Radiation, Ionizing

　　电离辐射

　　What is ionizing radiation?

　　什么是电离辐射?

　　Ionizing radiation is a type of energy released by atoms that travels in the form of electromagnetic waves (gamma or X-rays) or particles (neutrons, beta or alpha). The spontaneous disintegration of atoms is called radioactivity, and the excess energy emitted is a form of ionizing radiation. Unstable elements which disintegrate and emit ionizing radiation are called radionuclides.

　　电离辐射是原子以电磁波(伽马射线或者X射线)或粒子(中子、贝塔或者阿尔法)形式传递时所释放的一种能量。原子的自发解体称为放射性，发射的过剩能量是电离辐射的一种形式。分解和发射电离辐射的不稳定核素称为放射性核素。

　　All radionuclides are uniquely identified by the type of radiation they emit, the energy of the radiation, and their half-life.

　　所有的放射性核素均可通过所发射辐射的不同类型、辐射能量以及辐射的半衰期予以鉴别。

　　The activity — used as a measure of the amount of a radionuclide present — is expressed in a unit called the becquerel (Bq): one becquerel is one disintegration per second. The half-life is the time required for the activity of a radionuclide to decrease by decay to half of its initial value. The half-life of a radioactive element is the time that it takes for one half of its atoms to disintegrate. This can range from a mere fraction of a second to millions of years (e.g. iodine-131 has a half-life of 8 days while carbon-14 has a half-life of 5730 years).

　　活度(用以计算存在的放射性核素量)以贝可(Bq)为单位来表示：1贝可相当于每秒有1个原子衰变(裂解)。半衰期是指放射性核素的活性通过衰减减少到其初始值的一半所需的时间。放射性元素的半衰期是其原子裂解减少到原来数量的一半所需的时间。不同放射性元素的半衰期差异极大，从不足1秒到数百万年不等(例如，碘-131的半衰期是8天，而碳-14的半衰期为5730年)。

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