1,175 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
APEX: A Prime EXperiment at Jefferson Lab
APEX is an experiment at Thomas Jefferson National Accelerator Facility
(JLab) in Virginia, USA, that searches for a new gauge boson () with
sub-GeV mass and coupling to ordinary matter of . Electrons impinge upon a fixed target of high-Z material. An
is produced via a process analogous to photon bremsstrahlung,
decaying to an pair. A test run was held in July of 2010, covering
= 175 to 250 MeV and couplings g^\prime/e \; \textgreater \;
10^{-3}. A full run is approved and will cover 65 to 525
MeV and g^\prime/e \; \textgreater \; 2.3 \times10^{-4}.Comment: Contributed to the 8th Patras Workshop on Axions, WIMPs and WISPs,
Chicago, July 18-22, 2012. 4 pages, 4 figure
Evidence for narrow resonant structures at and GeV in real Compton scattering off the proton
First measurement of the beam asymmetry for Compton scattering off
the proton in the energy range GeV is presented. The
data reveals two narrow structures at and
GeV. They may signal narrow resonances with masses near
and GeV, or they may be generated by the sub-threshold
and production. Their decisive identification requires additional
theoretical and experimental efforts.Comment: Published versio
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.
Quasifission and difference in formation of evaporation residues in the O+W and F+Ta reactions
The excitation functions of capture, complete fusion, and evaporation residue
formation in the O+W and F+Ta reactions leading
to the same Pb compound nucleus has been studied theoretically to
explain the experimental data showing more intense yield of evaporation residue
in the former reaction in comparison with that in the latter reaction. The
observed difference is explained by large capture cross section in the former
and by increase of the quasifission contribution to the yield of fission-like
fragments in the F+Ta reaction at large excitation energies. The
probability of compound nucleus formation in the O+W reaction is
larger but compound nuclei formed in both reactions have similar angular
momentum ranges at the same excitation energy. The observed decrease of
evaporation residue cross section normalized to the fusion cross section in the
F+Ta reaction in comparison with the one in the
O+W reaction at high excitation energies is explained by the
increase of hindrance in the formation of compound nucleus connected with more
quick increase of the quasifission contribution in the F induced
reaction. The spin distributions of the evaporation residue cross sections for
the two reactions are also presented.Comment: 11 pages, 5 figure
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