It should be mentioned that particles will also produce scintillation in a phosphor . Alpha particles can be detected in the presence of other radiation by using very thin sheets of scintillating material. The phosphor may be a thin sheet of plastic scintillator or zinc sulphide embedded in a transparent tape. A very thin aluminized mylar foil is wrapped around this to exclude light but allow the alpha particles through. Because of their low penetrating power, alpha particles are stopped in the thin scintillator and so deposit all of their energy there. Beta particles and gamma photons will lose only a small fraction of their energy in the thin scintillator and so produce much smaller pulses. If the discriminator level is set to accept the larger pulses due to alpha radiation , and reject the smaller pulses produced by beta and gamma radiation , the instrument can be used for detecting alpha contamination, even when beta-gamma contamination is present as is often the case.