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## Impacts of the Cutoff of Coupled-Channels Effects on Heavy-Ion Fusion Reactions at Extreme Sub-Barrier Energies

Fonte: Oxford University Press
Publicador: Oxford University Press

Tipo: Artigo de Revista Científica
Formato: text/html

EN

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46.21%

Based on the one dimensional barrier penetration model with semiclassical WKB method, the dynamic polarization potentials in heavy-ion reactions are extracted from the fusion cross sections. By choosing the proper parameters, the real polarization potential can be calculated from the imaginary part according to the dispersion relation in the framework of the linear-schematic model. The imaginary potential comes from the coupled-channels effects and shows a rapid cuttoff at energies far below the Coulomb barrier. Due to the absence of the coupled-channels effects, the fusion excitation function fall off more quickly than the usual expectation. Moreover, the pure potential in fusion reactions is proposed in hopes to reproduce the fusion cross sections at all energies in the full coupled-channels calculation.

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## Laboratory Condition for Fusion Reactions in Nuclear Astrophysics

Fonte: Oxford University Press
Publicador: Oxford University Press

Tipo: Artigo de Revista Científica
Formato: text/html

EN

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46.22%

The laboratory condition where charged particle fusion reactions have been studied is not exactly the same as stellar condition. To probe details of solar fusion and to test the prediction of standard solar model, we need more precise data for charged particle fusion reactions in the laboratory. We propose several experimental approaches to reduce the ambiguity of the estimation of screening potential value which is crucial for obtaining the astrophysical S-factor. The laboratory experiments of reactions with bare target and bare beam will be achieved by using proposed Electron Beam Ion Trap Apparatus (NARITA).

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## Reconstituting Intracellular Vesicle Fusion Reactions: The Essential Role of Macromolecular Crowding

Fonte: PubMed
Publicador: PubMed

Tipo: Artigo de Revista Científica

EN

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46.23%

Intracellular vesicle fusion is mediated by SNAREs and Sec1/Munc18 (SM) proteins. Despite intensive efforts, the SNARE-SM mediated vesicle fusion reaction has not been faithfully reconstituted in biochemical assays. Here, we present an unexpected discovery that macromolecular crowding is required for reconstituting the vesicle fusion reaction in vitro. Macromolecular crowding is known to profoundly influence the kinetic and thermodynamic behaviors of macromolecules, but its role in membrane transport processes such as vesicle fusion remains unexplored. We introduced macromolecular crowding agents into reconstituted fusion reactions to mimic the crowded cellular environment. In this crowded assay, SNAREs and SM proteins acted in concert to drive efficient membrane fusion. In uncrowded assays, by contrast, SM proteins failed to associate with the SNAREs and the fusion rate decreased more than 30-fold, close to undetectable levels. The activities of SM proteins were strictly specific to their cognate SNARE isoforms and sensitive to biologically relevant mutations, further supporting that the crowded fusion assay accurately recapitulates the vesicle fusion reaction. Using this crowded fusion assay, we also showed that the SNARE-SM mediated fusion reaction can be modulated by two additional factors: NSF and α-SNAP. These findings suggest that the vesicle fusion machinery likely has been evolutionarily selected to function optimally in the crowded milieu of the cell. Accordingly...

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## Applications of Skyrme energy-density functional to fusion reactions spanning the fusion barriers

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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46.27%

The Skyrme energy density functional has been applied to the study of
heavy-ion fusion reactions. The barriers for fusion reactions are calculated by
the Skyrme energy density functional with proton and neutron density
distributions determined by using restricted density variational (RDV) method
within the same energy density functional together with semi-classical approach
known as the extended semi-classical Thomas-Fermi method. Based on the fusion
barrier obtained, we propose a parametrization of the empirical barrier
distribution to take into account the multi-dimensional character of real
barrier and then apply it to calculate the fusion excitation functions in terms
of barrier penetration concept. A large number of measured fusion excitation
functions spanning the fusion barriers can be reproduced well. The competition
between suppression and enhancement effects on sub-barrier fusion caused by
neutron-shell-closure and excess neutron effects is studied.; Comment: 28 pages, 13 figures and 2 tables. accepted by Nucl. Phys. A

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## Dynamic study on fusion reactions for $^{40,48}$Ca+$^{90,96}$Zr around Coulomb barrier

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/01/2003

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46.32%

By using the updated improved Quantum Molecular Dynamics model in which a
surface-symmetry potential term has been introduced for the first time, the
excitation functions for fusion reactions of $^{40,48}$Ca+$^{90,96}$Zr at
energies around the Coulomb barrier have been studied. The experimental data of
the fusion cross sections for $^{40}$Ca+$^{90,96}$Zr have been reproduced
remarkably well without introducing any new parameters. The fusion cross
sections for the neutron-rich fusion reactions of $^{48}$Ca+$^{90,96}$Zr around
the Coulomb barrier are predicted to be enhanced compared with a
non-neutron-rich fusion reaction. In order to clarify the mechanism of the
enhancement of the fusion cross sections for neutron-rich nuclear fusions, we
pay a great attention to study the dynamic lowering of the Coulomb barrier
during a neck formation. The isospin effect on the barrier lowering is
investigated. It is interesting that the effect of the projectile and target
nuclear structure on fusion dynamics can be revealed to a certain extent in our
approach. The time evolution of the N/Z ratio at the neck region has been
firstly illustrated. A large enhancement of the N/Z ratio at neck region for
neutron-rich nuclear fusion reactions is found.; Comment: 21 pages...

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## Screened Coulomb potentials for astrophysical nuclear fusion reactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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46.28%

The electron-screening acceleration of laboratory fusion reactions at
astrophysical energies is an unsolved problem of great importance to
astrophysics. That effect is modeled here by considering the fusion of
hydrogen-like atoms whose electron probability density is used in Poisson's
equation in order to derive the corresponding screened Coulomb potential
energy. That way atomic excitations and deformations of the fusing atoms can be
taken into account. Those potentials are then treated semiclassically in order
to obtain the screening (accelerating) factor of the reaction. By means of the
proposed model the effect of a superstrong magnetic field on laboratory
Hydrogen fusion reactions is investigated here for the first time showing that,
despite the considerable increase in the cross section of the $% dd$ reaction,
the $pp$ reaction is still too slow to justify experimentation. The proposed
model is finally applied on the $H^{2}(d,p) H^{3}$ fusion reaction describing
satisfactorily the experimental data although some ambiguity remains regarding
the molecular nature of the deuteron target. Notably, the present method gives
a sufficiently high screening energy for Hydrogen fusion reactions so that the
take-away energy of the spectator nucleus can also be taken into account.; Comment: 11 (RevTex) pages + 3 ps figures. Accepted for publication in
Eur.Phys.J. A

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## Production of exotic isotopes in complete fusion reactions with radioactive beams

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/11/2013

Relevância na Pesquisa

46.22%

The isotopic dependence of the complete fusion (capture) cross section is
analyzed in the reactions
$^{130,132,134,136,138,140,142,144,146,148,150}$Xe+$^{48}$Ca with stable and
radioactive beams. It is shown for the first time that the very neutron-rich
nuclei $^{186-191}$W can be reached with relatively large cross sections by
complete fusion reactions with radioactive ion beams at incident energies near
the Coulomb barrier. A comparison between the complete fusion and fragmentation
reactions for the production of neutron-rich W and neutron-deficient Rn
isotopes is performed.; Comment: 13 pages, 6 figures, accepted in PRC

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## Formation of superheavy nuclei in cold fusion reactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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Within the concept of the dinuclear system (DNS), a dynamical model is
proposed for describing the formation of superheavy nuclei in complete fusion
reactions by incorporating the coupling of the relative motion to the nucleon
transfer process. The capture of two heavy colliding nuclei, the formation of
the compound nucleus and the de-excitation process are calculated by using an
empirical coupled channel model, solving a master equation numerically and
applying statistical theory, respectively. Evaporation residue excitation
functions in cold fusion reactions are investigated systematically and compared
with available experimental data. Maximal production cross sections of
superheavy nuclei in cold fusion reactions with stable neutron-rich projectiles
are obtained. Isotopic trends in the production of the superheavy elements
Z=110, 112, 114, 116, 118 and 120 are analyzed systematically. Optimal
combinations and the corresponding excitation energies are proposed.; Comment: 18 pages, 8 figures

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## Microscopic dynamics simulations of heavy-ion fusion reactions induced by neutron-rich nuclei

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

46.32%

The heavy-ion fusion reactions induced by neutron-rich nuclei are
investigated with the improved quantum molecular dynamics (ImQMD) model. With a
subtle consideration of the neutron skin thickness of nuclei and the symmetry
potential, the stability of nuclei and the fusion excitation functions of
heavy-ion fusion reactions $^{16}$O+$^{76}$Ge, $^{16}$O+$^{154}$Sm,
$^{40}$Ca+$^{96}$Zr and $^{132}$Sn+$^{40}$Ca are systematically studied. The
fusion cross sections of these reactions at energies around the Coulomb barrier
can be well reproduced by using the ImQMD model. The corresponding slope
parameter of the symmetry energy adopted in the calculations is $L \approx 78$
MeV and the surface energy coefficient is $g_{\rm sur}=18\pm 1.5$ MeVfm$^2$. In
addition, it is found that the surface-symmetry term significantly influences
the fusion cross sections of neutron-rich fusion systems. For sub-barrier
fusion, the dynamical fluctuations in the densities of the reaction partners
and the enhanced surface diffuseness at neck side result in the lowering of the
fusion barrier.; Comment: 10 figures, the version published in PRC

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## Fusion reactions initiated by laser-accelerated particle beams in a laser-produced plasma

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 08/10/2013

Relevância na Pesquisa

46.25%

The advent of high-intensity pulsed laser technology enables the generation
of extreme states of matter under conditions that are far from thermal
equilibrium. This in turn could enable different approaches to generating
energy from nuclear fusion. Relaxing the equilibrium requirement could widen
the range of isotopes used in fusion fuels permitting cleaner and less
hazardous reactions that do not produce high energy neutrons. Here we propose
and implement a means to drive fusion reactions between protons and boron-11
nuclei, by colliding a laser-accelerated proton beam with a laser-generated
boron plasma. We report proton-boron reaction rates that are orders of
magnitude higher than those reported previously. Beyond fusion, our approach
demonstrates a new means for exploring low-energy nuclear reactions such as
those that occur in astrophysical plasmas and related environments.; Comment: 7 pages, 5 figures

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## Transfer/Breakup Channel Couplings in Sub-barrier Fusion Reactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

46.32%

With the recent availability of state-of-the-art radioactive ion beams, there
has been a renew interest in the investigation of nuclear reactions with heavy
ions near the Coulomb barrier. The role of inelastic and transfer channel
couplings in fusion reactions induced by stable heavy ions can be revisited.
Detailed Analysis of recent experimental fusion cross sections by using
standard coupled-channel calculations is first discussed. Multi-neutron
transfer effects are introduced in the fusion process below the Coulomb barrier
by analyzing 32S+90,96Zr as benchmark reactions. The enhancement of fusion
cross sections for 32S+96Zr is well reproduced at sub-barrier energies by NTFus
code calculations including the coupling of the neutron-transfer channels
following the Zagrebaev semi-classical model. Similar effects for 40Ca+90Zr and
40Ca+96Zr fusion excitation functions are found. The breakup coupling in both
the elastic scattering and in the fusion process induced by weakly bound stable
projectiles is also shown to be crucial. In the second part of this work, full
coupled-channel calculations of the fusion excitation functions are performed
by using the breakup coupling for the more neutron-rich reaction and for the
more weakly bound projectiles. we clearly demonstrate that
Continuum-Discretized Coupled-Channel calculations are capable to reproduce the
fusion enhancement from the breakup coupling in 6Li+59Co.; Comment: Invited Talk (Reaction and Structure parallel Session) given by C.
Beck at the 11th International Conference on Nucleus-Nucleus Collisions
(NN2012)...

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## Systematic investigations of deep sub-barrier fusion reactions using an adiabatic approach

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 03/10/2015

Relevância na Pesquisa

46.25%

To describe fusion hindrance observed in fusion reactions at extremely low
incident energies, I propose a novel extension of the standard CC model by
introducing a damping factor that describes a smooth transition from sudden to
adiabatic processes. I demonstrate the performance of this model by
systematically investigating various deep sub-barrier fusion reactions. I
extend the standard CC model by introducing a damping factor into the coupling
matrix elements in the standard CC model. I adopt the Yukawa-plus-exponential
(YPE) model as a basic heavy ion-ion potential, which is advantageous for a
unified description of the one- and two-body potentials. For the purpose of
these systematic investigations, I approximate the one-body potential with a
third-order polynomial function based on the YPE model. Calculated fusion cross
sections for the medium-heavy mass systems of $^{64}$Ni + $^{64}$Ni, $^{58}$Ni
+ $^{58}$Ni, and $^{58}$Ni + $^{54}$Fe, the medium-light mass systems of
$^{40}$Ca + $^{40}$Ca, $^{48}$Ca + $^{48}$Ca, and $^{24}$Mg + $^{30}$Si, and
the mass-asymmetric systems of $^{48}$Ca + $^{96}$Zr and $^{16}$O + $^{208}$Pb
are consistent with the experimental data. The astrophysical S factor and
logarithmic derivative representations of these are also in good agreement with
the experimental data. Since the results calculated with the damping factor are
in excellent agreement with the experimental data in all systems...

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## Effects of $\beta_{6}$ deformation and low-lying vibrational bands on heavy-ion fusion reactions at sub-barrier energies

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/08/1999

Relevância na Pesquisa

46.3%

We study fusion reactions of $^{16}$O with $^{154}$Sm, $^{186}$W and
$^{238}$U at sub-barrier energies by a coupled-channels framework. We focus
especially on the effects of $\beta_{6}$ deformation and low-lying vibrational
excitations of the target nucleus. It is shown that the inclusion of
$\beta_{6}$ deformation leads to a considerable improvement of the fit to the
experimental data for all of these reactions. For the $^{154}$Sm and $^{238}$U
targets, the octupole vibration significantly affects the fusion barrier
distribution. The effect of $\beta$ band is negligible in all the three
reactions, while the $\gamma$ band causes a non-negligible effect on the
barrier distribution at energies above the main fusion barrier. We compare the
optimum values of the deformation parameters obtained by fitting the fusion
data with those obtained from inelastic scatterings and the ground state mass
calculations. We show that the channel coupling of high multipolarity beyond
the quadrupole coupling is dominated by the nuclear coupling and hence higher
order Coulomb coupling does not much influence the optimum values of $\beta_4$
and $\beta_6$ parameters. We also discuss the effect of two neutron transfer
reactions on the fusion of $^{16}$O with $^{238}$U.; Comment: 11 pages...

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## Systematics of fusion probability in "hot" fusion reactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 27/12/2011

Relevância na Pesquisa

46.29%

The fusion probability in "hot" fusion reactions leading to the synthesis of
super-heavy nuclei is investigated systematically. The quasi-fission barrier
influences the formation of the super-heavy nucleus around the "island of
stability" in addition to the shell correction. Based on the quasi-fission
barrier height obtained with the Skyrme energy-density functional, we propose
an analytical expression for the description of the fusion probability, with
which the measured evaporation residual cross sections can be reproduced
acceptably well. Simultaneously, some special fusion reactions for synthesizing
new elements 119 and 120 are studied. The predicted evaporation residual cross
sections for 50Ti+249Bk are about 10-150fb at energies around the
entrance-channel Coulomb barrier. For the fusion reactions synthesizing element
120 with projectiles 54Cr and 58Fe, the cross sections fall to a few femtobarns
which seems beyond the limit of the available facilities.; Comment: 5 figures, 1 table

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## Dynamical analysis on heavy-ion fusion reactions near Coulomb barrier

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/11/2007

Relevância na Pesquisa

46.32%

The shell correction is proposed in the improved isospin dependent quantum
molecular dynamics (ImIQMD) model, which plays an important role in heavy-ion
fusion reactions near Coulomb barrier. By using the ImIQMD model, the static
and dynamical fusion barriers, dynamical barrier distribution in the fusion
reactions are analyzed systematically. The fusion and capture excitation
functions for a series of reaction systems are calculated and compared with
experimental data. It is found that the fusion cross sections for neutron-rich
systems increase obviously, and the strong shell effects of two colliding
nuclei result in a decrease of the fusion cross sections at the sub-barrier
energies. The lowering of the dynamical fusion barriers favors the enhancement
of the sub-barrier fusion cross sections, which is related to the nucleon
transfer and the neck formation in the fusion reactions.; Comment: 20 pages, 12 figures

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## Subbarrier fusion reactions and many-particle quantum tunneling

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

46.33%

Low energy heavy-ion fusion reactions are governed by quantum tunneling
through the Coulomb barrier formed by a strong cancellation of the repulsive
Coulomb force with the attractive nuclear interaction between the colliding
nuclei. Extensive experimental as well as theoretical studies have revealed
that fusion reactions are strongly influenced by couplings of the relative
motion of the colliding nuclei to several nuclear intrinsic motions. Heavy-ion
subbarrier fusion reactions thus provide a good opportunity to address a
general problem on quantum tunneling in the presence of couplings, which has
been a popular subject in the past decades in many branches of physics and
chemistry. Here we review theoretical aspects of heavy-ion subbarrier fusion
reactions from the view point of quantum tunneling in systems with many degrees
of freedom. Particular emphases are put on the coupled-channels approach to
fusion reactions, and the barrier distribution representation for multi-channel
penetrability. We also discuss an application of the barrier distribution
method to elucidation of the mechanism of dissociative adsorption of H$_2$
melecules in surface science.; Comment: 45 pages, 16 eps figures. An invited paper to be published in Prog.
Theo. Phys

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## Applications of Skyrme energy-density functional to fusion reactions for synthesis of superheavy nuclei

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/09/2006

Relevância na Pesquisa

46.42%

The Skyrme energy-density functional approach has been extended to study the
massive heavy-ion fusion reactions. Based on the potential barrier obtained and
the parameterized barrier distribution the fusion (capture) excitation
functions of a lot of heavy-ion fusion reactions are studied systematically.
The average deviations of fusion cross sections at energies near and above the
barriers from experimental data are less than 0.05 for 92% of 76 fusion
reactions with $Z_1Z_2<1200$. For the massive fusion reactions, for example,
the $^{238}$U-induced reactions and $^{48}$Ca+$^{208}$Pb the capture excitation
functions have been reproduced remarkable well. The influence of structure
effects in the reaction partners on the capture cross sections are studied with
our parameterized barrier distribution. Through comparing the reactions induced
by double-magic nucleus $^{48}$Ca and by $^{32}$S and $^{35}$Cl, the
'threshold-like' behavior in the capture excitation function for $^{48}$Ca
induced reactions is explored and an optimal balance between the capture cross
section and the excitation energy of the compound nucleus is studied. Finally,
the fusion reactions with $^{36}$S, $^{37}$Cl, $^{48}$Ca and $^{50}$Ti
bombarding on $^{248}$Cm, $^{247...

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## Anharmonic phonon excitations in subbarrier fusion reactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 29/09/1997

Relevância na Pesquisa

46.22%

Recently measured high precision data of fusion excitation function have
enabled a detailed study on the effects of nuclear collective excitations on
fusion reactions. Using such highly accurate data of the $^{16}$O +
$^{144,148}$Sm reactions, we discuss the anharmonic properties of collective
phonon excitations in $^{144,148}$Sm nuclei. It is shown that subbarrier fusion
reactions are strongly affected by the anharmonic effects and thus offer an
alternative method to extract the static quadrupole moments of phonon states in
a spherical nucleus.; Comment: 10 pages, To be published in the Proceedings of the Tours Symposium
on Nuclear Physics III, Tours, France, September 1997 (American Institute of
Physics)

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## Excitation of nuclear anharmonic vibrations in heavy-ion fusion reactions

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/11/1997

Relevância na Pesquisa

46.25%

We discuss the effects of multi-phonon excitations on heavy-ion fusion
reactions at energies near and below the Coulomb barrier, focusing especially
on the role of anharmonicities. We carry out a systematic study of those
effects on the excitation function of the fusion cross section and on the
fusion barrier distribution, by using the vibrational limit of the interacting
boson model. We also analyze the recently measured high-precision data of the
$^{16}$O + $^{148}$Sm fusion reaction with this model and discuss the
anharmonic properties of the quadrupole as well as the octupole vibrations in
$^{148}$Sm. Negative and positive static quadrupole moments are deduced for the
first 2$^+$ and 3$^-$ states in $^{148}$Sm, respectively. It is shown that the
fusion barrier distribution strongly depends on the sign of the quadrupole
moments, suggesting that subbarrier fusion reactions offer an alternative
method to extract the static quadrupole moments of phonon states in spherical
nuclei.; Comment: 21 pages, 9 figures, Submitted to Physical Review C

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## Unexpected inhibition of fusion in nucleus-nucleus collisions

Fonte: Macmillan Publishers Ltd
Publicador: Macmillan Publishers Ltd

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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#Keywords: Fission reactions#Fusion reactions#Liquids#Mass transfer#Projectiles#Electrostatic energy#Nuclear physics#physics#article#atom#elementary particle

Unstable heavy atomic nuclei not found in nature can be created by fusing two stable nuclei, in a process analogous to colliding charged droplets of liquid. Recently, the formation of a handful of super-heavy nuclei with atomic numbers 114 (ref. 1) and 116 (reft 2) has been achieved by fusion of heavy nuclei. The electrostatic energy of such systems is very large (which is the reason super-heavy nuclei are unstable), so although the two nuclei may initially be captured by the nuclear potential, rather than fusing, they almost always separate after transfer of mass to the lighter nucleus. This process, called quasi-fission3,4, can inhibit fusion by many orders of magnitude. Understanding this inhibition may hold the key to forming more super-heavy elements. Theoretically, inhibition is predicted (ref. 5 and references therein) when the product Z1Z2 of the charges of the projectile and target nuclei is larger than about 1,600. Here we report measurements of three fusion reactions with Z1Z2 around half this value, each forming 88216 Ra. We find convincing model-independent evidence both of inhibition of fusion, and of the presence of quasi-fission. These results defy interpretation within the standard picture of nuclear fusion and fission.

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