Becquerel’s discovery that uranium emanations could turn air into a conductor of electricity, prompted the Curies to measure these emanations. Their findings measured currents 300 times stronger than those produced by pure uranium. They hypothesized that a very active “unknown” substance, in addition to the uranium, must exist in order to produce such strong currents. The “unknown” element was later named polonium after Marie’s native Poland and the term “radio-active” was introduced. The Curies were able to extract enough polonium and another radioactive element – radium, to establish the chemical properties of these elements.
In 1903, Pierre Curie, Marie Curie and Henri Becquerel were jointly awarded the Nobel Prize in Physics; Becquerel for his discovery of spontaneous radioactivity and the Curies for their exhaustive research on radiation and its effects. After many years of hard work and Pierre’s subsequent death, Marie Curie established the first quantitative standards by which the rate of radioactive emission of charged particles from elements could be measured and compared. She also found that there was a decrease in the rate of radioactive emissions over time and that this decrease could be calculated and predicted. In her effort to establish quantitative standards, Curie isolated 100 mg of almost pure radium chloride from a ton of uranium ore by repeated crystallizations. One gram of this radium was found to decay at a rate of 37 billion nuclear disintegrations per second or 2.22 x 1012 nuclear disintegrations per minute [dpm].
It was later decided by international agreement that these disintegrations per second (dps) would be called a Curie, (Ci). Radon concentration in the atmosphere is usually measured in becquerel per cubic meter (Bq/m3), the SI derived unit and in the US, picocuries per liter (pCi/L). The Becquerel is the international measurement unit for radon gas, named after Henri Becquerel. It is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The conversion of pCi/L to Bq is as follows:
1 pCi/L = 37 Bq/m3
To convert from pCi/L to Bq simply multiply pCi/L times Bq. For example:
4 pCi/L x 37 Bq = 148 Bq