Medical Cyclotron: Definition, Structure, and Principle

During 1929-30, scientist Lawrence invented a particle accelerator device called the cyclotron. A cyclotron contains a hollow cylinder divided into two Dees in a vacuum chamber, in which the charged particles are accelerated under the influence of an electric field and static magnetic field along a spiral path. The charged particles accelerated in the cyclotrons are converted into beams and utilised in medical treatment and nuclear research.

Definition:-

A cyclotron is a particle accelerating device in which the charged particle is accelerated in a hollow cylindrical apparatus under the static magnetic field. This charged particle is then utilised as a beam for different purposes.

Principle of cyclotron:-

The working principle of a cyclotron is that the charged particle is accelerated by the electric field and the force on the charged particle will be given by Lorentz force.

F=Bqv

Here, q is the charge on the particle, E is the electric field under which the charged particle is accelerated, B is the static magnetic field on the particle, and v is the velocity of the charged particle.

Construction and Working of the cyclotron:

Cyclotron consists of a  hollow cylinder divided into two parts called Dees. These Dees are  placed in a vacuum chamber. Now, these Dees are connected with high-frequency oscillators.

When the positive charge having a mass m is released from the source, the negatively charged dee attracts the particle. Now, the Lorentz force acts on the particle, which moves the particle in a spiral path.

When the charged particle reaches the gap between the dees, the polarity of the dees is changed. So the dee just in front of the moving charged particle now becomes negative and attracts and accelerates the particle. Now, the charged particle again comes to the gap between the dees, and again the polarity is changed.

Thus, in this way, by continuing to change the polarity of the dees and under the influence of the Lorentz force, the charged particle is accelerated in the cyclotron.

Velocity, period, and frequency of a charged particle:

The Lorentz force acting on a charged particle moving in a circular path will be equal to the centripetal force acting on the particle.

Bqv=12mv2

v=2Bqvm

Thus, the velocity of the charged particle will be calculated by the above-mentioned formula.

Now, again from the above equation,

Bqv=12mv2

vr=Bqm

Now, the time for the half-circle is given as:

t=rv

t=mBq

Total time period of the accelerated particle is 

T=2mBq

So, the frequency of the charged particle will be given as –

f=Bq2m

Medical Uses of cyclotrons:-

1. Cyclotron in Radioisotope production:- The accelerated charged particles, coming out of the cyclotron in the form of a beam, are bombarded on the other atoms to produce radioisotopes, which are used in medical imaging and radiotherapy.

2. Beam therapy:- The beams produced by accelerating the charged particles in the cyclotrons are used in particle therapy to treat cancer. Ion beams of the cyclotrons are used to kill the tumour present in the body by penetrating it.

Limitation of cyclotron:

1. Cyclotrons cannot be used to accelerate the neutrons because they are neutral, and hence there will not be any effect of a magnetic or electric field on this particle.
2. Electrons can not be accelerated by cyclotrons because the electrons have a very small mass, and their speed increases rapidly, due to which the resonance between the voltage and the particle is lost.
3. It is very difficult to maintain a uniform electric field over a large area of the dees.

Conclusion:

In this article, we studied the working principle of cyclotrons. We have also learnt the application of cyclotrons in various fields and especially the medical application of cyclotrons in the treatment of cancer. We have also studied the construction of a cyclotron and the working of each of its parts.