第五部AtomicPhysics原子物理学.doc

SECTION F : Atomic Physics(原子物理學) Chapter 27: Radioactivity I 放射現象 27.1 Discovering Detecting Radioactivity Discovery of radioactivity In 1896, a French scientist, Henri Becquerel貝克, discovered that uranium鈾 compounds emitted radiation輻射 which can blacken a sealed photographic plate. Almost at the same time, other radioactive materials e.g. radium鐳 discovered by Marie Curie居里夫人. 1896年 法國科學家 貝克發現鈾化合物會發出能令負片感光的輻射，同一時間，居里夫人發現鐳有同一現象。 Ionizing effect of radiation Detecting radiation 探測輻射 1. Photographic film負片 a. the radiation affect the film even when wrapped in light-proof paper. 令被遮蓋的負片感光 b. used in film badges, the extent of blackening of the film shows the level of exposure to nuclear radiation. 可用作紀錄輻射程度 2. Diffusion cloud chamber擴散雲室 a. enable tracks of radiation to be seen.顯示輻射軌跡 b. alcohol vapour condenses around the ions, under strong illumination, it reflects light is revealed as white tracks in a dark background. ( In general, one track corresponds to one charged particle ) 酒精分子凝結在輻射造成的離子上，每條軌跡代表一粒輻射 c. d Radiation Tracks路徑 Explanation原因 ? 1. 2. 3. strongest ionization power強電離能力 ? 1. easily deflected by the air molecules質量輕, 容易被偏轉。 ? 1. 3. Spark counter火花計數器 high ionizing power radiation高電離能力 will produce lots of sparks, e.g. ????particles, ? ??? sources hardly produce any sparks. ???的? 和????則難以產生。 4. Geiger－Muller Tube (GM tube)蓋革－彌勒管 . suitable for detecting all three kinds of radiation.適合量度各種輻射 27.2 Types of Nuclear Radiation各種輻射 Ionizing ability電離能力 (An outer shell electron is knocked out from the atom, creating an ion – pair原子的外圍電子被輻射線撞開，成為離子偶) Ionizing power電離能力： ＞ ＞ Penetrating power穿透能力 ? 射線被 radiation is stopped by .隔絕 ? 射線被 radiation is stopped by . 隔絕 ? 射線被 rays is never . 隔絕 Penetrating power穿透能力： ＞ ＞ Deflection