How is radioactivity measured?
Radioactivity is a physical, not a biological, phenomenon. Simply stated, the radioactivit-y of a sample can be measured by counting how many atoms are spontaneously decaying each second. This can be done with instruments designed to detect the particular type of radiation emitted with each “decay” or disintegration. The actual number of disintegrations per second may be quite large.
Scientists have agreed upon common units to use as a form of shorthand. Thus, a curie (abbreviated “Ci” and named after Pierre and Marie Curie, the discoverers of radium) is simply a shorthand way of writing “37,000,000,000 disintegrations per second,” the rate of disintegration occurring in 1 gram of radium. The more modern International System of Measurements (SI) unit for the same type of measurement is the becquerel ( abbreviated “Bq” and named after Henri Becquerel, the discoverer of radioactivit-y), which is simply a shorthand for “1 disintegration per second.”