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1.
Entrance channel potentials in nucleus-nucleus collisions, relevant for the synthesis of superheavy elements, are systematically
studied within a semi-microscopic approach, where microscopic nuclear densities of the colliding spherical or deformed nuclei
are used in semi-classical expressions of the energy-density functional. From experimental data on fusion windows evidence
is found that the existence of pockets in the entrance channel potentials is crucial for fusion. Criteria for the choice of
the best collision systems for the synthesis of superheavy elements are discussed.
Received: 14 May 2002 / Accepted: 6 June 2002 / Published online: 26 November 2002
RID="a"
ID="a"e-mail: v.denisov@gsi.de, denisov@kinr.kiev.ua
RID="b"
ID="b"e-mail: w.nrnbrg@gsi.de
Communicated by P. Schuck 相似文献
2.
Chen Gang Li Di-Kai Liu Lian-Shou 《The European Physical Journal A - Hadrons and Nuclei》2008,37(2):227-232
Various nuclear reactions like quasi-fission, fusion-fission or particle and cluster evaporation from excited compound nuclei
were studied in heavy-ion reactions at the velocity filter SHIP of GSI. The velocity filter offers the possibility to detect
all reaction products under zero degree relative to the beam direction. Together with the measurement of the product velocity
distribution this allows for an identification of the underlying reaction mechanism. This article is focussed on reactions
of 25Mg and 64Ni beams on 206, 207Pb targets at energies of 5.9×AMeV and 8.7×AMeV . Besides evaporation residues from 25Mg + 206Pb collisions we found evidence for rotation and quasi-fission of nuclear molecules formed in the entrance channel after the
capture stage. The break-up of the systems showed a preferred clustering leading to isotopes in the region 84 ⩽ Z ⩽ 88 and 122 ⩽ N ⩽ 127 of the chart of nuclei. 相似文献
3.
R. Vlastou C. T. Papadopoulos C. Tsabaris P. A. Assimakopoulos A. A. Pakou G. Doukellis C. A. Kalfas A. C. Xenoulis 《The European Physical Journal A - Hadrons and Nuclei》2000,8(3):361-371
The 7Li + 11B reaction has been investigated in the energy range 5.5 MeV < E
lab < 19MeV, by detecting γ-ray resulting from the de-excitation of evaporation residues. Statistical compound-nucleus calculations
have been performed in order to extract both the cross-sections of individual exit channels and the fusion cross-section of
the system. The total angular momentum that the compoundn ucleus 18O can support has been deduced and is seen to exhibit saturation for a limiting value of 8.5ħ at the high-energy extreme. The results are discussed in terms of the entrance channel and statistical yrast line limitations. 相似文献
4.
G Giardina P D’Agostino G Fazio M Herman AI Muninov A Nasirov G Oliva R Palamara R Ruggeri 《Pramana》1999,53(3):409-418
The fusion-fission reaction mechanism leading to the massive nucleus formation is studied. We investigate the superheavy nucleus
formation in heavy-ion induced reactions by analysing the evaporation residue (ER) production in order to study the fusion
dynamics and the decay properties of nuclei close to the stability island at Z=114. We consider the 61Ni+208Pb, 48Ca+238U and 48Ca+244Pu reactions that lead to the Z=110, 112 and 114 superheavy elements respectively.
By using the dinuclear system (DNS) concept of the two interacting nuclei we calculate the quasifission-fusion competition
in the entrance channel and the fission-evaporation competition along the de-excitation cascade of the compound nucleus. The
dynamics of the entrance channel allows us to determine the beam energy window which is favorable to the fusion, while the
dynamic evolution of the compound nucleus on the shell correction to the fission barrier and the dissipative effects influence
the fission-evaporation competition in order to obtain the residue nuclei from the superheavy nucleus formation. We also calculate
the τ
n
/τtot ratio at each step of the de-excitation cascade of the compound nucleus and we present a systematics of τ
n
/τtot (at first step of the cascade) for many reactions that lead to nuclei with Z=102–114. 相似文献
5.
R.V. Jolos A.I. Muminov A.K. Nasirov 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):245-250
The role of the entrance channel in the fusion-fission reactions leading to nearly the same superheavy compound nucleus is
studied in the framework of dynamic model. The calculations are done for 48Ca +244Pu and 74,76Ge +208Pb reactions which could lead to formation of superheavy element Z = 114. It is shown that for these reactions there is an
energy window for the values of the bombarding energy at which a capture probability is sufficiently large. Together with
the restriction coming from the intrinsic barrier for fusion, it helps to find an optimal value of the bombarding energy for
a given projectile--target combination.
Received: 15 July 1998 相似文献
6.
7.
S. Hofmann 《Progress in Particle and Nuclear Physics》2009,62(2):337-343
8.
Relative cross sections for residual nuclei following fusion reactions were measured by γ-ray spectroscopy in the reactions 52Cr+ 12C at 56.00 MeV and 48Ti+ 16O at 57.74 MeV, in which the common “compound nucleus” 64Zn was excited at the same energies and the relative distributions of the entrance spins were nearly identical. It is shown that ratios of the measured cross sections in both entrance channels can be precisely determined experimentally and are insensitive to small changes of the parameters in calculations based on the evaporation model. Using these particular quantities, we have shown that the evaporation process is not the sole mechanism producing the observed residues, especially those resulting from α-particle emission. The assumption of preequilibrium α-particle emission at high channel spins is shown to reproduce the present data fairly well. 相似文献
9.
F. P. Heßberger 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):33-37
Isotopes of elements up to Z = 113 have been synthesized
using medium heavy projectiles and target nuclei around doubly
magic 208Pb. Synthesis of still heavier elements in reactions
of 48Ca projectiles with actinide target nuclei has been
reported. To obtain more information about production mechanism of
transfermium isotopes nuclear reaction studies including
investigations of massive transfer were resumed at SHIP, GSI.
Nuclear structure investigations at SHIP have been concentrated so
far mainly on systematic investigations of low lying Nilsson
levels in odd-mass nuclei. Recently this field has been extended
to decay studies of isomeric states in nobelium nuclei at E* > 1 MeV. 相似文献
10.
Yu. E. Penionzhkevich R. A. Astabatyan N. A. Demekhina G. G. Gulbekian R. Kalpakchieva A. A. Kulko S. M. Lukyanov E. R. Markaryan V. A. Maslov Yu. A. Muzychka Yu. Ts. Oganessian R. V. Revenko N. K. Skobelev Yu. G. Sobolev D.A.Testov T. Zholdybaev 《The European Physical Journal A - Hadrons and Nuclei》2007,31(2):185-194
Excitation functions for evaporation residues in the reactions 197Au(6He, xn)203-xnTl, x = 2-7, and 206Pb(6He, 2n)210Po, as well as for neutron transfer reactions for the production of 196Au and 198Au in the interaction of 6He with 197Au were measured. The 6He beam was obtained from the accelerator complex for radioactive beams DRIBs (JINR). The maximum energy of the beam was about
10AMeV and the intensity reached 2×107pps. The stacked-foil activation technique was used directly in the beam extracted from the cyclotron or in the focal plane
of the magnetic spectrometer MSP-144. The identification of the reaction products was done by their radioactive γ- or α-decay.
The fusion reaction with the evaporation of two neutrons was characterized by an increase in the cross-section compared to
statistical model calculations. The analysis of the data in the framework of the statistical model for the decay of excited
nuclei, which took into account the sequential fusion of 6He has shown good agreement between the experimental and the calculated values of the cross-sections in the case of sub-Coulomb-barrier
fusion in the 206Pb + 6He reaction. An unusually large cross-section was observed below the Coulomb barrier for the production of 198Au in the interaction of 6He with 197Au. Possible mechanisms of formation and decay of transfer reaction products are discussed. 相似文献
11.
C. Signorini Z.H. Liu Z.C. Li K.E.G. Löbner L. Müller M. Ruan K. Rudolph F. Soramel C. Zotti A. Andrighetto L. Stroe A. Vitturi H.Q. Zhang 《The European Physical Journal A - Hadrons and Nuclei》1999,5(1):7-11
The 9Be +209Bi fusion cross sections were measured in the 36.0 MeV ≤ Elab≤ 50.0 MeV range, down to 0.6 mb, with high accuracy via in-beam detection of the ground state α-decay of the evaporation
residues produced. The elastic scattering cross sections around 150° and 135° were also obtained with moderate angular resolution.
The cross sections below the barrier are reproduced by coupled channel calculations which include only one break-up channel
with a moderate strength and a phenomenological renormalization of the potential depth. These simple calculations overestimate
the cross sections above the barrier most likely due to the fact that the 9Be break-up process becomes much stronger. The barrier distributions extracted do not have evident break-up signature since
they show one-barrier structure.
Received: 22 February 1999 / Revised version: 26 March 1999 相似文献
12.
The Coulomb potential between spherical-deformed and deformed-deformed nuclei has been calculated using the Monte Carlo simulation.
The results obtained for the Coulomb potential in the
16O$ + $238U
and
27Al$ + $70Ge
reactions are in good agreement with those obtained using the double-folding method. The simulation technique employed here
has the ability of calculating the Coulomb potential taking into account the finite diffuseness parameter, all the possible
deformation degrees of freedom, and different orientations of the symmetry axes of the target and the projectile nuclei with
respect to each other. The accuracy of this simulation technique is high and the computer time taken to do these calculations
is much less than those of the double-folding method. 相似文献
13.
R. Arora R. K. Puri R. K. Gupta 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):103-114
We analyse the fusion cross-sections, calculated by using two different analytical parameterisations and compare them with
the experimental data. Both the parameterisations are based on ion-ion potentials calculated within the framework of Skyrme
energy density formalism. In the first case, the ion-ion potential (including the spin-density term) was parameterised and
then, by adding the Coulomb potential, one could compute the fusion barrier analytically. In the second case, the calculated
fusion barrier heights and positions were parameterised directly. Both of these (previously) reported parameterisations are
used here to calculate the fusion barriers and fusion excitation functions for more than 50 reactions belonging to the s-d and f-shell nuclei. A detailed comparison of these parametrisations with the experimental and several other theoretical results
shows that both of these parameterisations are able to reproduce the experimental data equally well. As the (second) direct
parameterisation depends only on the charges and masses of colliding nuclei, it is very useful for predicting/ understanding
the fusion process in low energy heavy-ion reactions.
Received: 24 February 1999 / Accepted: 16 March 2000 相似文献
14.
A. S. Zubov G. G. Adamian N. V. Antonenko S. P. Ivanova W. Scheid 《The European Physical Journal A - Hadrons and Nuclei》2007,33(2):223-230
Using the statistical approach, we study the isotopic dependence of the de-excitation of dinuclear systems formed in the entrance
channel of heavy-ion reactions. The probabilities of neutron emission from the dinuclear systems 62-73Ni + 208Pb are estimated and a possible experiment for the observation of this emission is discussed. 相似文献
15.
P. Armbruster 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):25-26
Complete fusion reactions (xn-channels) using actinide
targets are observed for values of the effective fissilities x eff ∼
0.80 in the sub-pb range of production cross sections. The elements
produced at this limit are Z = 108–112. Beyond complete fusion, heavier
elements might still be produced by reaction mechanisms releasing part of
the nuclear charge before an equilibrated compound system might have been
reached. Precompound Charged particle
Emission (PCE) is proposed as a possible mechanism following complete
fusion. A scheme delivering isotopes of elements Z = 110–115 is
discussed, and experimental evidence for such a process is presented.
Compound systems, the atomic numbers of which are smaller than in complete
fusion reactions, might be produced in 48Ca induced reactions on
actinides with larger cross sections than those at the limits of complete
fusion. Besides complete fusion, the PCE-mechanism should be considered as
an alternative to interpret the 48Ca-induced reactions on actinides. 相似文献
16.
Isotopic dependence of the fusion dynamics is studied by analyzing the collision of a large number of isotopes of Ca and Ni with 0.6
N/Z
2. This study, which results from the Skyrme energy density formalism, reveals that the addition of neutrons favors fusion of reacting partners, whereas the reverse happens with the removal of neutrons. The fusion barrier heights and positions follow a non-linear second-order dependence on (
-1 ), whereas fusion cross-sections can be parameterized by a straight line.-1 相似文献
17.
C. Signorini Z.H. Liu A. Yoshida T. Fukuda Z.C. Li K.E.G. Löbner L. Müller Y.H. Pu K. Rudolph F. Soramel C. Zotti J.L. Sida 《The European Physical Journal A - Hadrons and Nuclei》1998,2(3):227-231
The 9Be +209Bi fusion cross sections were measured in the range 37.5 MeV ≤ E
lab
≤ 45.0 MeV at the Munich Tandem via the observation of ground state α-decay of the evaporation residues. Fusion cross sections
of 209Bi with the “halo”11Be unstable projectile in the region around the Coulomb barrier were deduced from an experiment done with the same technique
at the RIKEN Ring Cyclotron. Above the Coulomb barrier the 11Be cross sections are larger than the 9Be ones in agreement with theoretical predictions based on the larger 11Be halo radius. Also below the barrier these theories foresee the same behavior in disagreement with the experimental results,
since the two cross sections are rather similar.
Received: 2 April 1998 相似文献
18.
We obtain a closed-form expression for the distribution of fusion barriers for vibrational nuclei using a generalization of
Dasso, Landowne, and Winther's model, which represents the nuclear surface vibrations as a number of harmonic oscillators,
and allows the excitation of an arbitrary number of phonons in the target and/or projectile. We find that this expression
is in reasonable agreement with the average trends of the empirical distributions for the fusion of 16O with 92Zr, 144Sm and 208Pb, but fails to reproduce the double peaking of the distribution for the 144Sm target. Only when we restrict the number of excited phonons to a limited number, we are able to reproduce such discrete
structures. We show that limiting the number of coupled channels, particularly in the case of strong coupling, increases the
spacings between the channel eigenvalues that determine the positions of the peaks of the barrier distribution and modifies
their heights.
Received: 6 March 2000 / Accepted: 31 January 2001 相似文献
19.
W. von Oertzen B. Gebauer G. Efimov V. Zherebchevsky Tz. Kokalova S. Thummerer Ch. Schulz H. G. Bohlen D. Kamanin C. Beck D. Curien P. Papka M. Rousseau G. Royer G. de Angelis 《The European Physical Journal A - Hadrons and Nuclei》2008,36(3):279-288
Coincidences between two heavy fragments have been measured from the fission of 56Ni compound nuclei formed in the 32S + 24Mg reaction at E
lab( ^32S ) = 165.4 MeV. A unique experimental set-up consisting of two large-area position-sensitive (x, y) gas detector telescopes has been used allowing the complete determination of the observed fragments and their momentum vectors.
In addition to binary fission events with subsequent particle evaporation, narrow out-of-plane correlations are observed for
two fragments emitted in purely binary events and in events with a missing charge consisting of 2α - and 3α -particles (12C). These events are interpreted as ternary cluster decay from 56Ni nuclei at high angular momenta through hyper-deformed shapes. 相似文献
20.
Y.X. Watanabe A. Yoshida T. Fukuda T. Sekine Y. Watanabe H. Ikezoe Y. Nagame T. Ikuta I. Nishinaka Y. Mizoi J. Nakano M. Hirai H. Sakurai H. Kobinata Y. Pu K. Kimura M. Ishihara 《The European Physical Journal A - Hadrons and Nuclei》2001,10(4):373-379
A systematic study of the sub-barrier fusion reactions with neutron-rich projectiles has been carried out for three isotopes
27,29,31Al bombarding a 197Au target. A target chamber equipped with a target stack and sets of MWPC was employed in order to enhance the efficiency
of the radioactive beam experiment. Coupled-channel calculations including the quadrupole excitations do not well fit the
measured fusion excitation functions, whereas flat barrier distributions to represent the coupling to the neutron transfer
largely account for the observed enhancement of the sub-barrier fusion cross-sections.
Received: 13 March 2001 / Accepted: 27 April 2001 相似文献