ARTIFICIAL RADIOACTIVITY
Tuesday, January 26, 2010
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Artificial Transmutation:Nuclear transmutation is the conversion of one chemical element or isotope into another, which occurs through nuclear reactions. Nuclear transmutation produced artificially through bombardment by high energy subatomic particles or photons is known as artificial transmutation.
Artificial transmutation was first discovered by
The reaction equation is:
Definition of artificial radioactivity:
The radioactivity of isotopes that have been artificially produced through the bombardment of naturally occurring isotopes by subatomic particles or by high levels of x-rays or gamma rays are called artificial radioactivity. It is also called induced radioactivity.
Discovery of Artificial Radioactivity:
In 1932, Irene Curie, the daughter of Madame Curie, 
and her husband, F. Joliot, discovered that boron gives off positrons (the positive electrons) and neutrons, leaving a nucleus having a charge of 7 and a weight of 13, when bombarded with alpha particle. They accidentally observed that the positron emission continued on after the alpha particle bombardment had been stopped. With this observation, they had discovered that a new kind of radioactivity is stimulated artificially in boron by alpha particle bombardment. They proved chemically that the radioactive substance formed is, in fact, an isotope of nitrogen, and christened it "radio-nitrogen." The positron emission converts the radio - nitrogen into C13.
The reaction equation is: 2He4 + 5B10 6C13 + 0n1 + +1e0 + energy
Irene Curie and Joliot suggested that such radioactive substances might well be produced artificially by bombardment with other atomic projectiles, especially protons, deuterons, and neutrons. Such radioactive substances are called radioisotopes.
Uses of Radioisotopes:
1. Medical Uses
· For Radio diagnosis and Therapy
Radioisotopes are used for radio diagnosis. Some radioisotopes are very effective in curing certain diseases.
Example:
Radio-cobalt (Co-60) - used in the treatment of brain tumour.
Radio-phosphorous (P-32) - used in the treatment of bone diseases.
Radio-iodine (I-131) - used in the treatment of thyroid cancer.
· To sterilize materials
Radio-isotopes are used as gamma ray sources to irradiate and sterilize medical instruments, plastic hypodermic needles, packets of antibiotics, and hospital blankets so that bacteria and other disease-carrying organisms can be destroyed. A portable source of γ -rays for sterilization is radio-cobalt (Co-60).
· To kill cancer cells
The picture below shows a large amount of radiation entering a living cell. The high dose of radiation kills the cell so no cancer cells can form. Co-60 is an important cancer-treatment agent.
http://www.youtube.com/watch?v=1xvBRF7l13Y&feature=related
· Used as Tracers
In the field of medicine the tracer technique is employed in a number of ways. For example, the doctor can find out any obstruction in the circulation of the blood in the human body. He injects radio phosphorous (P-32) into the blood of the patient and examines the movement of the blood by detecting radiations emitted by P-32 by means of G. M. counter. He can thus locate clots of blood present in the body. Co – 60 is also used as an important tracer.
2. Agricultural Uses
- Certain seeds and canned food can be stored for longer periods by gently exposing them to radiations.
- Better yields of milk from cows and more eggs from hens have been obtained on the basis of information gained by mixing radioisotopes with their diet.
- Radioisotopes are used for determining the function of fertilizer in different plants.
- Radioisotopes are also used for producing high yielding crop seeds. Thus the agricultural yield is increased.
- In agriculture, the tracer technique is used to study the rate and direction of movement of an element in a plant.
3. Industrial Uses
· By γ-ray photography we can find out wearing of cutting tools and lathes.
· We can use it to locate internal cracks in stones.
· We can check any non-uniformity in the thickness of a sheet by β or γ-absorption measurements.
· The tracer technique is used for testing the uniformity of mixtures.
· Radio-isotopes are used to detect pipeline leaks, and to trace underground water.
4. Other Uses
· Naturally occurring radio-isotopes can be detected in forensic science, to assist in solving crimes.
· Naturally occurring radio-isotopes are also used by archaeologists and related specialists to help establish the authenticity and age of specimens.
· Naturally occurring radio-isotopes are often used by geologists to establish the ages of rocks.
Carbon Dating:
Carbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis. 
Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere. This neutron bombardment produces the radioactive isotope carbon-14.
The carbon-14 forms at a rate which appears to be constant. 
When a plant, animal or human dies the Carbon-14 inside decays with a half-life of about 5730 years by the emission of an electron of energy 0.016 MeV. This changes the atomic number of the nucleus to 7, producing a nucleus of nitrogen-14.
By finding the ratio of Carbon-14 to stable Nitrogen-14 in a dead plant, animal or human the age of the specimen can be calculated.
The Radioisotope Carbon-14 Cycle:
posted by Lekshmi @ 10:19 PM,
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