Radioisotopes: Properties and Uses

1. Introduction to radioisotopes

All matter is made up from elements as carbon, hydrogen and oxygen. The smallest part of each element which is identical to one another is called an atom. Atoms can be further divided into three substructures which is proton, electron and neutron. The atoms of different elements differ in these three substructures. The number of protons in each atom of a particular element is called the atomic number or the proton number, Z. The nuclei of an atom contain neutrons as well as protons. The mass of an atom is almost entirely due to the protons and neutrons. Thus the mass number, A is the total number of protons plus neutrons which is also known as nucleon number. Isotopes refer to the same element having different mass number. The different in mass number will have the isotopes to share the similar chemical properties but differ in physical properties. For instance, chlorine occur naturally as ³⁵Cl and ³⁷Cl.

Figure 1: Atomic notation

Isotopes occur naturally and artificially. They can either be in stable or unstable condition. Most of the isotopes which occur in nature are stable. The forces within their nuclei are sufficient to keep the protons and neutrons in the same arrangement indefinitely. However, a few naturally occurring isotopes and almost all man made ones are unstable. Unstable nuclei can change in to a more stable arrangements by releasing energy and different types of particles. The energy and particles emitted is called radioactive decay. The particular isotopes of elements with nuclei that can undergo radioactive decay are called radioisotopes. The amount of energy and the types of particles released are measure by using Geiger counter and photographic film. Radioisotopes cover a very wide range of usage including in energy generation, industries, food processing, medical field and agriculture.

Table 1: Examples of natural occurring and man-made radioisotopes

2. Application of radioisotope technology in Malaysia

2.1 Gamma Radiography

One of the application of radioisotopes in Malaysia is in the Gamma radiography technology. Gamma Radiography behave in much the same way as x-rays screen baggage at airports. But in contrast to the bulky machine needed to produce x-rays, all that is needed to radiate gamma rays is a small pellet of radioactive material in a sealed capsule made of titanium. The capsule is placed on one side of the object to be screened while a photographic film is placed on the other side. Just like x-rays, gamma rays pass through the object and projects an image to the film. Similar to x-rays that show a break in a bone, gamma rays show flaws or empty spaces in metal castings or welded joints. The technique makes inspection for internal defects without damage involving critical components possible.

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The sources for Gamma rays are usually more portable than x-ray equipment so they possess a clear advantage in certain applications such as in remote areas. In contrast to x-ray sources that emit a broad band of radiation, gamma sources emit at most a few discrete wavelengths. Gamma sources may also have much higher energy than all but cost cheaper than x-ray equipment thus providing an advantage for such radiography. Gamma radiography is also used in an oil or gas pipeline where special film is taped over the weld around the outside of the pipe. An equipment called pipe crawler has a shielded radioactive source down from the inside of the pipe to the position of the weld. Along the pipe line, the radioactive source is exposed producing a radiographic image of the on the film. The film is later developed to images and further examined for signs of potential flaws in the weld.

X-ray equipment can only be used when electric power is available and the object to be x-rayed is small and mobile enough to be taken to the x-ray source and radiographed. Radioisotopes have bigger advantage in that sense because they can be taken to the site to examine an object and no external power is needed. The only drawback is that they cannot be simply turned off thus the equipment must be properly shielded during application.

Different types of isotopes are used for different situation. Examples of radioisotopes used in gamma radiography are ytterbium-169 to test material up to 15 mm thick and light alloys to 45 mm and iridium-192 to test material 12 to 60 mm thick and light alloys up to 190 mm.

2.2 Gauging

The radiation that originated from radioisotopes will have its intensity reduced by the material between the radioactive source the detector. Detectors are designed to measure the magnitude of the reduction. As the result, the same principle is able to be used to gauge the presence or the absence and even to measure the quantity and density of objects between the source and a detector. One of the advantage in using radioisotopes in gauging or measurement is the zero contact with the material being gauged. A huge list of processing industries is making use of fixed gauges to control the flow of materials in production line utilizing radioisotopes technology.

The height of the coal in a container that is used to carry coal is able to be determined by using high energy gamma sources at different heights along one side with detectors directed across the load thus registering the breaking of the beam causing the coal in the container to level. This type of gauge is one of the most common industrial applications of radioisotopes. Equipment used in plastic film manufacturing utilize radioisotope gauging using beta particles to measure and control the thickness of the plastic film produced. The film is rolled at high speed between the radioactive source and its detector to control the plastic film thickness. Beta gauges are used to control the paper thickness at speeds of up to 400 ms^-1 in paper manufacture lines.

While the intensity of radiation radiated from a radioisotope is reduced by material in the radiation beam some extra radiation is reflected back to the source of radiation. The amount of reflected radiation depends to the amount of material in the radiation beam thus can be used to measure characteristics of the material. This application of radioisotopes is used in measuring various types of coating thicknesses. Americium-241 is among the common use of radioisotopes in gauges.

2.3 Insect Control

In Malaysia, crop destruction by insects is reaching to about 10% of the total harvest nationwide. Chemical based insecticides have been the usual weapon for years in effort to minimize these losses yet they have not been very effective. This is due to some insects have grew resistant to the insecticides applied as well as some of them leave harmful residues on plants. Sterilizing insects is one solution making use of radioisotopes.

The radioisotopes technology in pest control called Sterile Insect Technique or short formed as Sterile Insect Technique comprising huge numbers of insects involving a process to irradiate their eggs using gamma radiation before they hatch to sterilise the insects. The sterile male insects will then be released in huge numbers in the areas of infestation. This ensure that there are no offspring are produced when they mate. The repeated releases of sterilised males to the area caused the population of the insect in the affected area is tremendously reduced.

Several Sterile Insect Technique operations have been implemented in Malaysia involving common paddy pest like brown plant hopper that was then declared a complete success. A very successful Sterile Insect Technique campaign was extended to aedes mosquito leading to health benefits to humans. Some of the livestock are unable to be farmed as a result of the tsetse fly which has parasite trypanosome inside their body causing the sleeping sickness disease on cattle. Thanks to the application of radioisotopes in pest controls this situation is starting to change. Three United Nation organizations that is the IAEA, the FAO and the World Health Organisation (WHO) are promoting this radioisotopes technology in many other countries.

2.4 Food Preservation

A major amount of food harvested in Malaysia is lost because of spoilage caused by microbes and pests. In a hungry world it’s a luxury we cannot afford. The reduction of food spoilage due to infestation is very important. It is imperative in Malaysia with hot and humid climates throughout the year that favour the survival of microbes and pest. This grave situation lead to the use of irradiation technology in food preservation. This radioisotopes technology is widely used in over 40 countries where health authorities have approved the use of irradiation involving more than 60 kinds of food ranging from spices, grains, fruit, vegetables and meat. Irradiation is able to replace the use of hazardous chemical to eliminate insects from infesting dried fruit, grain, legumes, and spices.

Besides to reduce spoilage after harvesting, application of food irradiation is driven by risks about food-borne diseases as well as rapidly increasing international trade in food stocks which ought to meet certain standards of quality. On our nation recent trip into space, our astronauts also eat foods preserved by irradiation technology.

Food irradiation is done by exposing high levels of gamma radiation to raw foods to kills bacteria and other hazardous microorganisms without reducing the nutritional value of food itself. This is so far the only way of destroying bacterial pathogens in raw and frozen food.

3. Recommendation of radioisotope applications for country that lacks natural resources

3.1 Gamma Radiography

Under the effort of making full use of radioisotopes technology in in under developed countries, gamma radiography is one of the considered technique. Being a country with limited resources, it is the utmost importance not to waste even a particle of available resources. This is mainly highly applicable in the production line in industries such as mills as well as gas and petroleum pipe lines. By introducing gamma radiography in industries, there will be an optimum usage of resources. That can be done by minimizing the waste of resources mainly related to the maintenance of production line. The use of gamma radiography over x-rays devices to identify the flaws in the production line is able to reduce the maintenance cost. Maintenance involving a remote equipment such as gas and petroleum pipeline can also be done much easier and cost wise by utilizing radiography technology.

This will boost the undergoing development effort in developing under developed countries by two main strategy that is optimum usage of resources and cost efficient maintenance line.

3.2 Insect Control

Limited food reserve is a critical problem that should be addressed involving under developed countries. Starvation has become the number one killer for many decades in under developed countries especially in Africa region. This has something to do with the poor food and resources management as well as the invasion of crop and plants by insects. Not only insects play a major role in causing starvation, they also affect the declining of health quality of a country by spreading fatal sickness such as malaria.

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The use of radioisotopes in a technique called Sterile Insect Technique or also known as SIT will be able to reduce starvation in under developed countries from a higher level of perspective. In conjunction to the effort of other countries to continue providing aid in food material by sending raw food material and improving health quality by sending respective vaccine to the under developed countries, the country itself has to come up with a more effective way to come out of these problem in the long run. The introduction to Sterile Insect Technique might be a good start. This technique without doubt will have positive impacts in reducing the number of crop destroying and diseases carrying insects tremendously.

3.3 Food Preservation

Being able to harvest crop is one thing, while the ability to have the stock preserved for a long run use is another different thing. The inability to preserve food stock in an efficient way will only cause a major food spoilage before they can even be distributed to the citizen. By implementing the use of radioisotopes technology to preserve food using irradiation technique help to prevent food spoilage from happening providing an extra amount of effective time for the food to reach its respective consumers. As a result, consumers has better access to ready stock food as well as contribute to the positive impact in reducing starvation in under developed countries.

Irradiation technique cover another aspect beside food preservation that is eliminating the risk of food borne diseases to be spread among the consumers. Exposure of gamma radiation to food has more positive impact besides extending food lifespan itself. It also indirectly improve the health quality of the citizen by avoiding unnecessary diseases that might come together with the food consumed.

4. Impacts of radioisotopes application

4.1 Gamma Radiography

The technology involving radioisotopes application in gamma radiography equipment has its own benefits mainly to the industries. This including the reduction of cost in buying gamma radiography equipment over x-ray machine. Cost reduction can also be related to the need of external electrical power by x-ray machine as compare to gamma radiography equipment that does not require power to operate. Gamma radiography has also makes the maintenance process much easier by eliminating the need to dismantle production line machine component to identify flaws.

The use of gamma radiography has minimal risk to the industry. The worst case to happen is the exposure to the staff operating the maintenance and inspection procedure. Exposure to gamma radiation may lead to the degeneration of health depends on the level amount of exposure received. To prevent this, the standard in manufacturing the sources of gamma radiation must be controlled. That of course to make sure the use of titanium case as the main material for radioactive capsules. Radiation suit must also be worn by maintenance staff at all times while operating such procedures.

4.2 Insect Control

Sterile Insect Technique or SIT has been proven effective in controlling insect population which has greatly contributed in improving crops production as well as reducing the number of health cases related to diseases carrying insects. The use of radioisotopes technology over conventional chemical insecticides also reduce the risk of hazardous chemical substance. This provide a much cleaner pest and insect control mechanism mainly in agriculture.

While SIT continue to carry such good reputation in agriculture, there has been some debate that the radiation might spread to general population not only affecting insects but also to the environment where the insects are released at. In contrary to that concern, the use of SIT is a calculated risk that ensure a zero harm to the environment. This was made sure by thorough research programmes to select the most suitable radioisotopes to be used in agriculture. The main criteria of radioisotopes used is the rate of half-life cycle and the minimal impact to the environment. Plus, the sterilization takes place in a controlled lab involving the exposure of radiation to the insects before it hatches. The insect will only be released to designed areas after they hatches and at the end of the half life cycle.

4.1 Food Preservation

Food irradiation has become the most reliable way of preserving food. In contrary to other preservation method, food irradiation does not alter the taste and the structure of the preserved food. Irradiation also covers a very wide range of food including meat, grains and vegetables. Plus, food radiation also kill potential harmful microorganism that might harm human health.

Like any other radioisotopes applications, irradiation has cause some concern to the society. One of the issues that came up is whether or not the radioisotopes used will affect ones who consume food preserved by irradiation. Radiation poisoning can be fatal to human thus elevating the number of people questioning the reliability of this technology. Little that they know that the technique is a result of numerous trials and research and decades of development before it was approved to be used in food preservation. Irradiation uses a safe amount of radiation which has already been proved harmless to human. Apart of the health issue posed by irradiation, this particular method of food preservation also has limitation on extending food lifespan. This related to the application involving meat preservation which still need a proper refrigeration to stay fresh.

Conclusion

Radioisotopes has been very beneficial to mankind. The application cover a wide range of field including gamma radiography, insect control and food preservation. Since the application of radioisotopes in atomic bomb, this technology were regarded as the most promising application of our new knowledge of the atom. Venturing into new fields come together with substantial risks. Risks due to our ignorance of what and how it should be used as well as risks due to the lack ethical values in developing radioisotopes technology. It is up to us to make full use of this great technology without diverging from our concern in ethics and scientific values.