辐射简介 辐射类型

辐射简介 目的 向感兴趣的读者提供关于辐射的有用信息 介绍关于辐射和放射性的基本概念 增强对辐射及其与物质相互作用的认识

电离辐射的类型 α粒子 辐射源 Β粒子 γ射线 一张纸可将其挡住 一层衣服可将其挡住， 或几毫米厚的物质可将其挡住， 如塑料 5. Types of Ionizing Radiation Alpha particles. Alpha particles are ejected from (thrown out of) the nuclei of some very heavy radioactive atoms (atomic number > 83). An alpha particle is composed of two neutrons and two protons. Alpha particles do not penetrate the dead layer of skin and can be stopped by a thin layer of paper or clothing. If an alpha-emitting radioactive material gets inside the body through inhalation, ingestion, or a wound, the emitted alpha particles can cause ionization that results in damage to tissue. It is less likely that a patient would be contaminated with an alpha emitter. Beta particles. A beta particle is an electron ejected from the nucleus of a radioactive atom. Depending on its energy, beta radiation can travel from inches to many feet in air and is only moderately penetrating in other materials. Some beta radiation can penetrate human skin to the layer where new skin cells are produced. If high-enough quantities of beta-emitting contaminants are allowed to remain on the skin for a prolonged period of time, they may cause skin injury. Beta emitting-contaminants may be harmful if deposited internally. Protective clothing (e.g., universal precautions) typically provides sufficient protection against most external beta radiation. Gamma rays and x rays (photons). Gamma rays and x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called “penetrating” radiation. Thick layers of dense materials are needed to shield against gamma radiation. Protective clothing provides little shielding from gamma and x radiation, but will prevent contamination of the skin with the gamma-emitting radioactive material. Gamma and x radiation frequently accompany the emission of beta and alpha radiation. γ射线 几十厘米厚的混凝土或几十毫米的铅 才可将其挡住

辐射类型- α辐射 一个α粒子由两个质子和两个中子组成 就原子尺度来说，α粒子是很大的 带正电荷

辐射类型- α辐射 对物质的穿透能力 α核素在体外不会造成危害，除非附着在皮肤上； 如果α核素能量沉积在体内敏感组织时，会造成较大危害。

辐射类型- α辐射 常见的α粒子发射体 环境中的氡-222 气体 环境中的铀-234 和铀-238 烟草中的钋-210

辐射类型- α辐射 常见的- α辐射核素用途 烟雾探测器 香烟/雪茄 静电消除器

辐射类型- β辐射 β粒子是带电粒子 β粒子的大小和重量与电子的相同。 β粒子可以是带正电荷的，也可是带负电荷的。

辐射类型- β辐射 对物质的穿透能力 低能β粒子的贯穿能力小，皮肤表皮或一张纸可将其挡住； 高能β粒子可以穿透皮肤生发层，10多毫米 厚的树脂玻璃可将其挡住。

辐射类型- β辐射 对物质的穿透能力(续) β粒子在体内的危害没有α粒子那么大，因为β 粒子没有α粒子那么大； β粒子较小，可与较多的组织发生相互作用，所以在体内的穿行距离较远，但给予单位组织的辐射能量也较小。，

辐射类型- β辐射 常见β 粒子发射体 环境中的氚（H-3) 环境中的碳 (C-14) 科研和医学中用的磷(P-32)

辐射类型- β辐射 β 粒子发射体的常见用途 碳年代测定 基础研究 癌症治疗

辐射类型- 光子辐射 光子是X射线或γ射线 没有重量 不带电荷

辐射类型- 光子辐射 光子在物质中的穿透能力 低能光子可以用一层很薄的铅或几厘米厚的组织阻挡； 高能光子需要几十厘米厚的铅才能挡住，能够直接穿透人体。

辐射类型- 光子辐射 常见光子发射体 铯 (Cs-137) 锝(Tc-99m), 医学应用 碘 (I-131), 医学应用

辐射类型- 光子辐射 常见光子发射体 土壤密度测定 疾病诊断 癌症治疗

光子衰变 99mTc 99Tc 稳定核 激发态核 Gamma ray Gamma emissions occur during transitions such as fission, radioactive disintegration and electron-positron annihilation. Gamma rays are monoenergetic electromagnetic radiations that are emitted from nuclei of excited atoms following radioactive transformation; they provide a mechanism for ridding excited nuclei of their excitation energy. Source: Cember, H, Introduction to Health Physics, 1989 稳定核 激发态核

放射性物质实例 放射性核素 物理半衰期 活度 用途 铯-137 30 年 1.5 x 106 Ci 食品辐照装置 放射性核素 物理半衰期 活度 用途 铯-137 30 年 1.5 x 106 Ci 食品辐照装置 钴t-60 5 年 15,000 Ci 癌症治疗 钚-239 24,000年 600 Ci 核武器 铱-192 74 天 100 Ci 工业探伤 氢-3 12 年 12 Ci 出入口显示 锶-90 29 年 0.1 Ci 眼睛治疗装置 碘-131 8 天 0.015 Ci 治疗 锝-99m 6 小时 0.025 Ci 放射照相 鎇-241 432 年 0.000005 Ci 烟雾探测器 氡-222 4 天 1 pCi/l 环境 10. Examples of Radioactive Materials Radioactive materials emit ionizing radiation. They are used in medical diagnosis (nuclear medicine), medical therapy (cancer treatment), and industry (food irradiation) and for research. Many radioactive materials, including radioactive waste, are commercially shipped in special containers. A radionuclide is chemically identical to and behaves in the body the same way as the nonradioactive form of the element. For example, radioactive iodine (e.g., I-131) is concentrated in the thyroid in the same way as nonradioactive iodine (i.e., I-127). Quantities of radioactive material (i.e., activity) range from trivial amounts in typical laboratories to much larger quantities, such as in nuclear reactors. Half-lives can range from seconds to millions of years. The nuclides that are in orange are those that are considered to be potential nuclides that could be present in a radiological dispersal device.

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