Apparatus and methods for determining one or more fluid parameters of interest by irradiating fluid with a source of nuclear electromagnetic radiation and subsequently measuring attenuation and absorption properties of the fluid from which parameters of interest are determined. Measurements are made with a formation tester tool comprising preferably two functionally configured flow lines. The source simultaneously irradiates fluid contained in opposing irradiation sections that can be integral sections of each of the two flow lines. A radiation detector is dedicated to each irradiation section and measures radiation attenuation and absorption properties fluid contained within each flow line section. Absolute and relative fluid parameters of interest are determined from the responses of the two radiation detectors.