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1.
S. P. Kamerdzhiev 《Physics of Atomic Nuclei》2006,69(7):1110-1118
Consideration is given to a short review of the main features, recent results, and prospects of the Extended Theory of Finite
Fermi Systems (ETFFS), which has been applied in the past 15 years to collective excitations in the neutral channel for nuclei
with and without pairing. The theory is an extension of the Migdal standard TFFS to include in a consistent way the single-particle
continuum and more complex 1p1h ⊗ phonon or 2qp ⊗ phonon configurations beyond the RPA or QRPA ones; i.e., the theory takes into account all three known
mechanisms of giant-resonance width. To the most extent, the theory was developed and applied to nuclei without pairing. A
quantitative explanation of the giant-resonance widths was obtained, with the complex configurations contributing about half
of the width. In addition, a large part of the observed giant-resonance gross and fine structures can be directly traced back
to the specific complex configurations, and the recent results of the (α, α′) experiments in 40Ca and 58Ni could be explained. Consistent use of the Green’s function method makes it possible to include and calculate some effects
which were practically unstudied earlier. These are ground-state correlations induced by complex configurations and “refined”
basis effects, in particular, the second (or quasiparticle-phonon) mechanism of pairing. Both of them can be studied in current
experiments. In the past five years, the ETFFS has been developed and applied actively to even—even and odd-mass nuclei with
pairing. Calculations of the E1 pygmy resonance in Ca and Sn isotopes have shown that this phenomenon, which is important for (n, γ) and (γ, n) reactions, cannot be explained without allowing for complex configurations. Consideration of the single-particle continuum
and the practical universality of the interaction parameters allow the ETFFS to be used for calculations of unstable nuclei.
The prospects and status of the necessary development of a self-consistent ETFFS for nuclei with pairing are discussed.
The text was submitted by the author in English. 相似文献
2.
G. Pantis F. Šimkovic J. Schwieger Amand Faessler 《Czechoslovak Journal of Physics》1998,48(2):209-212
The standard quasiparticle random phase approximation(QRPA) is widely used to describe the neutrinoless double beta decay
process. Although it has been quite successful in many cases of interest, it has some shortcomings. The most important one
is that its solutions collapse for physical values of the particle-particle strength. We shall show that modifications can
be done which can extend the validity of this standard QRPA beyond the point of collapse. Such modifications are: The introduction
of proton-neutron pairing, the inclusion of the Pauli principle and the extension of the Hilbert space. If all these modifications
are introduced into the standard QRPA then the collapse does not occur for physical values of the particle-particle strengths.
Thus, one might be able to extract more accurate values on the effective neutrino mass by using the best available experimental
limits on the half life of neutrinoless double beta decay.
Presented by G. Pantis at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’97), Prague, May 27–31,
1997. 相似文献
3.
The decay of “subcritical” nuclei in a solid solution has been revealed in the investigation of the CuCl phase nucleation
kinetics in glass. As soon as “supercritical” nuclei with an average radius R = 1.1 nm are created at 500°C, a sharp temperature increase up to 650°C transforms most nuclei created in the first annealing
stage into “subcritical” ones, and this results in the decay of 80% of the nuclei in 5 min, while the remaining 20% of the
nuclei grow in size to 2.4 nm. Their growth provides a sixfold increase in the CuCl phase growth rate against that in conventional
annealing at 650°C. The kinetic dependences of the nucleation parameters—the amount of the phase and the average radius and
concentration of the particles—were determined by the intrinsic absorption spectra of the CuCl nanocrystals. The critical
radius of the CuCl nanomelt at 650°C has been estimated as 1.3 nm and the evaporation heat of the CuCl phase molecules in
glass, as 13 kJ/mol. It is shown that multistage annealing makes it possible not only to control the parameters of the particles
of the new phase, but also to determine the critical parameters of the initial nucleation stage. 相似文献
4.
Th. Kröll T. Behrens R. Krücken V. Bildstein R. Gernhäuser P. Maierbeck I. Stefanescu O. Ivanov J. Van de Walle N. Warr P. A. Butler J. Cederkäll P. Delahaye L. M. Fraile G. Georgiev U. Köster T. Sieber D. Voulot F. Wenander P. E. Kent A. Ekström K.-H. Speidel J. Leske S. Schielke D. Habs R. Lutter P. Thirolf H. Scheit T. Davinson 《The European physical journal. Special topics》2007,150(1):127-129
We report on “safe” Coulomb excitation of neutron-rich 138,140,142Xe
nuclei.
The radioactive nuclei have been produced by ISOLDE at CERN and
post-accelerated
by the REX-ISOLDE facility. The γ-rays emitted by the decay of excited
states have been detected by the MINIBALL array. Recent results are
presented. 相似文献
5.
The spatial structure of the correlation function of the order parameter of the $
d_{x^2 - y^2 }
$
d_{x^2 - y^2 }
symmetry has been investigated within the t-J model in the generalized mean field approximation taking into account the “no-double occupancy” constraint due to strong
electron correlations. A slow decay of the correlation function to the thirtieth coordination sphere has been found. The limitation
by pairing of only the nearest neighbors makes it possible to take into account less than 17% of the superconducting correlations. 相似文献
6.
V. N. Berzhanskiĭ A. I. Gorbovanov S. N. Polulyakh N. V. Pronina 《Physics of the Solid State》1998,40(8):1357-1359
The effect of silicon impurities on the damping of spin-echo signals from the 57Fe nuclei of tetrahedral Fe3+ ions in epitaxial yttrium-iron-garnet films was investigated. It was found that for silicon concentrations 0.015⩽x⩽0.037 the damping of the spin echo is a two-component process, which made it possible to separate nuclei into two types,
differing by both the longitudinal and transverse magnetic relaxation times. For silicon concentrations 0.044⩽x⩽0.073 the decay of the echo can be described by one exponential and all nuclei in the sample have the same transverse relaxation
times and the same longitudinal relaxation times. The experimental results are interpreted on the basis of the supposition
that impurity “macromolecules” form around the Si4+ ions. The relaxation times of the iron nuclei in a “macromolecule” are much shorter than the relaxation times of iron nuclei
belonging to the matrix ions. The radius of a “macromolecule” is estimated on the basis of percolation theory.
Fiz. Tverd. Tela (St. Petersburg) 40, 1494–1497 (August 1998) 相似文献
7.
We introduce a new coupled map lattice model in which the weak interaction takes place via rare “collisions”. By “collision”
we mean a strong (possibly discontinuous) change in the system. For such models we prove uniqueness of the SRB measure and
exponential space-time decay of correlations. 相似文献
8.
Th. Kröll 《Physics of Atomic Nuclei》2007,70(8):1369-1374
We report on “safe” Coulomb excitation of neutron-rich nuclei. The radioactive nuclei have been produced by ISOLDE at CERN
and postaccelerated by the REX-ISOLDE facility. The γ rays emitted by the decay of excited states have been detected by the MINIBALL array. Recent results are presented and compared
to theoretical models.
on behalf of the MINIBALL and REX-ISOLDE Collaborations
The text was submitted by the author in English. 相似文献
9.
10.
O. P. Shustova N. N. Kalmykov A. V. Uryson 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(3):313-315
The composition of cosmic rays as they propagate from their source is noticeably distorted due to the photodisintegration
of nuclei against the background cosmic radiation. We analyze the propagation of different nuclei groups of ultrahigh-energy
cosmic rays on the way from their source to an earth-based facility. Two types of sources are considered: “nearby” (within
an area having a radius of ≈40 Mpc) and “remote” (at distances of hundreds of Mpc) active galactic nuclei. We show that within
the accepted model, the composition of the particles incident on the facility depends on the source type. 相似文献
11.
We assess the validity of “microscopic” approaches of glass-forming liquids based on the sole knowledge of the static pair
density correlations. To do so, we apply them to a benchmark provided by two liquid models that share very similar static
pair density correlation functions while displaying distinct temperature evolutions of their relaxation times. We find that
the approaches are unsuccessful in describing the difference in the dynamical behavior of the two models. Our study is not
exhaustive, and we have not tested the effect of adding corrections by including, for instance, three-body density correlations.
Yet, our results appear strong enough to challenge the claim that the slowdown of relaxation in glass-forming liquids, for
which it is well established that the changes of the static structure factor with temperature are small, can be explained
by “microscopic” approaches only requiring the static pair density correlations as nontrivial input. 相似文献
12.
Disordering effects in superconductors with anisotropic pairing: From Cooper pairs to compact bosons
In the weak-coupling BCS-theory approximation, normal impurities do not influence the superconducting transition temperature
T
c
in the case of isotropic s pairing. In the case of d pairing they result in a rapid destruction of the superconducting state. This is at variance with many experiments on the
disordering of high-T
c
superconductors, assuming that d pairing is realized in them. As the interelectronic attraction in a Cooper pair increases, the system transforms continuously
from a BCS-type superconductor with “loose” pairs to a picture of superconductivity of “compact,” strongly coupled bosons.
Near such a transition substantial deviations can be expected from the universal disorder dependence of T
c
, as determined by the Abrikosov-Gor’kov equation, and T
c
becomes more stable against disordering. Since high-T
c
super-conducting systems fall into the transitional region from BCS-type pairs to compact bosons, these results can explain
their relative stability against disordering.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 258–262 (10 February 1997) 相似文献
13.
Vadim Rodin Amand Faessler Fedor Šimkovic Petr Vogel 《Czechoslovak Journal of Physics》2006,56(5):495-503
The nuclear matrix elements M
0ν
of the neutrinoless double-beta decay (0νβ β) of most nuclei with known 2νββ-decay rates are systematically evaluated using the Quasiparticle Random Phase Approximation (QRPA) and Renormalized QRPA
(RQRPA). The experimental 2νβ β-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. With such procedure
the M
0ν
values become essentially independent of single-particle basis size, the axial vector quenching factor, etc. Theoretical
arguments in favor of the adopted way of determining the interaction parameters are presented. It is suggested that most of
the spread among the published M
0ν
’s can be ascribed to the choices of implicit and explicit parameters, inherent to the QRPA method.
Presented by V. Rodin at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September
26–29, 2005. 相似文献
14.
L. S. Schulman 《Foundations of Physics》1997,27(12):1623-1636
The quantum Zeno effect (QZE) is often associated with the ironic maxim, “a watched pot never boils”, although the notion
of “watching” suggests a continuous activity at odds with the usual (pulsed measurement) presentation of the QZE. We show
how continuous watching can provide the same halting of decay as the usual QZE, and, for incomplete hindrance, we provide
a precise connection between the interval between projections and the response time of the continuous observer. Thus, watching
closely, but not so closely as to halt the “boiling”, is equivalent to—gives the same degree of partial hindrance as—pulsed
measurements with a particular pulsing rate. Our demonstration is accomplished by treating the apparatus for the continuous
watching as a fully quantum object. This in turn allows us a second perspective on the QZE, in which it is the modified level
structure of the combined system/apparatus Hamiltonian that slows the decay. This and other considerations favor the characterization
“dominated time evolution” for the QZE. 相似文献
15.
F. Calvayrac A. Domps E. Suraud S. El-Gammal C. Kohl P. -G. Reinhard 《Czechoslovak Journal of Physics》1998,48(6-7):715-724
We discuss and compare the dipole resonance modes in nuclei and metal clusters under varying conditions: different excitation
mechanisms in the case of nuclei, changed back-ground structure in the case of clusters. The resonances are generally nicely
harmonic modes, even those with a large amplitude. Only extreme shapes, as they occur in fusion and fission, can perturb this
harmonicity.
Presented by P.-G. Reinhard at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5,
1997. 相似文献
16.
An algorithm has been proposed to build an estimate of the half-life of a “daughter” nucleus in case, when it is unknown,
which nucleus is its “mother” (“indefinite start time”). For a decay of the “mother” at an instant t we can determine P—a probability of such a decay, if we assume that each “mother”, which has been decayed before t has equal chances to be “mother” of this “daughter”:
$
\sum\limits_{i = 1}^{n_t } {exp\left( { - \frac{{t - t_i }}
{\tau }} \right)} ,
$
\sum\limits_{i = 1}^{n_t } {exp\left( { - \frac{{t - t_i }}
{\tau }} \right)} ,
相似文献
17.
Within the framework of quasiparticle random phase approximation (QRPA), Pyatov-Salamov method [23] for the self-consistent
determination of the isovector effective interaction strength parameter, restoring a broken isotopic symmetry for the nuclear
part of the Hamiltonian, is used. The isospin admixtures in the ground state of the parent nucleus, and the isospin structure
of the isobar analog resonance (IAR) state were investigated with the inclusion of the pairing correlations between nucleons
for the medium and heavy mass regions: 80 <A < 90, 102 <A < 124, and 204 <A < 214. It was determined that the influence of the pairing interaction between nucleons on the isospin admixtures in the
ground state and the isospin structure of the IAR state is more pronounced for the light isotopes (N ≈ Z) of the investigated nuclei 相似文献
18.
Yu.Ts. Oganessian V.K. Utyonkov Yu.V. Lobanov F.Sh. Abdullin A.N. Polyakov I.V. Shirokovsky Yu.S. Tsyganov G.G. Gulbekian S.L. Bogomolov B.N. Gikal A.N. Mezentsev S. Iliev V.G. Subbotin A.M. Sukhov O.V. Ivanov G.V. Buklanov K. Subotic A.A. Voinov M.G. Itkis K.J. Moody J.F. Wild N.J. Stoyer M.A. Stoyer R.W. Lougheed C.A. Laue 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):201-204
This paper presents results of the experiments aimed at producing long-lived superheavy elements located near the spherical-shell
closures with Z ⩾ 114 and N ⩾ 172 in the 244Pu + 48Ca and 248Cm + 48Ca reactions. The large measured α-particle energies of the newly observed nuclei, together with the long decay times and
spontaneous fission terminating the chains, offer evidence of the decay of nuclei with high atomic numbers. The decay properties
of the synthesized nuclei are consistent with the consecutive α-decays originating from the parent nuclides 288, 289114 and 292116, produced in the 3n and 4n evaporation channels with cross-sections of about a picobarn. The present observations can be considered as experimental
evidence of the existence of the “island of stability” of superheavy elements.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: utyonkov@sungns.jinr.ru 相似文献
19.
H. J. Krappe 《Czechoslovak Journal of Physics》1998,48(6-7):803-807
The gross features of potential-energy surfaces of metallic, liquid clusters are compared with the corresponding properties
of nuclei and their influence on the decay modes of excited systems is discussed. The interaction of two spherical, surface-charged
droplets is compared with heavy-ion interaction potentials.
Presented at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1998. 相似文献
20.
Ye.S. Golubeva L.A. Kondratyuk M. Büscher W. Cassing V. Hejny H. Ströher 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):237-245
The ω resonance production and its π0γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π0γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively.
The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for
the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different
kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between
the π0 and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated
π0's and γ's are produced.
Received: 2 April 2001 / Accepted: 5 June 2001 相似文献
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