共查询到20条相似文献,搜索用时 31 毫秒
1.
Zhi Yong He Gen Ming Jin Zu Yu Li Li Min Duan Guang Xi Dai Bao Guo Zhang He Yu Wu Wan Xin Wen Yu Jin Qi Qing Zheng Luo Su Fang Wang 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):61-64
Emission orders of light charged particles and Li fragments from highly excited fissioning nuclei in the reaction of 40Ar+197Au at E
beam
/A=25 MeV have been studied by measuring difference velocity distributions of two correlated particles at small relative angles
in coincidence with two fission fragments. By comparing the data with three-body trajectory calculations, we found that high
velocity deuterons are emitted prior to high velocity Li fragments but low velocity deuterons are emitted after low velocity
Li fragments. On the other hand, no preferential emission was observed among light particles, such as protons and deuterons.
Furthermore, the emission orders are found to depend only weakly on the mass asymmetry of fission fragments.
Received: 3 June 1997 / Revised version: 23 July 1997 相似文献
2.
3.
H. Baba N. Takahashi A. Yokoyama T. Saito 《The European Physical Journal A - Hadrons and Nuclei》1998,3(3):281-292
The reaction of 238U with 12C was studied radiochemically with the purpose of elucidating fast fission characteristics. From the difference in the mass
distribution below and above the critical energy where fast fission is predicted to set in, fast fission component was extracted
in far-asymmetric mass region and interpreted as the mass diffusion following the Fokker-Planck equation. Anomalous charge
dispersion widths in the corresponding mass region and a sudden increase of the whole mass distribution width at the critical
energy were also observed to support the above result. The reaction time of fast fission deduced from the width and position
of the mass distribution was 5×10−21s as well by taking into account the effect of neutron emission during the diffusion process, which turned out to be more
than one order of magnitude longer than the corresponding life time of typical deep inelastic scattering but substantially
short compared to ordinary fusion-fission life time. Evaluation of the driving potential for mass drift required dinuclear
configuration be of an elongated or deformed form for fast fission in contrast to a more compact form for the deep-inelastic
process.
Received: 11 November 1997 相似文献
4.
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
5.
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
6.
A.K. Dhara S. Bhattacharya K. Krishan 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):209-217
The dynamics of fission has been formulated by generalising the asymptotic expansion of the Fokker-Planck equation in terms
of the strength of the fluctuations where the diffusion coefficients depend on the stochastic variables explicitly. The prescission
neutron multiplicities and mean kinetic energies of the evaporated neutrons have been calculated and compared with the respective
experimental data over a wide range of excitation energy and compound nuclear mass. The mean and the variance of the total
kinetic energies of the fission fragments have been calculated and compared with the experimental values.
Received: 8 September 1999 / Revised version: 22 November 1999 相似文献
7.
J. Benlliure A.R. Junghans K.-H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):93-98
The secondary-beam facility at GSI allows to produce a large variety of exotic nuclei at relativistic energies. This technique
offers a unique oportunity to investigate systematically fission in inverse kinematics. In the present experiment, the fission
properties of more than 70 different actinides and preactinides were investigated at low excitation energy. The elemental
yields and kinetic energies of the fission residues present new signatures of shell structure and pairing correlations.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
8.
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
9.
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
10.
Yuan Shuanggui Yang Weifan Xu Yanbing Pan Qiangyan Xiong Bing He Jianjun Wang Dong Li Yingjun Ma Taotao Yang Zhenguo 《The European Physical Journal A - Hadrons and Nuclei》2001,10(1):1-3
The 230Ra has been produced via multinucleon transfer reaction and dissipative fragmentation by 60 MeV/u 18O ion irradiation of 232Th targets. The radium was radiochemically separated from the mixture of thorium and reaction products. Thin Ra sources were
prepared and exposed to the mica fission track detectors, and measured by a HPGe gamma detector. It is likely that the β-delayed
fission of 230Ac was observed for the first time and the β-delayed fission probability of 230Ac was tentatively found to be (1.19±0.40)×10-8.
Received: 2 November 2000 / Accepted: 30 January 2001 相似文献
11.
K. Helariutta J. Benlliure M.V. Ricciardi K.-H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):181-193
A two-step reaction scheme for the production of extremely neutron-rich radioactive beams, fission followed by cold fragmentation,
is considered. The cross-sections of the second step, the cold fragmentation of neutron-rich fission fragments, are estimated
with different computer codes. Discrepancies between an empirical systematics and nuclear-reaction codes are found.
Received: 27 January 2003 / Accepted: 6 March 2003 / Published online: 27 May 2003 相似文献
12.
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
13.
14.
F. Soramel P. Bednarczyk M. Sferrazza D. Bazzacco D. De Acuñna G. de Angelis M. De Poli E. Farnea N.H. Medina R. Menegazzo L. Müller D.R. Napoli C.M. Petrache C. Rossi Alvarez F. Scarlassara G.F. Segato C. Signorini J. Styczeń G. Vedovato 《The European Physical Journal A - Hadrons and Nuclei》1999,4(1):17-19
The 178Pt and 181Au nuclei have been studied with the (230 MeV) 46Ti +142Nd fusion-evaporation reaction; γ-rays, evaporated particles and recoiling nuclei have been detected by the γ-array GASP +
the Si ball ISIS + the recoil mass spectrometer RMS. The newly observed structures in 178Pt and 181Au are most probably built on the proton and quasi-proton h9/2 and i13/2 configurations.
Received: 2 January 1998 / Revised version: 27 May 1998 相似文献
15.
E. Gadioli G.F. Steyn C. Birattari M. Cavinato S.H. Connell A.A. Cowley E. Fabrici S.V. Förtsch E. Gadioli Erba J.J. Lawrie F.M. Nortier J.P.F. Sellschop E. Sideras Haddad 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):161-173
The spectra of 8Begs fragments emitted in the interaction of 100, 200, 300 and 400 MeV 12C with 59Co, 93Nb and 197Au have been measured and analysed. Our analysis suggests that, before breaking up, 12C may suffer a considerable energy loss which increases with increasing incident energy. The amount of excitation energy provided
to the target nucleus in this process increases with decreasing charge of the target nucleus.
Received: 3 May 2001 / Accepted: 5 June 2001 相似文献
16.
17.
The sequence of radioactive decays of an unknown isotope produced in a rare fusion reaction to known lighter isotopes is
used to identify mass and atomic number of the mother isotope, which has been separated before from the bulk of other reaction
products by an in-flight recoil separator. By this technique the elements 107 to 112 were produced by single atom decay-chain
analysis. Such a correlation technique reaches its limit by the occurrence of accidental sequences and it collapses beyond
a maximum possible correlation time, at which a true event cannot be distinguished anymore from a random event.
48Ca-induced fusion reactions with actinides are discussed. In 1983 at GSI, Darmstadt and LBL, Berkeley, 48Ca/248Cm-experiments (II) were performed, which are compared to recent 48Ca-experiments at FLNR-Dubna (I) irradiating 244Pu, 242Pu, and 238U. In these experiments production of isotopes of superheavy elements 112 and 114 is claimed. Our analysis of accidental sequences
in 48Ca-induced reactions is presented, which is at variance with the published analysis from FLNR-Dubna. We find that the maximum
correlation time using continuous beams at today existing separation systems is not in the one-hour regime, but in the few-minute
regime. The five spontaneous fission events observed in the FLNR experiments are preceded by signals in the (1–16)-minute
range. These times are shown to be longer than the maximum possible correlation times. The preceding signals are decoupled
from the spontaneous fission signal and carry no information on the spontaneous fission events observed. Moreover, random
probabilities of 0.2 to 0.6 for the signals preceding the fission events indicate that the correlations are of random origin.
The evidence to have discovered element 114 in the reported experiments is classified “very weak”.
Received: 13 October 1999 相似文献
18.
E. Gadioli G.F. Steyn F. Albertini C. Birattari M. Cavinato S.H. Connell A.A. Cowley E. Fabrici S.V. Förtsch E. Gadioli Erba J.J. Lawrie M. Pigni J.P.F. Sellschop E. Sideras Haddad 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):195-212
In this paper we study the emission of 8Begs, B and N fragments in the interaction of 16O ions with 59Co, 93Nb and 197Au at incident energies varying from 6 to 25 MeV/nucleon. The spectra of these fragments, as well as those of C fragments
studied in a previous paper, are dominated at forward angles by a component originating from break-up of 16O. At the higher incident energies break-up occurs after quite a sizeable projectile energy loss. Another mechanism which
dominates at large emission angles, favours the emission of low-energy fragments and is attributed to the coalescence of nucleons
during the cascade of nucleon-nucleon interactions by means of which the excited nuclei produced in the primary two-ion interaction
thermalize.
Received: 21 January 2003 / Accepted: 27 March 2003 / Published online: 5 June 2003 相似文献
19.
E. Gadioli M. Cavinato E. Fabrici E. Gadioli Erba R. Bassini C. Birattari S. Crippa G. F. Steyn S. V. Förtsch J. J. Lawrie F. M. Nortier S. H. Connell E. Sideras-Haddad J. P. F. Sellschop A. A. Cowley 《The European Physical Journal A - Hadrons and Nuclei》2000,8(3):373-376
It is suggested that the spectra of the 8Be ground-state (gs) nuclei produced in the interaction of 12C with 59Co at incident energies varying from 8.3 to 33.3 MeV/amu can be explained by introducing a dissipative friction interaction
mechanism preceding projectile break-up.
Received: 27 March 2000 / Accepted: 11 April 2000 相似文献
20.
S.P. Avdeyev V.A. Karnaukhov W.D. Kuznetsov L.A. Petrov V.K. Rodionov A.S. Zubkevich H. Oeschler O.V. Bochkarev L.V. Chulkov E.A. Kuzmin A. Budzanovski W. Karcz M. Janicki E. Norbeck A.S. Botvina W.A. Friedman W. Nörenberg G. Papp 《The European Physical Journal A - Hadrons and Nuclei》1998,3(1):75-83
Multiple emission of intermediate-mass fragments has been studied for the collisions p + Au at 2.16, 3.6 and 8.1 GeV with
the FASA setup. The mean IMF multiplicities for events with at least one IMF are equal to 1.7, 1.9 and 2.1 (±0.2) respectively.
The multiplicity, charge distributions and kinetic energy spectra of IMF are described in the framework of a intranuclear
cascade model followed by the statistical multifragmentation model. However, between the two parts of the calculation the
excitation energies and the residual masses and charges are modified to take into account the losses during expansion. The
results support a scenario of true thermal multifragmentation of a hot and expanded target spectator.
Received: 15 December 1997 / Revised version: 24 April 1998 相似文献