124 research outputs found
Semi-microscopic theory of two proton emission
We propose a semi-microscopic model for the simultaneous emission of two
protons. This model has the advantage of avoiding certain technical aspects of
a fully microscopic 3-body framework, while also allowing the investigation of
the influence of proton pairing on the total lifetime of the decaying nucleus.
Thus, we use the standard singlet two-proton wave function on the nuclear
surface, provided by the Bardeen-Cooper-Schrieffer (BCS) approach, as a
boundary condition for the propagator operator.
Our model allows for the estimation of all quantities related to the
emission process, since it provides the 3-body wave function over most of the
domain. We show that reasonable agreement with experimental values can be
reached by varying the pairing strength outside the nucleus in an interval
close to the "bare" singlet value
Systematics of 2+ states in semi-magic nuclei
We propose a simple systematics of low lying 2+ energy levels and
electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and
isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus
quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase
Approximation (QRPA). We derive a simple relation connecting the 2+ energy with
the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns
out that the systematics of energy levels and B(E2) values predicted by this
simple model is fulfilled with a reasonable accuracy by all available
experimental data. Both systematics suggest that not only active nucleons but
also those filling closed shells play an important role
Time-dependent approach to many-particle tunneling in one-dimension
Employing the time-dependent approach, we investigate a quantum tunneling
decay of many-particle systems. We apply it to a one-dimensional three-body
problem with a heavy core nucleus and two valence protons. We calculate the
decay width for two-proton emission from the survival probability, which well
obeys the exponential decay-law after a sufficient time. The effect of the
correlation between the two emitted protons is also studied by observing the
time evolution of the two-particle density distribution. It is shown that the
pairing correlation significantly enhances the probability for the simultaneous
diproton decay.Comment: 9 pages, 10 eps figure
Ternary cluster decay within the liquid drop model
Longitudinal ternary and binary fission barriers of Ar, Ni and
Cf nuclei have been determined within a rotational liquid drop model
taking into account the nuclear proximity energy. For the light nuclei the
heights of the ternary fission barriers become competitive with the binary ones
at high angular momenta since the maximum lies at an outer position and has a
much higher moment of inertia.Comment: Talk presented at the 9th International Conference on Clustering
Aspects of Nuclear Structure and Dynamics (CLUSTERS'07
A novel manifestation of -clustering: new ' + Pb' states in Po revealed by their enhanced E1 decays
Excited states in Po were populated by transfer using the
Pb(O, C) reaction and their deexcitation -rays
were studied with the Euroball array. Several levels were found to decay by a
unique E1 transition (E 1 MeV) populating the yrast state with the
same spin value. Their lifetimes were measured by the DSAM method. The values,
found in the range [0.1-1.4] ps, lead to very enhanced transitions, B(E1) =
2 - 1 W.u.. These results are discussed in terms
of an -cluster structure which gives rise to states with non-natural
parity values, provided that the composite system cannot rotate collectively,
as expected in the ' + Pb' case. Such states due to the
oscillatory motion of the -core distance are observed for the first
time.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let
Alpha-decay Rates of Yb and Gd in Solar Neutrino Detectors
The -decay rates for the nuclides Yb
and Gd have been estimated from transmission probabilities
in a systematic -nucleus potential and from an improved fit to
-decay rates in the rare-earth mass region. Whereas -decay of
Gd in natural gadolinium is a severe obstacle for the use of gadolinium
as a low-energy solar-neutrino detector, we show that
-decay does not contribute significantly to the background in a
ytterbium detector. An extremely long -decay lifetime of Yb
is obtained from calculation, which may be close to the sensitivity limit in a
low-background solar neutrino detector.Comment: 12 pages, 1 figure; An author name was correcte
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