Because of its short half-life of six hours, technetium-99^{m}[10] is
coming into use for diagnosis using scanning devices, particularly for
brain tumors. It lasts such a short time it obviously cannot be kept in
stock, so it is prepared by the beta decay of molybdenum-99.[11] A stock
of molybdenum is kept in a shielded container in which it undergoes
radioactive decay yielding technetium. Every morning, as the technetium
is needed, it is extracted from its parent by a brine solution. This
general procedure of extracting a short-lived isotope from its parent is
also used in other cases. We shall see later that radon gas is obtained
by an analogous method from its parent, radium.
[Illustration: _Using a “nuclear cow” to get technetium from its parent
isotope. The “cow” is being fed saltwater through a tube. The saltwater
drains through a high-radiation (hot) isotope. The resultant drip-off is
a daughter such as technetium-99^{m}. This new, mild isotope can be
mixed with other elements and these become the day’s supply of
radioisotopes for other scans. Technetium-99^{m} decays in 6 hours. Thus
greater amounts, with less possibility of injury, can be administered
and a better picture results._]