P. Blasi 20 M. Cinausero 20 A. Brondi 50 N. Gelli 60 E ... · CSNIII, 14 Settembre 2004 1 FI.E.S.T.A. 2005-2007 FIssion of Excited Systems at Tandem-Alpi FTE 1.0 1.2 2.6 V. Rizzi

CSNIII, 14 Settembre 2004 1

FI.E.S.T.A. 2005-2007

FIssion of Excited Systems at Tandem-Alpi

2.61.2 1.0FTE80E. Vardaci30V. Rizzi40M. Trotta30G. Prete50R. Moro20T. Gloriadu20F. Lucarelli40G. La Rana20E. Fioretto60N. Gelli50A. Brondi20M. Cinausero20P. Blasi%NA%LNL%FI

Totale FTE: 4.8


FIESTATemi di Ricerca:

1. Dinamica della Fissione in sistemi difissilita’ intermedia (misure di σER eσFF) e sistemi pesanti;

2. Dipendenza della densita’ dei livelli da (Z- Z0);

3. Collaborazioni:a. FLNR, Dubna (M. Itkis, E. Kozulin)

b. Department of Physics, Jyvaskyla(V. Rubchenya, W. Trzazka)

c. Omsk State University (P. Nadtochy)


Upgrade Strumentali

1. Rivelatori TOF per Frammenti(CORSET 2 arms + 2 arms)

2. Rivelatore PPAC anulare per ER

3. Upgrade Elettronica (TAC, CFD, trigger)

4. Modifica camera di scattering permontaggio nuova pompa criogenica

Progetto di Sezione di Napoli: Sviluppo di un TAC a 16 vie con start e stop indipendenti e 50 ps di risoluzione temporale


Milestones Concordate

Turno presso JYFL con l’apparato HENDES per la misura di molteplicita’ neutroniche30.12

Turno di misura con 8πlp sulla dinamica della fissione del sistema 32S + 126Te30.12

test sul nuovo rivelatore anulare per ER (PPAC a 8 settori)30.12

test sulle nuove braccia CORSET per FF30.12

Completamento analisi dati dell’esperimento con MAIALE effettuato nel 200430.06

Completamento analisi turni O + Sm 30.06

DescrizioneData


Piano Finanziario 2005

131.58014254.8Tot32.5318.519.52.6NA

83.5473.51.51.2LNL15.52241.0FI

Inv. (k€)Cons.(k€)ME (k€)MI (k€)FTESez.

Totale delle richieste: 250.5 (k€)


Stop

Start

8πLP-CORSET


8πLP-CORSET


8πLP-CORSET

beam

HVsupply

HVsupply

CFD

spliter

spliter

spliter

spliter

QDC

CFD

CFD

CFD

CFD

CFD

CFD

CFD

QDC

Scheme of coincidence

TAC

TAC

TAC

TAC

TAC

TAC

TAC

ADC

ADC

ADC

ADC

ADC

ADC

ADC

TOF1

TOF2

X1

Y1

X2

Y2

dT

Gate QDC

Gate ADC

Start

Y2X2

Sp2

St2

St1

Sp1

X1

Y1

Electronic modules1. HV supply - 4 channels2. QDC - 4 channels3. CFD - 8 channels4. TAC - 7 pieces5. ADC - 7 channels


180 MeV 32S + 109Ag: TKE vs. Mass


CORSET MASS RESOLUTION








Open questions

1. Fission time scale;

2. Strength and Nature of dissipation: one-body or two-body;

3. Dependence of the viscosity on the temperature and on the shape.

1. Fission time scale;

2. Strength and Nature of dissipation: one-body or two-body;

3. Dependence of the viscosity on the temperature and on the shape.


Effects of Nuclear Viscosity

Dynamical effect: path from equilibrium to scission slowed-down by the nuclear viscosity

Excess of pre-scissionn, p, α with respect to statistical model predictions

0 τd τssc time

Equilibrium Saddle-Point Scission-Point


Time ScalesDynamical fission time scale: τf = τd + τssc

n τf = (35 ± 15) x 10-21 s D. J. Hinde et al.

n, p, α τd = 10 x 10-21 s τssc = 50 x 10-21 s J. P. Lestone et al.

GDR τd = 200x10-21 s

The determination of the fission time scale and of the average deformation relies on Statistical Model calculations.The determination of the fission time scale and of the average deformation relies on Statistical Model calculations.

Use as many observables as possible to constraint the relevant

model parameters

Use as many observables as possible to constraint the relevant

model parameters GOAL: To reproduce many observables with one set of input parameters

GOAL: To reproduce many observables with one set of input parameters


Theoretical estimates for nuclear dissipation

One-body dissipation

Interaction between individual nucleons and the mean field created by all the other nucleons.weak dependence T, strong dependence on the nuclear shape

Two-body dissipation

Hydrodynamical model, collision between nucleonsStrong dependence on the temperature 1/T2

Weak dependence on the nuclear shape

Both reproduce well the experimental M-TKE


Modified Statistical Model

The presence of nuclear viscosity reduces the fission rate.

The full BW fission rate is never attained.

( ) ( )TE ff /10ln2/ 20ωβτ =

( )

−+Γ=Γ γγ 2

121BWf

Kramersf ( ) ( )[ ]f

Kramersff tt τ/3.2exp1 −−Γ=Γ

( )202/ ωβγ =

γ nuclear viscosity parameter

β reduced dissipation coefficient

τf transient buildup time of the flux over the barrier


Macroscopic Dynamical Models

Dynamics of fission consists in the study of gradual change of shape of a fissioning nucleus.

The shape is characterized in terms of collective variables (i.e. elongation parameter, the neck radius, mass asymmetry of exit fragments).The time evolution of these collective variables describes the fission dynamics.

1. Lagrange equation (deterministic)

2. Transport equations: Fokker-Planck and Langevin equations

Dissipation from TKE, n multiplicity


…but..

200.52020 ± 614

6225-82neck 30sci

3

β (1021 s−1)

Mn(pre), Mp(pre) Mα(pre)Mn(ER), Mp(ER) Mα(ER) σfiss

TKE

MGDR

MGDR

Mn(pre)

Mn(pre)

Mn(pre)

Mn(pre)

Mn(pre) Pf

Mn(pre) Pf

Exp. Observ.

KG + SM90141Eu70-16090Sr - 278110

KG + SM123175TaKG + SM64224ThSML70-140158Er

KG + SM70-140158ErWF164181,185,187IrFP164181,185,187IrL + K40-100178W – 251Es

L + K60-100200Pb

ref.E* (MeV)Nucleus

L+K: Langevin and Kramer; FP: Fokker-Plank; KG: Kramers-Grangé; SM: Statistical Model; WF: wall formula.


…but..

From the theoretical point of view the predictions vary almost by two or three orders of magnitude. Most of the theories predict indeed an overdamped motion (β > 2x1021 s-1)


The role of isospin in the dissipation

N/Z

1.49

1.40

1.32

N/Z

1.25

1.40

1.52

W. Ye, Eur. Phys. J. A18 (2003) 571


Research program with 8πLP aimed at studying the fisson time scale and the nuclear viscosity

1. Unique features of 8πLP: Observables: p, alpha particles multiplicities and energy spectra, ER and FF cross section

2. upgrade of 8πLP (FF detection CORSET-like)

3. Complementary use of other setups: HENDES, MAIALE, for n and ER excitation functions

Theoretical framework:

a) Modified statistical model (new version of PACE2) which includes: deformation effects (BE, MI and emission barriers) dynamical effects through the γ parameter (Kramer presc.)

b) Dynamical model: Langevin approach (Dr. Nadtochy)


…….riassumendo

Grandi incertezze per γ e τd

Estendere l’analisi fatta sui sistemi di fissilita’ intermedia adaltri sistemi in cui sono gia’ state misurate altre osservabili :Mn

PRE, TKE, σfiss.

Utilizzare la condizione unica realizzabile con 8πLP di poter misurare simultaneamente diverse osservabili cruciali (es. M-TKE distribution, lcp multiplicities in FF and ER channels) conelevata copertura angolare per un grande intervallo di masse.


Systems of Intermediate Fissility(χ ≅ 0.5 - 0.6)

ER cross section comparable or larger than the fission cross section: more constraints on the SM;

larger charged particle multiplicity (almost an order of magnitude)

role of pre-saddle dynamics enhanced compared to saddle-to-scission-one

no much data on these systems

ER cross section comparable or larger than the fission cross section: more constraints on the SM;

larger charged particle multiplicity (almost an order of magnitude)

role of pre-saddle dynamics enhanced compared to saddle-to-scission-one

no much data on these systems


Systems Studied

0152132Ce32S + 100Mo?93168Yb18O + 150Sm

26100132Ce32S + 100Mo

?132168Yb18O + 150Sm

5194147,9Tb40Ar + natAg4128147,9Tb40Ar + natAg8135149Gd121Sb + 27Al

2790141Eu32S + 109Ag

τd (10-21 s)Ex (MeV)CNSystem

G. La Rana et al., EPJ A16 (2003) 199E. Vardaci et al., Phys.Atomic Nuclei 66, (2003) 1182, Nucl.Phys. A734 (2004) 241


What observables ?

particle – FF coincidences

particle – ER coincidences

particle – FF coincidences

particle – ER coincidences

8πLP + Trigger for ER and FF


200 MeV 32S + 100Mo 132Ce:Fragment-Fragment Correlations

Ring F-GRing G-G


α = 35.4° β = 25.9°

α = 24.9° β = 36.1°

α = 9.2° β = 42.1°

α = 335.1° β = 36.1°

α = 324.6° β = 25.9°

α = 318.9° β = 13.5°

α = 41.1° β = 13.5°

α = 350.8° β = 42.1°

Elab (MeV)

d4 M/d

Ωαd

Ωf1

dΩf2

dEα

240 MeV 32S + 100Mo 132Ce

Out-Of-Plane Multiplicity Spectra

ring Gring G

CSF1

F2

α = in-plane angleβ = out-of-plane angle


New version of PACE21. Inclusion of deformation effects: shape

parameterization (Cassini ovals), binding energies, moment of inertia, emission barriers

2. PES to determine the deformations at equilibrium, saddle and scission points

3. Inclusion of dynamical effects: fission delay τd , viscosity parameter γ (Kramer prescription)

180MeV 32S + 109Ag -> 141Eu Ex = 90 MeVσfiss, p and α multipl. in FF and ER channels

M.A. Di Meo, Ph.D. Thesis


Systems to be Studied

180, 220158Er64Ni + 94Zr180, 220188Pt16O + 172Yb

207158Er16O + 142Nd180158Er32S + 126Te

Elab(MeV)CNSystem


Target

34.0°

CsI Telescopes

(E-DE & TOF)126 Si- CsI Teles

(E-DE & PSD)

4 PPACs

ring G

4.7°

60cm15cm

FF

ring A

8πLP layout116 Si-copes


The 8πLP setup

MAX ENERGYWall: up to 64 AMeVBall : up to 34 AMeV

ENERGY THRESHOLDS0.5 AMeV for p and α2-3 AMeV for 12C

TRIGGERS Fission Fragments in ring F & GEvaporation Residues (4 PPAC – PPAC)


FIESTAServizio Elettronica

1. Sviluppo di un TAC (4/8/16) con START/STOPindividuali e risoluzione di ~50 ps

2. 2 mesi-uomo per supporto turni e riparazione moduli

Servizio Officina Meccanica

1 mese-uomo per modifiche di alcune parti del supporto della BALL+ manutenzione della meccanica e vuoto



86Kr + 208PbHENDES Setup, Accelerator Facility, Jyvaskyla, Finland

n and lcp measured in coincidence with two-fragment channel

While in fusion-fission reactions the M-TKE distributions are not informative about the dynamics, in quasi-fission the mass drift toward symmetry is a sensitive probe of dissipative forces


Effetti dell’isospin sulla ρ

Z

1010

40 60 80 100St

ate

Den

sity

(MeV

-1)

Form AForm B

108

106

104

102

100

A = 100

A = 140

A = 200

A = 240

Aa α=A)

])ZZ(exp[/Aa 20−γα=B)

4541 Ua)aU2exp(

12)U( π=ρ

Al-Quraishi et al., Phys. Rev. C63,065803


Isospin effects on nuclei produced with stable beams @ Ex~100 MeV

32S + 107Ag 139Eu (Ex=90, 128 MeV)

Mn Mp Mα

Elab(MeV) 180 230 180 230 180 230

Standard 2.37 3.70 1.93 2.60 0.57 0.95

N-Z 2.29 3.56 1.82 2.61 0.69 1.08

Z-Zo 1.92 2.96 1.23 1.76 1.29 1.91

Lilita_N97 calculations, FGLD and FSTC Z-Zo=4.5


1

10

100

1000

0 10 20 30 40 50

Eα,cm(MeV)

Cou

nts

StandardZ-Zo

Lilita_N97 Calculations

230 MeV 32S + 107Ag

alpha

1

10

100

1000

0 10 20 30 40

Ep,cm(MeV)

Cou

nts Standard

Z-Zo

Lilita_N97 Calculations

230 MeV 32S + 107Ag

protoni


32S + 107Ag 139Eu (Ex=90 MeV)

Mo lteplic ità alfa in piano

0.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

3.00E-04

3.50E-04

4.00E-04

6.1

11.1

16 21 56.8

73.8

98.2

115

133

151

201

237

278

295

331

336

341

346

te ta_cor

Mol

tepl

icità

diff

eren

zial

e

a lfa_exp_down_a llrun

S tand08_M=0.54

S tand10_M=0.61

Z-Zo_0.4_M=0.79


Al Quraishi a=αΑ/exp[γ(Ζ−Ζ0)], α=0.1138 (1/8.8), γ=0.0493 Dall’analisi dello S+Ag a=αΑ/exp[γ(Ζ−Ζ0)], α=0.125 (1/8), γ=0.0197( γAl.4

Per il sistema 32S+112Sn a Elab=200 MeV Ex=96 MeV (144Dy) σfus=938 mb, σer=440 mb

Densità dei livelli Mp Mn Mα

Standard (A/8) 3.03 2.22 0.66

Ζ−Ζ0 2.5 2.0 1.07


Piano Finanziario 2005-2007

192123451054.8Tot652834722.6NA

115808121.2LNL12153211.0FI

Inv. (k€)Cons.(k€)ME (k€)MI (k€)FTESez.

Totale delle richieste: 465 (k€)


Thanks !!

Documents

P. Blasi 20 M. Cinausero 20 A. Brondi 50 N. Gelli 60 E ... · CSNIII, 14 Settembre 2004 1 FI.E.S.T.A. 2005-2007 FIssion of Excited Systems at Tandem-Alpi FTE 1.0 1.2 2.6 V. Rizzi