International Journal of Modern Physics E

The electromagnetic radiation generated by ultra-relativistic positrons channeling in a crystalline undulator is discussed. The crystalline undulator is a crystal whose planes are bent periodically with the amplitude much larger than the interplanar spacing. Various conditions and criteria to be fulfilled for the crystalline undulator operation are established. Different methods of crystal bending are described. We present the results of numeric calculations of spectral distributions of the spontaneous radiation emitted in the crystalline undulator and discuss the possibility to create the stimulated emission in such a system in analogy with the free electron laser. A careful literature survey covering the formulation of all essential ideas in this field is given. Our investigation shows that the proposed mechanism provides an efficient source for high energy photons, which is worth studying experimentally.

The Dirac equation is investigated in D+1 dimensional space-time. The radial equations of this quantum system are obtained and solved exactly by the confluent hypergeometric equation approach. The energy levels E(n,l,D) are analytically presented. For the continuous dimension D as proposed by Nieto, the dependences of the energy difference ΔE(n,l,D) for D and D-1 on the dimension D are demonstrated as three different kinds of change rules. The dependences of the energy E(n,l,D) on the dimension D are also discussed. It is found that the energies E(n,l,D) (l≠0) are almost independent of the quantum number l for a large D, while E(n,0,D) first decreases and then increases with the increasing dimension D. The dependences of the energies E(n,l,ξ) on the potential strength ξ are also studied for the given dimension D=3. We find that the energies E(n,l,ξ) decrease with ξ≤l+1.

The decay of bromine-76 was studied using high resolution HpGe detectors in singles and coincidence mode. Bromine-76 was produced via two reactions: ⁷⁵As(α,3n)⁷⁶Br and ⁷⁶Se(p,n)⁷⁶Br. The results of these experiments verified the previously reported levels of ⁷⁶Se. In addition to the previously described transitions and levels, 37 new γ-rays and 15 new energy levels were found for the first time.

We study isovector collective excitations in nuclear matter by employing the linearized Landau–Vlasov equation with and without a non-Markovian binary collision term at finite temperature. We calculate the giant dipole resonance (GDR) strength function for finite nuclei using the Steinwedel–Jensen model and also by Thomas–Fermi approximation, and we compare them for ¹²⁰Sn and ²⁰⁸Pb with experimental results.

Chiral boson theory is introduced and its relevance to the quantum Hall effect is explained. It is shown that the chiral boson theory admits mode expansions which are essentially those which appear and are made use of in bosonic string theories. This immediately leads to a way of quantizing the theory. Restrictions on various parameters appearing in the model can be imposed in a natural way. Finally, it is suggested that some of these ideas have important applications to other geometries which could give rise to new types of physical behavior.

Effective meson masses of σ, ω, ρ and π in nuclear matter are calculated from the meson self-energy of the particle–antiparticle excitations. Instead of the traditional renormalization, the dispersion relation method is used to calculate the real part from the finite imaginary part, since the tensor coupling of the pion and ρ meson is not renormalized in the usual sense. In this paper, we show the effects from antidelta-nucleon and delta-antinucleon excitations in π meson mass beside nucleon–antinucleon excitation. It is also shown that agreement is obtained on the ω meson mass predicted by the subtraction method and ρ meson mass by the QCD sum rule method. It is concluded that the dispersion equation method leads to the fact that all the meson mass decreases as the baryon density increases, and it supports the chiral symmetry restoration.

The variation of nuclear shell effects with nucleon numbers is evaluated using the modified Bethe–Weizsäcker mass formula (BWM) and the measured atomic masses. The shell effects at magic neutron numbers N=8, 20, 28, 50, 82 and 126 and magic proton numbers Z=8, 20, 28, 50 and 82 are found to vary rapidly approaching the drip-lines. The shell effect due to one magic number increases on approaching another magic number. Thus, shell effects are not always negligible near the drip-lines.

The relation between strong isospin I and weak isospin i is discussed. In particular an equation between the third components I₃ and i₃ is given. This relation indicates that the strong isospin and weak isospin symmetries are both SU(2) subgroups of a new SU(3) symmetry underlying the structure of leptons and quarks.

The excited states of ⁷³As have been investigated via the ⁷³Ge(p, nγ)⁷³As reaction with proton beam energies from 2.5–4.3 MeV. The lifetimes of the levels at 769.6, 860.5, 1177.8, 1188.7, 1274.9, 1344.1, 1557.1 and 1975.2 keV excitation energies have been measured for the first time using the Doppler shift attenuation method. The angular distributions have been used to assign the spins and the multipole mixing ratios using statistical theory for compound nuclear reactions. The ambiguity in the spin values for the various levels has been removed. The multipole mixing ratios for eight γ-transitions have been newly measured.