共查询到20条相似文献,搜索用时 32 毫秒
1.
M. Petrascu 《Physics of Atomic Nuclei》2003,66(8):1528-1535
The main characteristics of the halo neutron preemission in the fusion of 11Li nuclei with light targets are reviewed. The recent experiment with a new array detector aimed at investigating neutron pair preemission is described. The position distribution measurement confirms the preemission of the halo neutrons in a very narrow forward cone of ~9 msrad. A novel approach for cross-talk rejection is described. By means of this approach, the true n-n coincidence sample was obtained. In view of obtaining the n-n correlation function, the crucial problem of the denominator construction is thoroughly analyzed. It was found that the single-product denominator built by a random coupling of single detected neutrons followed by cross-talk rejection, exceeds by up to 70% the denominator constructed by the event-mixing technique. We consider this behavior of the single-product denominator together with the large fluctuations seen when represented in small steps of relative momentum q as experimental evidence for residual correlation of single detected halo neutrons. 相似文献
2.
E. S. Konobeevski V. P. Zavarzina S. V. Zuyev A. A. Kasparov A. S. Kurlovich V. V. Mitsuk 《Physics of Atomic Nuclei》2018,81(5):604-608
An experimental investigation of the reaction of core pickup from 6He and 11Li two-neutronhalo nuclei is proposed. In such experiments, neutron–neutron correlations in a halo nucleus will be assessed on the basis of the energy of a neutron–neutron quasibound state. A detailed kinematical simulation of the reaction 6He + 2H → 6Li + (nn) →6 Li + n + n is performed. It is shown that the energy of the quasibound state in question can determined from the shape of the energy spectrum of neutrons originating from the breakup of this state. In the proposed exclusive experiment, a beam of 6He (11Li) nuclei with an energy of about 5 to 10 MeV per nucleon interacts with a deuterated-polyethylene target. This will permit detecting charged particles (6Li and 11Be) and a neutron. On the basis of determining the energy of the neutron–neutron quasibound state, it will become possible to estimate the effective attraction between the valence neutrons in the field of the third particle (core). 相似文献
3.
The spatial structure of lithium isotopes is studied with the aid of the charge-exchange and (t, p) reactions on lithium nuclei. It is shown that an excited isobaric-analog state of 6Li (0+, 3.56MeV) has a halo structure formed by a proton and a neutron, that, in the 9Li nucleus, there is virtually no neutron halo, and that 11Li is a Borromean nucleus formed by a 9Li core and a two-neutron halo manifesting itself in cigar-like and dineutron configurations. 相似文献
4.
Recent data resulting from studies of two-nucleon transfer reaction on 11Li, analyzed through a unified nuclear-structure-direct-reaction theory have provided strong direct as well as indirect confirmation, through the population of the first excited state of 9Li and of the observation of a strongly quenched ground state transition, of the prediction that phonon-mediated pairing interaction is the main mechanism binding the neutron halo of the 8.5-ms-lived 11Li nucleus. In other words, the ground state of 11Li can be viewed as a neutron Cooper pair bound to the 9Li core, mainly through the exchange of collective vibration of the core and of the pigmy resonance arizing from the sloshing back and forth of the neutron halo against the protons of the core, the mean field leading to unbound two-particle states, a situation essentially not altered by the bare nucleon-nucleon interaction acting between the halo neutrons. Two-neutron pick-up data, together with (t, p) data on 7Li, suggest the existence of a pairing vibrational band based on 9Li, whose members can be excited with the help of inverse kinematic experiments as was done in the case of 11Li(p, t)9Li reaction. The deviation from harmonicity can provide insight into the workings of medium polarization effects on Cooper-pair nuclear pairing, let alone specific information concering the “rigidity” of the N = 6 shell closure. Further information concerning these questions is provided by the predicted absolute differential cross sections σ abs associated with the reactions 12Be(p, t)10Be(g.s.) and 12Be(p, t)10Be(pv) (≈10Be(p, t)8Be(g.s.)). In particular, concerning this last reaction, predictions of σ abs can change by an order of magnitude depending on whether the halo properties associated with the d 5/2 orbital are treated selfconsistently in calculating the ground state correlations of the (pair removal) mode, or not. 相似文献
5.
L. I. Galanina N. S. Zelenskaya 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(4):383-387
The spatial periphery structure of lithium isotopes with A = 9 and 11 is investigated using the (t, p) reaction for 7,9Li nuclei. It is shown that the neutron halo is almost absent in the 9Li nucleus, while the 11Li nucleus has the Borromean halo structure formed by two neutrons relative to the 9Li core, which manifests itself in both the cigar and the dineutron configurations. 相似文献
6.
V. P. Zavarzina E. S. Konobeevski A. V. Stepanov 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(6):797-805
The nuclear vertex functions for virtual decay of halo nuclei 6He → α + n + n (11Li-9Li + n + n) for dineutron and cigarlike configurations of the neutron halo have been analytically investigated using the diagram method of direct nuclear reactions. These vertex functions describe the one-step process of two-neutron transfer. It is shown that the angular and energy distributions of the reaction products (α particles, 9Li, etc.) in different ranges of variables correspond to different structural elements of the halo. The vertex function describing the two-step process of halo neutron transfer has also been analyzed. 相似文献
7.
The spatial structure of the periphery of lithium and beryllium isotopes is studied by means of charge-exchange reactions and the (t, p) and (d, p) reactions on their nuclei. It is shown that the 0+ isobaric-analog state of 6Li at 3.56 MeV has a halo structure formed by a proton and a neutron, that there is virtually no manifestation of a neutron halo in the ground state of the 9Li nucleus, and that the 11Li nucleus has a Borromean halo structure that two neutrons form with respect to the 9Li core and which manifests itself in cigar and dineutron configurations. The 10Be nucleus has a substantial two-neutron periphery in either configuration both in the ground and in the 2+ excited state at 3.37MeV. 相似文献
8.
B. D. Danilin I. J. Thompson M. V. Zhukov J. S. Vaagen 《Physics of Atomic Nuclei》2001,64(7):1215-1222
Modern few-body methods for investigating Borromean two-neutron halo nuclei are discussed together with recent experiments. Advances in the studies of 6He and 11Li are analyzed. Some new problems created by a large neutron excess and a halo phenomenon are considered. 相似文献
9.
《Nuclear Physics A》1995,588(1):c113-c119
The structure of neutron-rich unstable nuclei is discussed by focusing on three different subjects; (i) a superdeformed halo nucleus 11Be studied by a deformed Woods-Saxon potential, (ii) retarded β decay due to neutron halo in 11Li, and (iii) giant neutron excitations in nuclei with neutron skin. 相似文献
10.
《Nuclear Physics A》1995,588(1):c91-c97
We show that a large number of neutrons are expected to be transferred from the projectile to the target if a neutron rich unstable nucleus with a neutron skin is used as the projectile in heavy-ion collisions at energies about twice the Coulomb barrier. We then show that though the neutron halo enhances the fusion cross section through the size effect, the additional effect due to the molecular bond formation is not significant in the fusion between 11Li and 9Li at energies near and below the Coulomb barrier. 相似文献
11.
The proton and neutron densities, root-mean-square (rms) radii of proton density and neutron density, and neutron skin thickness
of 4–10He, 6–11Li, and 7–12Be isotopes are calculated using Skyrme-Hartree-Fock method with SLy4, SLy5, SLy6, and SLy7 force parameters. The evaluated
results are compared with experimental data. Also, the results of halo nuclei (6,8He, 11Li, and 11Be) are compared with the results of other isotopes for selected nuclei having the same neutron configuration. 相似文献
12.
I. N. Izosimov 《Physics of Particles and Nuclei Letters》2018,15(6):621-626
It is shown that when the parent nucleus has nn Borromean halo structure, then after Gamow–Teller (GT) β–-decay of parent state or after M1 γ-decay of Isobar Analogue Resonance (IAR) the states with np tango halo structure or mixed np tango + nn Borromean halo structure can be populated. Resonances in the GT β-decay strength function Sβ(E) of halo nuclei, may have np tango halo structure or mixed np tango + nn Borromean halo structure. Correct interpretation of halo structure is important in experiments on β-decay study, interpretation of M1 γ-decay of IAR, and charge-exchange nuclear reactions analysis. 相似文献
13.
F. Pougheon 《Zeitschrift für Physik A Hadrons and Nuclei》1994,349(3-4):273-278
A brief summary is done of the various types of experiment used in studies of the very neutron rich nuclei. Some highlights are given for the two-neutron halo and11Li nucleus and for the one-neutron halo and11Be nucleus. 相似文献
14.
《Nuclear Physics A》1999,650(1):47-61
The halo nuclei 11Be and 11Li have been studied in core-breakup reactions where the halo neutrons are expected to be released without a major distortion due to the reaction. The widths of the halo-neutron momentum distributions have been extracted in coincidence with He fragments, Γ = 32 ± 4 MeV/c, and Li fragments, Γ = 42 ± 4 MeV/c for 11Be and with He fragments, Γ = 42 ± 6 MeV/c for 11Li. The 11Be breakup gives a very low neutron multiplicity of 0.38±0.09 which is a manifestation of the shadowing of the neutron in the core-breakup reaction. This value can be understood from a simple theoretical calculation, which also accounts for the observed transverse momentum widths at small angles. 相似文献
15.
Isao Tanihata 《Acta Physica Hungarica A》1997,6(1-4):127-142
The use of radioactive nuclear beams (RNB) has provided an opportunity to study nuclei far from the stability line. Reaction studies using intermediate and high-energy (30–1000 AMeV) radioactive beams have revealed new structures of nuclei that are not seen in nuclei near to the stability line [1]. One such new structure is the neutron halo, a long low-density tail of the neutron distribution [2]. It has been observed in neutron drip-line nuclei, such as6He,11Li and11Be. The neutron halo has put light on many new structure problems. Among those, recent studies of a softE1 mode, a low-frequency oscillation of halo neutrons against the core, are discussed in the following section in connection with a recent (p, p′) reaction measurement [3]. Also, the effect of changes in single-particle orbitals on halo formation is discussed [4]. Another new finding is the formation of neutron skins in neutron-rich unstable nuclei [5]. The relation between the equation-of-state (EOS) of asymmetric nuclear matter and the neutron-skin thickness as well as the density distribution of nuclei far from the stability line is discussed in the last section. 相似文献
16.
B. Blank J. -J. Gaimard H. Geissel K. -H. Schmidt H. Stelzer K. Sümmerer D. Bazin R. Del Moral J. P. Dufour A. Fleury F. Hubert H. -G. Clerc M. Steiner 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(1):41-50
Total interaction cross sections have been measured for8Li on C and Pb targets, for9Li on C, Al, Cu, Sn and Pb targets as well as for11Li on C, Sn and Pb targets. For each beam, we also used a plastic scintillator as target. The measurements with the scintillator targets are used to extract reduced nuclear radii of the lithium isotopes. These radii are then used for the calculation of the nuclear part of the total cross section for the other targets. The total electromagnetic-dissociation (EMD) cross sections have been deduced and are compared to different models. A strong target-charge-dependent EMD cross section is measured for11Li reaching 2.96
–0.82
+0.84
b for the Pb target. In the9Li case, a large EMD cross section for high-Z targets has been observed which amounts to 0.75 ± 0.45 b for the Pb target. The EMD cross sections of both,9Li and11Li, may be understood by the giantdipole-resonance model.This work forms part of the PhD Thesis of B. Blank 相似文献
17.
J. S. Vaagen I. J. Thompson J. M. Bang M. V. Zhukov B. V. Danilin D. V. Fedorov 《Zeitschrift für Physik A Hadrons and Nuclei》1994,349(3-4):285-290
The discovery of light nuclei with neutron halos has opened new perspectives for nuclear structure and a possibility to study genuine few-body aspects of matter. A number of borromean systems where the system is bound but where no binary subsystems are bound, are realized by nature in the context of nuclei,11Li being the nucleus which has had most recent attention. Although a large number of calculations have addressed the detailed structure of the11Li neutron halo, no single model has yet explained all the data presently available. This is in part due to uncertainties in then+9Li interaction. For6He, also a borromean system, where then+core interaction is known, the best three-body and reaction models succeed in reproducing the data. In the11Li case, a major uncertainty concerns the effect of possible 1s intruder states. 相似文献
18.
B. V. Danilin N. B. Shul’gina S. N. Ershov J. S. Vaagen RNBT Collaboration 《Physics of Atomic Nuclei》2009,72(8):1272-1284
Hyperspherical-harmonics method to investigate the lightest nuclei having three-cluster structure is discussed together with
recent experiments. Properties of bound states and methods to explore three-body continuum are presented. The challenges created
by large neutron excess and halo phenomena are highlighted. Astrophysical aspects of the 7Li + n → 8Li + γ reaction and the solar-boron-neutrinos problem are analyzed. Three-cluster structure of highly excited states in 8Be is shown to be responsible for extreme isospin mixing. Progress in studies of 6He- and 11Li-induced inclusive and exclusive nuclear reactions is demonstrated, providing information on the nature of continuum structures
of Borromean nuclei.
The text was submitted by the authors in English. 相似文献
19.
P. Egelhof G.D. Alkhazov M.N. Andronenko A. Bauchet A.V. Dobrovolsky S. Fritz G.E. Gavrilov H. Geissel C. Gross A.V. Khanzadeev G.A. Korolev G. Kraus A.A. Lobodenko G. Münzenberg M. Mutterer S.R. Neumaier T. Schäfer C. Scheidenberger D.M. Seliverstov N.A. Timofeev A.A. Vorobyov V.I. Yatsoura 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):27-33
Proton-nucleus elastic scattering at intermediate energies, a well-established method for probing nuclear-matter density distributions
of stable nuclei, was applied for the first time to exotic nuclei. This method is demonstrated to be an effective means for
obtaining accurate and detailed information on the size and radial shape of halo nuclei. Absolute differential cross-sections
for small-angle scattering were measured at energies near 700 MeV/u for the neutron-rich helium isotopes 6He and 8He, and more recently for the lithium isotopes 6Li, 8Li, 9Li and 11Li, using He and Li beams provided by the fragment separator FRS at GSI Darmstadt. Experiments were performed in inverse kinematics
using the hydrogen-filled ionization chamber IKAR which served simultaneously as target and recoil-proton detector. For deducing
nuclear-matter distributions, differential cross-sections calculated with the aid of the Glauber multiple-scattering theory,
using various parametrizations for the nucleon density distributions as input, were fitted to the experimental cross-sections.
The results on nuclear-matter radii and matter distributions are presented, and the significance of the data for a halo structure
is discussed. Nuclear-matter distributions obtained for 6He and 8He conform with the concept that both nuclei compose of α-particle like cores and significant neutron halos. The matter distribution
in 11Li exhibits, as expected from previous reaction cross-section studies with nuclear targets, the by far most extended halo
component of all nuclei being investigated. In addition the present data allow a quantitative comparison of the structure
of the He and Li isobares of either the mass number A = 6 or A = 8. The measured differential cross-sections have also been used for probing density distributions as predicted from various
microscopic calculations. A few examples are presented.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: p.egelhof@gsi.de 相似文献
20.
In order to clear up the sensitivity of the nucleus-nucleus reaction cross sections σ R to the nuclear matter distributions in exotic halo nuclei, we have calculated the values of σ R for scattering of 6He, 11Li, and 19C nuclei on several nuclear targets at the energy of 0.8 GeV/nucleon. The calculations were performed in the “rigid target” approximation to the Glauber theory, different shapes of the nuclear density distributions in 6He, 11Li, and 19C being assumed. 相似文献