核子物理学Nuclear Physics.ppt

Nuclear Physics Radioactivity Properties of α, β and γ radiations Detectors Random nature of decay Natural nuclear deformation Radiation Hazards The Nucleus The Rutherford model of the atom Mass-energy relationship Binding energy Fission and fusion Decay Series It is often the case that one radioactive isotope decays to another isotope that is also radioactive. Such successive decays are said to form a decay series. Properties of ?, ? and ? radiations (1) Properties of ?, ? and ? radiations (3) Properties of ?, ? and ? radiations (4) Radiation Detectors Photographic Film To detect ?, ? and ? radiations Spark counter To detect ?-particles Ionization Chamber To detect ? -particles Cloud Chamber To detect ? and ? particles Geiger-Müller Tube To detect ?, ? and ? radiations Photographic Film The photographic film has been blackened by radioactivity except in the shadow of the key. Spark Counter The spark counter consists of positively charged wire mounted under an earthed metal grid. It produces sparks in the presence of ionized particles. It can only be used to detect α-radiation. Ionization Chamber (1) A diagram of the ionization is drawn in the diagram below. Ionization Chamber (2) The number of ions produced per second by the source of ionizing radiation can be estimated from the current flowing. This estimate depends on the following conditions: The ionization chamber must be sufficiently large to enable the radiation to travel its full range. The electric field must be large enough to ensure that all the ions travel to the electrode before recombining with free electrons. The ionization chamber can only be used to detect α-particles. Cloud Chamber (1) The diagrams below show a diffusion cloud chamber and its structure. Cloud Chamber (2) The felt strip round the top of the chamber is soaked with alcohol. The solid CO2 cools the chamber to a low temperature. The alcohol vapour condensed on the ions caused by the passage of ?-particles. A jet trail is left beh