The merging of unstable liquid jets, approaching with high momentum, results in atomization and liquid mixing within a rapidly deforming impingement zone. The complex geometry and high index-of-refraction gradients that occur near the point of impingement present a particularly difficult environment for optical interrogation. X-ray based diagnostics are performed to determine the liquid mass distribution and liquid mixing in the spray utilizing x-ray attenuation and x-ray fluorescence, respectively. Radiography and computed tomography are employed to determine the mass distribution through single-shot, high-speed, and three-dimensional attenuation measurements using broadband x-ray tube sources. The variable attenuation coefficients are compared to a model to account for beam hardening in the x-ray energy spectrum. The accuracy and precision of the techniques are evaluated through a comparison with data from a narrowband synchrotron-based x-ray source. The Advanced Photon Source (APS) at Argonne National Laboratory is used to generate high-fidelity time-averaged and time-resolved point-wise data for the evaluation of the broadband tube sources. X-ray fluorescence measurements quantify the mixing in the impinging jet spray using the APS. Fluorescent tracers are tailored to allow for the direct measurement of the mass distribution of each fluid and thus mixing. The advantages, limitations, and optimization of each technique are discussed, and recommendations for improving performance are presented. A parametric study is performed to determine the effects of spray geometry, flow conditions, and fluid properties, including viscoelasticity in non-Newtonian fluids.