Angular Momentum Mixing Research Articles

Study of Excited States ofO14by a Particle-Particle Angular-Correlation Technique

Excited states of $^{14}\mathrm{O}$ have been investigated with the $^{12}\mathrm{C}(^{3}\mathrm{He}, n)^{14}\mathrm{O}(p)^{13}\mathrm{N}$ reaction at an incident-beam energy of 12 MeV. Proton groups corresponding to $^{14}\mathrm{O}$ excited states were observed in time coincidence with the associated neutrons detected at ${\ensuremath{\theta}}_{n}=0\ifmmode^\circ\else\textdegree\fi{}$. The natural widths of these states (or limits thereof) were obtained directly from the proton spectrum. Angular-correlation data obtained for these proton groups were analyzed according to a general formalism which allows channel spin as well as orbital angular momentum mixing in the $^{14}\mathrm{O}\ensuremath{\rightarrow}^{13}\mathrm{N}+p$ exit channel. These analyses yield the following spin and width limitations: [${E}_{x}$ (MeV), $J$, $\ensuremath{\Gamma}$ (keV)]; 5.91, 0 or 1, \ensuremath{\le}47; 6.29, 2 or 3, 103\ifmmode\pm\else\textpm\fi{}6; 6.59, 2, \ensuremath{\le}56; and 7.78, 1, 2 or 3, 76\ifmmode\pm\else\textpm\fi{}10. The apparent dominance of a direct-transfer mechanism for the population of these states permits further spin and parity restrictions. Information regarding the wave-function configurations for these states is discussed on the basis of the observed proton decay. Of particular interest is the observance of an $f$-wave component in the proton decay of the 6.59-MeV state which implies an ${s}^{4}{p}^{8}$ ($p, f$) component in the wave function of that state.

A Note on the Mixing of Angular Momentum in a Neutrally Buoyant Fluid

The effect of turbulent mixing in a neutrally buoyant rotating fluid is considered in a region where the mean flow is axisymmetric. The separate actions of molecular and turbulent mixing are distinguished. It is shown that a rotating turbulent flow capable of mixing angular momentum must vary in the axial direction. In particular, it would seem that a secondary circulation is required for a flow to support turbulence over its whole volume. The relative roles of turbulence and secondary circulations in the mixing of angular momentum are discussed.

On the mixing of angular momentum in a stirred rotating fluid

It has been suggested on theoretical grounds that a vortex could be initiated in a cylindrical region of fluid, originally in solid rotation, by the horizontal mixing of angular momentum produced by external stirring. In this paper various arguments for and against the mechanism are examined and their difficulties exposed. No firm conclusion is reached. A series of mathematical models of the mixing motions has been used, to bring out the differences between mechanical stirring and the agitation of a gas by random molecular motions. They suggest the introduction of a diffusion coefficient for angular momentum, to be determined empirically. These theoretical ideas are then applied to the interpretation of the results of a laboratory experiment which has been designed to test the proposed mechanism directly.A wide, flat tank of liquid was set up on a rotating table and stirred with a vertically oscillated grid, whose elements were much smaller than the width of the tank. A neutrally buoyant particle was used as a tracer of fluid motions, to measure relative circulation velocities and the properties of the turbulence. The motion observed was dominated by the loss of angular momentum to the walls and the grid, an effect which has not been taken into account in previous theoretical assessments of the effects of mixing of angular momentum. The relative circulation present was not significantly different from zero, and the limits of error of the measurements imply that the rate of diffusion of angular momentum is less than 5% of that for fluid particles, with 95% probability.