New modifications in 15 UD pelletron at nuclear science centre

The 15 UD pelletron at NSC has been operational and performed well during the last 11 years. There have been major modifications performed for upgradation of pelletron system over this period. Major upgradations which have been implemented are new resistor network system for voltage gradient, doublet to singlet unit conversion for accelerator units, turbopump based gas stripper system etc. In addition accelerator mass spectroscopy program has also been started. A new multi-cathode source, Wien filter etc. have been procured and will be added soon in the system. An overview of the most significant upgradations undertaken and other activities for the system are being reported in the present paper.     

Excitation of giant resonances in intermediate energy heavy-ion reactions

Quasielastic and deep inelastic processes in the reaction ¹⁶O + ²⁰⁸Pb have been studied at bombarding energies of 10–80 MeV per nucleon. The excitation probability of the giant modes becomes larger with increasing energies. At a given bombarding energy the multiple excitation of low-lying modes becomes predominant as the angle of observation moves away from the grazing angle. Near grazing, no appreciable background of this character is found for bombarding energies above 30 MeV per nucleon. At these energies the electromagnetic interaction becomes the most effective way to excite the giant modes in the excitation energy interval of 10–20 MeV. The importance of Coulomb excitation for the highest bombarding energies makes the excitation of isovector modes no longer negligible.     

Formfactors for one- and two-nucleon transfer reactions induced by light and heavy ions

Formfactors and overlaps for light and heavy ion transfer reactions are evaluated including finite range and recoil effects. The treatment of the recoil is based on a separation into a transversal effect, responsible for a modification of the selection rules, and a longitudinal effect related to a scaling of the radial motion. The formfactors for multinucleon transfer can in this formulation be obtained either as products of single-particle overlaps and formfactors or, after transformation to center of mass and relative motion, in terms of cluster type representation. The extension of the nuclear field theory to include transfer reactions is indicated. Some examples of the application of the formfactors to calculations of cross sections by means of distorted wave Born approximation are given with the main emphasis on heavy ion reactions.     

On the capture of muons in atoms

In previous calculations on the capture of negative muons in atoms we used the average energy loss per unit path length as a frictional force in the classical equations of motion. In the present note it is shown that the rare events where the muon, because of its high velocity in the inner parts of the atom, loses an energy which is larger than its total energy, are important for the average stopping power. For the calculation of capture ratios these large energy losses should be treated separately. The results differ significantly from those obtained previously, and are in better agreement with experiment.     

Error estimates for a galerkin approximation of a parabolic control problem

Summary Numerical approximation of a parabolic control problem with a Neumann boundary condition control is considered. The observation is the final state. The numerical approximation is based on backward discretization with respect to time and a Galerkin method in the space variables. Optimal (except for a logarithmic term) L² error estimates are derived for the optimal state. Certain error estimates for the optimal control are also given. Entrata in Redazione il 4 maggio 1977. This work was supported by the Norwegian Research Council for Science and the Humanities.     

A first low‐resolution difference Fourier map of phosphorus in a membrane protein from near‐edge anomalous diffraction

Crystal diffraction of three membrane proteins (cytochrome bc₁ complex, sarcoplasmic reticulum Ca²⁺ ATPase, ADP‐ATP carrier) and of one nucleoprotein complex (leucyl tRNA synthetase bound to tRNAleu, leuRS:tRNAleu) was tested at wavelengths near the X‐ray K‐absorption edge of phosphorus using a new set‐up for soft X‐ray diffraction at the beamline ID01 of the ESRF. The best result was obtained from crystals of Ca²⁺ ATPase [adenosin‐5′‐(β,γ‐methylene) triphosphate complex] which diffracted out to 7 Å resolution. Data were recorded at a wavelength at which the real resonant scattering factor of phosphorus reaches the extreme value of ?20 electron units. The positions of the four triphosphates of the monoclinic unit cell of the ATPase have been obtained from a difference Fourier synthesis based on a limited set of anomalous diffraction data.     

Effect of substrate temperature on electrical and magnetic properties of epitaxial La1−x Pb x MnO3 films

Epitaxial La_1−x Pb _x MnO₃ (LPMO) thin films, grown on (100) SrTiO₃ substrates by laser ablation technique at different temperatures between 600 and 850°C, have been characterized for electrical and magnetic properties. The temperature dependence of resistivity showed that the metal-insulator transition temperature (T _MI) decreases with increasing substrate temperature, which has been attributed to decrease in Pb content in the filsm. The YBa₂Cu₃O _x /La_1−x MnO₃ heterostructures, exhibiting both superconductivity and ferromagnetism, have been fabricated.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.