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