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1.
The purpose of this note is to examine the conditions under which muon level crossing resonance with quadrupolar nuclei may
be used to characterise the elusive diamagnetic fraction which is formed when positive muons are stopped in various media
and associated chemically with the host molecules. A potential difficulty is identified for nuclei having integral spin, which
may explain why cross polarisation to14N has not yet been detected. The general suitability of nuclei with half-integral spin (I≥3/2) is illustrated with the case of17O, and suggestions are made for future studies with other nuclei, including species such as molecular ions and defect complexes
(muon-impurity pairs). 相似文献
2.
《Nuclear Physics A》1999,652(3):250-270
We investigate the ground state properties of proton-rich nuclei in the framework of the relativistic mean-field model. Calculations show that the experimental proton halo in the nuclei 26,27,28P can be reproduced by the model. The proton halos can appear in proton-rich nuclei because the total nuclear potential is attractive up to the radial distance r ≈ 5.5 fm. But the size of proton halos is finite due to the limitation of the Coulomb potential barrier. The mean-square radius of a halo proton is not very sensitive to the separation energy of the last proton in some very proton-rich nuclei due to the effect of the Coulomb barrier. This behavior is different from the case of a neutron halo where the mean-square radius of a halo neutron is inversely proportional to the separation energy of the last halo neutron. We have also analysed the differences of the relativistic mean-field potentials of 25Al and 26P and found that the isovector potential from the p meson has an important effect on the differences. 相似文献
3.
Odd-odd nuclei around double shell closures are a direct source of information on the proton-neutron interaction between valence nucleons. We have performed shell-model calculations for doubly odd nuclei close to 208Pb, 132Sn, and 100Sn using realistic effective interactions derived from the CD-Bonn nucleon-nucleon potential. The calculated results are compared with the available experimental data, attention being focused on particle-hole and particle-particle multiplets. While good agreement is obtained for all the nuclei considered, a detailed analysis of the matrix elements of the effective interaction shows that a stronger core-polarization contribution seems to be needed in the particle-particle case. 相似文献
4.
G. Fazio G. Giardina A. Lamberto R. Ruggeri F. Bonsignore R. Palamara A. I. Muminov A. K. Nasirov B. Benoit F. Hanappe T. Materna L. Stuttgé 《Physics of Atomic Nuclei》2003,66(6):1071-1085
By comparing theoretical and experimental excitation functions of evaporation residues resulting from the same compound nucleus or heavy and superheavy nuclei, it is possible to understand the effect of the entrance channel and the shell structure of reacting nuclei on the fusion mechanism. The competition of complete fusion with the quasifission process is strongly related to the intrinsic fusion barrier B fus * and the quasifission barrier B qf as well as the size of the well in the nucleus-nucleus potential. In our calculations of the excitation functions for capture, fusion, and evaporation residues, we use the relevant variables such as mass asymmetry of nuclei in the entrance channel, potential energy surface, driving potential, spin distribution, and surviving probability of compound nucleus that are responsible for the mechanism of the fusion-fission process. As a result, we obtain a beam energy window for the capture of the nuclei before the system fuses and the Γn/Γf ratio at each step along the deexcitation cascade of the compound nucleus. Calculations performed in the framework of the model taking into account the nuclear shell effect and shape of colliding nuclei allow us to reach useful conclusions about the mechanism of the fusion-fission process and the production of the evaporation residues. We analyze the 40Ar + 176Hf, 86Kr + 130Xe, and 124Sn + 92Zr reactions leading to 216Th*; the 32S + 182W and 60Ni + 154Sm reactions leading to 214Th*; the 48Ca + 248Cm reaction leading to the 296116 compound nucleus; and the 48Ca + 249Cf reaction leading to the 297118 compound nucleus. 相似文献
5.
A. Covello L. Coraggio A. Gargano N. Itaco 《The European physical journal. Special topics》2007,150(1):93-96
We report on a study of exotic nuclei around doubly magic 132Sn in terms of the shell model employing a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential.
The short-range repulsion of the bare potential is renormalized by constructing a smooth low-momentum potential, Vlow-k, that is used directly as input for the calculation of the effective interaction. In this paper we focus attention on the
nuclei
134Sn and 135Sb which, with an N/Z ratio of 1.68 and 1.65, respectively, are at present the most exotic nuclei beyond 132Sn for which information exists on excited states.
Comparison shows that the calculated results for both nuclei are in very good agreement with the experimental data. We present
our predictions of the hitherto unknown spectrum of
136Sn. 相似文献
6.
The halo-structure of a nucleus is analyzed on the basis of potential energy consideration and separation energy calculations and thereby characterized a nucleus as a halo nucleus. The separation energy analysis showed that 11Be, 14B, 15, 17, 19C, 22N, 23O, 24, 26F, and 29Ne are 1n-halo nuclei since the 1n separation energy S(n) is the lowest and 6, 8He, 11Li, 14Be, 17B, 22C, and 29F are 2n-halo candidates as 2n separation energy S(2n) is the lowest. The potential energy calculations are consistent with the predictions based on separation energy calculations except for 12Be, 19B, and 27F which can be considered as 2n-halo candidates by potential energy consideration. Also, a discrepancy is noticed in the case of the proposed 2n-halo 8He and 17B nuclei. Further, the possibility of emitting halo nucleus via heavy particle decay of heavy nuclei, within the range 82?≤?Z?≤?102, has been studied using the Coulomb and proximity potential model (CPPM). It is observed that the probability of emission of a halo nucleus is lower than that of a normal cluster Nevertheless, there is a finite chance of emission of a halo nucleus in the decay of a heavy nucleus. 相似文献
7.
Previously1 we have observed a 19 NMR asymmetric line in polycrystalline ThF4 in the 6–9 kOe fields, which was ascribed to the anisotropy of the 19F nuclei screening constant. However, the accepted interpretation in the case of a powder sample is not the only possible one, since in the presence of chemically or structurally non-equivalent fluorine atom groups spectrum asymmetry may also arise on account of the difference in the nuclei magnetic screening constants due to non-equivalent positions. This dilemma in the case of polycrystalline samples may be solved only when recording spectra in the highest fields. Non-equivalence of the nuclei may lead, to a split of the NMR spectrum into components, corresponding to the various positions. When spectrum asymmetry is due to the anisotropy of the screening constant, field strength rise may but lead to an increase of the total spectrum width, its shape remaining unaltered. 相似文献
8.
《Physics letters. [Part B]》1988,207(4):393-396
To seek for a possible way to determine ∑−-nuclear interactions even in the case of a shallow nuclear potential and/or a strong ∑-Λ conversion, theoretical discussions are given on the formation of Coulomb-assisted hybrid bound states of ∑− in nuclei, where the short-range strongly absorptive potential coexists with the long-range Coulomb potential. Bound states of hybrid character of medium widths are predicted, which can well be populated in (stopped K−, π+) reactions. 相似文献
9.
《Physics letters. [Part B]》1987,191(3):222-226
We study the damping width of the giant dipole resonance (GDR) built on the ground state and on excited states of 90Zr, which is spherical at zero spin and temperature, and 164Er which is deformed. Neither of these nuclei changes appreciably their equilibrium shape when excited. Nonetheless, fluctuations due to finite temperature produce a marked increase in the width of the GDR of 90Zr, leaving essentially unchanged that of 164Er. This is because in the case of deformed nuclei thermal fluctuations imply the sampling of both larger and smaller deformations around the equilibrium shape, while spherical nuclei can only feel larger distortions. In spite of the stability of the GDR of 164Er, the angular distribution of the associated γ-rays is strongly affected by the temperature. 相似文献
10.
The influence of the Pauli exclusion principle on the relative motion of light neutron-rich nuclei in their collision is investigated
within the microscopicmethod using as an example 11Be + n and 10Be + 2
n nuclear reactions, as well as 3
n + n and 2
n + 2
n reactions. Antisymmetrization effects related to the kinetic and potential energy of the relative motion of colliding nuclei
are analyzed. The influence of the Pauli exclusion principle on the kinetic energy of the relative motion of the 11Be nucleus and a neutron is shown to result in their attraction. The same phenomenon is observed for the case of the 3
n + n cluster system. The strength of such attraction is high enough to ensure the existence of a bound state in the 12Be nucleus and a low-energy resonance in the tetraneutron. The conclusion is drawn that, for a resonance state in the 4
n system to exist, the value of the oscillator length must be large enough. It is shown also that increasing the oscillator
length results in depression of the cluster-cluster potential.
The text was submitted by the authors in English. 相似文献
11.
Yu. E. Penionzhkevich 《Physics of Atomic Nuclei》2011,74(11):1615-1622
Experimental results on excitation functions for complete-fusion and transfer reactions in the interaction of 6He and 6,8,9Li nuclei with various target nuclei are presented. Data on fusion-reaction cross sections in the case of 6He differ strongly from the predictions of the statistical model. A strong enhancement of the cross section at barrier energies
is observed for this reaction channel. Also, an increase in the cross sections for neutron-transfer reactions (in the case
of 6He and 8,9Li beams) and deuteron-transfer reactions (in the case of 6Li) is observed in the deep-subbarrier energy region. The results are discussed from the point of view of the effect of the
cluster structure of nuclei on the probability of interaction at barrier energies. The results of employing heavy-ion beams
in new technologies are presented. 相似文献
12.
V. L. Litnevsky G. I. Kosenko F. A. Ivanyuk V. V. Pashkevich 《Physics of Atomic Nuclei》2011,74(7):1001-1009
The motion of two nuclei toward each other in fusion-fission reactions is considered. The state of the system of interacting
nuclei is specified in terms of three collective coordinates (parameters). These are the distance between the centers of mass
of the nuclei and the deformation parameter for each of them (the nose-to-nose orientation of the nuclei is assumed). The
evolution of collective degrees of freedom of the system is described by Langevin equations. The energies of the Coulomb and
nuclear (Gross-Kalinovsky potential) interactions of nuclei are taken into account in the potential energy of the system along
with the deformation energy of each nucleus with allowance for shell effects. The motion of nuclei toward each other are calculated
for two reaction types: reactions involving nuclei that are deformed (42100Mo + 42100Mo → 84200Po) and those that are spherical (82208Pb + 818O → 90226Th) in the ground state. It is shown that the shell structure of interacting nuclei affects not only the fusion process as
a whole (fusionbarrier height and initial-reaction-energy dependence of the probability that the nuclei involved touch each
other) but also the processes occurring in each nucleus individually (shape of the nuclei and their excitation energies at
the point of touching). 相似文献
13.
The direct proton capture and resonance proton capture properties of stellar reactions 22Mg(p,γ)23Al and 26Si(p,γ)27P are studied by employing a mean-field potential obtained from the Skyrme-Hartree-Fock(SHF) model.Calculations with the SHF potential reproduce well the loosely-bound structure of the ground states as well as the widths of the resonant states in these nuclei.With the obtained potential we estimate the reaction rates of direct proton capture and resonance proton capture to nuclei 23Al and 27P.... 相似文献
14.
The total binding energy of nuclei is determined by means of many-body field theory. The problem is then reduced to finding the energy-dependent average potential (mass operator) and solving the single-particle equations of motion. Such a potential can be established phenomenologically by using data on low excitations and reactions knocking out nucleons from deep “hole” levels. Calculations of the total binding energy of the nuclei 16O, 40Ca and 58Ni with this potential are in satisfactory agreement with experiment. 相似文献
15.
R. Dymarz J. L. Molina K. V. Shitikova 《Zeitschrift für Physik A Hadrons and Nuclei》1981,299(3):245-249
The interaction potential of heavy ions4He,6Li,12C and16O is constructed in the folding model. The density distribution of nuclear matter for these nuclei is calculated in the framework of the hyperspherical function method. For the calculation of the folding potentials we have employed the Skyrme nucleon-nucleon forces. The influence of several effects on the results of calculations is studied: the role of the three-body forces of the nucleon-nucleon interaction, dependence of the folding potential on the mass numbers of the colliding nuclei and the possibility of observing the monopole resonance in the ion inelastic scattering. Using our folding potential as a real part of the optical potential we have calculated the differential cross section of elastic scattering of6Li from12C at laboratory energy of lithium ionsT L =90.0 MeV. Reasonable agreement with experiment is obtained. 相似文献
16.
V. Yu. Denisov A. A. Khudenko 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(4):554-558
The expression for the α-nuclear potential was found. This potential describes the α-decay half-lives for the ground states
of nuclei and the α-particle capture cross sections for 40Ca, 44Ca, 59Co, 208Pb, and 209Bi nuclei well. The potential was used to calculate the probabilities of α-transitions from the ground states of parent nuclei
to different excited states of daughter nuclei. Simple analytical relations for calculating α-decay half-lives for transitions
between the ground states of nuclei are determined. 相似文献
17.
A. Faessler M. Rashdan M. Ismail N. Ohtsuka W. Wadia 《Zeitschrift für Physik A Hadrons and Nuclei》1989,333(2):153-162
The effect of nuclear and Coulomb interactions on the shapes of two colliding208Pb nuclei at finite temperature is investigated. The complex potential energy density derived by Faessler and collaborators and the kinetic energy density and entropy density for two Fermi spheres at finite temperature are used to calculate the free energy of the208Pb +208Pb system in the energy density formalism. Shell corrections are added to the free energy in the framework of the Strutinsky method. The total free energy is minimized with respect to the quadrupole deformation and the diffuseness to determine the density distribution of208Pb nucleus at certain distanceR and temperatureT assuming the deformed Woods-Saxon shape for each nucleus. It is found that the nucleus acquires larger deformation and diffuseness as the temperature increases. The interaction potential between two208Pb nuclei is calculated from the minimized free energy. The total (nuclear + Coulomb) potential is found to decrease with increasing temperature, whereas the real part of the nuclear potential becomes more repulsive as the temperature increases. 相似文献
18.
G. Fazio G. Giardina A. Lamberto R. Ruggeri C. Saccá R. Palamara A. I. Muminov A. K. Nasirov U. T. Yakhshiev F. Hanappe T. Materna L. Stuttgé 《The European Physical Journal A - Hadrons and Nuclei》2004,19(1):89-104
The effects of the entrance channel and shell structure on the experimental evaporation residues have been studied by analyzing the 32S + 182W, 48Ti + 166Er and 60Ni + 154Sm reactions leading to 214Th*; the 40Ar + 181Ta reaction leading to 221Pa*; the 48Ca + 243Am, 248Cm, 249Cf reactions leading to the 291115, 296116 and 297118 superheavy compound nuclei, respectively. The fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei have been studied. In calculations of the excitation functions for capture, fusion and evaporation residues we used such characteristics as mass asymmetry of nuclei in the entrance channel, binding energies and shape of colliding nuclei, potential energy surface, driving potential, partial-fusion cross-sections and survival probability of the compound nucleus,
ratio at each step along the de-excitation cascade of the compound nucleus. The calculations have allowed us to make useful conclusions about the mechanism of the fusion-fission process, which is in competition with the quasifission process, and the production of the evaporation residues.Received: 22 April 2003, Revised: 26 June 2003, Published online: 18 December 2003PACS:
25.70.Gh Compound nucleus - 25.70.-z Low and intermediate energy heavy-ion reactions - 27.80. + w
- 27.90. + b
相似文献
19.
V. I. Isakov K. A. Mezilev Yu. N. Novikov K. I. Erokhina B. Fogelberg H. Mach 《Physics of Atomic Nuclei》2000,63(10):1740-1746
The mass surface of nuclei close to the doubly magic nuclide 78Ni is calculated by two methods. The first relies on the multiparticle shell model based on an effective interaction and a mean nuclear potential. The second employs the concept of so-called “magic crosses” and enables us to determine the masses of odd-odd nuclei close to 78Ni by using similarity of the shell structure and neutron-proton interaction in the region of nuclei under consideration and in the region of heavy magic nuclides. The energies of the separation of one and two neutrons from nuclei close to 78Ni and the energies of the β decay of these nuclei—recall that these quantities of astrophysical interest—are presented. 相似文献
20.
We study ΛK~+ pair production in the interaction of protons of 2.83 GeV kinetic energy with C, Cu,Ag, and Au target nuclei in the framework of the nuclear spectral function approach for incoherent primary proton–nucleon and secondary pion–nucleon production processes, and processes associated with the creation of intermediate Σ~0K~+ pairs. The approach accounts for the initial proton and final Λ hyperon absorption, final K~+ meson distortion in nuclei, target nucleon binding, and Fermi motion, as well as nuclear mean-field potential effects on these processes.We calculate the Λ momentum dependence of the absolute ΛK~+ yield from the target nuclei considered, in the kinematical conditions of the ANKE experiment, performed at COSY, within the different scenarios for the Λ-nucleus effective scalar potential. We show that the above observable is appreciably sensitive to this potential in the low-momentum region. Therefore, direct comparison of the results of our calculations with the data from the ANKE-at-COSY experiment can help to determine the above potential at finite momenta. We also demonstrate that the two-step pion–nucleon production channels dominate in the low-momentum ΛK~+ production in the chosen kinematics and, therefore, they have to be taken into account in the analysis of these data. 相似文献