The directions of emission of millions of such pairs of gamma rays detected over several
minutes allow for a computer reconstruction of an image of the tissue containing the
positron emitter.
The energy produced by the decay of plutonium-238 is converted into electrical energy
in heart pacemakers. The relatively long half-life of the isotope allows the device to be
used for 10 years before replacement.Agricultural Uses
The pesticide DDT is toxic to humans and animals repeatedly exposed to it. DDT persists
in the environment for a long time. It concentrates in fatty tissues. The DDT once used
to control the screwworm fly was replaced by a radiological technique. Irradiating the
male flies with gamma rays alters their reproductive cells, sterilizing them. When great
numbers of sterilized males are released in an infested area, they mate with females, who,
of course, produce no offspring. This results in the reduction and eventual disappearance
of the population.
Labeled fertilizers can also be used to study nutrient uptake by plants and to study the
growth of crops. Gamma irradiation of some foods allows them to be stored for longer
periods without spoiling. For example, it retards the sprouting of potatoes and onions. In
1999, the FDA approved gamma irradiation of red meat as a way to curb food-borne
illnesses. In addition to significantly reducing levels of Listeria, Salmonella,and other
bacteria, such irradiation is currently the only known way to completely eliminate the
dangerous strain of Escherichia coli bacteria in red meat. Absorption of gamma rays
by matter produces no radioactive nuclides, so foods preserved in this way are not
radioactive.Industrial Uses
There are many applications of radiochemistry in industry and engineering. When great
precision is required in the manufacture of strips or sheets of metal of definite thicknesses,
the penetrating powers of various kinds of radioactive emissions are utilized. The thick-
ness of the metal is correlated with the intensity of radiation passing through it. The flow1020 CHAPTER 26: Nuclear Chemistry
The procedure works because the
female flies mate only once. In an area
highly populated with sterile males, the
probability of a “productive” mating is
very small.
A weak radioactive source such as
americium is used in some smoke
detectors. Radiation from the source
ionizes the air to produce a weak
current. Smoke particles interrupt
the current flow by attracting the
ions. This decrease in current
triggers the alarm.
Moderate irradiation with gamma rays from radioactive isotopes has kept the strawberries at
the right fresh for 15 days, while those at the left are moldy. Such irradiation kills mold
spores but does no damage to the food. The food does notbecome radioactive.