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Mathematical descriptions of an excited state multilevel system are developed to include progressively the effects of coherent coupling, feeding, decay and relaxation, and the expressions are illustrated with several pulse coherence experiments utilizing zero field optically detected magnetic resonance of excited triplet states. A new method is described in which the time development of the coherent components in a multilevel system is monitored by using an observable that can measure only relative populations between the levels. The method is illustrated. By treating a coherently driven excited state system as two levels in contact with a population reservoir, exact expressions are obtained for both transient and steady-state behavior in the presence of transverse and spin lattice relaxation, constant incoherent pumping, spontaneous emission between the two levels, and also decay back into the reservoir. The general mathematical development is applied specifically to zero field microwave phosphorescence double resonance. Experimental methods and apparatus are discussed in detail and results of optically detected transient mutations, spin echoes, and Fourier transform spectroscopy are presented. (26 figs, 220 refs) (auth)

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Few attempts have been made to measure accurately the proton-proton analyzing powers at low energies. With the advent of polarized particle beams the measurement can now be made with high accuracy. Analyzing powers were measured at nine scattering angles from 10$sup 0$ to 35$sup 0$ in the laboratory system. As a check on systematic errors, analyzing power measurements were also made by scattering protons from $sup 4$He. In the p Vector-p case the measured values are in very good agreement with the phase shift predictions. The p Vector- $sup 4$He measurements, while giving the same form and sign as the phase shift predictions, differ from the predictions by as much as 11 standard deviations. The p Vector-p analyzing powers had a maximum value of -0.0043 +- 0.0004 at 10$sup 0$ (laboratory) and decreased to zero near 25$sup 0$. A new technique to measure analyzing powers without symmetric detectors is explained. This technique preserves the advantages of the symmetric arm method in that current integration, target density, detector efficiencies, and geometry are cancelled from the final expressions. A new scattering chamber, named the Supercube, is described. The Supercube was designed primarily to perform scattering experiments with a polarized beam. It contains …

The effect of free-particle collisions in simple ''knockout'' reactions of the form (a,aN) and in more complex nuclear reactions of the form (a,X) was investigated by using protons and pions. Cross sections for the $sup 48$Ti(p,2p)$sup 47$Sc and the $sup 74$Ge(p,2p)$sup 73$Ga reactions were measured from 0.3 to 4.6 GeV incident energy. The results indicate a rise in (p,2p) cross section for each reaction of about (25 +- 3) percent between the energies 0.3 and 1.0 GeV, and are correlated to a large increase in the total free-particle pp scattering cross sections over the same energy region. Results are compared to previous (p,2p) excitation functions in the GeV energy region and to (p,2p) cross section calculations based on a Monte Carlo intranuclear cascade-evaporation model. Cross section measurements for ($pi$/sup +-/, $pi$N) and other more complex pion-induced spallation reactions were measured for the light target nuclei $sup 14$N, $sup 16$O, and $sup 19$F from 45 to 550 MeV incident pion energy. These measurements indicate a broad peak in the excitation functions for both ($pi$,$pi$N) and ($pi$,X) reactions near 180 MeV incident energy. This corresponds to the large resonances observed in the free-particle $pi$$sup +$p and $pi$$sup -$p cross sections at the …