Fusion-Fissions and Quasi-fissions of 32,34S- and 48Ti-induced Fissions

at Near-barrier Energies

H. Q. ZhangChina Institute of Atomic Energy

中国原子能科学研究院China Institute of Atomic Energy

Outline

1. Angular distributions of 32S+184W system

2. Mass-TKE distributions of 34S+186W System

3. Mass distributions of 48Ti-induced reaction systems

4. Summary

1. Angular distributions of 32S+184W systemExperiment was performed at the China Institute of Atomic Energy (CIAE).

Ebeam = 140, 145, 150, 155, 160, 165, and 170 MeV.

Si-Strip

Si(Au)

Experimental setup

Angular distributions, fitted by

To extract c.s., K0

2, <l2>, and Aexp.

To compare with the calculations of di-nuclear system (DNS) model.

To understand the dynamic processes of capture, fusion, fast-fission, quas-ifission, fusion-fission, and evaporation residue.

216Th

Pote

ntial

-ene

rgy

surf

ace

15

45

Orientation dependent driving-potential

DNS model

Results

Exist quasi-fissions to a certain extent.

2. Mass-TKE distributions of 34S+186W systemExperiment was performed at the Japan Atomic Energy Agency (JAEA).

Ebeam = 143, 163, 180 MeV. Forward: Si(Au) – Backward Si-strips

FF = 60.63

BF = -75.39

Angle resolved Mass-TKE

distributions(in 4.2 steps)

More forward, more asymmetric mass distributions

A

E

kk

TsciA

5.812

k = 0.0048 MeV/u

34S+186W

No pronounced quasi-fission.

Conclusion:

1) No pronounced quasi-fission components are observed in the

mass distributions, but

2) Pronounced quasi-fission components are observed in the

angular distributions, and

3) Anisotropies can be explained by pre-equilibrium mode.

Relaxation time of K > relaxation time of mass

3. Mass distributions of 48Ti-induced reaction systemsExperiment was performed at the Australian National University (ANU).

Beam: pulsed 48Ti beam (width: 1.5 ns, interval: 106.7 ns),

E = 206 - 296 MeV ( VB).

Target: 144,154Sm, 162Dy, 174Yb, 186W, 192Os, 196Pt, 200Hg, and 208Pb.

Measured by two MWPPACs (CUBE), covered c.m. = 40 – 140 .

50 mass-angle-distribution spectra were measured.

Mass widths depend on excitation energies

compound saddle-point scission-pointSystematic tendency:

Differences in lighter and heavier, as well as in spherical and deformed targets.

Dependence on reaction energy

Importance of

target deformation &

fissility of composite nucleus.

Dependence on fissility

Minimum proportion of QF:

Dependence on deformation

Mass distributions are broadened by quasi-fissions induced by the tip collisions at low energies for the deformed targets, while such orientation effects vanish at high energies. And this effects can be estimated by an so-called enhancement factor:

where Eref: Ec.m./VB = 1.15.

4. Summary Angular distributions of fission fragments for the 32S+184W system have

been measured at 7 energies. The quasi-fission components are observed and can be explained by the DNS model.

Mass-TKE distributions of fission fragments for the 34S+186W system have been measured at 3 energies. No pronounced quasi-fission components are observed and in agreement with the scission-point statistical calculations.

K pre-equilibrium fission may occur in the S+W systems, which requires the detail Mass-TKE-Angle correlated measurements (MEADs).

Systematic tendencies of mass distributions have been explored for the 48Ti-induced fissions at near-barrier energies. The observed behavior is a complex function of the fissility, deformation, and reaction energy. The quasi-fission induced by the orientation effects may be reduced for the targets with large deformations.

Thanks to all the collaborators:

C. J. Lin, F. Yang, C. L. Zhang, Z. H. Liu, H. M. Jia, X. X. Xu, L. Yang, P. F. Bao,and L. J. SunChina Institute of Atomic Energy, P. O. Box 275 (10),Beijing 102413, China

R. du Rietz, D. J. Hinde, M. Dasgupta, R. G. Thomas, M. L. Brown, M. Evers,L. R. Gasques, and M. D. RodriguezDepartment of Nuclear Physics, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia

H. Ikezoe, K. Nishio, S. Mitsuoka, and K. SatouJapan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan

A. K. NasirovJoint Institute for Nuclear Research, RU-141980, Dubna, Russia

C. Mandaglio, M. Manganaro, and G. Giardina,Dipartimento di Fisica dell’ Universita di Messina, 98166 Messina,and Istituto Nazionale di Fisica Ncleare, Sezione di Catania, Italy

Thank you !

China Institute of Atomic Energy