A photomultiplier used in liquid scintillation counting has an envelope, a base, an anode, a curved dynode structure and a photocathode. A specimen is inserted in a measuring area of the envelope for liquid scintillation counting. The photocathode has a concave surface, so that the specimen is encircled by the photocathode as completely as possible. The photocathode is positioned at a concave window of the envelope, so that a maximum number of photons directly impinge on the photocathode.