57 research outputs found

### 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 $3/2^{-}$ state of $^{17}$Ne and $3/2^{-}$ ground state of $^{45}$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

### 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 $3/2^{-}$ state of $^{17}$Ne and the $3/2^{-}$ ground state of
$^{45}$Fe. The convergence of three-body hyperspherical model calculations to
the exact result for widths and energy distributions are studied. The
theoretical results for $^{17}$Ne and $^{45}$Fe decays are updated and
uncertainties of the derived values are discussed in detail. Correlations for
the decay of $^{17}$Ne $3/2^-$ state are also studied.Comment: 19 pages, 20 figure

### Evidence for the pair-breaking process in 116,117Sn

The nuclear level densities of 116,117Sn below the neutron separation energy
have been determined experimentally from the (3He,alpha gamma) and (3He,3He
gamma') reactions, respectively. The level densities show a characteristic
exponential increase and a difference in magnitude due to the odd-even effect
of the nuclear systems. In addition, the level densities display pronounced
step-like structures that are interpreted as signatures of subsequent breaking
of nucleon pairs.Comment: 7 pages, 5 figures, accepted for publication in Phys. Rev. C, 22
December 200

### Nuclear level densities and gamma-ray strength functions in 44,45Sc

The scandium isotopes 44,45Sc have been studied with the 45Sc(3He,alpha
gamma)44Sc and 45Sc(3He,3He' gamma)45Sc reactions, respectively. The nuclear
level densities and gamma-ray strength functions have been extracted using the
Oslo method. The experimental level densities are compared to calculated level
densities obtained from a microscopic model based on BCS quasiparticles within
the Nilsson level scheme. This model also gives information about the parity
distribution and the number of broken Cooper pairs as a function of excitation
energy. The experimental gamma-ray strength functions are compared to
theoretical models of the E1, M1, and E2 strength, and to data from (gamma,n)
and (gamma,p) experiments. The strength functions show an enhancement at low
gamma energies that cannot be explained by the present, standard models.Comment: 21 pages, 13 figures. Published versio

### Microcanonical entropies and radiative strength functions of $^{50,51}$V

The level densities and radiative strength functions (RSFs) of $^{50,51}$V
have been extracted using the ($^3$He,$\alpha \gamma$) and
($^3$He,$^3$He$^{\prime} \gamma$) reactions, respectively. From the level
densities, microcanonical entropies are deduced. The high $\gamma$-energy part
of the RSF is described by the giant electric dipole resonance. A significant
enhancement over the predicted strength in the region of $E_{\gamma} \lesssim
3$ MeV is seen, which at present has no theoretical explanation.Comment: 16 pages including 9 figure

### Level density of $^{56}$Fe and low-energy enhancement of $\gamma$-strength function

The $^{55}$Mn$(d,n)^{56}$Fe differential cross section is measured at $E_d=7$
MeV\@. The $^{56}$Fe level density obtained from neutron evaporation spectra is
compared to the level density extracted from the
$^{57}$Fe$(^3$He,$\alpha\gamma)^{56}$Fe reaction by the Oslo-type technique.
Good agreement is found between the level densities determined by the two
methods. With the level density function obtained from the neutron evaporation
spectra, the $^{56}$Fe $\gamma$-strength function is also determined from the
first-generation $\gamma$ matrix of the Oslo experiment. The good agreement
between the past and present results for the $\gamma$-strength function
supports the validity of both methods and is consistent with the low-energy
enhancement of the $\gamma$ strength below $\sim 4$ MeV first discovered by the
Oslo method in iron and molybdenum isotopes.Comment: 7 pages, 5 figure

### Proton Decay from Excited States in Spherical Nuclei

Based on a single particle model which describes the time evolution of the
wave function during tunneling across a one dimensional potential barrier we
study the proton decay of $^{208}$Pb from excited states with non-vanishing
angular momentum $\ell$. Several quantities of interest in this process like
the decay rate $\lambda$, the period of oscillation $T_{osc}$, the transient
time $t_{tr}$, the tunneling time $t_{tun}$ and the average value of the proton
packet position $r_{av}$ are computed and compared with the WKB results.Comment: 12 pages, 4 figure

### Alpha-nucleus potential for alpha-decay and sub-barrier fusion

The set of parameters for alpha-nucleus potential is derived by using the
data for both the alpha-decay half-lives and the fusion cross-sections around
the barrier for reactions alpha+40Ca, alpha+59Co, alpha+208Pb. The alpha-decay
half-lives are obtained in the framework of a cluster model using the WKB
approximation. The evaluated alpha-decay half-lives and the fusion
cross-sections agreed well with the data. Fusion reactions between
alpha-particle and heavy nuclei can be used for both the formation of very
heavy nuclei and spectroscopic studies of the formed compound nuclei.Comment: 10 pages, 5 figure

### Self-consistent symmetries in the proton-neutron Hartree-Fock-Bogoliubov approach

Symmetry properties of densities and mean fields appearing in the nuclear
Density Functional Theory with pairing are studied. We consider energy
functionals that depend only on local densities and their derivatives. The most
important self-consistent symmetries are discussed: spherical, axial,
space-inversion, and mirror symmetries. In each case, the consequences of
breaking or conserving the time-reversal and/or proton-neutron symmetries are
discussed and summarized in a tabulated form, useful in practical applications.Comment: 26 RevTex pages, 1 eps figure, 9 tables, submitted to Physical Review

### Level densities and $\gamma$-ray strength functions in Sn isotopes

The nuclear level densities of $^{118,119}$Sn and the $\gamma$-ray strength
functions of $^{116,118,119}$Sn below the neutron separation energy are
extracted with the Oslo method using the ($^3$He, \,$\alpha \gamma$) and
($^3$He,$^3$He$^\prime\gamma$) reactions. The level density function of
$^{119}$Sn displays step-like structures. The microcanonical entropies are
deduced from the level densities, and the single neutron entropy of $^{119}$Sn
is determined to be $(1.7 \pm 0.2)\,k_B$. Results from a combinatorial model
support the interpretation that some of the low-energy steps in the level
density function are caused by neutron pair-breaking. An enhancement in all the
$\gamma$-ray strength functions of $^{116-119}$Sn, compared to standard models
for radiative strength, is observed for the $\gamma$-ray energy region of
$\simeq (4 -11)$ MeV. These small resonances all have a centroid energy of
8.0(1) MeV and an integrated strength corresponding to $1.7(9)\%$ of the
classical Thomas-Reiche-Kuhn sum rule. The Sn resonances may be due to electric
dipole neutron skin oscillations or to an enhancement of the giant magnetic
dipole resonance

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