Physics of Atomic Nuclei

The gamma-quanta emission is considered within the framework of the non-Markovian kinetic theory. It is shown that the memory effects have a strong influence on the spectral distribution of gamma quanta in the case of long-time relaxation regime. It is shown that the gamma radiation can be used as a probe for both the time-reversible hindrance force and the dissipative friction caused by the memory integral.

Most of the destructions of machine parts are of fatigue character. Under cyclic loading, the surface layer, in which hardening–softening processes rapidly occur, is formed almost at once after its beginning. The interaction of plastic-deformation traces with each other and with other structural elements, such as grains, results in the formation of a characteristic microstructure of the machine-part surface subject to cyclic loadings. The character of accumulation of slip bands and their shape (narrow, wide, twisting, and broken) depends on the conditions under which (under what factors) the cyclic loading occurs. The fatigue-resistance index expressed in terms of the slope of left portion of the fatigue curve linearized in logarithmic coordinates also depends on the set of relevant factors. The dependence of the surface damageability on the fatigue resistance index makes it possible to implement the method of predicting the fatigue curve by the description of the factors acting on a detail or construction. The position of the inflection point on the curve in the highcycle fatigue region (the endurance limit and the number of loading cycles, the ordinate and abscissa of the inflection point on the fatigue curve, respectively) also depends on the set of relevant factors. In combination with the previously obtained value of the slope of the left portion of the curve in the high-cycle fatigue region, this makes it possible to construct an a priori fatigue curve, thus reducing the scope of required fatigue tests and, hence, high expenses because of their long duration and high cost. The scope of tests upon using the developed method of prediction may be reduced to a minimum of one or two samples at the predicted level of the endurance limit.

A general algebraic approach incorporating both invariance groups and dynamical symmetry algebras is developed to reveal hidden coherent structures (closed complexes and configurations) in quantum manybody physics models due to symmetries of their Hamiltonians H. Its general ideas are manifested on some recent new examples: (1) G-invariant biphotons and a related SU(2)-invariant treatment of unpolarized light; (2) quasispin clusters in nonlinear models of quantum optics; and (3) construction of composite particles and (para)fields from G-invariant clusters due to internal symmetries.

The formation of dense groups (fluctuations) of particles produced in the central CCu and MgMg collisions at the projectile momenta of, respectively, 4.5 and 4.3 GeV/c per nucleon is analyzed. The distributions of the maximum densities and of the centers of charged-particle fluctuations in pseudorapidity space are studied in searches for dynamical multiparticle correlations. The distributions of the centers show two peaks above the statistical background with a structure similar to that which is expected in the model of coherent gluon emission and which was observed in hadronic interactions. The charge independence of the distributions in question and an azimuthal isotropy of events involving pseudorapidity fluctuations are observed. The distributions of events with respect to the maximum density of fluctuations are governed primarily by the statistical contribution, although the behavior of the distributions in CCu collisions is in qualitative agreement with the prediction of the one-dimensional intermittency model. It is found that the resulting distributions are of a non-Poisson character both in CCu and in MgMg collisions. The results of this study indicate that, in describing local dynamical fluctuations in multiparticle production processes, the coherent and the stochastic approach supplement each other. The procedure employed in the analysis described here makes it possible to draw a direct comparison of the present results with the results of similar investigations of different reactions.

The paper is devoted to study electron screening effect influence on the rate of d(d, n)3He reaction in the ultralow deuteron collision energy range in the deuterated polyethylene (CD2), frozen heavy water (D2O) and deuterated metals (ZrD2 and TiD2). The ZrD2 and TiD2 targets were fabricated via magnetron sputtering of titanium and zirconium in gas (deuterium) environment. The experiments have been carried out using high-current plasma pulsed accelerator with forming of inverse Z pinch (HCEIRAS, Russia) and pulsed Hall plasma accelerator (NPI at TPU, Russia). The detection of neutrons with energy of 2.5MeV from dd reaction was done with plastic scintillation spectrometers. As a result of the experiments the energy dependences of astrophysical S factor for the dd reaction in the deuteron collision energy range of 2–7 keV and the values of the electron screening potential U e of interacting deuterons have been measured for the indicated above target: U e (CD2) ⩽ 40 eV; U e (D2O) ⩽ 26 eV; U e (ZrD2) = 157 ± 43 eV; U e (TiD2) = 125±34 eV. The value of astrophysical S factor, corresponding to the deuteron collision energy equal to zero, in the experiments with D2O target is found: S b (0) = 58.6 ± 3.6 keV b. The paper compares our results with other available published experimental and calculated data.

Employing a four-body classical model, various mechanisms responsible for the production of fast light particles in heavy-ion collisions at low and intermediate energies have been studied. It has been shown that, at energies lower than 50 A MeV, light particles of velocities of more than two times the projectile velocities are produced due to the acceleration of the target light particles by the mean field of the incident nucleus. It has also been shown that precision experimental reaction research in normal and inverse kinematics is likely to provide vital information about which mechanism is dominant in the production of fast light particles.

On the basis of the continuity equation, the concept of a complex potential, and the exciton model of nuclear reactions, an expression was derived that establishes the relation between three time characteristics associated with different reaction stages. It is shown that an empirical systematics relating the coherence widths to the temperature of compound nuclei is a high-temperature limit of this expression, which determines empirical coefficients in terms of quantities similar to volume absorption integrals per nucleon that appear in optical-model calculations. The possibility of estimating the energy dependence of these quantities on the basis of experimental data on the total widths of neutron resonances, measured mean lifetimes of compound nuclei, and data on coherence widths is discussed.