1,112 research outputs found
Exploring manifestation and nature of a dineutron in two-neutron emission using a dynamical dineutron model
Emission of two neutrons or two protons in reactions and decays is often
discussed in terms of "dineutron" or "diproton" emission. The discussion often
leans intuitively on something described by Migdal-Watson approximation. In
this work we propose a way to formalize situations of dineutron emission. It is
demonstrated that properly formally defined dineutron emission may reveal
properties which are drastically different from those traditionally expected,
and properties which are actually observed in three-body decays.Comment: 11 pages, 11 Figure
Two-proton radioactivity and three-body decay. IV. Connection to quasiclassical formulation
We derive quasiclassical expressions for the three-body decay width and
define the ``preexponential'' coefficients for them. The derivation is based on
the integral formulae for the three-body width obtained in the semianalytical
approach with simplified three-body Hamiltonian [L.V. Grigorenko and M.V.\
Zhukov, arXiv:0704.0920v1]. The model is applied to the decays of the first
excited state of Ne and ground state of Fe.
Various qualitative aspects of the model and relations with the other
simplified approaches to the three-body decays are discussed.Comment: 9 Pages, 2 figure
Decay mechanism and lifetime of Kr
The lifetime of the recently discovered emitter Kr was recently
found considerably below the lower limit predicted theoretically. This
communication addresses this issue.Different separation energy systematics are
analyzed and different mechanisms for emission are evaluated. It is found
that the most plausible reason for this disagreement is a decay mechanism of
Kr, which is not "true " emission, but "transition dynamics" on the
borderline between true and sequential decay mechanisms. If this is
true, this imposes stringent limits MeV on the ground state
energy of Br relative to the Se- threshold.Comment: 7 pages, 8 figure
Possibility to study a two-proton halo in Ne
The nuclide Ne is studied theoretically in a three-body
O++ model. We demonstrate that the experimental condition for
existence of a proton halo in Ne can be reasonably quantified in terms
of configuration mixing. We discuss experimental evidences for a proton
halo in Ne. We define which kind of experimental data could elucidate
this issue.Comment: 5 pages, 5 figure
From Coulomb excitation cross sections to non-resonant astrophysical rates in three-body systems: Ne case
Coulomb and nuclear dissociation of Ne on light and heavy targets are
studied theoretically. The dipole E1 strength function is determined in a broad
energy range including energies of astrophysical interest. Dependence of the
strength function on different parameters of the Ne ground state
structure and continuum dynamics is analyzed in a three-body model. The
discovered dependence plays an important role for studies of the strength
functions for the three-body E1 dissociation and radiative capture. The
constraints on the configuration mixing in Ne and on
-wave interaction in the O+ channel are imposed based on
experimental data for Ne Coulomb dissociation on heavy target.Comment: 12 pages, 13 figure
Two-proton radioactivity and three-body decay. III. Integral formulae for decay widths in a simplified semianalytical approach
Three-body decays of resonant states are studied using integral formulae for
decay widths. Theoretical approach with a simplified Hamiltonian allows
semianalytical treatment of the problem. The model is applied to decays of the
first excited state of Ne and the ground state of
Fe. The convergence of three-body hyperspherical model calculations to
the exact result for widths and energy distributions are studied. The
theoretical results for Ne and Fe decays are updated and
uncertainties of the derived values are discussed in detail. Correlations for
the decay of Ne state are also studied.Comment: 19 pages, 20 figure
Molecular Structures in T=1 states of 10B
Multi-center (molecular) structures can play an important role in light
nuclei. The highly deformed rotational band in 10Be with band head at 6.179 MeV
has been observed recently and suggested to have an exotic alpha:2n:alpha
configuration. A search for states with alpha:pn:alpha two-center molecular
configurations in 10B that are analogous to the states with alpha:2n:alpha
structure in 10Be has been performed. The T=1 isobaric analog states in 10B
were studied in the excitation energy range of E=8.7-12.1 MeV using the
reaction 1H(9Be,alpha)6Li*(T=1, 0+, 3.56 MeV). An R-matrix analysis was used to
extract parameters for the states observed in the (p,alpha) excitation
function. Five T=1 states in 10B have been identified. The known 2+ and 3-
states at 8.9 MeV have been observed and their partial widths have been
measured. The spin-parities and partial widths for three higher lying states
were determined. Our data support theoretical predictions that the 2+ state at
8.9 MeV (isobaric analog of the 7.54 MeV state in 10Be) is a highly clustered
state and can be identified as a member of the alpha:np:alpha rotational band.
The next member of this band, the 4+ state, has not been found. A very broad 0+
state at 11 MeV that corresponds to pure alpha+6Li(0+,T=1) configuration is
suggested and it might be related to similar structures found in 12C, 18O and
20Ne.Comment: 10 pages, 10 figures, accepted in Physical Review
First observation of 54Zn and its decay by two-proton emission
The nucleus 54Zn has been observed for the first time in an experiment at the
SISSI/LISE3 facility of GANIL in the quasi-fragmentation of a 58Ni beam at 74.5
MeV/nucleon in a natNi target. The fragments were analysed by means of the
ALPHA-LISE3 separator and implanted in a silicon-strip detector where
correlations in space and time between implantation and subsequent decay events
allowed us to generate almost background free decay spectra for about 25
different nuclei at the same time. Eight 54Zn implantation events were
observed. From the correlated decay events, the half-life of 54Zn is determined
to be 3.2 +1.8/-0.8 ms. Seven of the eight implantations are followed by
two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and
the partial half-life are compared to model predictions and allow for a test of
these two-proton decay models.Comment: 4 pages, 4 figures, accepted for publication in PR
Universal Dynamic Conductivity and Quantized Visible Opacity of Suspended Graphene
We show that the optical transparency of suspended graphene is defined by the
fine structure constant, alpha, the parameter that describes coupling between
light and relativistic electrons and is traditionally associated with quantum
electrodynamics rather than condensed matter physics. Despite being only one
atom thick, graphene is found to absorb a significant (pi times alpha=2.3%)
fraction of incident white light, which is a consequence of graphene's unique
electronic structure. This value translates into universal dynamic conductivity
G =e^2/4h_bar within a few percent accuracy
Spin-dependent effective interactions for halo nuclei
We discuss the spin-dependence of the effective two-body interactions
appropriate for three-body computations. The only reasonable choice seems to be
the fine and hyperfine interactions known for atomic electrons interacting with
the nucleus. One exception is the nucleon-nucleon interaction imposing a
different type of symmetry. We use the two-neutron halo nucleus 11Li as
illustration. We demonstrate that models with the wrong spin-dependence are
basically without predictive power. The Pauli forbidden core and valence states
must be consistently treated.Comment: TeX file, 6 pages, 3 postscript figure
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