1. Occurrence
Radium is a radioactive member of the alkaline earth family and is widely disseminated throughout the earth’s crust. It has 4 naturally occurring isotopes:
• 11.43-d 223Ra (member of 235U series or actinium series),
• 3.66-d 224Ra (member of the 232U or thorium series),
• 1600-year 226Ra (member of 238U or uranium series), and
• 5.75-year 228Ra (member of the 232U or thorium series).
The contribution of 228Ra (a beta-emitter) to the total radium alpha activity is negligible because of the 1.9-year half-life of its first alpha-emitting daughter product, 228Th. The other 3 radium isotopes are alpha-emitters; each gives rise to a series of relatively short-lived daughter products, including 3 more alpha-emitters.
Because of their longer half-lives and health significance, 226Ra and 228Ra are the most important radium isotopes found in water. Even though it has a short half-life, 224Ra in groundwater is important in certain geographical areas because of their geochemistry and the short delivery time of well water to consumers. Radium is a bone-seeker, and high concentrations in bone can lead to malignancies.