Issue # 45 Uses of radioisotopes

[Source: Understanding Chemistry for Advanced Level, Second Edition, by Ted Lister and Janet Renshaw, p.55-56)

Radioisotopes have a larger number of industrial and medical applications.

Leak tracing

A small amount of a radioisotope, placed in an inaccessible system of pipework such as in manufacturing industry or transportation pipelines, can be detected by a nuclear radiation detector, allowing the localization of the point of leakage.

Detecting flaw in the thickness gauging

Sheets of paper, metal foil or rubber are manufactured by passing the product between two rollers to the required thickness. The thickness can be measured by beaming a radioactive source at the sheet and detecting it on the other side. If the sheet is too thick or too thin the reading will vary and the pressure of the rollers can be automatically adjusted.

Measuring fill levels in bottles containing liquids

A radioactive source may be used to check that the bottles or cans have filled to the correct level. The filled bottles on a conveyor belt pass in front of a source and detector of radiation. Unfilled bottles absorb less radiation than full ones and can be automatically rejected.

Food irradiation

Because of its ability to kill living organisms, nuclear radiation can be used to treat foods to prevent sprouting, kill infecting insects, or completely sterilize the food. Irradiation does not make food itself radioactive.

Medical uses

Radioisotopes are used both in treatment and diagnosis. Radiation is used to kill cancer cells. In diagnosis, isotopes of iodine (ex: I-131) are injected into the patient to test the activity of the thyroid which concentrates iodine.

Technetium is absorbed by bones, so radioactive technetium is used to monitor bone growth during a fracture healing.

Generally in medical treatment, isotopes that can be rapidly excreted or with a short half-life are used so to minimize the side effects of those radioisotopes in the whole body.

Dating: see Issue # 41

The most used isotope for dating is the radioactive isotope C-14, with a half-life of 5558 years. Carbon is continually generated in the upper atmosphere by nuclear reactions caused by cosmic ray bombardment. Thus atmospheric CO₂ contains a small known proportion of CO₂ (C-14), which is incorporated into the tissues of all living things when they are still alive. This enables archaeological specimens which contain any once-living material, such as wood or natural fibers to be dated by measuring the proportion of C-14 remaining and calculating back the age of the material.

Chemical studies and Research

Radioisotopes can be used in chemical studies and research. For example, radioisotopes can be used to help decide which atom in a compound is involved in a particular reaction, such as in the following reaction:

CH₃COOH +  C₂H₂OH  →  CH₃COOC₂H₅  +  H₂O

Ethanoic acid Ethanol         Ethyl ethanoate    Water

The question is: Which oxygen atom is the one that appears in the water molecule? The one from ethanoic acid or the one from ethanol?

If ethanol with a radioactive isotope of oxygen could be prepared, it would be easy to find out the answer to the above question:

-if the radioactivity appears in H₂O, this means that O from ethanol is the one that forms water molecule.

-if the radioactivity appears in CH₂COOC₂H₅, this means that O from ethanol is not the one that forms water molecule, in other words, O from ethanoic acid is the one that is in water molecule.