151 research outputs found
Mechanisms producing fissionlike binary fragments in heavy collisions
The mixing of the quasifission component to the fissionlike cross section
causes ambiguity in the quantitative estimation of the complete fusion cross
section from the observed angular and mass distributions of the binary
products. We show that the partial cross section of quasifission component of
binary fragments covers the whole range of the angular momentum values leading
to capture. The calculated angular momentum distributions for the compound
nucleus and dinuclear system going to quasifission may overlap: competition
between complete fusion and quasifission takes place at all values of initial
orbital angular momentum. Quasifission components formed at large angular
momentum of the dinuclear system can show isotropic angular distribution and
their mass distribution can be in mass symmetric region similar to the
characteristics of fusion-fission components. As result the unintentional
inclusion of the quasifission contribution into the fusion-fission fragment
yields can lead to overestimation of the probability of the compound nucleus
formation.Comment: 15 pages, 6 figures, International Conference on Nuclear Reactions on
Nucleons and Nuclei, Messina, Italy, October 5-9, 200
The Threshold effects for the two-particle Hamiltonians on lattices
For a wide class of two-body energy operators on the three-dimensional
lattice \bbZ^3, being the two-particle quasi-momentum, we prove that if
the following two assumptions (i) and (ii) are satisfied, then for all
nontrivial values , , the discrete spectrum of below its
threshold is non-empty. The assumptions are:
(i) the two-particle Hamiltonian corresponding to the zero value of
the quasi-momentum has either an eigenvalue or a virtual level at the bottom of
its essential spectrum and (ii) the one-particle free
Hamiltonians in the coordinate representation generate positivity preserving
semi-groups
A study of the almost sequential mechanism of true ternary fission
We consider the collinear ternary fission which is a sequential ternary decay
with a very short time between the ruptures of two necks connecting the middle
cluster of the ternary nuclear system and outer fragments. In particular, we
consider the case where the Coulomb field of the first massive fragment
separated during the first step of the fission produces a lower pre-scission
barrier in the second step of the residual part of the ternary system. In this
case, we obtain a probability of about for the yield of massive
clusters such as \nuclide[70]{Ni}, \nuclide[80-82]{Ge}, \nuclide[86]{Se}, and
\nuclide[94]{Kr} in the ternary fission of \nuclide[252]{Cf}. These products
appear together with the clusters having mass numbers of --. The
results show that the yield of a heavy cluster such as \nuclide[68-70]{Ni}
would be followed by a product of -- with a large probability as
observed in the experimental data obtained with the FOBOS spectrometer at the
Joint Institute for Nuclear Research. The third product is not observed. The
landscape of the potential energy surface shows that the configuration of the
Ni + Ca + Sn decay channel is lower about 12 MeV than that of the Ca + Ni + Sn
channel. This leads to the fact, that the yield of Ni and Sn is large. The
analysis on the dependence of the velocity of the middle fragment on mass
numbers of the outer products leads to the conclusion that, in the collinear
tripartition channel of \nuclide[252]{Cf}, the middle cluster has a very small
velocity, which does not allow it to be found in experiments.Comment: 11 pages, 9 figure
Quasifission and fusion-fission in massive nuclei reactions. Comparison of reactions leading to the Z=120 element
The yields of evaporation residues, fusion-fission and quasifission fragments
in the Ca+Sm and O+W reactions are analyzed
in the framework of the combined theoretical method based on the dinuclear
system concept and advanced statistical model. The measured yields of
evaporation residues for the Ca+Sm reaction can be well
reproduced. The measured yields of fission fragments are decomposed into
contributions coming from fusion-fission, quasifission, and fast-fission. The
decrease in the measured yield of quasifission fragments in
Ca+Sm at the large collision energies and the lack of
quasifission fragments in the Ca+Sm reaction are explained by
the overlap in mass-angle distributions of the quasifission and fusion-fission
fragments. The investigation of the optimal conditions for the synthesis of the
new element =120 (=302) show that the Cr+Cm reaction is
preferable in comparison with the Fe+Pu and Ni+U
reactions because the excitation function of the evaporation residues of the
former reaction is some orders of magnitude larger than that for the last two
reactions.Comment: 27 pages, 12 figures, submitted to Phys. Rev.
Peculiarities of Nuclear Fusion in Synthesis of Superheavy Elements
The small probabilities of synthesis of new superheavy elements at GSI (Darmstadt, Germany), Joint Institute for Nuclear Research (Dubna, Russia), and RIKEN (Wako, Japan) during the last decade stimulate the experimental and theoretical studies of the nuclear reaction mechanism. 1– 4 In preparation of these experiments, the main aim is to reach maximum cross sections of the yield of evaporation residues (ER) as a result of the de-excitation of the heated compound nucleus which is formed in complete fusion of the projectile and target nuclei. Because the ER excitation function in the synthesis of superheavy elements has very narrow width for "cold fusion" reactions (5–10 MeV) with 208 Pb and 209 Bi targets 5 and the width of the "hot fusion" reactions with 48 Ca projectile on actinide ta
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