Electro-nuclear neutron generator — XADS at ITEP

In this report, the purpose and status of the currently constructed ITEP experimental accelerator driven system (XADS) are discussed. This hybrid electro-nuclear facility of moderate power integrates the pulse proton linac (36 MeV, 0.5 mA) and heavy water sub-critical blanket assembly (heat power of 100 kW). Most parts of the equipment units are ordered for industrial manufacturing and some are under development. The facility is supposed to be used for investigations of a wide range of problems concerning both the target-blanket assembly and the accelerator-driver and at the same time explore the dynamical processes arising during their combined operation. Some other applications of the proton beam and neutron source are also discussed. It is possible in future to increase the current and energy of proton or heavy ion beam.      

Poisson's ratio of foamed plastics

Six-sided and 14-sided cell models are used as a basis for calculating the Poisson ratio of foamed plastics as a function of the properties of the polymer base and the parameters of the cellular structure. The extremal nature of the dependence of the Poisson ratio on the apparent density of foamed plastics is established and explained.Vladimir Scientific-Research Institute of Synthetic Resins. Translated from Mekhanika Polimerov, No. 1, pp. 45–49, January–February, 1973.     

The nature of color centers in γ-irradiated poly(tetrafluoroethylene)

The quantum-chemical investigation of tentative products of radiation-chemical transformations in PTFE under the action of γ radiation at a temperature higher than the melting point of the crystalline phase has been carried out. The excited electronic states of fluorinated alkylpolyenes of the general formula F₃C-(CF=CF) _n -CF₃(n = 1?7), the same compounds with CFO terminal groups, and the dimers of monomer fragments containing two or more conjugated double bonds have been calculated by means of the semiempirical PM3 method. In addition, the excited states for PTFE chain fragments of different lengths have been calculated. On the basis of calculations, it has been concluded that the coloration of the irradiated PTFE may be caused by formation of polyconjugated structures in the polymer chain with the number of double bonds n = 2–6.     

New type of asymmetric fission in proton-rich nuclei

A very exotic process of β-delayed fission of 180Tl is studied in detail by using resonant laser ionization with subsequent mass separation at ISOLDE (CERN). In contrast to common expectations, the fission-fragment mass distribution of the post-β-decay daughter nucleus 180Hg (N/Z=1.25) is asymmetric. This asymmetry is more surprising since a mass-symmetric split of this extremely neutron-deficient nucleus would lead to two 90Zr fragments, with magic N=50 and semimagic Z=40. This is a new type of asymmetric fission, not caused by large shell effects related to fragment magic proton and neutron numbers, as observed in the actinide region. The newly measured branching ratio for β-delayed fission of 180Tl is 3.6(7) × 10(-3)%, approximately 2 orders of magnitude larger than in an earlier study.     

Interplay between single-particle and collective effects in the odd-A Cu isotopes beyond N=40

Collective properties of the low-lying levels in the odd-A 67-73Cu were investigated by Coulomb excitation with radioactive beams. The beams were produced at ISOLDE and postaccelerated by REX-ISOLDE up to 2.99 MeV/u. In 67,69Cu, low-lying 1/2(-), 5/2(-), and 7/2(-) states were populated. In 71,73Cu, besides the known transitions deexciting the single-particle-like 5/2(-) and core-coupled 7/2(-) levels, gamma rays of 454 and 135 keV, respectively, were observed for the first time. Based on a reanalysis of beta-decay work and comparison with the systematics, a spin 1/2(-) is suggested for these excited states. Three B(E2) values were determined in each of the four isotopes. The results indicate a significant change in the structure of the odd-A Cu isotopes beyond N=40 where single-particle-like and collective levels are suggested to coexist at very low excitation energies.     

Charge radii and magnetic moments of odd- A 183-189Pb isotopes

Unexpected features of the BaBar data on e ⁺ e ^- $ \rightarrow$ B $ \overline{{B}}$ cross-sections (B stands for baryon) are discussed. These data have been collected, with unprecedented accuracy, by means of the initial-state radiation technique, which is particularly suitable in giving good acceptance and energy resolution at threshold. A striking feature observed in the BaBar data is the non-vanishing cross-section at threshold for all these processes. This is the expectation due to the Coulomb enhancement factor acting on a charged fermion pair. In the case of e ⁺ e ^- $ \rightarrow$ p $ \overline{{p}}$ it is found that Coulomb final-state interactions largely dominate the cross-section and the form factor is | G ^p(4M ² _p)| ～ 1 , which could be a general feature for baryons. In the case of neutral baryons an interpretation of the non-vanishing cross-section at threshold is suggested, based on quark electromagnetic interaction and taking into account the asymmetry between attractive and repulsive Coulomb factors. Besides strange baryon cross-sections are compared to U -spin invariance predictions.     

Metal Nanoparticles on Polymer Surfaces: 2. Catalytic Activity of Platinum Nanoparticle Ensembles on Polystyrene

Catalytic properties of platinum nanoparticles deposited onto polystyrene surface from their hydrosol stabilized with sodium polyacrylate are studied. It is shown that, during the adsorption on polymer substrate, metal nanoparticles form rather densely packed ordered monolayer ensembles with high catalytic activity in the model reaction of hydrogen reduction of methyl viologen. This allows one to measure the reaction rate with standard spectrometric method using polymer film with the surface area of 1 cm² or less as a catalyst support.