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Medical and  industrial use of radioactive isotopes 

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adioactive isotopes, such as uranium-235 (235U), can be used as a source of energy

A nuclear power station only differs from a gas-fired power station in that the thermal energy (heat) comes from a nuclear reaction not from burning gas or coal. In both cases, this energy is used to produce steam to drive turbines and hence alternators

The nuclear reaction used in most power stations is the splitting of a uranium-235 nucleus into two parts when it is hit by a neutron. The result is two smaller nuclei and several extra neutrons and a big amount of energy.

The smaller nuclei are called fission fragments

A wide range of nuclei may be produced.  
A useful demonstration is to tear a piece of polystyrene into two parts. There will be two large (but randomly sized) pieces and some smaller fragments. The small fragments represent the neutrons and the two large pieces represent the fission fragments.
If you repeat the process, the number of crumbs may be different and the larger lumps not exactly the same size.
It is just the same with nuclear fission. The neutrons are important because they can in turn hit more nuclei of uranium-235 and cause further fission.  
This process is called a fission chain reaction.
The following demonstration is a good model of a chain reaction.

YouTube Video

YouTube Video

The big problem of using radioactive isotopes in generating electricity is that in a nuclear reactor, up to one-third of the thermal energy is generated by alpha and beta decay of the fission fragments. The result is that a nuclear reactor cannot be totally shut down in an emergency. It follows that it is necessary to provide cooling even when reactors are not working. 

Rate of energy released

In a nuclear reactor, the reaction is controlled so that energy is released at a steady rate.

The energy released in nuclear fission is far greater than the energy released in a chemical reaction, such as burning fuel. This means that the power output of a nuclear power station is large. 

Advantages and disadvantages

 The advantages:

  • no carbon dioxide is produced when the station is operating.
  • there is a high power output
  • a small amount of fuel is needed, when compared with coal or gas

These are some of the disadvantages:

  • hazardous radioactive waste is produced.
  • building the power stations is quite expensive
  • decommissioning of the power stations at the end of their lifetime is very costly.
  • It can cause a disaster if something went wrong in the operation system (like Chernobyl reactor ) 

YouTube Video