Isotopically resolved residues Isotopically resolved residues produced in the fragmentation of produced in the fragmentation of
136136Xe and Xe and 124124Xe projectilesXe projectiles
Daniela Henzlova
GSI-Darmstadt, Germanyon leave from NPI Rez, Czech Republic
OutlineOutline
introduction
extraction of properties of highly excited nuclear system
the experimental set-up
high-resolution magnetic spectrometer - Fragment Separator
experimental results
<N>/Z and extraction of nuclear temperature
isoscaling and extraction of symmetry energy coefficient
summary
IntroductionIntroduction
• properties of nuclear system under conditions of extreme temperatures and densities
• relevant for many astrophysical scenarios:
• study the properties of highly excited system from the isotopic distributions of the final residues in the complete Z range
abrasion
participants
projectile spectator
target spectator
supernovae explosions (formation of elements), properties of neutron stars
relativistic heavy-ion collisions
IntroductionIntroduction
• width and position of the isotopic distributions of hot fragments determined by the physical conditions of the reaction:
•from initial isotopic distributions the properties of hot system may be extracted
-> temperature (T)+symmetry coefficient (γ) and initial N/Z
γ = 25 MeVγ = 14 MeV
SMM calculation
A.S.Botvina et al., Phys. Rev. C 65 (2002), 044610
IntroductionIntroduction
•only distributions of cold residues accessible experimentally•evaporation ->
follow the influence of evaporation on N/Z reconstruct the excitation energy ~ temperature
the isospin-thermometer method
affects both position and width
•isotopic distributions of final residues available
BUT:
•deduce the temperature of hot system from the position deduce the temperature of hot system from the position of the final isotopic distributionsof the final isotopic distributions
R.J.Charity, Phys. Rev. C 58 (1998), 1073
yield ratio of isotopes produced in reaction systems differing in N/Z exhibits exponential dependence on N or Z
IntroductionIntroduction
M.B.Tsang et al., Phys. Rev. C 64 (2001) 054615
N
Y12
4 Sn+
124 S
n(N
,Z) \\
Y11
2 Sn+
112 S
n(N
,Z)
)(422
22
21
21
A
Z
A
Z
T
)exp(),(
),(
1
221 ZN
ZNY
ZNYR
exponent of isoscaling may be related to coefficient of symmetry energy
strength of symmetry energy contribution in strength of symmetry energy contribution in the nuclear binding of the hot fragments may the nuclear binding of the hot fragments may be extractedbe extracted
isoscaling
•The experimental set-up
Experimental complex at GSI, DarmstadtExperimental complex at GSI, Darmstadt
UNILAC
SIS
FRS
12 A MeV ~1 A GeVion source
target
Fragment Separator (FRS) – a high-Fragment Separator (FRS) – a high-resolution magnetic spectrometerresolution magnetic spectrometer
high resolving high resolving power:power:
ToF
dE in ionisatio
n chamber
position in scintillators
mass identification:
Z/ΔZ ~ Z/ΔZ ~ 200200A/ΔA ~ A/ΔA ~ 400400
inverse kinematics in-flight identification
Fragment Separator (FRS) – a high-Fragment Separator (FRS) – a high-resolution magnetic spectrometerresolution magnetic spectrometer
±15 mrad in angle
±1.5% in momentum
combination of several B settings to scan all N/Z and momenta
acceptance of the Fragment Separator
intermediatefocal plane
finalfocal plane
intermediatefocal plane
finalfocal plane
mass resolution with FRSmass resolution with FRS
136Xe + Pb 1A GeV
136Xe
Z
N
Experimental resultsExperimental results
Mean N-over-Z ratio and the isospin-thermometer
method
memory on initial memory on initial NN//ZZ preserved over the whole nuclear charge range preserved over the whole nuclear charge range (high excitation energies)(high excitation energies)
evaporation does not remove memory on evaporation does not remove memory on the the NN//ZZ of the projectile of the projectile
<N>/Z in full nuclear charge range<N>/Z in full nuclear charge range
136Xe
124Xe
<<NN>/>/ZZ investigated in the full nuclear charge investigated in the full nuclear charge rangerange
stability lin
e
Excitation energy introduced in abrasionExcitation energy introduced in abrasion
136Xe+Pb 1A GeV
124Xe+Pb 1A GeV
ABRABLA (abrasion+ablation) calculation
excitation energy far above 3 MeV/A introducedexcitation energy far above 3 MeV/A introduced
break-up of highly excited break-up of highly excited systemsystem
shorter evaporation shorter evaporation cascadecascade
Break-up reflected in the final <N>/ZBreak-up reflected in the final <N>/Z
<<NN>/>/ZZ of the residues sensitive to the length of the evaporation process of the residues sensitive to the length of the evaporation process
explore this sensitivity to determine E* -> the explore this sensitivity to determine E* -> the isospin thermometer methodisospin thermometer method
only inclusion of break-up reproduces isotopic composition of the only inclusion of break-up reproduces isotopic composition of the datadata
stability lin
e
Backtracking of E* from evaporationBacktracking of E* from evaporation
mass, E* and N/Z of the nucleus changes in each evaporation step due to the emission of nucleon or light cluster
excited fragment follows certain rather well defined path in the chart of nuclides
knowing the final knowing the final NN//ZZ and and NN//ZZ after break-up, the excitation after break-up, the excitation energy may be traced backenergy may be traced back
break-up
abrasion
experimental data
evaporation
136Xe
N/Z~N/Zproj
The isospin thermometer methodThe isospin thermometer method
E* available for evaporation E*=aTf
2
•assume a common temperature at freeze-out
136XeTTff
Universal Universal temperatutemperatu
re in a re in a broad broad
range of Zrange of Z
evaporation
Tf= 3MeV
Tf= 4MeV TTff= =
5MeV5MeV
Tf= 7MeV
final <final <NN>/>/ZZ reflects the thermal conditions at the reflects the thermal conditions at the freeze-out freeze-out
N/Z~N/ZN/Z~N/Zprojproj
Comparison of Comparison of 136136Xe and Xe and 124124XeXe
temperature at the freeze-out extracted from temperature at the freeze-out extracted from 124124Xe Xe ~ 4MeV ~ 4MeV <<NN>/>/ZZ of residues from of residues from 124124Xe less sensitive to length of Xe less sensitive to length of evaporation cascadeevaporation cascade
less n-rich projectile final isotopic distribution closer to residue corridor, isospin-thermometer method starts to saturate
136Xe+Pb 1A GeV
124Xe+Pb 1A GeV
Temperature dependence on N/ZTemperature dependence on N/Z
hot liquid-drop model: J.Besprovany and S. Levit, Phys. Lett. B 217 (1989) 1
higher higher NN//ZZ -> higher -> higher temperature temperature
although different in absolute value, the results of the although different in absolute value, the results of the isospin-thermometer method are consistent with the hot isospin-thermometer method are consistent with the hot liquid-drop model prediction liquid-drop model prediction
136Xe
124Xe
Experimental resultsExperimental results
Isoscaling and coefficient of symmetry energy
Isoscaling from Isoscaling from 136136Xe and Xe and 124124Xe dataXe data
isoscaling observed in broad nuclear charge range
),(
),(
Xe
21124
Xe136
ZNY
ZNYR
initial decrease consistent with production of large fragments by evaporation process at small excitation energy
isoscaling exponent in charge range Z=10-13: α ~ 0.35
Extraction of symmetry coefficientExtraction of symmetry coefficient
symmetry energy coefficient lower than for cold heavy symmetry energy coefficient lower than for cold heavy nuclei, where nuclei, where γγ~21-25 MeV~21-25 MeV
Experimental isoscaling
Isospin-thermomete
r
)(422
22
21
21
A
Z
A
Z
T
in the relativistic energy regime change of Z/A in the abrasion negligible
Isotopic composition
of projectiles
γγ=11-14 MeV=11-14 MeV
~ projectile
temperature from isospin-thermometer
T~4-5MeV
symmetry energy coefficient:
Influence of evaporationInfluence of evaporation
SMM calculation for γ=4,8,14,25 MeV and 136Xe, 124Xe E*/A=4 MeV
experimentally value reproduced only with the experimentally value reproduced only with the symmetry coefficient of hot fragments symmetry coefficient of hot fragments γγ ~ ~ 12 MeV12 MeV
evaporation affects the exponent of isoscaling but does not remove its dependence on γ
by A.Botvina
Comparison with <N>/ZComparison with <N>/Z
decrease of symmetry coefficient for hot fragments decrease of symmetry coefficient for hot fragments supported also by analysis of <supported also by analysis of <NN>/>/ZZ
experimental <N>/Z reproduced with γ=14 MeV
SMM calculation for γ=4,8,14,25 MeV and 136Xe, 124Xe E*/A=4 MeVby A.Botvina
Z=10-13
SummarySummary
isotopic identification in the complete Z rangeisotopic identification in the complete Z range was was obtained for residues from obtained for residues from 136136Xe (Xe (NN//ZZ=1.52) and =1.52) and 124124Xe Xe ((NN//ZZ=1.30) projectiles=1.30) projectiles final <final <NN>/>/ZZ reveal a sensitivity to the length of an reveal a sensitivity to the length of an evaporation cascadeevaporation cascade
isoscaling was observed in broad isoscaling was observed in broad ZZ range range
Universal freeze-out temperature Universal freeze-out temperature deduced deduced in the in the broad Z range:broad Z range:
From isotopes with Z=10-13From isotopes with Z=10-13 the symmetry the symmetry coefficient coefficient γγ=11-14 MeV =11-14 MeV was extractedwas extracted
Comparison with SMM calculation and Comparison with SMM calculation and <<NN>/>/ZZ of data of data supports decrease of supports decrease of symmetry coefficient for hot fragmentssymmetry coefficient for hot fragments
TTff~5MeV for ~5MeV for 136136XeXe
TTff~4MeV for ~4MeV for 124124XeXe
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