共查询到20条相似文献,搜索用时 656 毫秒
1.
D.J. Hinde A.C. Berriman R.D. Butt M. Dasgupta C.R. Morton A. Mukherjee J.O. Newton 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):149-154
In the fusion of heavy nuclei, there is a distribution of fusion barrier energies resulting from coupling between intrinsic
motion and internal degrees of freedom. Precise experimental measurements of excitation functions have allowed the extraction
of the distributions by taking the second derivative using a point-difference method. In the case of statically deformed nuclei,
experimental data shows that the different fusion barrier energies correspond to different physical configurations of the
colliding nuclei, the latter affecting the subsequent dynamical trajectories over the potential energy surface, influencing
the ultimate reaction products, as for example in quasi-fission. The fusion barrier distribution is also valuable in understanding
the fusion of weakly bound nuclei, enabling a reliable prediction of the expected fusion cross-sections, and thus the determination
of fusion suppression factors at above-barrier energies.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
2.
3.
Rajeev K. Puri Manoj K. Sharma Raj K. Gupta 《The European Physical Journal A - Hadrons and Nuclei》1998,3(3):277-280
A systematic study of isotopic dependence of fusion cross-section is carried out by adding neutrons gradually to N=Z colliding
nuclei. We find that fusion barrier position increases and height decreases, both linearly with the increase of N/Z ratio
of the compound system. The increase in barrier position is larger compared to decrease in barrier height. In terms of these
linear relationships, a parameterized form of fusion cross-sections is given for the neutron-rich colliding nuclei. The fusion
cross-sections are also enhanced linearly with the N/Z ratio, and this enhancement is larger for lower incident centre-of-mass
energies and independent of the choice of reaction partners. Experimental data and other theoretical studies are called for
to verify these results.
Received: 27 February 1998 / Revised version: 22 May 1998 相似文献
4.
S. Mukherjee A. Sharma S. Sodaye B.S. Tomar A. Goswami S.B. Manohar 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):199-205
Incomplete fusion reactions were investigated by measuring the excitation functions of nine evaporation residues in 16O + 51V reaction in the beam energy 4-6 MeV/amu, using the well-known recoil catcher technique and gamma-ray spectrometry. The experimental
data were compared with that obtained from Monte Carlo simulation calculations using the PACE2 code. The results indicate
the presence of incomplete fusion process in the production of two alpha emission products. This was further confirmed by
the measurement of recoil range distribution of these isotopes at 96 MeV beam energy. Calculations of the average angular
momentum associated with these products revealed the peripheral nature of these ICF reactions.
Received: 20 June 2001 / Accepted: 11 September 2001 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.
G. Montagnoli S. Beghini F. Scarlassara A.M. Stefanini L. Corradi C.J. Lin G. Pollarolo Aage Winther 《The European Physical Journal A - Hadrons and Nuclei》2002,15(3):351-356
The two systems 40Ca + 90,96Zr have been studied by measuring nucleon transfer reactions at two energies near the Coulomb barrier, thus complementing
the available sub-barrier fusion cross-sections. Angular distributions for various transfer channels have been determined.
Significantly larger neutron transfer cross-sections are found for the target 96Zr that exhibits the larger enhancement in the sub-barrier fusion cross-sections. All data have been analyzed with a new model
for heavy-ion collisions that calculates simultaneously transfer cross-sections, fusion excitation functions and barrier distributions.
The model gives a good account of both transfer and fusion data.
Received: 2 May 2002 / Accepted: 4 June 2002 / Published online: 26 November 2002
RID="a"
ID="a"e-mail: montagnoli@pd.infn.it, Fax +39049 8277102, Tel. +39049 8277117.
RID="b"
ID="b"On leave from the China Institute for Atomic Energy, 102413 Beijing, China.
Communicated by C. Signorini 相似文献
7.
S. Sodaye K. Sudarshan B.S. Tomar A. Goswami S. Mukherjee K. Mahata 《The European Physical Journal A - Hadrons and Nuclei》2002,14(3):371-376
Kinetic-energy spectra and angular distribution of projectile-like fragments have been measured in the reaction of 84 MeV
12C on 169Tm, using the surface barrier silicon-based ΔE-E telescopes. The fragments close to the projectile show typical spectra of quasi-elastic transfer reactions, which were found
to be in agreement with the calculations based on the direct surface transfer reaction model. A significant cross-section
of fast alpha-particles was found at forward angles, reminiscent of incomplete fusion reactions, which could be explained
in terms of the direct surface transfer reaction model after taking into account the level density of continuum states in
the heavy reaction product. The results have been explained in terms of the continuous evolution of the reaction mechanism
as a function of the mass transfer.
Received: 13 March 2002 / Accepted: 3 May 2002 相似文献
8.
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
9.
The compound nucleus formation is considered as a two-step process of touching and subsequent tunneling of the projectile
into the target. The deep minima in the potential energy curve are due to shell effects in the experimental binding energies
and give possible target-projectile combinations for the synthesis of heavy and superheavy elements. The asymmetric channels
thus obtained are in remarkable agreement with the known experimental channels. In our model, the colliding partners are first
shown to be captured in the pocket behind the outer (touching) barrier and the composite system so formed finally tunnels
through the inner (fusion) barrier to form the resulting compound nucleus. These calculations reveal the importance of the
fusion barrier, which occur only for the asymmetric target-projectile combinations. The calculated fusion cross-sections show
a reasonable comparison with the observed one-neutron evaporation residue cross-sections. An estimate of the excitation energy
carried by the compound nucleus is also obtained from our model calculations. 相似文献
10.
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
11.
R.I. Badran D.J. Parker I.M. Naqib 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):317-325
Excitation functions for the production of eight radioactive products of the reactions of 7Li on 56Fe have been measured up to E(7
Li) = 89 MeV. Recoil range distributions for these products, together with inclusive proton, deuteron, triton and alpha spectra,
have been measured at energies of 50 and 68 MeV. The α, t and d spectra show characteristic “break-up” components at forward
angles, while the recoil distributions show evidence of complete fusion and incomplete-fusion process 56Fe( 7Li,α) 59Co * . A parallel study on 55Mn shows some evidences of the ( 7Li,t) incomplete-fusion process, but the cross-section for this process is significantly less than for the triton fusion process.
The recoil distributions can be reproduced on the assumption that essentially all the observed break-up fragments are in fact
associated with incomplete fusion, but uncertainties in normalisation leave open the possibility of a significant contribution
of pure break-up. A diffraction model of the ( 7Li,α) transfer process reproduces the observed break-up α spectra with some success.
Received: 29 March 2001 / Accepted: 12 November 2001 相似文献
12.
Synthesis and decay properties of superheavy atoms in nuclear reactions induced by stable and radioactive ion beams 总被引:2,自引:0,他引:2
Yu. Oganessian 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):135-141
This talk consists of two parts. The first one presents the results of investigations performed in 1998-2000 in Dubna on the
synthesis of superheavy nuclei in reactions induced by 48Ca ions. The radioactive decay properties of the nuclei, indicating a considerable increase in the α-decay and spontaneous
fission half-lives of the isotopes of elements 110-116 when approaching the closed neutron shell at N = 184, are given. In the second part the possible ways of advancing into the region of more neutron-rich nuclei, using stable
and radioactive ion beams, are discussed. Since so far no intense radioactive ion beams are available, some experiments with
stable beams are considered as a test for the suggested ideas.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
13.
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
14.
C. Signorini 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):129-133
The experimental data relative to the interaction for the systems 9, 10, 11Be + 209Bi at the Coulomb barrier are critically discussed and compared also with present theories. The break-up (BU) of the two loosely
bound projectiles, 9, 11Be, seems to influence the fusion process by “hindering” the fusion cross-sections; but, contrary to expectations, the 11Be halo structure has no influence, since no “enhancement” is evident from the existing data. Attempt to describe simultaneously
all the 9Be + 209Bi system data: fusion, elastic scattering and BU, within a coupled-channel (CC) approach is only partly successful. It is
important, from a theoretical viewpoint, to include in the CC formalism as well as possible the BU process both to continuum
states as well as to unbound resonances. More accurate and well-focused experiments are also necessary to pin down this problem.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
15.
C. Beck R. Nouicer D. Mahboub B. Djerroud R.M. Freeman A. Hachem T. Matsuse Sl. Cavallaro E. De Filippo G. Lanzanó A. Pagano M.L. Sperduto R. Dayras E. Berthoumieux R. Legrain E. Pollacco 《The European Physical Journal A - Hadrons and Nuclei》1998,2(3):281-293
Fusion-fission and fully energy-damped binary processes of the 35Cl+24Mg reaction were investigated using particle-particle coincidence techniques at a 35Cl bombarding energy of Elab≈ 8 MeV/nucleon. Inclusive data were also taken in order to determine the partial wave distribution of the fusion process.
The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with a relatively
large multiplicity of secondary light-charged particles emitted by the two primary excited fragments in the exit channel.
No evidence is observed for ternary-breakup processes, as expected from the systematics recently established for incident
energies below 15 MeV/nucleon and for a large number of reactions. The binary-process results are compared with predictions
of statistical-model calculations. The calculations were performed using the Hauser-Feshbach method, based on the available
phase space at the scission point of the compound nucleus. This new method uses temperature-dependent level densities and
its predictions are in good agreement with the presented experimental data, thus consistent with the fusion-fission origin
of the binary fully-damped yields.
Received: 12 March 1998 相似文献
16.
E. Vardaci G. La Rana A. Brondi R. Moro A. Principe D. Fabris G. Nebbia G. Viesti M. Cinausero E. Fioretto G. Prete F. Lucarelli E.M. Fiore L. Fiore V. Paticchio P.F. Bortignon 《The European Physical Journal A - Hadrons and Nuclei》1998,2(1):55-60
The α-particle emission from the 28Si+170Er fusion-evaporation reaction at 165 and 185 MeV has been measured and compared with published data relative to the pre-scission
emission in the same reaction. The spectra in the two channels exhibit nearly the same shape in the low energy region, whereas
in the high energy region the spectrum for the fusion-evaporation case features a larger apparent temperature. The interpretation
of the difference in shape between the two decay channels is based on statistical model calculations which account for the
effects due to the different length of the decay chain. Statistical model calculations with standard parameters describe well
the gross features of the alpha particle spectra in the fusion-evaporation channel and the proton spectra in the pre-scission
channel. On the contrary, the model predictions seem to overestimate by ≃2 MeV the emission barrier for the alpha particles
in the pre-fission channel. This effect is ascribed to the larger elongation of the nucleus during the fission process. An
average axis ratio b/a∼ 2 for the emitter is suggested.
Received 29 April 1997 / Revised version 10 September 1997 相似文献
17.
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
18.
19.
L.M. Pant R.K. Choudhury A. Saxena D.C. Biswas 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):47-58
Fission fragment mass and energy distributions and their correlations have been measured for the 16O and 19F + 209Bi reactions over a wide range of excitation energies ( E
* = 30-50 MeV). It is observed that in the case of 16O + 209Bi reaction, the average total fragment kinetic energy, <TKE> is nearly independent of the bombarding energy. However, in the case of 19F + 209Bi reaction, the average total kinetic energy of the fission fragments shows a peaking behaviour near the barrier. The variation
in <TKE> at near barrier energies in the 19F + 209Bi system seems to be correlated with corresponding strong variation in the variance of the fragment mass distribution. The
present results may imply certain dynamical effects leading to compact scission configurations in the fission of 19F + 209Bi system at near barrier bombarding energies.
Received: 9 April 2001 / Accepted: 26 May 2001 相似文献
20.
P. Jänker H. Leitz K.E.G. Löbner M. Moralles H.G. Thies 《The European Physical Journal A - Hadrons and Nuclei》1999,4(2):147-155
This paper contributes to the discussion on the phenomena of the enhanced emission of low–energetic charged particles during
compound nuclei decay. The decay of compound nuclei 52Fe, 56Ni, and 59Cu was studied. Energy spectra and emission angles of evaporated charged particles were measured in coincidence with gamma
rays to determine the corresponding evaporation residue nucleus. Additionally, evaporation residue distributions were determined
with the Munich rf recoil spectrometer. In this way, detailed channel–specific evaporation data were obtained for theoretical
analysis. We extracted evaporation barriers and compared them with corresponding fusion barriers. The main result was revealed
to be a lowering of the evaporation barrier for protons and alpha particles relative to the fusion barriers. But the observed
effect is not as intensive as reported in recent studies.
Received: 15 June 1998 / Revised version: 5 November 1998 相似文献