1. A radiation detection network, comprising: a central monitoring system having a data server connected to a wireless communications network; and a plurality of mobile radiation detection instruments for use by a plurality of mobile users in a geographic region so that the instruments are widely and dynamically distributed in the geographic region, each instrument comprising: a mobile communications device having wireless means for communicating with the data server of the central monitoring system over the wireless communications network as the user moves about in the geographic region with the instrument; a radiation detector operably connected to said mobile communications device for measuring the individual energies of detected photons; a clock-calendar operably connected to said mobile communications device for determining the time-date associated with each detected photon; and a locator operably connected to said mobile communications device for determining the location of said instrument associated with each detected photon, said mobile communications device adapted to transmit data of the individual photon energies and the corresponding detection time-dates and detection locations associated with each to the data server of said central monitoring system, wherein said central monitoring system includes means for collectively analyzing said data received from the plurality of mobile radiation detection instruments to produce a background radiation map of the geographic region as a function of at least the time-date and location data accumulated in the course of user movement in the geographic region, and to detect, identify and/or track a radiation source(s) in the geographic region by determining correlations and deviations against the background radiation map.