STUDY OF ANGULAR DISTRIBUTION OF HELIUM PROJECTILE FRAGMENTS IN INTERACTIONS OF 200 A GeV 32S IONS WITH EMULSION NUCLEI

This paper presents data on the emission of helium fragments due to break up of 200 A GeV 32S ions in collision with emulsion nuclei. A total of 499 minimum bias events have been studied in an emulsion stack and 97 events in emulsion chambers. Emission angles of He fragments have been measured with high precision. This data has been compared with data of breakup of heavier as well as lighter projectiles and we observe that the value of the momentum spread, σ(p), increases with increasing projectile mass. The bulk part of the helium emission is consistent with a single source for helium fragments with an average excitation energy of (9.1±0.9) MeV. A tail of a few (<1%) He fragments with higher momenta is observed.

Zur theoretischen Interpretation der Anisotropie der 13C-NMR-chemischen Verschiebungen des Ethylens und Benzens auf halbempirischer Grundlage

u r th e o re tis c h e n I n te r p r e ta t io n d e r A n is o tr o p ie d e r 13C -N M R -c h e m is d ie n V e rs c h ie b u n g e n des E th y le n s u n d B en zen s a u f h a lb e m p iris c h e r G r u n d la g e On the Semiempirical Theoretical Interpretation of the Anisotropy of 13C n.m.r. Chemical Shifts of Ethylene and Benzene The paramagnetic contribution of the 13C screening constants and their anisotropics are cal­ culated by using localized orbitals and the CNDO/2 method in the molecular orbital description. A comparison of the average energy method for calculating of shielding tensors with the sum-over-states method is performed. It is concluded that the average excitation energy is higher for the screening perpendicular to the molecular plane.

Lamb shift in the metastable states of the helium atom

The radiative corrections of order α 3 rydbergs are evaluated for the ionization energy of the metastable states 2 1 , 3 S, of the helium atom. In the calculation of the average excitation energy k 0 , the main contribution comes from the transition to and ( ms, np ) and ( ms, ∊p ) states. The oscillator strengths for transitions to (1 s, ∊p ), (2 s, ∊p ) and (3 s, ∊p ) states are evaluated by using six-parameter wavefunction for the metastable states and a product of a hydrogenic wavefunction with Z = 2 for the s electron and a wavefunction analogous to the Hartree wavefunction for the excited p electron. Making use of these oscillator strengths and a method used by Pekeris, the values of the average excitation energies for the singlet and triplet states are found to be 77.09 ± 1.6 and 79.84 ± 1.0 rydbergs respectively. With these values of the average excitation energies, the Lamb shift corrections, including the estimate of a α 4 Ry order corrections, to the ionization energies of the singlet and triplet states become – 0.106 ± 0.018 cm -1 and –0.129 ± 0.013 cm –1 respectively. When they are added to the theoretical values of the ionization energies obtained by Pekeris, the values of the ionization energies become 32033.212 ± 0.018 an d 38454.698 ± 0.013 cm -1 compared with Herzberg’s experimental values of 32033.24 ± 0.05 an d 38454.73 ± 0.05 cm -1 for the singlet and triplet states respectively.

The stopping powers of atoms and molecules

A procedure is described for calculating the average excitation energy of an atom or molecule appropriate to the slowing down of a beam of charged particles in a gas. The procedure is applied to helium with the result that its average excitation energy is 42∙0 eV.