m Si(IP), S1/ 2-3cm CsI(Tl) At 19 cm, = 7.37-14.5 with = 0.4
T3 : 300 m Si(IP), S1/ 2-3cm CsI(Tl) At 9 cm, = 15.2-28.5 with = 0.7
Device dedicated to measure the decay of the PLF* :
Limiting temperature Dynamical process PLF* fragmentation ...
Large number of channels use of ASIC
Design : P.H. Sprunger
HiRA Telescope Design
• 20 Telescopes • 62.3 x 62.3 mm2 Active Area• Pitch 1.8 mm• 1024 Pixels per telescope
4x CsI(Tl) 4cm
32 strips v. (front)Target Beam
Si-E 65 m
32 strips v (front)
Si-E 1.5 mm
pixel
32 strips h. (back)
(High Resolution Array)
Designed to study transfer reactions, resonance decay spectroscopy, etc with radioactive beams
Design characteristics
• =± 0.15° at 35cm• E/E=40 keV for 5 MeV ’s
Si(IP) specifics
•Bulk material is n type•Interstrip on junction side is 25 m•Interstrip on ohmic side is 40 m
•P+ implant for better interstrip isolation
•Depletion voltage for 1.5 mm detector < 500 V•10 guard ring structure on periphery (2mm dead area region)
Detectors are mounted on (G10) frames with a flexible polyimide cable for readout in tight packing geometry
Developed at IU/IUCF
Silicon detectors
Electronic Readout developed at Washington University (St. Louis) And Southern Illinois University, Edwardsville
With 2000 channels to readout, cost of “traditional” readout is prohibitive.
Design Includes:• Multiple Preamps (100 MeV, 250 MeV, external)• Slow Shaper and Timing Filter Amplifier• Discriminator (5 bit)• Time to amplitude converters
Design Characteristics1. Excellent energy resolution ( 25-40 keV) 2. Dynamically switchable range3. Excellent time resolution (~500 pS) 4. Sparsified readout of both energy and time information.
Application Specific Integrated Circuit
ASIC Chip
ULM for control of ASIC
ADC module, used for ALL 20 telescopes
Electronic ReadoutASIC 32 channels in 6mm x 6mm format (presently 16)
• Mid-peripheral collisions of two heavy-ions at intermediate energies (via PLF* decay) provides the opportunity to study phase diagram of nuclear matter as a function of isospin (with radioactive beams)
• It also allows one to study the dynamics of the collision process (equilibration of charge, mass, and energy) and dynamical decay.
Summary