A scintillation detector with an area of 4 m2and a transistorized amplifier with a logarithmic height‐to‐time converter are described. The detector employs tapered sheets of plastic scintillator and a single 16‐in. photomultiplier mounted in a pyramidal can, coated inside with a commercial 90% reflecting white paint. The response is uniform to within 5% over the entire sensitive surface. A traversal by one relativistic charged particle (energy loss ∼10 Mev) generates approximately 20 photoelectrons in the photomultiplier. The amplifier and converter yield a rectangular pulse whose duration is accurately proportional to the logarithm of the input pulse amplitude over a range of four decades. The gain is constant to 1 db from 10 to 45°C, and the equivalent noise input is 200 &mgr;v.