A “4π-type” study of the reaction p(d,pp)n at Ed = 26.5 MeV

Experimental data on the three-nucleon reaction p(d, pp)n at E_d = 26.5 MeV obtained with the multidetector system BOL, covering most of the phase space, are presented. The data are compared with Faddeev calculations using a local S-wave potential for the nucleon-nucleon interaction. The calculated cross sections, which are in general not sensitive to the precise choice of the nucleon-nucleon potential, agree well with the data over the major part of phase space. We have, though, discovered a region in phase space with a strong discrepancy. In the same region, around a neutron c.m. angle of 140°, the calculations are sensitive to the N-N potential. Theoretical and experimental angular distributions in the p-n recoil c.m. subsystem for proton- neutron energies below 0.5 MeV agree in absolute magnitude, both being isotropic. For larger relative energies, a discrepancy develops, part of which might be related to missing higher par- tial wave components in the N-N interaction, rather than to Coulomb or S-wave scattering effects. The total breakup cross section has been deduced from the data as 169 ± 36 mb.     

On the magnetic threshold for the alignment of a twisted nematic crystal

A computation of the capacitance and the optical transmission between parallel polarizers of a twisted nematic liquid crystal in a magnetic field shows that the “optical threshold” occurs at a higher value of the field strength than the “capacitive threshold”.     

Determination of silicon in natural and pollution aerosols by 14-MeV neutron activation analysis

The determination of silicon via the ²⁸Si(n,p)²⁸ Al reaction by means of 14-MeV neutrons is applied to the analysis of pollution and natural aerosols. A Whatman 41 filter (40 cm²) on which airborne particulate material has been collected is compressed into a 3 × 12.7 mm pellet. Standards are prepared in the same way from clean filters spiked with a silicate solution. After a 50-s irradiation and a 75-s decay time, the sample is counted for 2 min with 5” × 5” NaI(Tl) well detector. The 1.779-MeV photopeak of ²⁸Al is measured with a single channel sealer chain or with a multichannel analyser. The reproducibility, sensitivity and liability to interference from other elements were investigated for both counting systems. The homogeneity of the pellets and the filters was checked. The overall precision of one single-channel determination was estimated to be 3.5% after a 24-h high-volume sampling time. Samples collected in urban, industrial and remote areas with concentrations ranging from 0.05 to 15 μg Si m^-3 air were analysed and the results are discussed.     

Lifetimes of rotational levels in170W

Lifetimes of the first 2⁺, 4⁺ and 6⁺ levels in¹⁷⁰W have been measured by the recoil-distance method based on the Doppler effect, using the¹⁵⁵Gd (²⁰Ne, 5n)¹⁷⁰W reaction. The following conclusions can be drawn from the results: if there are any deviations from the predictions of the rotational model for the lifetimes of the 4⁺ and 6⁺ states, they are smaller than 8.5 %; if this model accurately describes the nucleus¹⁷⁰W, the intrinsic quadrupole moment of this nucleus is: Q₀=5.93±0.06 barns, and its deformation is: β=0.240±0.003. The value of Q₀ is compared with the predictions of various calculations for the tungsten isotopes.     

A kinetic model for predicting oxidative degradation rates in combined radiation-thermal environments

The complex degradation behavior of a poly(vinyl chloride) (PVC) cable jacketing material in combined radiation/temperature/air aging environments is experimentally separated into two dominant radiation dose-rate effect mechanisms. The first, operative at high dose rates, involves diffusion-limited oxidation, which leads to heterogeneously oxidized samples. The second, important at low dose rates, involves thermally-induced breakdown of intermediate peroxides. In the homogeneous degradation regime, a theoretical kinetic model is derived which, based on experimental evidence, assumes unimolecular termination kinetics and rate-determining, hydroperoxide-mediated branching reactions. Dependent upon the ratio of particular rate constants, the model predicts that dose-rate effects will either continue to increase or eventually disappear as the dose rate is lowered. Theoretical analysis of sequential (radiation followed by temperature exposures) aging experiments allows a time–temperature–dose rate shifting procedure to be developed. Using this procedure, higher temperature combined environment results can be shifted to a lower reference temperature, thereby extending the lower temperature results to lower (and experimentally inaccessible) dose rates. By applying this procedure to experimental PVC data, evidence in support of the theoretical model is obtained. In addition, model predictions are shown to agree with 12-year real-time aging results.     

Calculation of the activation energy from the tsee peaks of MgO

In this paper the analysis of the TSEE curves of MgO is presented and two methods of the calculations of the activation energy and the frequency factor of the TSEE peaks of MgO are compared. There is good agreement concerning the activation energy of the trapping centres between the least squares method for the fitting of experimental and theoretical curves and the universal calculation method developed by de Muer.     

Nuclear spin magnetic ordering with four spin exchange in solid bcc 3He

Some consequences of four spin exchange are analysed: 1) the negative sign of the T^-3 term in the specific heat; 2) the existence of thirteen possible magnetic arrangements, in particular a pseudo-ferromagnetic pahse; 3) a susceptibility, in the ordered phase, larger than that deduced from the Heisbnberg Hamiltonian.     

A critical study of the application of graphite-furnace non-flame atomic absorption spectrometry to the deter-mination of trace base metals in complex heavy-matrix sample solutions

Because of the extravagant claims made for the usefulness of non-flame atomic absorption spectroscopy, a critical evaluation of its performance in heavy matrix solutions, for selected trace heavy metals, was made. Studies of physical and chemical interference problems are presented for a range of inorganic and organic matrices. Often quoted remedies (e.g. selective volatilization, standard addition etc.) for solution of the more serious problems were found to be of little help in most cases. The influence of variables such as nature and flow rate of purge gas, ashing temperature and atomization temperature are also evaluated. Analyses for Cd, Cu, Pb, Zn, Ni, Co were done on samples by flame and nonflame methods in high solids solutions. While there appears to be an advantage to the non-flame method in dealing with sample solutions of high organic content, no advantage is apparent for either technique with highly inorganic matrices.     

Investigations of sol–gel-derived highly (100)-oriented Ba0.5Sr0.5TiO3 : MgO composite thin films for phase-shifter applications

Sol–gel deposition of highly oriented Ba_0.5Sr_0.5TiO₃:MgO composite thin films has shown desirable dielectric constant reduction and higher figure of merit for phase-shifter applications. In this multilayer configuration, MgO distributed homogeneously through the Ba_0.5Sr_0.5TiO₃ (BST50) matrix, and it helped in tailoring the dielectric constant and reducing the loss tangent significantly. In the present study, the high-frequency dielectric behavior of the films has been evaluated by fabricating an eight-element coupled microstrip phase shifter and measuring the degree of phase shift and insertion loss as a function of applied voltage at room temperature. An increase in phase-shifter figure of merit (degree of phase shift per dB insertion loss) from 28°/dB for pure BST50 to 71°/dB for a BST50:MgO film (at 14 GHz and 333 kV/cm) has been observed. PACS 77.55.+f; 81.20.Fw; 73.40.-c; 85.50.-n