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تسجيل مستخدم جديدEnhanced radiative strength in the quasi-continuum of 117Sn
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Radiative strength functions of 117Sn has been measured below the neutron separation energy using the (3He,3Hegamma) reactions. An increase in the slope of the strength functions around E_gamma= 4.5 MeV indicates the onset of a resonance-like structure, giving a significant enhancement of the radiative strength function compared to standard models in the energy region 4.5 <= E_gamma <= 8.0 MeV. For the first time, the functional form of this resonance-like structure has been measured in an odd tin nucleus below neutron threshold in the quasi-continuum region.
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Radiative strength functions (RSFs) in 93-98Mo have been extracted using the (3He,alpha gamma) and (3He,3He gamma) reactions. The RSFs are U-shaped as function of gamma energy with a minimum at around E_gamma=3 MeV. The minimum values increase with n
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is extremely sensitive to their $gamma$-emission probability at very low $gamma$ energies. In this work, we present measurements of the $gamma$-decay strength of $^{70}$Ni over the wide range $1.3 leq E_{gamma} leq 8 $ MeV. A significant enhancement is found in the $gamma$-decay strength for transitions with $E_gamma < 3$ MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed $E1$-strength calculations within the quasiparticle time-blocking approximation, which describe our data above $E_gamma simeq 5$ MeV very well. Moreover, large-scale shell-model calculations indicate an $M1$ nature of the low-energy $gamma$ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich $^{72,74,76}mathrm{Ni}$.
Photoabsorption cross sections and gamma-decay strength function are calculated and compared with experimental data to test the existing models of dipole radiative strength functions (RSF) for the middle-weight and heavy atomic nuclei. Simplified ver
sion of the modified Lorentzian model are proposed. New tables of giant dipole resonance (GDR) parameters are given. It is shown that the phenomenological closed-form models with asymmetric shape can be used for overall estimates of the dipole RSF in the gamma -ray energy region up to about 20 MeV when GDR parameters are known or the GDR systematics can be adopted. Otherwise, the HFB-QRPA microscopic model and the semi-classical approach with moving surface appear to be more adequate methods to estimate the dipole photoabsorption RSF.
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V.A. Plujko
, M.O. Kavatsyuk
, O.O. Kavatsyuk (Taras Shevchenko Nationaln University; Institute for Nuclear Research
2002
The semiclassical method for description of the radiative strength function is used for asymmetric nuclei with $N e Z$. The theory is based on the linearized Vlasov-Landau equations in two-component finite Fermi liquid. The dependence of the shape $
E1$ strength on the coupling constant between proton and neutron subsystems was studied.
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