Puzzling features of heavy-ion fission at sub-barrier energies

Samant, A. M.; Kailas, S.

doi:10.1007/bf02769234

Cited by 5 publications

(6 citation statements)

References 13 publications

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“…Anomalous anisotropies have also been interpreted in terms of target deformation [2] and target spin [3]. It is interesting to consider fission fragment anisotropies as a probe for shell effects.…”

mentioning

confidence: 99%

Shell Effects in Fission Fragment Anisotropies forC12+P194,
Shrivastava
¹
,
Kailas
²
,
Chatterjee
³

et al. 1999
Phys. Rev. Lett.
Self Cite
44
2
31
1
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The fission fragment anisotropies for 12 C 1 198 Pt populating 210 Po are found to be systematically higher than that for 12 C 1 194 Pt, the difference decreasing over the energy range 1.0 # E͞V B # 1.4. The parameters required for a statistical model analysis of the data were constrained by fission cross section data and by measuring evaporation residue cross sections. While the measured anisotropies for 12 C 1 194 Pt are in agreement with the saddle point model calculations, those for 12 C 1 198 Pt are considerably larger. The data are suggestive of a significant shell effect in the anisotropies of fission fragments emitted from 210 Po with neutron magic number, N 126. [S0031-9007(98)08289-1] PACS numbers: 25.70.JjShell effects play a central role in determining the stability of nuclei and the nuclear structure. It is generally believed that shell effects are washed out at high excitation energies and angular momenta produced in medium energy heavy ion reactions. It is of interest to investigate an energy region where shell effects are still visible and observe the gradual decrease of the effect with increasing excitation energy. This information is important in the context of production and stability of super heavy elements.In recent years, the unexpected deviation of some fission fragment angular anisotropies from the transition state model has been taken to imply noncompound reaction mechanisms [1]. Anomalous anisotropies have also been interpreted in terms of target deformation [2] and target spin [3]. It is interesting to consider fission fragment anisotropies as a probe for shell effects. We have made anisotropy measurements for 12 C 1 194,198 Pt. This allows a comparison of the fragment anisotropies for 210 Po (with N 126) to be made with that for 206 Po (with N 122). In the limited number of such measurements in the literature for this mass region, no significant isotopic dependence was observed for 12 C 1 182,183,184,186 W [4] and 6 Li 1 194,198 Pt [5].Statistical model calculations which take into account differences in angular momenta, fusion cross sections, fissility values, prefission neutrons and shell corrections to the level densities between the two systems have been made. The statistical model parameters have been constrained by making measurements of partial evaporation residue (ER) cross sections in addition to fission cross sections and also comparing the calculations with the earlier measurements [6-9] for 210,206 Po compound nuclei. Since shell corrections in the level densities are included in the calculation, comparison with the measured anisotropies for 206,210 Po could reveal the effects of the underlying shell structure on other nuclear properties such as the deformation at the fission saddle point.The measurements were carried out using 12 C beams from the BARC-TIFR 14UD Pelletron accelerator at Bombay in the energy range from 59 to 85 MeV. The targets were self supporting rolled foils of 194 Pt (97.4% enriched, 1 mg͞cm 2 thick) and 198 Pt (95.7% enriched, 1.3 mg͞cm 2 thick). The e...

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mentioning

confidence: 99%

Shell Effects in Fission Fragment Anisotropies forC12+P194,
Shrivastava
¹
,
Kailas
²
,
Chatterjee
³

et al. 1999
Phys. Rev. Lett.
Self Cite
44
2
31
1
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“…It was observed that the fission anisotropies for essentially all target-projectile combinations involving an actinide target do not decrease when energy is lowered (up to 10% below barrier) in the sub-barrier region [18,[24][25][26]. Several plausible explanations have been suggested to understand this feature [24].…”

Section: Fission Data Formentioning

confidence: 95%

Heavy-ion induced fission reactions at near-barrier energies — what have we learnt?

Kailas

1999

Pramana - J Phys

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Systematic studies of heavy-ion induced fission reactions at near-barrier energies carried out in the last decade have brought out many interesting aspects of fission process in general. The recent experimental findings which show dependence of fission fragment angular distributions on entrance channel, shape, size and spin of the interacting nuclei and shell closure of the intermediate compound nucleus are summarised in the present paper.

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“…While the deformed actinide targets exhibit 'anomalous' values of anisotropies, irrespective of the entrance channel mass asymmetry, the A for the spherical Pb and Bi targets (figure 3) are nearly normal . Several plausible explanations [2] have been advanced by various groups for the description of these puzzling features.…”

Section: Fission Data For E/v B <1mentioning

confidence: 99%

“…However, for spherical targets like Pb and Bi, the anisotropies measured for different projectiles exhibit normal values of anisotropies from below to above the fusion barrier. Several plausible reasons have been proposed to describe the puzzling features observed at subbarrier energies [1,2].…”

Section: Introductionmentioning

confidence: 99%

Heavy-ion induced fission fragment angular distributions at near-barrier energies

Kailas¹

1997

J. Phys. G: Nucl. Part. Phys.

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Heavy-ion induced fission fragment angular distribution measurements performed in recent years have provided interesting results. From a systematic study involving several projectiles and actinide targets, the entrance channel mass asymmetry dependence of fission anisotropies has been brought out at energies above the fusion barrier. It has been observed that the fission fragment anisotropies, essentially for all target - projectile combinations involving actinide targets increase as bombarding energy is lowered below the barrier and are anomalously large when compared to the saddle-point model expectations. However, similar measurements carried out for spherical targets are consistent with the calculations based on the saddle-point model.

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Puzzling features of heavy-ion fission at sub-barrier energies

Cited by 5 publications

References 13 publications

Shell Effects in Fission Fragment Anisotropies forC12+P194,
Shrivastava
¹
,
Kailas
²
,
Chatterjee
³

et al. 1999
Phys. Rev. Lett.
Self Cite
44
2
31
1
View full text Add to dashboard Cite

Shell Effects in Fission Fragment Anisotropies forC12+P194,
Shrivastava
¹
,
Kailas
²
,
Chatterjee
³

et al. 1999
Phys. Rev. Lett.
Self Cite
44
2
31
1
View full text Add to dashboard Cite

Heavy-ion induced fission reactions at near-barrier energies — what have we learnt?

Heavy-ion induced fission fragment angular distributions at near-barrier energies

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Puzzling features of heavy-ion fission at sub-barrier energies

Cited by 5 publications

References 13 publications

Shell Effects in Fission Fragment Anisotropies forC12+P194,Shrivastava1, Kailas2, Chatterjee3 et al. 1999Phys. Rev. Lett.Self Cite442311View full textAdd to dashboardCite

Shell Effects in Fission Fragment Anisotropies forC12+P194,Shrivastava1, Kailas2, Chatterjee3 et al. 1999Phys. Rev. Lett.Self Cite442311View full textAdd to dashboardCite

Heavy-ion induced fission reactions at near-barrier energies — what have we learnt?

Heavy-ion induced fission fragment angular distributions at near-barrier energies

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Product

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About

Shell Effects in Fission Fragment Anisotropies forC12+P194,
Shrivastava
¹
,
Kailas
²
,
Chatterjee
³

et al. 1999
Phys. Rev. Lett.
Self Cite
44
2
31
1
View full text Add to dashboard Cite

Shell Effects in Fission Fragment Anisotropies forC12+P194,
Shrivastava
¹
,
Kailas
²
,
Chatterjee
³

et al. 1999
Phys. Rev. Lett.
Self Cite
44
2
31
1
View full text Add to dashboard Cite