Bill Schmidt, age 16, of Columbia, Tenn., for his question:

HOW WAS THE CHEMICAL ELEMENT HAFNIUM NAMED?

Hafnium is a rare chemical element that is silver colored. Hafnium was discovered in 1923 by a scientist from The Netherlands named Dirk Coster and one from Hungary named Georg von Hevesy. The two men were working in Copenhagen, Denmark, and named the element hafnium from the Latin name for Copenhagen, Hafnia.

Hafnium absorbs neutrons better than most other metals. For this reason, rods made of hafnium are used to control the rate of reaction in some nuclear reactors.

When the reaction rate is too high, the rods are pushed into the reactor to absorb some of the neutrons. When the rate is too low, the rods are withdrawn.

The rare element hafnium occurs in small amounts in the minerals zircon and babbeleyite. It is always found with the similar and much more common element, zirconium.

Hafnium is a common byproduct in the production of zirconium. Hafnium can also be obtained by heating hafnium tetraiodide so that it breaks down to iodine and hafnium.

The element has an atomic number of 72 and its atomic weight is 178.49. Hafnium melts at 3902 degrees Fahrenheit and boils at 9752 degrees Fahrenheit.