Inadequacy of the statistical model: Some evidence for compound nuclei in the A $ \approx$ 150 and Ex $ \approx$ 100-200 MeV region

Vardaci, E.; Nitto, A. Di; Brondi, A.; Rana, G. La; Moro, R.; Nadotchy, P.N.; Trotta, M.; Ordine, A.; Boiano, A.; Cinausero, M.; Fioretto, E.; Prete, G.; Rizzi, V.; Shetty, D. V.; Barbui, M.; Fabris, D.; Lunardon, M.; Montagnoli, G.; Moretto, S.; Viesti, G.; Gelli, N.; Lucarelli, F.; Knyazheva, G. N.; Козулин, Э. М.

doi:10.1140/epja/i2009-10912-5

Cited by 29 publications

(38 citation statements)

References 22 publications

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“…A short presentation of the data analysis and conclusions has already been published as a letter [14]. Here we discuss in detail the experimental methods for the extraction of the various observables that we measured in the ER and FF channels, namely proton and alpha particles energy spectra in coincidence with FF and ER, multiplicities, angular distributions, and ER and FF channels cross-sections.…”

Section: Introductionmentioning

confidence: 99%

Evaporation and fission decay of 132Ce compound nuclei at Ex=122 MeV: some limitations of the statistical model

et al. 2011

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Abstract. Light charged particle (LCP) emission in the evaporation residue (ER) and fusion fission (FF) channels have been studied for the 200 MeV32 S+ 100 Mo reaction, leading to 132 Ce composite nuclei at Ex=122 MeV. The main goal was to study the decay of 132 Ce on the basis of an extended set of observables, to get insights on the fission dynamics. The proton and alpha particle energy spectra, their multiplicities, ER-LCP angular correlations, ER and FF angular distributions, and ER and FF crosssections were measured. The measured observables were compared with the Statistical Model (SM). Using standard parameters, the model was able to reproduce only the pre-scission multiplicities and the FF and ER cross-sections. The calculation was observed to strongly overestimate the proton and alpha particle multiplicities in the ER channel. Disagreements were also observed for the ER-LCP correlations, the LCP energy spectra and the ER angular distribution. By varying the SM input parameters over a wide range of values, it is shown that it is not possible to reproduce all the observables simultaneously with a unique set of parameters. The inadequacy of the model in reproducing the ER particle multiplicities is also observed analysing data from the literature for other systems in the A ≈ 150 and E x ≈ 100-200 MeV region. These results indicate serious limitations about the use of the SM in extracting information on fission dynamics.

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Section: Introductionmentioning

confidence: 99%

Evaporation and fission decay of 132Ce compound nuclei at Ex=122 MeV: some limitations of the statistical model

et al. 2011

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“…This may be justified by the fact that the maximum value of the spin is otherwise much larger than the critical value, I c , corresponding to B f = 0. This is not the case for 32 S bombardment and the discrepancy between measured and calculated cross sections must for this case be found elsewhere, perhaps in the competition from emission of light, charged particles [29][30][31]. The omission of these channels in the simulations is a deficiency but it appears difficult to include them in a consistent manner [30,31].…”

Section: Statistical Simulations Of Fissionmentioning

confidence: 98%

“…The fill-in of the blocking-dip minimum is due to fission after emission of several neutrons (here two to four). For simplicity, we ignore emission of light, charged particles 044609-6 (protons and α particles), although it is known that this can be a significant channel for the fused nuclei [29][30][31]. Our aim is mainly to investigate whether the blocking results are consistent with the standard picture of multichance fission and a very broad lifetime distribution.…”

Section: Statistical Simulations Of Fissionmentioning

confidence: 99%

Time delays in heavy-ion-induced fission of medium-Znuclei, measured by crystal blocking

et al. 2012

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Time delays in fission induced by bombardment of Mo with 170-and 180-MeV 32 S, 225-and 240-MeV 48 Ti, and 300-MeV 58 Ni have been measured by observation of crystal blocking of fission fragments. In contrast to earlier measurements with a W target, the results are consistent with fission of a compound nucleus in competition with mainly neutron emission. Most of the fissions happen on a time scale much shorter than attoseconds but there is a significant component of fission with much longer lifetimes. The measurements are reproduced with a standard statistical model, including a Kramers correction to fission widths from the viscosity of hot nuclear matter. These new results support the interpretation of our earlier measurements with a W target, which indicate that there is a transition in heavy-ion-induced fission at large atomic number and mass, from multichance fission in the standard Bohr-Wheeler picture to fission without formation of a compound nucleus. The process is slowed down by nuclear viscosity, with measured delays of order attoseconds.

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“…In a first step, this whole set of data was analyzed in the frame of the SM [22][23][24][25][26] and it was concluded that although the SM is able to reproduce the observables related to the fission channel alone without delay, it overestimates the multiplicities of the protons and alpha particles in the ER channel. The only way found to reproduce the whole set of data is through the use of a dynamical model in which the fission process, along with the evaporation of light particles in the fission and ER paths, is treated with a 3D-Langevin approach coupled to the SM [25].…”

Section: Dissipation In Systems Of Intermediate Fissilitymentioning

confidence: 99%

Fission Dynamics: The Quest of a Temperature Dependent Nuclear Viscosity

Vardaci

Nitto

Nadtochy

et al. 2013

JNP

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Abstract. This contribution presents a journey within the open questions about the current use of a temperature dependent nuclear viscosity in models of nuclear fission and proposes an alternative experimental approach by using systems of intermediate fissility. This study is particularly relevant because: i) systems of intermediate fissility offer a suitable framework since the intervals between the compound nucleus and scission point temperatures with increasing excitation energy are much smaller than in the case of heavier systems, ii) the measurement of observables in the ER channel translates into a larger set of effective constraints for the models.

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Inadequacy of the statistical model: Some evidence for compound nuclei in the A $ \approx$ 150 and Ex $ \approx$ 100-200 MeV region

Cited by 29 publications

References 22 publications

Evaporation and fission decay of 132Ce compound nuclei at Ex=122 MeV: some limitations of the statistical model

Evaporation and fission decay of 132Ce compound nuclei at Ex=122 MeV: some limitations of the statistical model

Time delays in heavy-ion-induced fission of medium-Znuclei, measured by crystal blocking

Fission Dynamics: The Quest of a Temperature Dependent Nuclear Viscosity

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