Detailed study of relativistic 9Be → 2α fragmentation in peripheral collisions in a nuclear track emulsion

Recent studies of clustering in light nuclei with an initial energy above 1 A GeV in a nuclear track emulsion are overviewed. The results of investigations of the relativistic ₉Be nuclei fragmentation in emulsion, which entails the production of α particles, are presented. It is shown that most precise angular measurements provided by this technique play a crucial role in the restoration of the excitation spectrum of the α particle system. In peripheral interactions ₉Be → 2α nuclei are dissociated practically totally through the 0⁺ and 2⁺ states of the ⁸Be nucleus.     

Fragmentation of ^16O nuclei in nuclear emulsion

We present the topology of 16O fragmentation at 60A GeV in reactions with emulsion nuclei.We discuss the multiplicity distributions of projectile fragments.charged secondaries and their dependence on the target residues.     

Measurement of the sizes of a source of α particles from the collisions of relativistic 22Ne and 24Mg nuclei with photoemulsion nuclei

The correlation of two α particles has been measured. In the case of a one-dimensional parameterization of the correlation function, the size of the source of the α particles is R(α) = 2.84 ± 0.28_stat ± 0.23_sist fm. This result is compared to similar measurements for protons and deuterons.     

Modeling of the γ → α transformation in steels

A mathematical physically based model of the decomposition of undercooled austenite (γ-phase) with the formation of ferrite (α-phase) and pearlite has been developed. The model differs from the currently existing analogs by a new approach to the inclusion of the effect of complex alloying of steels on the nucleation rate of ferrite grains and on the mobility of the α/γ-phase boundary. In the model, the effect of alloying of steels with substitutional elements on the diffusion coefficient of carbon in the bulk of austenite is taken into account. The results of the modeling of the kinetics of austenite decomposition and the calculation of the final ferrite grain size are in good quantitative agreement with the experimental data obtained for a set of steels with a wide range of chemical compositions.     

Role of the quasiparticle structure in α-decays of superheavy nuclei

The one-quasiparticle structures of nuclei in the α-decay chains of ²⁸⁷114 and ²⁹³116 are studied using a modified two-center shell model. Two-quasiparticle states are revealed in the α-decay chain of even-even nuclei ^286,288114. The calculated values for Q _α are compared to the available experimental data. The termination of the α-decay chains by spontaneous fission is analyzed.     

Peculiarities of α → β transformation in the Pd-In-Ru-H system

A precise X-ray diffractometry method is employed to investigate a Pd-In-Ru alloy foil subjected to electrolytic hydrogenation. It is revealed that an increase in the scattering volume of the sample and its multiphase disintegration are caused by the α → β transformation. The basic characteristics of the given transformation are established.     

Dynamic polarization of 6,7Li nuclei in the elastic scattering of α particles

The elastic scattering of α particles on weakly bound ^6,7Li cluster nuclei is considered with allowance for their dynamic polarization within the three-particle model. The considered states of the αd and αt continuums are projected on a finite basis of stationary wave packets, which allows the total three-body problem to be reduced to a matrix problem. The results from calculating α + ^6,7Li-elastic scattering differential cross sections are considered as illustration of the three-particle approach and is compared to the results of other authors.     

Microscopic investigation of electric dipole transitions in the α + 16O system

A microscopic calculation of forbidden E1 transitions is presented in the framework of the generator coordinate method. Isovector and isoscalar origins of E1 transitions are studied in the case of the α + ¹⁶O system. Two-cluster T = 0 and T = 1 configurations are coupled by the exact microscopic Coulomb interaction. The γ- widths of the 1₁⁻ and 3₂⁻, states of ²⁰Ne are fairly reproduced by the model but the anomalous branching ratios observed experimentally remain unexplained. Simplified formulas for the isospin-mixing rates and reduced E1 transition probabilities are compared with the microscopic results and are employed to discuss them. The non-resonant E1 contribution to the ¹⁶O(α, γ)²⁰Ne reaction is shown to be almost negligible at astrophysical energies.     

Description of the Properties of nuclei far from βstability line in relativistic Hartree approach

In the usual relativistic mean field(RMF) calculation of stable nuclei, the tensor coupling of ρ meson is not taken into account. It is necessary to clarify thecontribution of the tensor coupling of ρ meson when the RMF is extended to nucleifar from β stability line. The tensor coupling of ρ meson is included and its effectis discussed in the present work.     

Covalently bound molecular structures in the α + 16O system

Using the concept of covalent molecular orbitals for neutrons and the known properties of the local α + ¹⁶O potential the formation of asymmetric molecular structures in neon isotopes is discussed. Experimental evidence for parity doublets in ²¹Ne is reviewed and a corresponding band structure for the states in ²¹Ne at moderate excitation energy of E _x = 0-8 MeV is proposed. The structure of some bands can be interpreted as consisting of an instrinsic asymmetric ( ⁴He + ¹⁶O) structure bound by a covalent neutron in σ and π orbitals. An extension of the observed structures to symmetric molecular structures in isotopes of Mg and heavier nuclei is suggested. In particular shape isomers in isotopes of magnesium, namely (He)₂O molecules, can be predicted and an extended Ikeda diagram is proposed. Received: 11 July 2001 / Accepted: 22 August 2001     

Electromagnetic dissociation of 3.7 A GeV^16O in nuclear emulsion

The electromagnetic dissociation (ED) of 3.7 A GeV {}^{16}O in nuclear emulsion is investigated with high statistics. It is found that the electromagnetically dissociated cross section increases with increasing beam energy, the charge distribution of projectile fragments is the same as the results at 60 and 200 A GeV, and the production probability of projectile fragments with charge 3≤Z≤5 is less than that of the other projectile fragments. These results can be well explained by use of Weizsacker and Williams method for calculating the ED contributions. The percentile abundance of various decay modes for ED at 3.7 A GeV is close to the result at 60 and 200 A GeV, but it is different from the result at 14.6 A GeV. The ED of 3.7 A GeV is mainly caused by the giant dipole and quadrupole resonance of E1 and E2, which can be qualitatively explained by the multiplicity distribution of projectile proton in ED. The multiplicity distribution of the α fragments in ED and nuclear events have different functional forms. This difference may be a consequence of the different reaction mechanism involved.     

Effect of nuclear structure on the single particle β− transitions in deformed nuclei

In the framework of the Nilsson model the calculations of the so called shape factor for the first forbidden ^– transitions 5/2^{+ 241}Pu 5/2^{– 241}Am and 7/2^{+ 177}Lu 7/2^{– 177}Hf are carried out. The dependence on the Nilsson potential parameters is studied. It turns out that for the transitions considered the calculated shape factor depends linearly on the electron energy and its slope is 10^–3 per 20 keV. This can affect the analysis of electron spectra if the endpoint energy is sufficiently large.     

Variation in the structural state of the α-phase in the Pd-In-H system during the β → α transformation

Increasing the concentration of indium atoms and hydrogen was found in the α-phase of the foil of a Pd-In alloy (with 5.3 and 5.0 at % In) after its electrolytic hydrogenation and 500-h relaxation. It is shown that the structural variations in the foil during the β → α transformation are nonmonotonic.     

Electron screening in the 7Be + p → 8B + γ reaction

We evaluate the effect of screening by bound electrons in the ⁷Be(p,γ)⁸B reaction, where the ⁷Be target contains bound electrons, in the framework of the adiabatic representation of the three-particle problem. A comparison with two other approximations (united atom and folding) is presented. A good agreement between the “united atom” approximation and the exact solution is found. We also discuss the screening corrections induced by two K-shell electrons on a ⁷Be target. The consequences of bound electron screening for ⁷Be and ⁸B solar neutrino fluxes are discussed.     

Dosimetry of cosmic particles in nuclear emulsions for the apollo 16, 17 and apollo-soyouz-test-project experiments (1972–1975)

In the Biostack I, II and III experiments flown on the Apollo 16 and 17 and ASTP missions, nuclear emulsion plates have been used for the first time for heavy-ion identification in connection with biological layers. After the calibration step using the heavy ions available at the Bevalac at Berkeley, the nuclear emulsion can give dosimetric results for the heavy ions hitting biological materials. These results have been sent for exploitation to the biological laboratories of Toulouse, Frankfurt and Marburg. We summarize all the dosimetric results in the field of heavy-ion tracks and nuclear stars induced by cosmic-ray particles. The last results from Biobloc (December, 1975) are presented.     

Estimation of the nuclear distortion in the Coulomb breakup of 6Li into α + d in the field of 208Pb ion

In this article the results of the evaluation of the contribution of nuclear disintegration, based on the basis of diffraction theory in the ²⁰⁸Pb(⁶Li, αd)²⁰⁸Pb Coulomb breakup at an energy of 156 MeV is presented. Comparison of the results of the calculation with the experimental data of Kiener et al. [Phys. Rev. C 44, 2195 (1991)] gives evidence for the dominance of the Coulomb dissociation mechanism and contribution of nuclear distortion, but essentially smaller than the value reported byHammache et al. [Phys. Rev. C 82, 065803 (2010)] and Sümmerer [Prog. Part. Nucl. Phys. 66, 298 (2011)].     

Angular momentum limitation of cluster emission from the compound nucleus: 16O(16O, α)28Si and 16O(16O, 8Be)24Mg

Excitation functions of the (¹⁶O, α) and (¹⁶O, ⁸Be) compound reactions on ¹⁶O have been measured and compared with Hauser-Feshbach model calculations. Using transmission coefficients for penetration of the real potential barrier in the exit channels we find global agreement, in contrast to systematic deviations obtained with optical-model transmission coefficients.     

Molecular dynamics investigation of the size effect upon the β → α transformation in Zr nanocrystals

The stability of the β phase in cubic zirconium nanoparticles has been calculated as a function of the size r (r varies in the range from 2.5 to 11.5 nm) by the molecular dynamics method with the many-body interatomic interaction potential obtained within the embedded-atom model. It has been demonstrated that the temperature T _k at which the cubic cluster of body-centered cubic zirconium becomes structurally unstable depends nonlinearly on the particle size. The curve T _k (r) exhibits a pronounced maximum in the range r ≈ 4.3−4.7 nm. It has been established that the mechanism of the structural transition from the body-centered cubic phase to the hexagonal close-packed phase depends substantially on the particle size. For particles with sizes in the range from 2.5 to 5.0 nm, there exists a temperature range in which the transition from the body-centered cubic phase to the hexagonal close-packed phase remains incomplete for a long time. In this case, two phases coexist and the initial particle undergoes a strong deformation along the habit plane.