Measuring Radioactivity: Videos & Practice Problems

Radioactivity can be measured using several units, each focusing on different properties. The common units include curies (Ci), roentgens (R), rads, and rems. One curie equals 3.7 × 10¹⁰ disintegrations per second, measuring decay events. Roentgens measure ionizing intensity, particularly for gamma and X-rays. Rads quantify the energy absorbed by tissue, with 1 rad equal to 1 × 10^-5 joules per gram. The SI equivalent of rad is gray (Gy), where 1 Gy equals 1 joule per kilogram. Rems measure tissue damage and are calculated as rad times the relative biological effectiveness (RBE). The SI unit for rem is the sievert (Sv), where 1 Sv equals 100 rems.

The curie (Ci) is a unit of radioactivity that measures the number of disintegrations per second. Specifically, 1 curie is defined as 3.7 × 10¹⁰ disintegrations per second. This unit is used to quantify the rate at which a radioactive substance undergoes decay. The SI unit equivalent to the curie is the becquerel (Bq), where 1 Bq equals 1 disintegration per second.

Rads and rems are both units used to measure radiation, but they focus on different aspects. Rads measure the energy absorbed by tissue, with 1 rad equal to 1 × 10^-5 joules per gram. The SI equivalent is the gray (Gy), where 1 Gy equals 1 joule per kilogram. Rems, on the other hand, measure the biological effect of the absorbed radiation. Rems are calculated as rad times the relative biological effectiveness (RBE). The SI unit for rem is the sievert (Sv), where 1 Sv equals 100 rems. Essentially, rads quantify energy absorption, while rems assess biological damage.

Relative biological effectiveness (RBE) is a factor used to compare the biological damage caused by different types of radiation. It accounts for both ionizing intensity and biological effect. For example, X-rays and gamma rays have an RBE of 1, meaning they have a standard level of biological impact. In contrast, alpha particles, which are larger and more ionizing, have an RBE of 20, indicating they cause significantly more biological damage. RBE is crucial for calculating rems, as rems equal rads times RBE.

Converting between different units of radiation measurement involves understanding their relationships. For example, 1 curie (Ci) equals 3.7 × 10¹⁰ disintegrations per second, and the SI unit is the becquerel (Bq), where 1 Bq equals 1 disintegration per second. For absorbed dose, 1 rad equals 1 × 10^-5 joules per gram, and the SI unit is the gray (Gy), where 1 Gy equals 1 joule per kilogram. To convert rems to sieverts (Sv), use the relationship 1 Sv equals 100 rems. Understanding these equivalences allows for accurate conversions between units.