isotopic effects on the level density and symmetry energy ...lea-colliga/public-docs/2008... · mc...

Isotopic effects on the level density and symmetry Isotopic effects on the level density and symmetry energy: an experimental perspectiveenergy: an experimental perspective

Measurements at Ebeam 10-20 AMeV allow to measure the symmetry energy at finite temperature near the

saturation density

LoI presented to the Legnaro PAC for a campaign of measurements starting in 2009


Bao-An Li PRC74(2006)034610Skyrme Hartree-Fock

Y.Alhassid et al. PRL 79(1997)2939MC Shell Model




Ebeam ≈102 AGeVEbeam ≈50 AMeV


Measurements at ρ ≈ ρ0 and moderate ε*,T are

missing



Ebeam ≈102 AGeVEbeam ≈50 AMeV


Experiments@ALPI-LNL (Ebeam≈ 15 AMeV) can build the a bridge between reaction mechanisms and structure:

evaporation chains are expected to be short => IMF yields can be corrected to access the finite temperature physics



Experiments@ALPIExperiments@ALPI-- Central collisionsCentral collisions

J. Pochodzalla et al., P.R.L. 75 (1995)1040;

C. Sfienti et al., Nucl.Phys. A734(2004) 528

In this energy range in central

collisions one can observe :

• evaporation events (ρ≈ρ0)

• multifragmentation events (ρ<ρ0).

Due to “more expensive”

Q-values associated to many

fragment partitions, the excitation

energy of primary fragments is

expected to be low.

ReactionElab

(A.MeV)θ θ θ θ grazing

σσσσ fus.

(mb)A Z N/Z c.n.

E*

(A.MeV)

(14,28)Si + (28,58)Ni 19 6 425 80 39 1.05 3.8

(16,32)S + (28,58)Ni 17 7 470 84 41 1.05 3.6

(20,40)Ca + (28,58)Ni 16 7 480 91 45 1.02 3.7

(20,48)Ca + (28,64)Ni 16 6 570 103 44 1.34 3.8

(28,58)Ni + (28,58)Ni 13 9 565 109 53 1.06 3.2

(29,63)Cu + (28,58)Ni 12 9 630 116 54 1.15 3.0

Ring

counter

GARFIELD deviceGARFIELD device-- new setupnew setup

•High granularity (~400 ∆E-E telescopes ϑ ≈4o-150o)

•Low energy thresholds (ionization chambers as ∆E)

•Z identification: ϑ ≈ 4o-150o

•A and Z identification:

(1<=Z<=12) ϑ ≈ 4o - 20o (Si-CsI digital pulse shape)

(Z=1-3) ϑ ≈ 30o - 150o (CsI digital pulse-shape)

•Digital electronics also for gas detectors

Garfield@ALPI: Garfield@ALPI: 3232S+S+58,6458,64Ni at 14.5 AMeV Ni at 14.5 AMeV Data (~complete events,central collisions)Data (~complete events,central collisions)

largest fragment

2nd largest

3rd largest

Garfield@ALPI: Garfield@ALPI: 3232S+S+58,6458,64Ni at 14.5 AMeV Ni at 14.5 AMeV Data (~complete events,central collisions) & model comparisonData (~complete events,central collisions) & model comparison

MODEL:breakup

Microcanonical Multifragmentation Model (Ad.Raduta):

source=90% of (Ap+At), ε*=3 A MeV

only normalization to the number of events


MODEL:finalMODEL:breakup



only normalization to the number of events


MODEL:finalMODEL:breakup

Measured final products are produced by short de-excitation chains



Questions:Questions:


At ε*≈1 AMeV, do structure effects appear in evaporation/fragmentation?



If yes:�Which is their intensity?



If yes:�Which is their intensity?�Up to which E* are they apparent?



If yes:�Which is their intensity?�Up to which E* are they apparent?�Are they present in other reactions?



If yes:�Which is their intensity?�Up to which E* are they apparent?�Are they present in other reactions?

Answers provide information for higher energy experiments and fragmentation models!!!!!!!!!!

Garfield@ALPI: Garfield@ALPI: 3232S+S+58,6458,64Ni 14.5 AMeVNi 14.5 AMeVRaw calculation of the symmetry energy Raw calculation of the symmetry energy

σσ22ZZ (A) (A) ≈≈ A T /[2 Csym(T,A)]A T /[2 Csym(T,A)]

M.Colonna, B.Tsang; Eur. Phys. J. A 30 (2006) 165

Ad.Raduta,F.Gulminelli; PRC75 (2007) 044605

A word of caution:A word of caution:Csym refers to the hot fragments

σ, T experimentally come from cold IMFs.

Garfield@ALPIGarfield@ALPI: : 3232S+S+58,6458,64Ni 14.5 AMeVNi 14.5 AMeVRaw calculation of the symmetry energy Raw calculation of the symmetry energy


Odd-even effects in Csym

(in the isotope widths)?









E.Geraci et al.,NPA732 (2004) 173

and paper in preparation

Ni58 +Sn112 35 AMeV (open points)

Ni64 +Sn124 35 AMeV (full points)







E.Geraci et al.,NPA732 (2004) 173

and paper in preparation

Ni58 +Sn112 35 AMeV (open points)

Ni64 +Sn124 35 AMeV (full points)

The Z-odd-even effect has been observed also in other observables

Z oddZ odd--even anomaly @GSI and ALPIeven anomaly @GSI and ALPI

238U

56Fe

124Sn

107Sn

GSI FRS inclusive data

W.Trautmann-NN2006, V.Ricciardi-NPDC18 2004,

C.Sfienti-NUFRA2007

Garfield@ALPI 32S+58Ni 14.6 AMeV

An enhancement for even-Z fragments observed from spontaneous fission to the breakup of AGeV heavy projectiles.

Pairing effects acting in the last steps of the evaporation chain only partially explained this anomaly.


238U

56Fe

124Sn

107Sn



C.Sfienti-NUFRA2007


The anomaly seems to be:

• independent of the beam energy and of the centrality of the events,


238U

56Fe

124Sn

107Sn



C.Sfienti-NUFRA2007




• slightly depending on the number of neutrons,


238U

56Fe

124Sn

107Sn



C.Sfienti-NUFRA2007




• slightly depending on the number of neutrons,

• more pronounced in Ni reactions,


238U

56Fe

124Sn

107Sn



C.Sfienti-NUFRA2007


The anomaly seems to be:• independent of the beam energy and of the centrality of the events,• slightly depending on the number of neutrons,• more pronounced in Ni reactions,• absent in reactions involving stable Ca,Kr,Xe projectile and targets.

Ca projectile and/or target:Ca projectile and/or target:

G.Cardella (private communication)

Limiting experimentLimiting experiment--LNS Cyclotron LNS Cyclotron -- Inclusive dataInclusive data

Cross fertilization between data and evaporation modelsCross fertilization between data and evaporation models


� Staggering comes from pairing effects in the binding energies & level density in the last evaporation steps(model):sucheffect must be controlled to access Csym at finite T

A=87 Z=40 e*=3 A.MeV

Microcanonical Multifragmentation Model:


A=87 Z=40 e*=3 A.MeVA=87 Z=40 e*=3 A.MeV

Break-up

Asymptotic



� The staggering amplitude depends on the relative excited state population in neighbor nuclei at low ε* (data)

A=87 Z=40 e*=3 A.MeV



Break-up

Asymptotic




� The contribution from discrete particle-unstable levels is dominant for even-even nuclei, and can be traced back from correlations (data)

A=87 Z=40 e*=3 A.MeV



Break-up

Asymptotic




� The contribution from discrete particle-unstable levels is dominant for even-even nuclei, and can be traced back from correlations (data)

� Back-tracing the decay through evaporation models: the tuning between data and model will be done by comparing measured and calculated resonance probabilities. (data+model)

A=87 Z=40 e*=3 A.MeV



Break-up

Asymptotic

Last stage of the decay revealed by correlation functions of Last stage of the decay revealed by correlation functions of the relative momentumthe relative momentum

Observed 23 resonances from Li* to O*, ε* up to 1.5 AMeV +4He* at ε* =24 MeV



To properly backtrace primary fragments,

we have to extract the probability for a pair

to come from a resonance-decay.

A problem is to separate resonant and

uncorrelated yields

(F.Grenier,A.Chbihi et al. NPA(2008) in press)



for each resonance, by gaussian fits,

we extracted the probability for a pair

to come from a resonance-decay

(e.g. 23% for α-d)

THeLi thermometer corrections!!!

BacktraceBacktrace of the last step of the decayof the last step of the decay

From the probability for a pair to be

generated by a resonance-decay, we

calculated for each mother nucleus the

average decay probability and excitation

energy

odd-Z nuclei mainly decay by emitting p,d

even-Z mainly by emitting α

BacktraceBacktrace of the last step of the decayof the last step of the decay

from the probability for a pair to be

generated by a resonance-decay, we

calculated for each mother nucleus the

average decay probability and excitation

energy

The decay probability results higher

and E* lower for odd than for even Z

Summary, perspectivesSummary, perspectives

� Odd-even effects in the level densities result in staggering in different isotopic observables

� Correlations: an experimental constraint of excited levels population should help disentangling the influence of the binding energy and the level density in the observed staggering.

� Back-tracing the decay through evaporation models: the tuning between data and model will be done by comparing measured and calculated resonance probabilities.

� This study can be performed for different classes of event (evaporation-fragmentation) for reactions involving projectile and targets from Ca to Ni






Break-up

Asymptotic

A=87 Z=40 ε*=3 A.MeV






Break-up

Asymptotic

A=87 Z=40 ε*=3 A.MeV

At this stage At this stage Csym(TCsym(T) )

could be accessiblecould be accessible


LoI presented to the Legnaro PAC for a campaign starting in 2009

“The committee felt that this is an important line of research for the Laboratory to

pursue both for the understanding of existing data on multi-fragmentation and also

for future work, which will be carried out in this field, using radioactive beam

facilities such as EURISOL.”

In view of next proposals comments, suggestions from your side are

warmly acknowledged!

M.D’Agostino (Bologna Univ. and INFN)

thanks to: Nuclex collaboration, F.Gulminelli (Caen Univ. and LPC),

Ad.Raduta (NIPNE-Bucharest), E.Geraci(Catania Univ. and INFN)

Garfield@ALPIGarfield@ALPI: : 3232S+S+58,6458,64Ni 14.5 AMeV Ni 14.5 AMeV -- Event selectionEvent selection

),(i,j wppTk

M

k

k

j

k

iij31

)(

1

)()(=∑=

=

J.Cugnon,NPA(1985)

PCA analysis;For events where Ztot >70% ZP+T

and θflow >60 o (central collisions)

1. Comparison with models, source characterization (Z,A,ε*,T, ρ)

2. Isotope analysis for different classes of events

He4 24.2 d + d

Li6 2.186 d + α

Be8 g.s. α + α

Be8 17.64 p + Li7

Be9 2.43 α + α + n

Be9 16.97, 17.3, 17.5 p + Li8

B10 5.166 α + Li6

B11 11.35,11.44,11.59,11.89 p + Be10

C11 8.70,9.8 α + Be7

C12 27.9 p + n + B10

C12 16.5,17.3 p + B11

C14 12.96 α + Be10

N12 1.19 p + C11

N13 2.36 p + C12

N14 8.01,9.17 p + C13

N14 11.21 d + C12

N14 13.3 α + B10

N15 11.62 α + B11

O15 10.3 α + C11

O16 8.87 α + C12

O17 7.17,7.76 α + C13

O18 7.12 α + C14

F19 4.65 α + N15

23 resonances

ε* from 0.1 to 1.5 AMeV

odd-Z nuclei mainly decay through p,d emission

even-Z mainly through α

ZZ--oddodd--even anomalyeven anomaly

Garfield@ALPIGarfield@ALPI 3232S+S+58,6458,64Ni 15 AMeVNi 15 AMeV

G.Cardella (private communication)

Limiting experimentLimiting experiment--LNS CyclotronLNS Cyclotron

Inclusive dataInclusive data

How to backtrace the decay?

isotopic effects on the level density and symmetry energy ...lea-colliga/public-docs/2008... · mc...

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