Element Radium, Ra, Alkaline Earth Metal

Pierre and Maria Curie's found out that pitchblende and some other uranium minerals radioactivity is significantly higher than it could be expected according to the amount of uranium they contained. They reported to the Paris Academy explaining this anomaly by the presence in these materials of some highly radioactive element. They initiated the pitchblende analysis. After polonium discovery the Curie couple continued the barium fraction investigation. In December 26 of 1898 announced that different reasons made them believing that they might assuredly affirm that the radioactive matter contained a new element which they wished to be called radium. Radium means "ray" in Latin.

In spite of relatively short half-life, comparing with the age of the Earth (approx. 5 billion years) small amounts of some Alkaline Earth Metal Radium isotopes may be found in nature. It becomes possible because of existence of three radioactive series in which radium isotopes continuously appear after decay of long-lived radionuclides (so-called parent radionuclides): uranium-238 which brings forth ²²⁶Ra, uranium-235 (²²³Ra, T_1/2 = 11.4 days), and thorium-232 (²²⁸Ra and ²²⁴Ra, T_1/2 = 3.7 days). Obviously, the less is the isotope half-life, the less is its abundance in minerals. Even the concentration of the most long-lived ²²⁶Ra in the Earth's crust is approximately one ten billionth of a percent, commonly in uranium-bearing rocks.

Radium is accumulated in plant tissues according to the common principle of absorption of mineral substances and depends on the plant species and the environmental conditions. Usually the roots and leaves contain more radium than the stem and reproductive organs; the largest amount is contained in cortex and timber. Radium concentration in flowering plants is approximately 0.3-9.0x10^-11 Ci/kg, and in seaweed 0.2-3.2x10^-11 Ci/kg.