V. P. Likhachev

Momentum distribution in heavy deformed nuclei: Role of effective mass

The impact of nuclear deformation and effective mass m{sup *}/m on the momentum distributions (MD) of occupied proton states in {sup 238}U is investigated in the self-consistent Skyrme-Hartree-Fock (SHF) scheme with parameterizations SkT6, SkM*, SLy6, and SkI3 as well as with the phenomenological Woods-Saxon (WS) shell model. The deformation effect turns out to be significant in the low-momentum domain of K{sup {pi}}=1/2{sup {+-}} states (mainly of those lying near the Fermi surface) and negligible for other states. The most remarkable result is that all Skyrme parameterizations (with essentially different m{sup *}/m) and the WS potential give very similar MD. This means that the value of effective mass, although crucial for single-nucleon spectra, is not important for the spatial shape of the wave functions and thus for the MD. For the description of MD at 0{<=}k{<=}300 MeV/c, one may use any single-particle scheme fitted properly to the global ground state properties.

Nuclear photofissility of natPb and 232Th at energies above the pion photoproduction threshold

A new, simple approach based on the intranuclear cascade plus the evaporation–fission competition mechanisms of photonuclear reactions has been developed to calculate fissility values at energies above ~200 MeV. This approach has been successfully used in explaining fissility data for natPb and 232Th target nuclei at energies up to 3.8 GeV recently obtained at the Thomas Jefferson Laboratory. Predictions of photofissility up to 5–6 GeV for these nuclei are also given.

Developement of crisp package for spallation reaction studies and its utilization in ADS (Accelerator Driven System)

The progress of nuclear physics had allowed a better understanding of nuclear structure and reaction mechanisms, but also enables important applications of nuclear energy in our modern way of life. We can point out those ones related to power generation from nuclear reactors, providing an almost inexhaustive power source due to the huge quantities of nuclear fuel existent in our planet, which guaranties its utilization for thousands of years. The main interest is the so-called Hybrid Reactors (ADS - Accelerator Driven System), in which the reactor has a sub critical core and the chain reaction is sustained by an external source that comes from spallation reactions induced by high energy protons (about 1 GeV) from an accelerator, producing a large number of secondary particles (mainly neutrons). For those applications, precise knowledge about nuclear structure and nuclear reaction characteristics is needed.

New approach to nuclear photofission reactions above 0.15 GeV

A simple approach to evaluate nuclear photofissilities at energies above the pion photoproduction threshold has been developed. It is based on the current, two-step model for intermediate-energy photonuclear reactions, i.e. a photon-induced intranuclear cascade followed by a fission-evaporation competition process for the excited, post-cascade residual nucleus. The calculation method (semiempirical by nature) shows that fissility (i.e., total fission probability) is governed by two basic quantities, namely, the first-chance fission probability for the average cascade residual, and a parameter which defines an evaporative sequence of residuals in which the average, equivalent chance-fission probabilities of nuclides belonging to the same generation are located. The natPb photofissility data measured recently in the range ~ 0.2 - 3.8 GeV at the Thomas Jefferson Laboratory could be explained very satisfactorily by the present approach.

Deformation effects in low-momentum distributions of heavy nuclei

Momentum distributions (MD) of deep hole proton states in 238U are studied paying particular attention to the influence of deformation. Two essentially different mean-field models, Woods–Saxon (WS) and Skyrme–Hartree–Fock with the SkM* force, are used. Noticeable deviations between the WS and SkM* results are found. They are mainly due to the difference in the effective nucleon mass. In particular, SkM* gives much weaker deformation effects at low momenta than WS. It is shown that, in spite of the deformation mixing, MD at low momenta can serve for identification of Kπ = 1/2+ hole states originating from s1/2 spherical subshells. Moreover, following the WS calculations, the deformation results in additional Kπ = 1/2+ states with strong l = 0 contributions. A possibility of probing such states in knock-out experiments is discussed.

Quasifree electrofission of238U

We present the result of a theoretical study of the quasi free electrofission of

Residual nucleus excitation energy in (e, e'p): reaction

^{238}

The potentialities of coherent X-radiation for self-assembled systems and liquid crystal research

U. The exclusive differential cross sections for the quasi free scattering reaction stage have been calculated in PWIA, using a Macroscopic-Microscopic approach for the description of the proton bound states. The nuclear shape was parametrized in terms of cassinian ovaloids. The equilibrium deformation parameters have been calculated by minimizing the total nuclear energy. In the calculation the axially deformed Woods-Saxon single particle potential was used. The obtained single particle momentum distributions were averaged over the nuclear symmetry axis direction. The occupation numbers were calculated in the BCS approach. The fissility for the single hole excited states of the residual nucleus

102Rhm: Could it be a cosmic-ray chronometer?

^{237}

Statistical and direct aspects of64Zn(γ,n)and(γ,np)decay channels in the giant dipole resonance and quasideuteron energy regions

% Pa was calculated on the statistical theory grounds both without taking into account the pre-equilibrium emission of the particle, and with preequilibrium emission in the framework of the exciton model.