Measuring Radioactivity: Videos & Practice Problems

The Curie (Ci) and Becquerel (Bq) are both units used to measure radioactivity, but they differ in scale and origin. The Curie, named after Marie Curie, is a traditional unit where 1 Ci equals 3.7 × 10¹⁰ disintegrations per second. In contrast, the Becquerel is the SI unit for radioactivity, defined as 1 disintegration per second. Therefore, 1 Ci is equivalent to 3.7 × 10¹⁰ Bq. The Curie is often used in contexts where large amounts of radioactivity are present, while the Becquerel is more commonly used in scientific and medical settings due to its alignment with the International System of Units (SI).

The Roentgen (R) is a unit used to measure the exposure of ionizing radiation, specifically gamma and X-rays. It quantifies the amount of ionization produced in air by these high-energy photons. One Roentgen is defined as producing 2.1 × 10⁹ ion pairs per cubic centimeter of air. Unlike other units, the Roentgen does not have a direct SI equivalent. It is primarily used in radiology and radiation protection to assess the intensity of radiation fields and ensure safety standards are met.

The Rad and Gray (Gy) are units used to measure the absorbed dose of radiation by tissue. One Rad is defined as the absorption of 0.01 joules of radiation energy per kilogram of tissue. The Gray, an SI unit, is defined as the absorption of 1 joule of radiation energy per kilogram of tissue. Therefore, 1 Gy is equivalent to 100 Rads. The Gray is more commonly used in scientific and medical contexts due to its alignment with the International System of Units (SI).

The Sievert (Sv) is a unit that measures the biological effects of ionizing radiation. It accounts for both the type of radiation and its impact on different tissues. The Sievert is calculated by multiplying the absorbed dose (in Grays) by a quality factor known as the Relative Biological Effectiveness (RBE). For example, X-rays, gamma rays, and beta particles have an RBE of 1, while alpha particles have an RBE of 20. This means that 1 Sv of alpha radiation causes the same biological effect as 20 Sv of X-rays or gamma rays. This unit is crucial for assessing radiation exposure risks and ensuring safety in medical and occupational settings.

REM (Roentgen Equivalent Man) is a unit used to measure the biological effect of ionizing radiation on human tissue. It is calculated by multiplying the absorbed dose (in Rads) by the Relative Biological Effectiveness (RBE) of the radiation type. For example, X-rays, gamma rays, and beta particles have an RBE of 1, while alpha particles have an RBE of 20. This means that 1 REM of alpha radiation has the same biological effect as 20 REM of X-rays or gamma rays. The REM is essential for evaluating radiation exposure in medical, industrial, and environmental contexts, helping to ensure safety and compliance with regulatory standards.