Dynamical fission in Sn induced reactions at 35 A.MeV CHIMERA-ISOSPIN Collaboration(*)

(*) presented by Paolo Russotto INFN CT-LNS

XII Nuclear Physics Workshop Marie and Pierre Curie Nuclear Structure and Low Energy Reactions

September 21-25, 2005 Kazimierz Dolny, Poland

Analysed systems

124Sn+64Ni at 35 A.Mev neutron rich

112Sn+58Ni at 35 A.Mev neutron poor

Phenomenon

Fission of projectile like fragments (PLF) in peripheral and semi-peripheral reaction

Competition

Statistical “slow” equilibrated fission

Vs

“Dynamical” “fast” non-equilibrated fission

E.De Filippo et al., Phys. Rev. C 71, 064604 (2005)

100Mo + 100Mo at 19 A.MeV

A.A. Stefanini et al.,

Z. Phys. A351 (1995) 167

1m

1°

30°

176°

•good angular resolution

•identification in mass and/or charge of the detected particles

•low detection threshold and high dynamical range in energy

•direct velocity measurement (TOF)

The CHIMERA detector

TARGET

Beam

REVERSE

Forward part

1°

30°

REVERSE Experiment: 688 Telescopes, forward part. (2000-2002)

2003/2004- CHIMERA-ISOSPIN 1192 telescopes

Si

CsI(Tl)p

t

d

4He6He

3He

LiH.I.

E-TOF E-TOF M,E E-E E-E Z,E

PSD LCP

NOTE:Z2F=37-57 Zproj log scaleAH/AL Mass asymmetries

2 < multiplicity < 7 (peripheral reactions) Data Analysis focused on two heaviest fragmentsE

2F =

kin

etic

en

ergy

of

the

two

frag

men

ts

Cen

tral

ity

of c

olli

sion

Coulomb ring < Vbeam = 8 cm/ns

Well defined PLF source: sequential scattering of PLF followed by its splitting into 2 fragments.

The lighter fragments are emitted

preferentially backwards in the PLF reference system, i.e.,

towards the target nucleus:

Dynamical Fission

Angular distribution are not forward/backward symmetric.

fast process Time interval between the two steps

much shorter than PLF rotational time

In the neutron rich system the Dynamical effects are

stronger than in the neutron poor system

In-plane () and out-of-plane () angles definition [A.A. Stefanini et al., Z.Phys. A 351(1995)167]]

Note:VLpar>4 cm/ns

Time estimation

Time interval between collision and PLF splitting: 100-300 fm/c

Asymmetric cases (outside Coulomb ring) shortest time scale: 40-120 fm/c

E.De Filippo et al., Phys. Rev. C 71, 064604 (2005)

E.De Filippo et al., Phys. Rev. C 71, 044602 (2005)

V.Baran et al., Nucl. Phys. A730, 329 (2004)

Difference: ??? no models nor simulations capable of describing

Dynamical fission

DYN/TOT [%]

-180 -135 -90 -45 0 45 90 135 1800

500

1000

1500

2000

2500

3000

Equilibrated

Dynamical

124Sn+64Ni E2F

=2700-3060 MeV AH/AL=1.6-2.6Y

ield

plane

(deg)

Conclusion

Analysed system 124Sn+64Ni at 35 A.Mev

112Sn+58Ni at 35 A.Mev

•Peripheral and semi-peripheral reactions are basically binary:PLF+TLF

•We have analysed the sequential splitting of PLF in two fragments of comparable masses

•In 20-80% of cases we have observed a fast non-equilibrated dynamical fission of PLF (100<t<300 fm/c): this process is one or two order of magnitude faster than equilibrated fission

•In the neutron rich system the Dynamical effects are stronger (+1030%) than in the neutron poor system

•We are not able to explain the reason of this difference because we have no models nor simulations capable of describing Dynamical fission

•Further analysis and theoretical model are required!!

COLLABORAZIONE ISOSPINCOLLABORAZIONE ISOSPINE. De Filippob, A. Paganob, E. Piaseckic, F. Amorinia, A. Anzalonea, L. Auditored, V. Barana, I. Berceanue, J.

Blicharskaf, J. Brzychczykg, A. Bonaseraa, B. Borderieh, R. Bougaulti, M. Brunoj, G. Cardellab, S. Cavallaroa, M.B. Chatterjeek, A. Chbihil, M. Colonnaa, M. D'Agostinoj, R. Dayrasm, M. Di Toroa, J. Franklandl, E.

Galicheth, W. Gawlikowiczg, E. Geracij, F. Giustolisia, A. Grzeszczukf, P. Guazzonin, D. Guineto, M. Iacono-Mannoa, S. Kowalskif, E. La Guidaraa, G. Lanzanob, G. Lanzalonea, N. Le Neindreh, S. Lip, S. Lo Nigroa, C. Maiolinoa, Z. Majkag, M. Papab, M. Petrovicie, S. Pirroneb, R. Planetag, G. Politib, A. Pope, F. Portoa, M.F.

Riveth, E. Rosatoq, F. Rizzoa, S. Russon, P.Russottoa M. Sassin, K. Schmidte, K. Siwek-Wilczynskac, I. Skwirac, M.L. Sperdutoa, J. C. Steckmeyeri, L. Swiderskic, A. Trifiròd, M. Trimarchid, G. Vanninij, M. Vigilanteq, J.P.

Wieleczkol, J. Wilczynskir, H. Wup, Z. Xiaop, L. Zettan, and W. Zipperf

a) INFN, Laboratori Nazionali del Sud and Dipartimento di Fisica e Astronomia, Università di Catania, Italyb) INFN, Sezione di Catania and Dipartimento di Fisica e Astronomia, Università di Catania, Italy c) Institute of Experimental Physics, Warsaw University, Warsaw, Polandd) INFN, Gruppo Collegato di Messina and Dipartimento di Fisica, Università di Messina, Italy e) Institute for Physics and Nuclear Engineering, Bucharest, Romaniaf) Institute of Physics, University of Silesia, Katowice, Polandg) M. Smoluchowski Institute of Physics, Jagellonian University, Cracow, Polandh) Institute de Physique Nucléaire, IN2P3 and Université Paris-Sud, Orsay, Francei) LPC, Ensi Caen and Université de Caen, Francej) INFN, Sezione di Bologna and Dipartimento di Fisica, Università di Bologna, Italyk) Saha Institute Of Nuclear Physics, Kolkata, Indial) GANIL, CEA, IN2P3, Caen, Francem) DAPNIA/SPhn, CEA-Saclay,Francen) INFN, Sezione di Milano and Dipartimento di Fisica, Università di Milano, Italyo) IPN, IN2P3-CNRS and Université Claude Bernard, Lyon, Francep) Institute of Modern Physics, Lanzhou, Chinaq) INFN, Sezione di Napoli and Dipartimento di Fisica, Università di Napoli, Italyr) A. Soltan Institute for Nuclear Studies, Swierk/Warsaw, Poland

Relative velocities between two fragments normalized to velocity resulting from Coulomb repulsionViola Systematics [D.J. Hinde et al., Nucl. Phys. A472, 318 (1987)]

The velocity field of various parts of the PLF did not attain

equilibrium as in statistical fission

<Vratio> larger then 1 (+20%) in plane dynamical region

Note:VLpar>4 cm/ns

out=90°

in-plane emission

Exponentially decreasing distribution: dynamical

Flat distribution: statistical

NOTE: TLF’s fragments have been cut off; VLpar >4cm/ns.

Dyn: -30°< plane <45°

Eq: -130°<plane<-90° and -90°<plane<130°

Dyn: -30° < plane< 45°

Eq: -130° < plane< -90° and -90° <plane <130°

NOTE:

Angular coverage

1°<lab< 30°

log scale

Outside Coulomb ring and largest asymmetries neck emission

[E.De Filippo et al., Phys. Rev. C 71, 044602 (2005)]

VLpar>4 cm/ns and Z2F Zproj

PLF splitting into 2 main fragments

Low velocity and Z2F >Zproj

Target remnants

AH/AL Mass asymmetries

E2F

peripherality

NOTE:in the highest asymmetry ZL> 9

Data Analysis focused on two heaviest fragments

Conditions

2 < multiplicity < 7 (peripheral reactions)

30<ZTOT<80 and Z2F>15

log scale

AH/AL Mass asymmetries

E2F

peripherality

log scale

How to select peripherality in both system to compare them????????

Angular coverage 1°<lab< 30° no Energy Transverse lcp,

no Total Kinetic Energy Loss (TKEL)

E2F TKEL and centrality of the collision

The global variables show

a similar behaviour for both system

Selection of same percentage of events in the E2F distribution

Example:velocity of the source of the two heaviest fragments

DYN/TOT [%]

(124Sn+64Ni) – (112Sn+58Ni)

2.6-4.6 1.6-2.6 1.0-1.62700-3060 7% 17% 6%3060-3450 15% 26% 6%3450-4000 19% 22% 11%

(124Sn+64Ni)-(112Sn+58Ni)DYN/(DIN+EQ)

AH/AL.

E2F(MeV)

2.6-4.6 1.6-2.6 1.0-1.6

2700-3060 83% 71% 37%

3060-3450 78% 57% 26%

3450-4000 71% 53% 42%

AH/AL.

E2F(MeV)

DYN/(DIN+EQ)124Sn+64Ni

2.6-4.6 1.6-2.6 1.0-1.62650-3000 76% 53% 31%3000-3360 63% 31% 20%3360-4000 52% 31% 30%

DYN/(DIN+EQ)AH/AL.

E2F(MeV)

112Sn+58Ni