The investigation of plastic deformation nucleation in metals and alloys under irradiation and mechanical loading is one of the topical issues of materials science. Specific features of nucleation and evolution of the defect system in stressed and irradiated iron, vanadium, and copper crystallites were studied by molecular dynamics simulation. Mechanical loading was performed in such a way that the modeled crystallite volume remained unchanged. The energy of the primary knock-on atom initiating a cascade of atomic displacements in a stressed crystallite was varied from 0.05 to 50 keV. It was found that atomic displacement cascades might cause global structural transformations in a region far larger than the radiation-damaged area. These changes are similar to the ones occurring in the process of mechanical loading of samples. They are implemented by twinning (in iron and vanadium) or through the formation of partial dislocation loops (in copper).
The study of energy production and nucleosynthesis in stars requires an increasingly precise knowledge of the nuclear reaction rates at the energies of interest. To overcome the experimental difficulties arising from the small cross sections at those energies and from the presence of the electron screening, the Trojan Horse Method has been introduced. The method provides a valid alternative path to measure unscreened low-energy cross sections of reactions between charged particles, and to retrieve information on the electron screening potential when ultra-low energy direct measurements are available.
The status of our investigation of low-energy K +Xe collisions in the xenon bubble chamber DIANA is reported. In the charge-exchange reaction K +Xe → K 0 pXe′, the spectrum of K 0 p effective mass shows a resonant enhancement with M=1539±2 MeV/c 2 and Γ≤9 MeV/c 2. The statistical significance of the enhancement is near 4.4σ. The mass and width of the observed resonance are consistent with expectations for the lightest member of the antidecuplet of exotic pentaquark baryons, as predicted in the framework of the chiral soliton model.
The influence of an effective spinisospin interaction in the particleparticle channel on the beta-decay half-lives and multineutron-emission probabilities is studied. The contributions of tensor correlations and coupling of the one- and two-phonon configurations are taken into account within a self-consistent approach that relies on the quasiparticle random-phase approximation and which employs Skyrme interaction. The beta-decay properties of neutron-rich cadmium isotopes are calculated.
The idea of the magnetorotational explosion mechanism is that the energy of rotation of the neutron star formed in the course of a collapse is transformed into the energy of an expanding shock wave by means of a magnetic field. In the two-dimensional case, the time of this transformation depends weakly on the initial strength of the poloidal magnetic field because of the development of a magnetorotational instability. Differential rotation leads to the twisting and growth of the toroidal magnetic-field component, which becomes much stronger than the poloidal component. As a result, the development of the instability and an exponential growth of all field components occur. The explosion topology depends on the structure of the magnetic field. In the case where the initial configuration of the magnetic field is close to a dipole configuration, the ejection of matter has a jet character, whereas, in the case of a quadrupole configuration, there arises an equatorial ejection. In either case, the energy release is sufficient for explaining the observed average energy of supernova explosion. Neutrinos are emitted as the collapse and the formation of a rapidly rotating neutron star proceeds. In addition, neutrino radiation arises in the process of magnetorotational explosion owing to additional rotational-energy losses. If the mass of a newborn neutron star exceeds the mass limit for a nonrotating neutron star, then subsequent gradual energy losses may later lead to the formation of a black hole. In that case, the energy carried away by a repeated flash of neutrino radiation increases substantially. In order to explain an interval of 4.5 hours between the two observed neutrino signals from SN 1987A, it is necessary to assume a weakening of the magnetorotional instability and a small initial magnetic field (10(9)-10(10) G) in the newly formed rotating neutron star. The existence of a black hole in the SN 1987A remnant could explain the absence of any visible pointlike source at the center of the explosion.
The energy as determined experimentally for the first excited 2(+) state of the Gd-156 rotational band based on the mixed-symmetry state is extremely small in relation to characteristic values of this energy in deformed nuclei. The possibility of explaining this experimental fact by a large value of the decoupling parameter is explored. The result is that the decoupling-parameter values obtained under various assumptions on the structure of the mixed-symmetry state are too small for explaining the experimental excitation energy of the state in question.
Via simulating the contribution of spin-orbit interaction to nuclear masses by orthogonal Chebyshev polynomials, the mass excesses are calculated for a group of atomic nuclei characterized by the isospins of T-z = 51/2, 26, 53/2, 55/2, 28, and 57/2 and by the presence of restored Wigner's spin-isospin SU(4) symmetry. The root-mean-square deviation of the results of these calculations from their experimental counterparts is sigma = 140 keV. The potential of the proposed method is discussed.
In order to explain elastic neutral-pion photoproduction on a 7Li nucleus in the excitation-energy region of the Δ(1232)3/2+ resonance, a new interpretation of coherent pion photoproduction on nuclei featuring two or more shells is proposed with allowance for a special feature of inelastic pion photoproduction on a nucleon. Coherence originating from nucleons of different nuclear shells is retained, while coherence from all of the nucleons is removed, since, after pion production on nucleons from different shells, they cannot cannot be in the same phases because of the difference in the conditions of their residence in the nucleus. Under this assumption, a noncontradictory description of all experimental data is obtained upon additionally including the interaction of Δ isobars in the nucleus that are produced along with neutral pions.
A new threshold resummation S-factor in quantum chromodynamics is obtained for a composite system of two relativistic spin-1/2 quarks having identical masses and interacting via a Coulomb-like chromodynamical potential. The pseudoscalar, vector, and pseudovector cases are considered. The present analysis is performed on the basis of the relativistic quasipotential approach in the Hamiltonian formulation of quantum field theory via a transition to the relativistic configuration representation for the case of a composite system formed by two relativistic particles of equal mass.
We build a simple Standard Model extension based on T-7 flavor symmetry which accommodates lepton mass, mixing with non-zero (13), and CP violation phase. The lepton mixing matrix is obtained from three triplets and one singlet under T-7 symmetry, and the charged-lepton mass is derived through the spontaneous symmetry breaking by just one T-7 triplet (phi), while neutrinos get small masses from one SU(2) (L) doublet and two SU(2)(L) singlets in which one is in 1 and the two others are in 3 and 3* under T-7, respectively. There exist viable parameters of the model that predict the effective Majorana neutrino mass with values m similar or equal to 10(-2) eV and 4.95 x 10(-2) eV as well as a lightest neutrino mass m(light) similar or equal to 4.97 x 10(-3) eV and 1.61 x 10(-3) eV for the normal and inverted neutrino mass hierarchies, respectively. The model also gives a remarkable prediction of Dirac CP violation (CP) similar or equal to 303.3 degrees in the normal hierarchy and (CP) similar or equal to 56.69 degrees in the inverted hierarchy which is still missing in the neutrino mixing matrix. The quark mixing angles of the model are closed to the experimental data, whereas the obtained values for the quark masses are consistent with with the experimental data at the tree level.
Experimental data on N scattering in the elastic energy region w 1.45 GeV are analyzed within the K-matrix approach with effective lagrangians. The charge splitting in ++ and phases obtained in the phase-shift analisys is studed. It is shown that the change in the sign in the energy dependence of the phase difference can be obtained with different form factors of the (++) and (0) only. This means that N++ and N-0 interactions have a different range. The underlying nature of the observed phenomena is discussed.
The possibility of experimentally determining the ratio of the axial weak-interaction constant G(A) to the vector weak-interaction constant G(V) by simultaneously measuring the electron and neutrino asymmetries at the same setup is discussed. The proposed measurement and data-processing procedures are described in detail. The determination of by the method in question permits disregarding the possible contribution of the Fierz interference term and dispensing with an accurate measurement of the neutron polarization. It is shown that this method makes it possible to measure to a precision at a level of 10(-4).
The results obtained from a phenomenological analysis of the ratio of the elastic-to-total cross sections for proton-proton (pp) and antiproton-proton ((pp)) scattering as a function of energy are presented. Analytic functions proposed on the basis of studying low- and high-energy experimental data for various scattering parameters make it possible to obtain a statistically acceptable quantitative description of the energy dependence of this ratio over a broad energy region of s3 GeV for individual samples of pp and pp collisions and over the region of s5 GeV for a combined ensemble of experimental data. On the basis of the resulting approximations, the ratio of the elastic-to-total cross sections for pp collisions are estimated at various values of s up to an ultrahigh energy of s=10 PeV. The resulting estimates may prove to be useful for experiments at currently operating and future hadron colliders, as well as for measurements of ultrahigh-energy cosmic rays. An indication of the onset of the asymptotic region for the cross-section ratio in question is observed in the region of s-10 PeV.
Experimental data on πN scattering in the elastic energy region w ≤ 1.45 GeV are analyzed within the K-matrix approach with effective lagrangians. The charge splitting in δ33++ and δ330 phases obtained in the phase-shift analisys is studed. It is shown that the change in the sign in the energy dependence of the phase difference can be obtained with different form factors of the Δ++ and Δ0 only. This means that πNΔ++ and πNΔ0 interactions have a different range. The underlying nature of the observed phenomena is discussed.
The formation of the quark and lepton mass matrices through intermediate states of heavy mirror fermions is able to reproduce basic observable qualitative properties of weak-mixing matricesspecifically, the CabibboKobayashiMaskawa (CKM) matrix and the PontecorvoMakiNakagawa-Sakata (PMNS) matrix. The reproduction in question includes the hierarchy of the CKM matrix elements and a general form of the PMNS matrix, including the smallness of the neutrino mixing angle (13) and leads to extremely small neutrino masses. For leptons, these properties arise only if Standard Model neutrinos are Dirac particles and if the spectrum of their generations has an inverse character. In such a lepton system, the mechanism of spontaneous mirror-symmetry violation and the observed mass hierarchy of charged leptons (e, , and ) specify the structure of the PMNS matrix and make it possible to estimate the complex-valuedness of its elementsthat is, to assess the CP properties of leptons. In this case, the PMNS matrix does not involve Majorana phases, whereas its Dirac phase (CP) corresponds to | sin (CP) | that is substantially smaller than unity.
It is shown that, upon the stopping of a negatively charged kaon and its absorption by a nucleus, there arise particles whose appearance does not comply with thermodynamic evaporation theory. An identification of these particles by various methods makes it possible to evaluate the nearly identical yields of H-3 and He-3 nuclei. This result may serve as an indication that direct reactions induced by interaction with He-4 are observed in Kmeson absorption in nuclei.
Because of a high energy of the neutrinoless double-beta decay (02) of the isotope Nd-150 and a high value of the daughter-nucleus charge Z(f), Nd-150 is one of the most promising isotopes for 02-decay searches. A Nd-150-containing detector on the basis of a liquid organic scintillator permits employing large isotope masses. Requirements on the radiation purity of the neodymium sample used are determined. The possible design of a large-scale detector of this type and expected results are considered.
Because of a high energy of the neutrinoless double-beta decay (0ν2β) of the isotope 150Nd and a high value of the daughter-nucleus charge Zf, 150Nd is one of the most promising isotopes for 0ν2β-decay searches. A 150Nd-containing detector on the basis of a liquid organic scintillator permits employing large isotope masses. Requirements on the radiation purity of the neodymium sample used are determined. The possible design of a large-scale detector of this type and expected results are considered.
In order to explain elastic neutral-pion photoproduction on a Li-7 nucleus in the excitation-energy region of the (1232)3/2(+) resonance, a new interpretation of coherent pion photoproduction on nuclei featuring two or more shells is proposed with allowance for a special feature of inelastic pion photoproduction on a nucleon. Coherence originating from nucleons of different nuclear shells is retained, while coherence from all of the nucleons is removed, since, after pion production on nucleons from different shells, they cannot cannot be in the same phases because of the difference in the conditions of their residence in the nucleus. Under this assumption, a noncontradictory description of all experimental data is obtained upon additionally including the interaction of isobars in the nucleus that are produced along with neutral pions.