贝可勒尔Becquerel

1 Bq = 1 s⁻¹。旧单位居里（Ci）定义为 1 克镭-226 的活度，1 Ci = 3.7 × 10¹⁰ Bq。贝可勒尔是很小的单位，实际常用 kBq、MBq、GBq。活度 A = λN = (ln2/t₁/₂)·N：同样数目的原子，半衰期越短活度越大。比活度表示单位质量的活度，如 Bq/kg。活度只表示衰变次数，不反映射线能量和对人体的危害，后者用戈瑞和希沃特衡量。

1 Bq = 1 s⁻¹. The older unit, the curie (Ci), was the activity of one gram of radium-226: 1 Ci = 3.7 × 10¹⁰ Bq. The becquerel is tiny, so kBq, MBq and GBq are common. Activity A = λN = (ln2/t₁/₂)·N, so for the same number of atoms a shorter half-life means higher activity. Specific activity is activity per unit mass, such as Bq/kg. Activity counts decays only; it says nothing about radiation energy or harm to people, which are measured in grays and sieverts.

1910 年国际放射学大会定义居里为放射性单位。1975 年第 15 届国际计量大会采用贝可勒尔作为 SI 导出单位，以纪念 1896 年发现铀放射性的亨利·贝可勒尔。

The 1910 International Radiology Congress defined the curie as the unit of radioactivity. In 1975 the 15th General Conference on Weights and Measures adopted the becquerel as an SI derived unit, honouring Henri Becquerel, who discovered uranium's radioactivity in 1896.

人体内天然的 ⁴⁰K 和 ¹⁴C 使一个 70 kg 成年人的活度约为 8000 Bq；1 kg 香蕉约含 130 Bq 的 ⁴⁰K；室内空气氡浓度通常为 10–100 Bq/m³；一次 PET 检查注射 ¹⁸F-FDG 约 200–400 MBq。食品放射性限值也以 Bq/kg 表示，如日本规定一般食品中放射性铯不超过 100 Bq/kg。

Natural ⁴⁰K and ¹⁴C give a 70 kg adult an activity of about 8,000 Bq; a kilogram of bananas holds about 130 Bq of ⁴⁰K; indoor radon is usually 10–100 Bq/m³; a PET scan injects about 200–400 MBq of ¹⁸F-FDG. Food limits are also in Bq/kg; Japan, for example, limits radioactive caesium in general foods to 100 Bq/kg.