Waynette Fish, Age 10, Of Stanley, No.Car., for her question:

What use is rubidium?

Rubidium is one of the basic chemical elements. It is named for the ruby red of the salts it forms when it combines with other elements. It belongs in a family of six, two of which are the plentiful elements sodium and potassium. All these elements are very active and tend to fly apart or team up in a hurry with other elements to form chemical compounds.

Both potassium and rubidium are slightly radioactive, but not dangerous to a healthy human body. Rubidium tends to gather in growths and tumor tissues and nowhere else. When given to a patient, all its atoms will gather in, say, a suspected brain tumor, and the exact spot can be detected with radioactive counters. Rubidium also is used in the electric eye cells that open doors by magic, and experts predict that someday it may be used as a fuel to take mankind into space.