共查询到20条相似文献,搜索用时 531 毫秒
1.
V. N. Tarasov K. A. Gridnev W. Greiner S. Schramm D. K. Gridnev D. V. Tarasov X. Viñas 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(7):569-575
Properties of even-even nuclei with extreme neutron excess in the vicinity of neutron magic numbers up to and beyond the neutron drip line (NDL) are calculated by the Hartree-Fock (HF) method using Skyrme forces (Ska, SkM*, Sly4, SkI2, SkP) with allowance for axial deformation and BCS-approximation pairing. It is shown that chains of isotones with the neutron numbers N = 32, 58, 82, 126, 184, and 258 beyond the NDL form peninsulas of nuclei stable with respect to emission of one neutron, and occasionally peninsulas of nuclei stable with respect to the emission of two neutrons. The length of these peninsulas in (N, Z) space depends on the choice of the Skyrme forces, while their locations are at the same N = 32, 58, 82, 126, 184, and 258 and do not depend on the choice of forces. The investigated isotones restore stability beyond the NDL due to the complete filling of subshells with high angular momentum and to the intrusion of corresponding neutron levels in the region of discrete bound states. The stability of the numerical solution to the HF equations for nuclei belonging to the peninsulas of stability is analyzed. 相似文献
2.
V. N. Tarasov D. V. Tarasov K. A. Gridnev D. K. Gridnev W. Greiner V. G. Kartavenko V. I. Kuprikov 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(6):842-846
The properties of neutron-rich Zr isotopes up to the neutron drip line and beyond it have been investigated on the basis of the Hartree-Fock method with the Skyrme forces (Ska, Sly4), taking into account the deformation. By the example of chains of Zr isotopes, good agreement is shown for the two-neutron separation energies and mean-square radii with the known results of Hartree-Fock-Bogolyubov calculations with the Sly4 forces. For the extremely neutron-rich Zr isotopes, states with very large deformation parameters (β ≈ 0.4?0.45) of neutron and proton density distributions can be realized. Beyond the neutron drip line with respect to emission of two neutrons, the existence of 150,152Zr isotopes, which are stable with respect to one-neutron emission, is predicted. 相似文献
3.
K. A. Gridnev W. Greiner V. N. Tarasov S. Schramm D. K. Gridnev D. V. Tarasov X. Vi?as 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(8):871-875
Manifestations of the neutron halo in extremely neutron-rich nuclei are investigated by the Hartree-Fock method using the Skyrme forces (SkM*, Ska, Sly4, SkI2) with allowance for axial deformation. The investigated nuclei, which lie beyond the theoretical neutron drip line (NDL), form peninsulas of nuclei stable with respect to one-neutron emission and belong to chains of isotones with the neutron number N = 32, 58, 82, 126, 184, and 258. 相似文献
4.
V. N. Tarasov K. A. Gridnev D. K. Gridnev V. I. Kuprikov D. V. Tarasov W. Greiner X. Vinyes 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(11):1559-1569
Properties of extremely neutron-rich even-even O, Ar, Kr, and Rn isotopes in the ground state are calculated by the Hartree-Fock
method using Skyrme forces with allowance for axial deformation of the density distribution. It is shown that beyond the familiar
two-neutron drip line there can be regions (islands) of nuclei stable with respect to the emission of one or two neutrons.
The stability recovery mechanism is described in consideration of the deformation effect. Certain isotopes are compared to
calculations performed by the Hartree-Fock-Bogolyubov method, and 40,42O is compared to calculations performed within the relativistic Hartree-Bogolyubov theory. 相似文献
5.
V. N. Tarasov K. A. Gridnev W. Greiner S. Schramm D. K. Gridnev D. V. Tarasov X. Viñas 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(7):842-848
The properties of the ground state of even-even nuclei with extreme neutron excess that are remote from the known neutron drip line (NDL) are calculated. The calculations are based on the Hartree-Fock method with Skyrme forces SkM*, SkI2, Sly4, Ska) with allowance for axial deformation and the BCS pairing approximation. It is shown that the isotone chain at the neutron number N = 126 beyond the NDL forms a peninsula of nuclei that are stable with respect to the emission of one neutron (PNS). The neutron and proton density distributions of the PNS nuclei have spherical symmetry. A mechanism for restoring the stability of nuclei beyond the NDL is discussed. The obtained results are compared with those from Hartree-Fock-Bogoliubov calculations for long isotope chains of Zr and Pd up to the NDL. 相似文献
6.
Ground-state properties of even-even nuclei were calculated over a broad region of mass numbers, including nuclei that contain a neutron excess in the vicinity of the neutron drip line. The calculation of the properties of such nuclei relied on the method of the relativistic and the nonrelativistic mean field and took into account the axial deformation of nuclei. Particular attention was given to nuclei beyond the theoretical neutron drip line, which form a peninsula of nuclei in the (N, Z) space at N = 184 that are stable against the emission of one or two neutrons.
相似文献7.
V. N. Tarasov D. V. Tarasov K. A. Gridnev D. K. Gridnev W. Greiner V. G. Kartavenko V. V. Pilipenko 《Physics of Atomic Nuclei》2008,71(7):1255-1261
On the basis of the Hartree-Fock method with Skyrme forces of the Ska, SkM*, and Sly4 type, the position of the neutron drip line and the properties of neutron-rich lead isotopes are studied with allowance for deformations. It is shown that, in extremely neutron-rich nuclei, the neutron and proton density distributions are characterized by an anomalously large deformation parameter of β ~ 0.6. Also, nuclei of superdeformed lead isotopes have anomalously large root-mean-square radii. The existence of the isotopes 266–288Pb, which are stable to the emission of one neutron, is predicted. 相似文献
8.
We study the proton magic O, Ca, Ni, Zr, Sn, and Pb isotope chains from the proton drip line to the neutron drip line with
the relativistic continuum Hartree-Bogoliubov (RCHB) theory. Particulary, we study in detail the properties of even-even Ca
isotopes due to the appearance of giant halos in neutron rich Ca nuclei near the neutron drip line. The RCHB theory is able
to reproduce the experimental binding energiesE
b and two neutron separation energiesS
2n very well. The predicted neutron drip line nuclei are28O,72Ca,98Ni,136Zr,176Sn, and266Pb. Halo and giant halo properties predicted in Ca isotopes withA>60 are investigated in detail through analysis of two neutron separation energies, nucleon density distributions, single
particle energy levels, and the occupation probabilities of energy levels including continuum states. The spin-orbit splitting
and the diffuseness of nuclear potential in these Ca isotopes, as well as the neighboring lighter isotopes in the drip line
Ca region and find certain possibilities of giant halo nuclei in the Ne−Na−Mg drip line nuclei are also studied. 相似文献
9.
V. N. Tarasov K. A. Gridnev W. Greiner S. Schramm D. K. Gridnev D. V. Tarasov X. Vi?as 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(8):876-880
The properties of extremely neutron-excessive nuclei with Z ?? 70, including the region of transuranium elements, are calculated beyond the previously theoretically known neutron drip line (NDL). The calculations are based on the Hartree-Fock approach using Skyrme forces (SkM*, SkI2, SLy4, Ska) with allowance for axial deformation and pairings in the BCS approximation. It is shown that the series of isotones with neutron number N = 258 outside of 2n NDL forms a peninsula of stable nuclei (PSN) with respect to the emission of one neutron. For SkM* forces, a PSN is formed by 344Rn, 346Ra, 348Th, and 350U nuclides. 相似文献
10.
《Nuclear Physics A》1998,628(2):221-254
We have made a detailed study of the ground-state properties of nuclei in the light-mass region with atomic numbers Z = 10–22 in the framework of the relativistic mean-field (RMF) theory. The nonlinear σω model with scalar self-interaction has been employed. The RMF calculations have been performed in an axially deformed configuration using the force NL-SH. We have considered nuclei about the stability line as well as those close to proton and neutron drip lines. It is shown that the RMF results provide good agreement with the available empirical data. The RMF predictions also show reasonably good agreement with those of the mass models. It is observed that nuclei in this mass region are found to possess strong deformations and exhibit shape changes all along the isotopic chains. The phenomenon of shape coexistence is found to persist near the stability line as well as near the drip lines. It is shown that the magic number N = 28 is quenched strongly, thus enabling the corresponding nuclei to assume strong deformations. Nuclei near the neutron and proton drip lines in this region are also shown to be strongly deformed. 相似文献
11.
C N Davids P J Woods D Seweryniak A A Sonzogni J C Batchelder C R Bingham T Davinson D J Henderson R J Irvine G L Poli J Uusitalo W B Walters 《Pramana》1999,53(3):631-631
The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically unbound to the emission of a constituent proton from their ground states. For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction of nuclear structure information from nuclei well beyond the proton drip line. 相似文献
12.
M S Samant R P Anand R K Choudhury S S Kapoor K Kumar D M Nadkarni A Saxena 《Pramana》1993,40(4):299-309
The emission spectra of prompt fission neutrons from mass and kinetic energy selected fission fragments have been measured
in235U(n
th,f). Neutron energies were determined from the measurement of the neutron time of flight using a NE213 scintillation detector.
The fragment energies were measured by a pair of surface barrier detectors in one set of measurements and by a back-to-back
gridded ionization chamber in the second set of measurements. The data were analysed event by event to deduce neutron energy
in the rest frame of the emitting fragment for the determination of neutron emission spectra and multiplicities as a function
of the fragment mass and total kinetic energy. The results are compared with statistical model calculations using shell and
excitation energy dependent level density formulations to deduce the level density parameters of the neutron rich fragment
nuclei over a large range of fragment masses. 相似文献
13.
The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier
properties and neutron emission characteristics in the fission process. 233U and 235U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used
in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich
uranium isotopes is examined here. The neutron number N = 162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium
isotopes around it with N = 154–172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics;
a manifestation of the close shell nature of N = 162 (or 164). We consider here the thermal neutron fission of a typical representative 249U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that 250U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis
of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory,
this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number
of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties
will have important implications in stellar evolution involving r-process nucleosynthesis.
相似文献
14.
《Nuclear Physics A》1998,635(4):484-494
The proton and neutron radii of even-even β-stable nuclei with A ⩾ 40 and a few chains of isotopes with Z = 50, 56, 82, 94 protons and isotones with N = 50, 82, 126 neutrons are analyzed. The average isospin dependence of the radii evaluated within the relativistic mean field theory is studied. A simple, phenomenological formula for neutron radii is proposed. 相似文献
15.
O. V. Bespalova B. S. Ishkhanov A. A. Klimochkina A. A. Kostyukov E. A. Romanovsky T. I. Spasskaya 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(5):401-404
Experimental data on single-particle neutron energies of Cd isotopes are analyzed within a dispersive optical model. Parameters of the potential are extrapolated to the region of unstable isotopes with a neutron excess. The evolution of calculated single-particle spectra and occupation probabilities of single-particle orbits corresponds to formation of magic features in Cd isotopes with N = 50, 82. The results from calculations agree with the concept that the 174Cd isotope with N = 126 forms the end of the peninsula at the neutron drip line. 相似文献
16.
V. I. Vysotskii M. V. Vysotskii 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(2):330-334
Based on the Dirac equation, the features of long-range electromagnetic orientational interaction of slow neutrons with even-even
and even-odd nuclei are considered. This interaction is controlled by a narrow potential barrier arranged beyond the nucleus.
The barrier height is U
tot = 20–40 eV and depends on Z, A, and the nucleus magnetic moment μnucl. The barrier formation is associated with the ponderomotive nonlinear interaction of the anomalous neutron moment with the
nucleus electric field. The barrier transparency for thermal neutrons is D(E) ≈ 0.8–0.95. For cold neutrons, the barrier transparency and their reaction cross sections with nuclei sharply decrease and,
at E → 0, their cross sections tend toward zero. It was shown that the combined effect of the magnetic dipole-dipole and ponderomotive
interaction of the neutron and even-odd nucleus results in the formation of removed symmetrically positioned potential wells
for neutrons beyond the nucleus. The presence of these wells results in the possible existence of short-lived or virtual nucleus-neutron
molecules and the “neutron halo” effect beyond the nucleus. 相似文献
17.
C N Davids P J Woods D Seweryniak A A Sonzogni J C Batchelder C R Bingham T Davinson D J Henderson R J Irvine G L Poli J Uusitalo W B Walters 《Pramana》1999,53(3):631
The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically
unbound to the emission of a constituent proton from their ground states.
For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors
derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent
quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction
of nuclear structure information from nuclei well beyond the proton drip line.
The rare-earth proton emitters 141Ho and 131Eu have recently been observed [4], and their decay rates can only be explained by assuming large deformation for these nuclei.
In addition to providing information on the wavefunctions and deformations of these nuclei, these results offer the opportunity
to study the phenomenon of quantum mechanical tunneling through a deformed potential barrier.
Work supported by the U.S. Department of Energy, Nuclear Physics Division, under contract W-31-109-ENG-38. 相似文献
18.
Inclusion of the coupling of quasiparticle degrees of freedom with phonon degrees is a natural extention of the standard QRPA
approach. The paper presents the quantitative impact of this phonon coupling on the dipole strength and radiative neutron
capture for the stable 124Sn and very exotic 150Sn isotopes, as an illustration, using the self-consistent version of the Extended Theory of Finite Fermi Systems. It was
found that the phonon contribution to the pygmy-dipole resonance and radiative neutron capture cross section is increased
with the (N − Z) difference growth. The results show that the self-consistent nuclear structure calculations are important for unstable nuclei,
where phenomenological approaches do not work. 相似文献
19.
N. Aoi K. Yoneda H. Miyatake H. Ogawa Y. Yamamoto E. Ideguchi T. Kishida T. Nakamura M. Notani H. Sakurai T. Teranishi H. Wu S. S. Yamamoto Y. Watanabe A. Yoshida M. Ishihara 《Zeitschrift für Physik A Hadrons and Nuclei》1997,358(2):253-255
Experimental studies of β-decay measurements of the neutron drip line nuclei 11Li and 14Be are presented. β- decay schemes of these nuclei are determined by measuring β-rays, delayed neutrons and γ-rays in triple coincidence. The decay schemes of both 11Li and 14Be associated with single neutron emission are unambiguously determined. New levels in their daughter nuclei, 11Be and 14B, are found. In addition, the deduced level scheme of 14B indicates the lowering of 2s 1/2 single neutron orbital with respect to 1p 1/2 orbital in the N=9 isotones. Such behavior is known to exist in N=7. 相似文献