35 research outputs found
Recent experimental results in sub- and near-barrier heavy ion fusion reactions
Recent advances obtained in the field of near and sub-barrier heavy-ion
fusion reactions are reviewed. Emphasis is given to the results obtained in the
last decade, and focus will be mainly on the experimental work performed
concerning the influence of transfer channels on fusion cross sections and the
hindrance phenomenon far below the barrier. Indeed, early data of sub-barrier
fusion taught us that cross sections may strongly depend on the low-energy
collective modes of the colliding nuclei, and, possibly, on couplings to
transfer channels. The coupled-channels (CC) model has been quite successful in
the interpretation of the experimental evidences. Fusion barrier distributions
often yield the fingerprint of the relevant coupled channels. Recent results
obtained by using radioactive beams are reported. At deep sub-barrier energies,
the slope of the excitation function in a semi-logarithmic plot keeps
increasing in many cases and standard CC calculations over-predict the cross
sections. This was named a hindrance phenomenon, and its physical origin is
still a matter of debate. Recent theoretical developments suggest that this
effect, at least partially, may be a consequence of the Pauli exclusion
principle. The hindrance may have far-reaching consequences in astrophysics
where fusion of light systems determines stellar evolution during the carbon
and oxygen burning stages, and yields important information for exotic
reactions that take place in the inner crust of accreting neutron stars.Comment: 40 pages, 63 figures, review paper accepted for EPJ
β and γ bands in N = 88 , 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory : vibrations, shape coexistence, and superdeformation
CITATION: Majola, S. N. T. et al. 2019. β and γ bands in N=88, 90, and 92 isotones investigated with a five-dimensional collective Hamiltonian based on covariant density functional theory: Vibrations, shape coexistence, and superdeformation. Physical Review C, 100(4). doi:10.1103/PhysRevC.100.044324.The original publication is available at https://journals.aps.org/prc/A comprehensive systematic study is made for the collective β and γ bands in even-even isotopes with neutron numbers N = 88 to 92 and proton numbers Z = 62 (Sm) to 70 (Yb). Data, including excitation energies,
B(E0) and B(E2) values, and branching ratios from previously published experiments are collated with new
data presented for the first time in this study. The experimental data are compared to calculations using a
five-dimensional collective Hamiltonian (5DCH) based on the covariant density functional theory (CDFT). A
realistic potential in the quadrupole shape parameters V (β,γ ) is determined from potential energy surfaces
(PES) calculated using the CDFT. The parameters of the 5DCH are fixed and contained within the CDFT.
Overall, a satisfactory agreement is found between the data and the calculations. In line with the energy
staggering S(I) of the levels in the 2γ
+ bands, the potential energy surfaces of the CDFT calculations indicate
γ -soft shapes in the N = 88 nuclides, which become γ rigid for N = 90 and N = 92. The nature of the 02
+
bands changes with atomic number. In the isotopes of Sm to Dy, they can be understood as β vibrations, but in
the Er and Yb isotopes the 02
+ bands have wave functions with large components in a triaxial superdeformed
minimum. In the vicinity of 152Sm, the present calculations predict a soft potential in the β direction but do not
find two coexisting minima. This is reminiscent of 152Sm exhibiting an X(5) behavior. The model also predicts
that the 03
+ bands are of two-phonon nature, having an energy twice that of the 02
+ band. This is in contradiction
with the data and implies that other excitation modes must be invoked to explain their origin.https://journals.aps.org/prc/abstract/10.1103/PhysRevC.100.044324Publisher’s versio
Coulomb excitation of and a change in structure approaching N = Z = 40
Background: Nuclei approaching are known to exhibit strongly deformed structures and are thought to be candidates for shape coexistence. In the krypton isotopes, are poorly characterized, preventing an understanding of evolving deformation approaching . Purpose: The present work aims to determine electric quadrupole transition strengths and quadrupole moments of in order to better characterize their deformation. Conclusions: Comparison of measured and values indicates that neutron-deficient () isotopes of krypton are closer to axial deformation than other isotopic chains in the mass region. A continuation of this trend to higher may result in Sr and Zr isotopes exhibiting near-axial prolate deformation. Methods: Sub-barrier Coulomb excitation was employed, impinging the isotopes of krypton on and targets. Utilizing a semiclassical description of the safe Coulomb-excitation process matrix elements could then be determined. Results: Eleven new or improved matrix elements are determined in and seven in . The new value in disagrees with the evaluated value by , which can be explained in terms of deficiencies in a previous Coulomb-excitation analysis
If not now, when? Time for the European Union to define a global health strategy
Speakman, E. M., McKee, M., & Coker, R. (2017). If not now, when? Time for the European Union to define a global health strategy. Lancet Global Health, 5(4), e392-e393. https://doi.org/10.1016/S2214-109X%2817%2930085-
In-beam spectroscopy of
High-spin states in the nucleus 72Ge were investigated via the 70Zn(, 2n)72Ge reaction at a beam energy of 30MeV, using the AFRODITE spectrometer. One aim of the study was to search for tetrahedral states. There was no evidence for such states in our coincidence data. The existing decay scheme was substantially revised and extended. Several -ray placements and level spin-parities were changed, and some 30 new transitions were added to the level scheme. One new negative-parity rotational band was identified. The new band is likely the unfavoured signature partner of the band built on the previously known \ensuremath I^{\pi}=3^{-} state at 2515keV. The two negative-parity bands are interpreted as involving an aligned octupole vibration which evolves to a four-quasiparticle structure at higher spins. The upbend in the yrast band is interpreted as the AB neutron alignment. The band structures are discussed with reference to Cranked Shell Model calculations, the aligned angular momenta, experimental routhians, and moments of inertia