Different forms of radiation originate in the nuclei of radioactive atoms. There are three kinds of radioactive radiation: alpha particles, which were first identified by Becquerel; beta rays, identified by Ernest Rutherford; and gamma rays, identified by Marie and Pierre Curie. Emission of alpha or beta rays causes transmutation, but gamma radiation does not result in transformation.
One element can be changed into another artificially. Ail artificial radioisotope is produced by making stable isotopes radioactive—i.e., unstable, their nuclei breaking apart to release small particles and energy (radioactivity). Every element with atomic number greater than that of lead (82) is radioactive.
Artificial radioisotopes may be produced by bombarding atoms with particles and rays emitted by radioactive elements in a nuclear reactor. They can also be produced by smashing atoms in particle accelerators such as the cyclotron. The fact that radioactive materials can be detected by their radiation makes them useful in many fields.
Radioactive isotopes are effectively used as tracers for diagnostic purposes in medicine. Arsenic-74 is used to detect tumours. Sodium-24 is used to detect blood clots in the circulatory system. Iodine-131 (1-131) is used to determine the activity of the thyroid gland. Cobalt-60 is used in the treatment of cancer; also in use are iridium-192, and caesium-137.
The production of radioisotopes in India began in 1956 with the commissioning of the research reactor Apsara at Trombay. The radioiso¬tope production capability was augmented in 1963 when the 40MWt Cirus became operational at Trombay. In 1985 with Dhruva being made operational by BARC, India came to the fore as a major producer of wide spectrum of radioisotopes.
The research reactors at Trombay produce a variety of radioisotopes for various uses. Power reactors are also equipped to produce cobalt-60 radioisotope.
The variable energy cyclotron at VECC is also used for manufacture of radioisotopes, which are processed for medical applications. Radiation and radioisotope based products and services offered by DAE through BARC and BRIT include radio sources and industrial radiography equip¬ment; radiotracer technologies in leak detection, silt movement, and applications in hydrology; radiation processing, radiation polymerisation, soil-salinity and others.
BRIT has been entrusted with the responsibility for processing a variety of radioisotopes and their derived products and supply of industrial radiography equipment and gamma irradiation equipment for applications of this technology.
BARC’s Radiation Medicine Centre (RMC) at Mumbai, a premier centre in the country in the field of radio diagnosis and radiotherapy, is a regional referral centre of the World Health Organisation (WHO) for South-East-Asia.
The activities of the centre cover the fields of nuclear medicine and allied services, clinical diagnosis and treatment, in-house development of radiopharmaceuticals, RIA technology for thyroid hor¬mones and tubercular antigen and antibodies, etc.
Radioisotopes for medical applications are also manufactured by using the variable energy cyclotron at Kolkata. The regional radiation medicine centre (RRMC) meets the radio diagnostic and radiotherapy requirements of the eastern region of the country. CAT at Indore has developed lasers for medical applications.
In India, radiation has been in use for decades for sterilisation of medical products. A commercial radiation sterilisation plant (ISOMED) at Trombay provides sterilisation services to the medical industry. A large radiopharmaceuticals laboratory named ISOPHARM has been set up at Vashi, Mumbai.
Plants similar to Isomed have been working at Bengaluru, New Delhi and Jodhpur. For use in blood banks and hospitals, BRIT has developed a blood irradiator equipment which is an important import substitute.
Uses of Radioisotopes:
In Industry Gamma rays can be used to examine metallic castings or welds in oil pipelines for weak points. The rays pass through the metal and darken a photographic film at places opposite the weak spots. Manufacturers may place a radio-isotope that emits beta particles above a sheet of material.
A beta-particle detector on the other side measures the strength of the radiations coming through. If the sheet thickness increases, fewer particles reach the detector. The detector can control rollers and keep the sheet at desired thicknesses. Gamma radiation may be used in pest control, especially ingrain stores. Irradiated food has a longer shelf life.
In Research Scientists use radio-isotopes as tracers, to determine how chemicals act in the bodies of plants and animals. All isotopes of an element are chemically the same, so the radio-isotope can be used in the same way as the ordinary isotopes.
For example, to trace the course of phosphorus in a plant, a botanist may mix radioactive phosphorus with the ordinary phosphorus. To learn when the phosphorus reaches a leaf, he may place a Geiger counter, which detects radioactivity, on the leaf. To find where the phosphorus lodges in the leaf, he may place the leaf on a photographic plate. In the developed plate, called an autoradiograph, darkened regions show the position of the radio-isotope.
The use of radio-isotopes is part of a speciality called nuclear medicine. The chief use of radio-isotopes is to study the function of various body organs. To accomplish this, a doctor administers a radio¬isotope attached to a carrier substance. The carrier substance accumulates in the organ that the doctor wants to study.
For example, if the doctor wishes to study a patient’s kidney function, a radio-isotope will be attached to a carrier substance that accumulates in the kidneys. As the radio-isotope breaks down, it emits gamma rays. Some of the rays are picked up by a device called a scanner. The doctor “reads” the image on the scanner to determine if the kidneys are working properly.
Radioisotopes are also used to treat cancer. Radiation in large doses destroys living tissues, especially cells undergoing division. Because cancer cells divide more frequently than do normal cells, radiation kills more cancerous cells than normal ones. A doctor may take advantage of this fact by administering a radio-isotope that accumulates in a cancerous organ.
For example, a radio-isotope of iodine, 1-131 may be used to treat cancer of the thyroid gland, because this gland accumulates iodine. As the radioactive iodine transforms, it gives off radiation that kills the cancerous cells. Cobalt-60 is also used in treatment of cancer. Arsenic- 74 is employed to detect tumours. Blood clots in the circulatory system are located by Sodium-24.
Radioisotopes have been used to promote natural genetic mutation in plants so as to hasten breeding, or to develop plants with new characteristics. Efficiency of fertilisers can also be studied with radioisotopes. BARC has a programme for the development and produc¬tion of phosphorus-32 labelled biomolecules to aid research in genetic engineering, enzyme technology and energy-related areas.
Isotopes are being used to study groundwater recharge, seepages in dams and canal systems, sea water intrusion into coastal aquifers.