International Journal of Modern Physics E

Applying exact QCD sum rules for the baryon charge and energy–momentum conservation we demonstrate that if the only degrees of freedom in nuclei were nucleons, the structure function of a nucleus would be the additive sum of the nucleon distributions at the same Bjorken x = AQ²/2(p_A⋅q)≤0.5 up to very small Fermi motion corrections if 1/2m_N x is significantly less than the nucleus radius. Hence QCD implies that the proper quantity to reveal violation of the additivity due to presence of nonnucleonic degrees of freedom in nuclei is the ratio R_A(x, Q²) = (2/A)F_2A(x, Q²)/F_2D(x, Q²). Use of variable x_p = Q²/2q₀m_p in the experimental studies instead of x leads to the deviation of R_A(x_p, Q²) from one even if the nucleus would consist only of nucleons with small momenta. Implementation of QCD dynamics accounts in the case of the light nuclei for at least a half of the deviation of R_A(x_p, Q²) from one for x≤0.55. In the case of heavy nuclei account of the QCD dynamics and of light-cone momentum fraction carried by Fermi, Weizsacker, Williams equivalent photons are responsible for ≈ one half the deviation of R_A(x, Q²) from one at x≤0.55. We argue that direct observation of large and predominantly nucleonic short-range correlations (SRCs) in nuclei impacts strongly on the understanding of the EMC effect for x≥0.6 posing a serious challenge for most of the proposed models of the EMC effect. The data are consistent with a scenario in which the hadronic EMC effect reflects suppression of rare quark–gluon configurations in nucleons belonging to SRC appears to be the only viable. The dynamic realization of this scenario is presented in which quantum fluctuations of the nucleon wave function with x≥0.5 parton have a weaker interaction with nearby nucleons, leading to suppression of such configurations in bound nucleons and to the significant suppression of nucleon Fermi motion effects at x≥0.55 giving a right magnitude of the EMC effect. Implications of discussed effects for the analyses of the neutron structure function and nuclear parton distributions are presented. The directions for the future studies and challenging questions are outlined.

Neutron rich nuclei has been studied with a new phenomenological mass formula. Predictions of different mass formulas for the location of the neutron drip line are compared with those from the present calculation. The implications of the new mass formula for r-process nucleosynthesis are discussed. It is found that though the neutron drip line obtained from this formula differs substantially from other formulas, the r-process abundance upto mass 200 are unlikely to be significantly different. The errors inherent in the mass formula are found to play an insignificant role beyond mass A = 80.

Some properties of variable cosmological constant (VCC) models in generalized mass-varying neutrino (MaVaN) scenarios are examined through an effective parametrization method. The limits of VCC models in case of power-law and exponential potentials are investigated in the nonrelativistic regime. The evolution of a resulting universe state parameter, ω, coupled to a neutrino dynamical mass is obtained. The coupling to MaVaN's constrains the values of the state parameter, ω, to a cosmologically acceptable interval given by -1<ω⁰≲-0.882. This simplified parametrization method sheds some light on the conventional discussions involving the intricate integrals over neutrino Fermi–Dirac distributions by simplifying the interpretation of MaVaN's contributions to the VCC scenarios.

Deformed even–even nuclei with quadrupole and octupole deformations are investigated on the basis of a nonadiabatical collective model. It is shown that the model satisfactorily describes energy levels of the yrast and first nonyrast bands with alternating parity in the rare-earth nuclei ¹⁵⁰Nd, ^{152, 154}Sm, ¹⁵⁴Gd, ¹⁵⁶Dy, ^{162, 164}Er and the actinides ^{232, 234, 236, 238}U. In the nuclei ^{156, 158}Gd, ²²⁴Ra, ²²⁸Th and ²⁴⁰Pu the energy levels of second nonyrast bands are also described. The structure of the considered alternating-parity bands is examined in terms of odd–even staggering diagrams.

The effect of the particle-number symmetry restoration on the root mean square (rms) proton and neutron radii of neutron-deficient nuclei is studied in the isovector pairing case. As a first step, an expression of the nuclear radii which includes the neutron–proton pairing effects and which strictly conserves the particle-number has been established using the SBCS (Sharp BCS) method. It is shown that this expression generalizes the one obtained in the pairing between like-particles case. As a second step, the proton and neutron rms radii are numerically evaluated for even–even nuclei such as 16⩽Z⩽56 and 0⩽(N-Z)⩽4 using the single-particle energies of a Woods–Saxon mean-field. The results are compared with experimental data when available and with the results obtained when one considers only the pairing between like-particles.

We study Uranium isotopes and surrounding elements at very large neutron number excess. Relativistic mean field and Skyrme-type approaches with different parameterizations are adopted in the study. Most models show clear indications for isotopes that are stable with respect to neutron emission far beyond N = 184 up to the range of around N = 258.

The form factor of the transition ργ*→π⁰ is investigated by analyzing the γγ*→π⁰ transition in the framework of the light-cone local duality quantum chromodynamics sum rules. Both finite- and zero-width forms for the low-energy physical absorptive part of the γγ*→π⁰ transition are considered. The numerical results for the transition form factor F^ρπ(Q²) in the asymptotic form and the CZ one of the pion distribution amplitude are obtained respectively, the difference between the finite- and zero-width form is not big but still distinguishable. It is found that the results for the form factor F^ρπ(Q²) from CZ, asymptotic and the flat pion DAs are compatible with the predictions of perturbative QCD. Our results will be helpful to distinguish the shape of the pion DA of twist-two, when the concrete information of the experimental data for the transition ργ*→π⁰ are provided.

We have performed shell model calculations for neutron deficient even ^102-108Sn and odd ^103-107Sn isotopes in sdg_7/2h_11/2 model space using two different interactions. The first set of interaction is due to Brown et al. and second is due to Hoska et al. The calculations have been performed using doubly magic ¹⁰⁰Sn as core and valence neutrons are distributed over the single particle orbits 1g_7/2, 2d_5/2, 2d_3/2, 3s_1/2 and 1h_11/2. In more recent experimental work for ¹⁰¹Sn [I. G. Darby et al., Phys. Rev. Lett.105 (2010) 162502], the g.s. is predicted as 5/2⁺ with excited 7/2⁺ at 172 keV. We have also performed another two set of calculations by taking difference in single particle energies of 2d_5/2 and 1g_7/2 orbitals by 172 keV. The present state-of-the-art shell model calculations predict fair agreement with the experimental data. These calculations serve as a test of nuclear shell model in the region far from stability for unstable Sn isotopes near the doubly magic ¹⁰⁰Sn core.

The construction and performance of the parallel plate avalanche counters (PPACs) using a spontaneous fission source ²⁵²Cf is described in this paper. The parallel plate circular electrodes are made of aluminum foils having a thickness less than ten microns. After fabrication, the detectors and the source are mounted inside a reaction chamber, the source between the two detectors. A low pressure is created inside the chamber using isobutane (C₄H₁₀) and a high voltage is applied to the electrodes. The detectors are first operated at different pressures and voltages to find the optimum values of the pressure and the voltage. This is necessary to avoid the sparking threshold, to achieve a good time resolution and to keep the gain of the detectors high and constant. The PPACs are operated in 2π- and 4π-geometries. In 4π-geometry the detectors are allowed to function in coincidence and noncoincidence mode. The resulting pulse height and the time spectra are studied using the computer code ROOT and some conclusions are drawn from these analyses. The pulse height spectrum shows a clear separation between the fission fragments and the alpha particles and the time spectrum indicates a good intrinsic time resolution, 0.76 ns.