The acrylic slab phantom is designed for the use with photon radiation in the range from 70 kV up to 50 MV and for electron radiation from 1 MeV up to 50 MeV. The RW3 phantom is water-equivalent in the energy ranges from 60Co to 25 MV photons and from 4 MeV to 25 MeV electrons. The phantoms are used for monitor calibration and quality assurance measurements. Depth dose measurements are made by varying the measuring depth. To provide for backscatter, slabs are placed below the radiation detector.