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| Cyclotron |
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| The sub-atomic charged particles experience large forces when subjected to electric and magnetic fields due to their extremely small mass. In nuclear physics such energized particles are used to bombard nuclei causing nuclear reactions. This helps to obtain information about the nucleus. |
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| A cyclotron is device by which positively charged particle can be accelerated and the desired nuclear reaction can be brought about. |
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| Principle |
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| A positively charged particle can be accelerated to high energy with the help of an oscillating electric field, by making it cross the same electric field time and again with the use of a strong magnetic field. |
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| Construction |
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| It consists of two dees or D-shaped metal chambers D1 and D2. The dees are separated by a small distance. The two dees are perpendicular to their plane. P is the position where the ion source is placed. |
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| The dees are maintained to a potential difference whose polarity alternates with the same frequency as the circular motion of the particles. The dees are closed in a steel box placed between the poles of a strong electromagnet. The magnetic field is perpendicular to the plane of the dees. |
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| Theory and Working |
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| The positive ion P to be accelerated is placed in between the two dees. If at any instant, D1 is at negative potential and D2 is at positive potential, then the ion gets accelerated towards D1 but since its perpendicular to B, it describes a circular path of radius r and Lorentz force provides the centripetal force. |
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| Time taken to describe a semicircle is |
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| If this time is equal to the time during which D1 and D2 change their polarity, the ion gets accelerated when it arrives in between the gaps. The electric field accelerates the ion further. Once the ion is inside the dee D2, it now describes a greater semicircle due to the magnetic field. This process repels and the ion goes on describing a circular path of greater radius and finally acquires a high energy. The ion is further removed from a window W. The maximum energy acquired by the ion source is |
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| The frequency of cyclotron is given by |
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 Only when the speed of the circulating ion is less than 'c' the speed of light, we find the frequency of revolution to be independent of its speed. |
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| At higher speeds, the mass of the ion will increase and this changes the time period of the ion revolution. This results in the ion lagging behind the electric field and it eventually loses by collisions against the walls of the dees. |
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 The cyclotron is suitable for accelerating heavy charged particles but not electrons. |
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 Cyclotrons cannot accelerate in charged particles. |
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 It is not suited for very high kinetic energy. |
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