The Peaceful Atom

The first power station to produce electricity by using heat from the splitting of uranium atoms began operating in the 1950s. Today most people are aware of the important contribution nuclear energy makes in providing 16% of the world's electricity, - more than all electricity produced worldwide in 1960.

Not so well known are the many other ways the peaceful atom has slipped quietly into our lives, often unannounced and in many cases unappreciated.

Radioisotopes and radiation have many applications in agriculture, medicine, industry and research. They greatly improve the day to day quality of our lives.

What is a radioisotope?

Isotopes are different forms of an atom of the same chemical element. They have identical chemical properties but a different relative atomic mass. While the number of protons is the same, the number of neutrons in the nucleus differs. Some isotopes are referred to as 'stable' and others as 'unstable' or 'radioactive'. It is the radioactive nature of these unstable isotopes, usually referred to as 'radioisotopes', which gives them so many applications in modern science and technology. Any isotope can be used as a tag to follow the movement of some material.

 see also ANSTO paper on  Radioactivity, Radioisotopes etc 

 George de Hevesy: 

The first practical application of a radioisotope was made by George de Hevesy in 1911. At the time de Hevesy was a young Hungarian student working in Manchester with naturally radioactive materials. Not having much money he lived in modest accommodation and took his meals with his landlady. He began to suspect that some of the meals that appeared regularly might be made from leftovers from the preceding days or even weeks, but he could never be sure. To try and confirm his suspicions de Hevesy put a small amount of radioactive material into the remains of a meal. Several days later when the same dish was served again he used a simple radiation detection instrument - a gold leaf electroscope - to check if the food was radioactive. It was, and de Hevesy's suspicions were confirmed.

History has forgotten the landlady, but George de Hevesy went on to win the Nobel prize in 1943 and the Atoms for Peace award in 1959. His was the first use of radioactive tracers - now routine in environmental science.

Scientists continue to find new and beneficial ways of using nuclear technology to improve our lives. In our daily life we need food, water and good health. Isotopes play an important part in technologies that provide us with these basic needs. The UN's International Atomic Energy Agency (IAEA) is a base for international cooperation in hundreds of development projects.

Food and Agriculture

Some 800 million of the world's six billion inhabitants are chronically malnourished, and tens of thousands die daily from hunger and hunger-related causes. Radioisotopes and radiation used in food and agriculture are helping to reduce these tragic figures.

As well as directly improving food production, agriculture needs to be sustainable over the longer term. The UN's Food and Agriculture Organisation (FAO) works with the IAEA on programs to improve food sustainability through nuclear and related biotechnologies.

 Fertilisers: 

Fertilisers are expensive and if not properly used can damage the environment. Efficient use of fertilisers is therefore of concern to both developing and developed countries. It is important that as much of the fertiliser as possible finds its way into plants and that the minimum is lost to the environment.

Fertilisers 'labelled' with a particular isotope, such as nitrogen-15 and phosphorus-32 provide a means of finding out how much is taken up by the plant and how much is lost, allowing better management of fertiliser application. Using N-15 also enables assessment of how much nitrogen is fixed from the air by soil and by root bacteria in legumes.

Increasing Genetic Variability:

Ionising radiation to induce mutations in plant breeding has been used for several decades, and some 1800 crop varieties have been developed in this way. Gamma or neutron irradiation is often used in conjunction with other techniques, to produce new genetic lines of root and tuber crops, cereals and oil seed crops.

New kinds of sorghum, garlic, wheat, bananas, beans and peppers are more resistant to pests and more adaptable to harsh climatic conditions. In Mali, irradiation of sorghum and rice seeds has produced more productive and marketable varieties.

 Insect Control 

Crop losses caused by insects may amount to more than 10% of the total harvest worldwide, - in developing countries the estimate is 25-35%. Stock losses due to tsetse in Africa and screwworm in Mexico have also been sizeable. Chemical insecticides have for many years been our main weapon in trying to reduce these losses, but they have not always been effective. Some insects have become resistant to the chemicals used, and some insecticides leave poisonous residues on the crops. One solution has been the use of sterile insects.

The Sterile Insect Technique (SIT) involves rearing large numbers of insects then irradiating them with gamma radiation before hatching, to sterilise them. The sterile males are then released in large numbers in the infested areas. When they mate with females, no offspring are produced. With repeated releases of sterilised males, the population of the insect pest in a given area is drastically reduced.

Major SIT operations have been conducted in Mexico, Argentina and northern Chile against the Medfly (Mediterranean fruit fly) and in 1981 this was declared a complete success in Mexico. In 1994-95 eradication was achieved in two fruit-growing areas of Argentina and 95% success in another, as well as in Chile. The program is being extended to all of southern South America. Meanwhile the EU is financing a 'fly factory' on Portugal's Madeira island to produce up to 100 million sterile males Medflies per week.

A very successful SIT campaign was screwworm eradication in southern USA, Mexico and nearby. By 1991 the screwworm eradication had yielded some US$ 3 billion in economic benefits due to healthier livestock, not to mention humans. The Mexican plants and equipment were then applied to infestations in Libya, Jamaica and Central America, providing 20 million sterile pupae per week.

A number of the most fertile parts of Africa cannot be farmed because of the tsetse fly which carries the parasite trypanosome that causes the African sleeping sickness disease and the cattle disease Nagana. Economic losses due to this are estimated by FAO at US$ 4 billion per year. However, SIT in conjunction with conventional pest controls is starting to change all this. Zanzibar was declared tsetse-free in 1997 and Nigeria has also benefited. In southern Ethiopia a major tsetse SIT program is under way, with a million sterile males per month being produced in a 'fly factory' at Addis Ababa and then released.

Three UN organizations - the IAEA, the FAO, the World Health Organisation (WHO), with the governments concerned are promoting new SIT programs in many countries. Food Preservation 

Some 25-30% of the food harvested is lost as a result of spoilage by microbes and pests. In a hungry world we cannot afford this. The reduction of spoilage due to infestation and contamination is of the utmost importance. This is especially so in countries which have hot and humid climates and where an extension of the storage life of certain foods, even by a few days, is often enough to save them from spoiling before they can be consumed. Many countries lose a high proportion of harvested grain due to moulds and insects.

  In all parts of the world there is growing use of irradiation technology to preserve food. In over 40 countries health and safety authorities have approved irradiation of more than 60 kinds of food, ranging from spices, grains and grain products to fruit, vegetables and meat. It can replace potentially harmful chemical fumigants to eliminate insects from dried fruit and grain, legumes, and spices.

Following three decades of testing, a worldwide standard was adopted in 1983 by a joint committee of WHO, FAO and IAEA. In 1997 another such joint committee said there was no need for the earlier recommended upper limit on radiation dose to foods.

As well as reducing spoilage after harvesting, increased use of food irradiation is driven by concerns about food-borne diseases as well as growing international trade in foodstuffs which must meet stringent standards of quality. On their trips into space, astronauts eat foods preserved by irradiation.

Raw foods are exposed to high levels of gamma radiation which kills bacteria and other harmful organisms without affecting the nutritional value of food itself or leaving any residue It is the only means of killing bacterial pathogens in raw and frozen food. Of course, irradiation of food does not make it radioactive!

 Food irradiation applications 

Radiation is also used to sterilise food packaging. In the Netherlands, for example, milk cartons are freed from bacteria by irradiation.

 Water Resources

Adequate water is essential for life. Yet in many parts of the world water has always been scarce and in others it is becoming scarcer. Yet for any new development, whether agricultural, industrial or human settlement, a sustainable supply of good water is vital.

  Isotope hydrology techniques enable accurate tracing and measurement of the extent of underground water resources. Such techniques provide important analytical tools in the management and conservation of existing supplies of water and in the identification of new, renewable sources of water. They provide answers to questions about origin, age and distribution, the interconnections between ground and surface water and aquifer recharge systems. The results permit planning and sustainable management of these water resources.

For surface waters they can give information about leakages through dams and irrigation channels, the dynamics of lakes and reservoirs, flow rates, river discharges and sedimentation rates. From Afghanistan to Zaire there some 60 countries, developed and developing, that have used isotope techniques to investigate their water resources in collaboration with IAEA.

Neutron probes can measure soil moisture very accurately, enabling better management of land affected by salinity, particularly in respect to irrigation.

 Medicine

Many of us are aware of the wide use of radiation and radioisotopes in medicine particularly for diagnosis (identification) and therapy (treatment) of various medical conditions. In developed countries (a quarter of the world population) the frequency of diagnostic nuclear medicine is 1.9% of the population per year, and the frequency of therapy with radioisotopes is about one tenth of this.

 Diagnosis 

Radioisotopes are an essential part of diagnostic treatment. In combination with imaging devices which register the gamma rays emitted from within. they can study the dynamic processes taking place in various parts of the body. An advantage of nuclear over x-ray techniques is that both bone and soft tissue can be imaged very successfully.

 In using radiopharmaceuticals for diagnosis, a radioactive dose is given to the patient and the activity in the organ can then be studied either as a two dimensional picture or, with a special technique called tomography, as a three dimensional picture.

The most widely used diagnostic radioisotope is technetium-99m*, with a half-life of six hours, and which gives the patient a very low radiation dose. Such isotopes are ideal for tracing many bodily processes with the minimum of discomfort for the patient. They are widely used to indicate tumours and to study the heart, lungs, liver, kidneys, blood circulation and volume, and bone structure.

 * Technetium generators, a lead pot enclosing a glass tube containing the radioisotope, are supplied to hospitals from the nuclear reactor where the isotopes are made. They contain molybdenum-99, with a half-life of 66 hours, which progressively decays to technetium-99. The Tc-99 is washed out of the lead pot by saline solution when it is required. After two weeks or less the generator is returned for recharging.

  A major use of radioisotopes for diagnosis is in radio-immuno-assays for biochemical analysis. They can be used to measure very low concentrations of hormones, enzymes, hepatitis virus, some drugs and a range of other substances in a sample of the patient's blood. The patient never comes in contact with the radioisotopes used in the diagnostic tests. In the USA alone it is estimated that some 40 million such tests are carried out each year.

Therapy:

The uses of radioisotopes in therapy are comparatively few, but important. Cancerous growths are sensitive to damage by radiation, which may be external- using a gamma beam from a cobalt-60 source, or internal - using a small gamma or beta radiation source. 

Iodine-131 is commonly used to treat thyroid cancer, probably the most successful kind of cancer treatment, and also for non-malignant thyroid disorders. Iridium-192 wire implants are used especially in the head and breast to give precise doses of beta rays to limited areas, then removed. A new treatment uses samarium-153 complexed with organic phosphate to relieve the pain of secondary cancers lodged in bone.

(See also information paper Radioisotopes in Medicine)

 Sterilisation: 

Many medical products today are sterilised by gamma rays from a cobalt-60 source, a technique which generally is much cheaper and more effective than steam heat sterilisation. The disposable syringe is an example of a product sterilised by gamma rays. Because it is a 'cold' process radiation can be used to sterilise a range of heat-sensitive items such as powders, ointments and solutions and biological preparations such as bone, nerve, skin, etc, used in tissue grafts.

The benefit to humanity of sterilisation by radiation is tremendous. It is safer and cheaper because it can be done after the item is packaged. The sterile shelf life of the item is then practically indefinite provided the package is not broken open. Apart from syringes, medical products sterilised by radiation include cotton wool, burn dressings, surgical gloves, heart valves, bandages, plastic and rubber sheets and surgical instruments.

Smoke Detectors

One of the commonest uses of radioisotopes today is in household smoke detectors. These contain a small amount of americium-241 which is a decay product of plutonium-241 originating in nuclear reactors. The Am-241 emits alpha particles which ionise the air and allow a current between two electrodes. If smoke enters the detector it absorbs the alpha particles and interrupts the current, setting off the alarm. (See also information paper Smoke Detectors and Americium)

 Science and Industry

 Environmental tracers 

Radioisotopes also play an important role in detecting and analysing pollutants, since even very small amounts of a radioisotope can easily be detected, and the decay of short-lived isotopes means that no residues remain in the environment.

Nuclear techniques have been applied to a range of pollution problems including smog formation, sulphur dioxide contamination of the atmosphere, sewage dispersal from ocean outfalls and oil spills.

Tracers added to lubricating oils can help measure the rate of wear of engines and plant and equipment. Tracer techniques have been used in plant operations to check the performance of equipment and improve its efficiency, resulting in savings in energy and the better use of raw materials.

 Instruments: 

Gauges containing radioactive sources are in wide use in all industries where levels of gases, liquids and solids must be checked. These gauges are most useful where heat, pressure or corrosive substances, such as molten glass or molten metal, make it impossible or difficult to use direct contact gauges.

  Radioisotope thickness gauges are used in the making of continuous sheets of material including paper, plastic film, metal, glass, etc, when it is desirable to avoid contact between the gauge and the material.

Density gauges are used where automatic control of a liquid, powder or solid is important, for example, in detergent manufacture. Tobacco companies use radioisotope density gauges to check the amount of tobacco packed into each cigarette.

Radioisotope instruments have three great advantages:

Other forms of radiography (neutron radiography/ autoradiography), based on different principles, can be used to gauge the thickness and density of materials or locate components that are not visible by other means.

(See also information paper Radioisotopes in Industry)

 Radioisotope power sources 

Some radioisotopes emit a lot of energy as they decay. Such energy can be harnessed for heart pacemakers and to power navigation beacons and satellites. The decay heat of plutonium-238 has powered many US space vehicles. It enabled the Cassini space probe to investigate Saturn.

 Dating

Analysis of radioisotopes is of vital importance in determining the age of rocks and other materials that are of interest to geologists, anthropologists and archaeologists. 

From the moment we get up in the morning, until we go to sleep, we benefit unknowingly from many ingenious applications of radioisotopes and radiation. The water we wash with (origin, supply assurance), the textiles we wear (manufacture control gauging), the breakfast we eat (improved grains, water analysis), our transport to work (thickness gauges for checking steels and coatings on vehicles and assessing the effects of corrosion and wear on motor engines), the bridges we cross (neutron radiography), the paper we use (gauging, mixing during production processes), the drugs we take (analysis) not to mention medical tests (radioimmunoassay, perhaps radiopharmaceuticals), or the environment which radioisotope techniques help to keep clean, are all examples that we sometimes take for granted. 

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