Embodiments of the present invention relate in general to methods and apparatus for determining downhole mud flow rates and other downhole parameters. More specifically, but not by way of limitation, an embodiment of the present invention may provide a method for determining a downhole parameter that includes operating a pulsed neutron generator, detecting the activated drilling fluid at-least one known distance (d) from the pulsed neutron generator, and determining a time-of-flight (t) for the activated drilling fluid slug to travel from the pulsed neutron generator to a detection point, or between detection points