共查询到20条相似文献,搜索用时 406 毫秒
1.
Yu. Ts. Oganessian 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):17-23
Experiments are described and main results presented on the synthesis and decay properties of superheavy nuclides, produced
in fusion reactions induced by a 48Ca-beam on heavy actinide targets. In such reactions neutron-rich nuclei are formed. For them, according to theory, an abrupt
enhancement of stability due to nuclear shell effects is expected. The decay properties of the new nuclides are compared with
calculations of theoretical models, which predict the existence of “islands of stability” in the region of hypothetical superheavy
elements. 相似文献
2.
The shell evolution at N = 20, a disappearing neutron magic number observed experimentally in very neutron-rich nuclides, is investigated in the constrained relativistic mean field (RMF) theory. The trend of the shell closure observed experimentally towards the neutron drip-line can be reproduced. The predicted two-neutron separation energies, neutron shell gap energies and deformation parameters of ground states are shown as well. These results are compared with the recent Hartree-Fock-Bogliubov (HFB-14) model and the available experimental data. The perspective towards a better understanding of the shell evolution is discussed. 相似文献
3.
The shell evolution at N=20, a disappearing neutron magic number observed experimentally in very neutron-rich nuclides, is investigated in the constrained relativistic mean field (RMF) theory. The trend of the shell closure observed experimentally towards the neutron drip-line can be reproduced. The predicted two-neutron separation energies, neutron shell gap energies and deformation parameters of ground states are shown as well. These results are compared with the recent Hartree-Fock-Bogliubov (HFB-14) model and the available experimental data. The perspective towards a better understanding of the shell evolution is discussed. 相似文献
4.
M. Schädel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(1):67-74
Superheavy elements have been synthesized and chemically
characterized one-atom-at-a-time up to element 108. Presently, the quest for
identification and investigation of element 112 is one of the hottest topics
in this field. The transactinide elements 104 to 108 are members of group 4
to 8 of the periodic table and element 112 belongs into group 12. For some
of these elements detailed chemical properties have been revealed which show
stunning deviations from simple extrapolations within their respective group
while others exhibit great similarities with their lighter homologues. All
presently known chemical properties of seaborgium (Sg, element 106) — the
heaviest element whose behavior was investigated in aqueous solution — and
hassium (Hs, element 108) were obtained in experiments performed at the GSI
in large international collaborations. Recently, the highly efficient and
very clean separation of Hs was applied for nuclear studies of various Hs
nuclides investigating their cross section and their nuclear decay
properties in the region of the N=162 neutron shell. To overcome certain
limitations of the presently used on-line chemical separations the new
TransActinide Separator and Chemistry
Apparatus (TASCA) — with a gas-filled recoil separator as
a front-end tool — was designed and built at the GSI in a collaborative
effort. Presently in its commissioning phase, TASCA shall be a key
instrument for a big leap into quantitatively and qualitatively new
experiments in the region of superheavy elements. 相似文献
5.
V. I. Zagrebaev S. G. Zemlyanoy E. M. Kozulin Yu. Kudryavtsev V. Fedosseev R. Bark H. A. Othman 《Hyperfine Interactions》2013,216(1-3):109-113
A new setup is proposed to produce and investigate heavy neutron-rich nuclei located along the neutron closed shell N = 126. This “blank spot” of the nuclear map can be reached neither in fusion–fission reactions nor in fragmentation processes widely used nowadays for the production of exotic nuclei. The present limits of the upper part of the nuclear map are very close to stability while the unexplored area of heavy neutron-rich nuclides along the neutron closed shell N = 126 is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleosynthesis. A new way was recently proposed for the production of these nuclei via low-energy multi-nucleon transfer reactions. The estimated yields of neutron-rich nuclei are found to be rather high in such reactions and several tens of new nuclides can be produced, for example, in the near-barrier collision of 136Xe with 208Pb. This setup could definitely open a new opportunity in the studies at heavy-ion facilities and will have significant impact on future experiments. 相似文献
6.
V. I. Zagrebaev S. G. Zemlyanoy E. M. Kozulin Yu. Kudryavtsev V. Fedosseev R. Bark Z. Janas H. A. Othman 《Hyperfine Interactions》2014,227(1-3):181-189
The present limits of the upper part of the nuclear map are very close to stability while the unexplored area of heavy neutron-rich nuclides along the neutron closed shell N = 126 is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleosynthesis. This area of the nuclear map can be reached neither in fusion–fission reactions nor in fragmentation processes widely used nowadays for the production of exotic nuclei. A new way was recently proposed for the production of these nuclei via low-energy multi-nucleon transfer reactions. The estimated yields of neutron-rich nuclei are found to be significantly high in such reactions and several tens of new nuclides can be produced, for example, in the near-barrier collision of 136Xe with 208Pb. A new setup is proposed to produce and study heavy neutron-rich nuclei located along the neutron closed shell N = 126. 相似文献
7.
The isospin dependence of shell closure phenomena is studied for light neutron-rich nuclei within a microscopic self-consistent
approach using the Gogny force. Introducing configuration mixing, 32Mg is found to be dynamically deformed, although the N = 20 spherical shell closure persists at the mean-field level for all N = 20 isotones. In contrast, the N = 28 spherical shell closure is found to disappear for N - Z≥ 10 whereas deformed shell closures are preserved and lead to shape coexistence in 44
S. Configuration mixing shows that the ground state of this nucleus is triaxially deformed. The first 2+ excitation energy Ex = 1.46 MeV and the reduced transition probability B(E2;0+
gs→ 2+
1)= 420 e
2
fm
4 obtained with our approach are in good agreement with experimental data.
Received: 26 July 2000 / Accepted: 30 August 2000 相似文献
8.
简单地介绍了远离β-稳定线重质量丰中子核的合成和研究的科学意义,报告了元素指定对远离β-稳定线重丰中子核研究的重要作用.The significance of the synthesis and study of heavy neutron-rich nuclides far from β-stability is briefly introduced. The important role of element assignment for studying heavy neutron-rich nuclides far from β-stability is reported. 相似文献
9.
Yu. Oganessian 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):361-367
The setting of the experiments is described and the results obtained on the synthesis of the heaviest nuclides in reactions
induced by 48Ca projectiles are presented. The decay properties of the new nuclei confirm the theoretical predictions about the new nuclear
shells and the “islands of stability” of superheavy elements. Briefly, also the results of the first experiments aimed to
study the atomic and chemical properties of element 112 are reported. 相似文献
10.
XUChang RENZhong-Zhou 《理论物理通讯》2004,42(5):745-752
The cluster model of a-decay is extended to the regions around doubly magic spherical nucleus ^208Pb and around deformed shell closure ^270Hs, respectively. The effects of spherical shell closures (N=126 and Z=82) on α-decay are investigated by introducing an N-dependent α-preformation factor and a Z-dependent one inspired by a microscopic model. Good agreement between the theoretical a-decay half-lives and the measured ones is obtained for the spherical nuclei near the doubly magic nucleus ^208Pb, where the nuclear shell effect is included in the expression of α-preformation factor. The cluster model is also generalized for the decay of deformed nuclei. The branching ratios of α-decays from the ground state of a parent nucleus to the ground state (0^ ) of its deformed daughter nucleus and to the first excited state (2^ ) are calculated in the framework of the cluster model. The results indicate that a measurement of α spectroscopy is a feasible method to extract the information of nuclear deformation of superheavy nuclei around the deformed nucleus ^270Hs. 相似文献
11.
John McMinn 《Zeitschrift für Physik A Hadrons and Nuclei》1972,257(5):389-401
A least squares method is used to fit a smooth curve to known thermal neutron fission cross section data for nuclei of evenN. By making use of fission barriers resulting from a modified liquid drop formalism coupled with the Strutinsky Normalization Procedure, the result is generalized and applied to the prediction within this framework of some 59 cross sections in the actinide and adjacent sub-actinide and trans-actinide regions, as well as to the prediction of an additional 37 cross sections in the superheavy region. In the first group is included a number of nuclides for which presently available cross section data are necessarily cited as upper limits. In the second group, interest is focussed on the predicted island of stability surrounding a neutron shell closure at 184 and a proton shell closure at 114. The results, while they are regarded as plausible estimates and not precise determinations, indicate that many cross sections in this region can be expected to undergo a pronounced reduction in magnitude relative to the limited number of estimates previously given in the literature. 相似文献
12.
This paper investigates the mass,shell and even-odd effects of the nonstatistical and statistical processes in the radiative nucleon capture reactions.The (n,γ) cross sections for 33 even-neutron target nuclides were studied at En of 0.1 to 3MeV.The results indicate that the nonstatistical capture cross sections do not present any systematically varying pattern with mass number,except for a weak shell effect.The statistical capture cross sections,which depend strongly on the level density,display obvious mass,shell and even-odd effects.The nonstatistical fractions show prominent downward tendency with mass number,as well as the shell effect. 相似文献
13.
用自洽的相对论平均场模型研究了核271110及其α衰变链核的结构.理论的α衰变能与实验数据符合.理论的核寿命也与实验数据比较接近.预言了未知核素275112的性质,并讨论了质子数Z=108附近的形变壳效应. 相似文献
14.
Yu. P. Gangrsky D. V. Karaivanov K. P. Marinova B. N. Markov Yu. E. Penionzhkevich S. G. Zemlyanoi 《Hyperfine Interactions》2005,162(1-4):85-91
The present paper aims to discuss the prospects for nuclear structure investigation of the transuranium elements by laser
spectroscopy. The authors lay stress on two peculiarities of the nuclear structure in this region: The deformed shell closure
at neutron number N = 152 and the appearance of superdeformed isomeric states. A laser spectroscopic experimental method is proposed to study
these features. 相似文献
15.
超重元素(新核素)合成研究进展情况分析和展望 总被引:2,自引:0,他引:2
本文在介绍和分析国际、国内在超重元素(新核素)合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素(核)合成研究工作提出一些看法和建议,提供讨论。 相似文献
16.
K.D. Hildenbrand H. Freiesleben A. Gobbi U. Lynen A. Olmi H. Sann E.C. Wu 《Nuclear Physics A》1983,405(1):179-204
A kinematically complete study of the symmetric systems 144Sm+144Sm and 154Sn+154Sm has been performed at energies 30% in excess of the interaction barrier. They have been chosen because of their different internal structure: 144Sm has a closed N = 82 neutron shell and a spherical ground-state configuration; 154Sm with ten neutrons outside this shell is strongly deformed. The observed gross features of both reactions like energy, angular and total mass or element distributions are very similar; the ratio of the mass variances as function of the total kinetic energy loss indicates the number of exchanged nucleons to be comparable in all stages of the reactions. At small energy losses, however, the element distributions of the 144Sm + 144Sm reaction are considerably broader, pointing at an enhanced proton transfer at the cost of the number of exchanged neutrons in this system. This observation is attributed to the influence of the closed shell which seems to block the transfer of neutrons at low excitation energies. These results can be explained quantitatively by the different gradients of the shell-corrected potential energy surfaces of the two systems. 相似文献
17.
本文在介绍和分析国际、国内在超重元素 (新核素 )合成实验研究与理论研究进展情况的基础上对我国今后如何从理论与实验的结合上开展超重元素 (核 )合成研究工作提出一些看法和建议 ,提供讨论 相似文献
18.
Mass spectrometer measurements of the neutron rich sodium isotopes show a sudden increase at 31Na in the values of the two-neutron separation energies. The spherical shell model naturally predicts a sudden decrease at 32Na after the N = 20 shell closure. We propose that the explanation for this disagreement lies in the fact that sodium isotopes in this mass region are strongly deformed due to the filling of negative parity orbitais from the 1f shell. Hartree-Fock calculations are presented in support of this conjecture. 相似文献
19.
P. Armbruster 《The European Physical Journal A - Hadrons and Nuclei》2008,37(2):159-167
The recent experiments at FLNR, Dubna, demonstrated that cross-sections to produce SHEs by 48Ca-induced reactions on actinide targets increase beyond Z = 111, reach a maximum of 5 pb at Z = 114 and fall below the 1 pb level at Z = 118. A scenario is proposed to understand the findings within the frame of former experimental results of heavy-element
production and theoretical predictions about the stability of the nuclides concerned. New ingredients introduced are: 1) to
shift the next proton shell beyond Pb from Z = 114 to Z = 122; 2) the isotopes of the elements Z = 112 to Z = 118 are deformed and their nuclei have oblate shapes; 3) the fission barriers around the next nucleus with doubly closed
shells 306184122 are larger than the neutron separation energies and reach values in the range of 10MeV. The ascent of the flat top at
306184122 is described by the proposed scenario, which likewise excludes reaching the doubly closed shell region at the top by today’s
experimental methods.
Communicated by T.S. Bíró 相似文献
20.
Using a silicon filtered fission neutron beam of an energy width of 20 keV around 143 keV we measured the total cross sections for 37 nuclides and elements having mass numbers between 87 and 140 and determined thep-wave strength functions. The 3P-resonance atA=98 shows no splitting into theP 3/2?P 1/2 doublet. The narrow resonance peak and the following broad distribution of thep-strength function (A=103 to 140) can approximately be reproduced by deformed optical model calculations. The spin-orbit term in the optical potential is consistent with the spin orbit force in the shell model. For nuclei around the closed (N=50) neutron shell a shell effect in thep-wave strength function is indicated. 相似文献