"A study of the nuclear changes in atoms is termed as Nuclear chemistry".
- A nuclear reaction is different from a chemical reaction.
- In a chemical reaction, atoms of the reactants combine by a rearrangement of extra nuclear electrons but the nuclei of the atoms remain unchanged.
- In a nuclear reaction, however, it is the nucleus of the atom which is involved.
- The number of protons or neutrons in the nucleus changes to form a new element itself.
So, nuclear chemistry is the study of phenomenon involving nuclear reactions
, like radioactivity. Nuclear chemistry also deals with the energy released from nuclear reactions, and its usage.
The history of Nuclear chemistry dates back to 1895, with the discovery of X- rays by William Roentgen. In early 1896, Henri Becquerel was carrying out a series of experiments on fluorescence. He had used photographic film between two pieces of paper.
When he developed the photographic film, he found that it had the same appearance as if it had been exposed to light. And after this, by accident, he developed the photographic plates, which was kept in the same drawer as Uranium. To his surprise, the plate had been blackened. He thought that it was a new type of fluorescence. But, actually, he had come across a phenomenon of radioactivity. So, accidentally, radioactivity was discovered by Henri Becquerel
The name radioactivity, was coined some time later by Marie Curie
. She won the Nobel prize for her discovery in 1903 with Henri Becquerel and Pierre Curie
. Thereby evolved the branch of chemistry called Nuclear chemistry.
The discovery of radioactivity
also brought into account many other processes, such as fission and fusion, which again were used as a source of energy in many reactors. And also, with the discovery of radioactivity and other phenomenon related to radioactive elements
, many new elements were brought into light.
There are various types of radiations involved in Nuclear chemistry. They have their own representations. Let us look into these radiations and their symbols.
Types of radiations and nuclear symbols
The radioactive radiations are of three types. They were sorted out by Rutherford in 1902, by passing them between two oppositely charged plates. The ones bending towards negative plate carried positive charge and were named as alpha rays. Those bending towards the positive plate and carrying negative charge were called as beta rays. The third type of radiation, being uncharged, passed straight through the electric field and were named gamma rays.Symbols of these rays1. Alpha rays
Represented as α.
These are positively charged rays. Since the alpha rays have a mass of 4 amu and charge _2, they are actually helium nuclei. So, they are also represented as
4 2He or 4 2 α
2. Beta Rays
Negatively charged rays. They are represented as: β
. Since they have a mass similar to electron, they are also represented as e-. They have a unit negative charge. 0-1e or 0-1 β 3. Gamma rays
These rays are neutral, with no charge. They are simply represented by the symbol : γ
- A number of elements such as Uranium, and radium are unstable.
- Their atomic nucleus breaks on its own accord to form a smaller atomic nucleus of another element.
- The protons and neutrons, in the unstable nucleus, regroup to give the new nucleus.
- This causes the release of excess particles and energy from original nucleus, which we know as radiation.
- The elements whose atomic nucleus emits radiation are said to be radioactive.
Radioactive decay can be defined as: " The spontaneous breaking down of the unstable atoms is termed radioactive disintegration or radioactive decay."" The disintegration or decay of unstable atoms accompanied by emission of radiation is called radioactivity".
The radioactive radiations can be detected and measured by a number of methods. Some important methods are:
Three types of radioactive decay occurs
- Cloud chamber method
- Geiger-Muller counter
- Ionization chamber method
- Scintillation counter method
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- Alpha decay.
- Beta decay
- Gamma decay
The major concern, on using the nuclear materials for any purpose, is their disposal. It is a known fact that the nuclear reactions, or rather the radioactivity, does not stop anytime. It is a spontaneous process
, therefore, continues even after the material has been discarded. Thus, the disposal of the nuclear waste
has to be done with utmost care.
The products of fission, like Ba-139 and Kr-92 are themselves radioactive. They emit dangerous radiations for several hundred years. The waste is usually packed in concrete barrels which are buried deep in the earth or dumped in sea. But the fear is that any leakage and corrosion of the storage vessels may eventually contaminate the water supplies.
Nuclear chemistry finds its use in many fields. Though there are disadvantages in the form of atom bombs, nuclear reactivity for war fare, etc, they find many useful applications too. Some of them are1. Light -water nuclear power plan
2. Breeder reactor
- Most commercial power plants today are light-water reactors. U-235 is used as a fuel here.
- The Uranium -235 rods are submerged into it.
- A lot of energy is produced from the reaction in the nuclear reactor.
- A reactor, once started, can supply power for many generations.
- About 15% of consumable electricity in U.S.A is provided by Light-water reactors.
This is again another reactor which taps energy from nuclear reactions. Here too, U-235 is used for the production of electricity.
3. Radioactive dating
- This is a very important use of radioactivity.
- The age of an old piece of wood can be determined using radioactive dating technique.
- A plant, while alive, takes up both normal carbon, C-12 and radioactive carbon, C-14.
- When the plant dies, uptake of carbon from atmosphere stops.
- Though, the C-12 does not show any change, the decay of C-14 starts with the release of Beta radiation.
- This helps in detecting of the age of a wood piece.
Many radionuclide are used in medicine to detect cancerous cells, any other defect in organs, etc. These radioactive elements are combined with other compounds, or elements and administered orally. And, after some time, the path traveled by these radio isotopes are detected using a detector. The complete length traveled by it can be seen and the problems can be easily detected.