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Sunday, 13 November 2011

A PROJECT REPORT ON CYCLOTRON


INTRODUCTION:
A cyclotron is a machine Used to accelerate charged particles to high energies. The first cyclotron was built by Ernest Orlando Lawrence and his graduate student, M. Stanley Livingston, at the University of California, Berkley, in the early 1930's.
A cyclotron consists of two D-shaped cavities sandwiched between two electromagnets. A radioactive source is placed in the center of the cyclotron and the electromagnets are turned on. The radioactive source emits charged particles. It just so happens that a magnetic field can bend the path of a charged particle so, if everything is just right, the charged particle will circle around inside the D-shaped cavities. However, this doesn't accelerate the particle. In order to do that, the two D-shaped cavities have to be hooked up to a radio wave generator. This generator gives one cavity a positive charge and the other cavity a negative charge. After a moment, the radio wave generator switches the charges on the cavities. The charges keep switching back and forth as long as the radio wave generator is on. It is this switching of charges that accelerates the particle.
Let's say that we have an alpha particle inside our cyclotron. Alpha particles have a charge of +2, so their paths can bent by magnetic fields. As an alpha particle goes around the cyclotron, it crosses the gap between the two D-shaped cavities. If the charge on the cavity in front of the alpha particle is negative and the charge on the cavity in back of it is positive, the alpha particle is pulled forward (remember that opposite charges attract while like charges repel). This just accelerated the alpha particle! The particle travels through one cavity and again comes to the gap. With luck, the radio wave generator has changed the charges on the cavities in time, so the alpha particle once again sees a negative charge in front of it and a positive charge in back of it and is again pulled forward. As long as the timing is right, the alpha particle will always see a negative charge in front of it and a positive charge in back of it when it crosses the gap between cavities. This is how a cyclotron accelerates particles!
A cyclotron consists of two D-shaped regions known as Dee's. In each dee there is a magnetic field perpendicular to the plane of the page. In the gap separating the dees there is a uniform electric field pointing from one dee to the other. When a charge is released from rest in the gap it is accelerated by the electric field and carried into one of the dees. The magnetic field in the dee causes the charge to follow a half-circle that carries it back to the gap.
While the charge is in the dee the electric field in the gap is reversed, so the charge is once again accelerated across the gap. The cycle continues with the magnetic field in the dees continually bringing the charge back to the gap. Every time the charge crosses the gap it picks up speed. This causes the half-circles in the dees to increase in radius, and eventually the charge emerges from the cyclotron at high speed


Definition of Cyclotron

A circular particle accelerator in which charged subatomic particles generated at a central source are accelerated spirally outward in a plane perpendicular to a fixed magnetic field by an alternating electric field. A cyclotron is capable of generating particle energies between a few million and several tens of millions of electron volts.

PRINCIPLE OF CYCLOTRON :

It is based on the principle that a positive ion can acquire sufficiently large energy with a comparatively smaller alternating potential difference by making them to cross the same electric field time and again by making use of a strong magnetic field.
A cyclotron is a device used to accelerate charged particles.

DIAGRAM OF CYCLOTRON

The diagram below is a schematic of a cyclotron. Charged particle starts out at the central point and, for a given magnetic field perpendicular to the plane of motion, follows circular path. The cyclotron takes advantage of the fact that the time for the particle to execute a half-circle is independent of the particle's velocity. An alternating voltage is applied across the gap between the two 'De es' (the semicircular regions), so that,when the particle crosses the gap, the voltage acts to accelerate it. When the particle gets to the gap again after having completed half-circle, the voltage has changed sign, and the particle is once again accelerated. The frequency of the oscillating voltage must match the cyclotron frequency. In this way, the particle is always accelerated, completing even bigger circles in the same time until the beam is extracted at maximum radius. If the magnetic field has strength 0.95e-02 T and the circulating particle is an electron, q=-e and m = 9.11e-31 kg, what is the cyclotron frequency?










 

 

 






How the cyclotron works

In the cyclotron, a high-frequency alternating voltage applied across the "D" electrodes (also called "dees") alternately attracts and repels charged particles. The particles, injected near the center of the magnetic field, accelerate only when passing through the gap between the electrodes. The perpendicular magnetic field (passing vertically through the "D" electrodes), combined with the increasing energy of the particles forces the particles to travel in a spiral path.
dees and so they are accelerated (at the typical sub-relativistic speeds used) and will increase in mass as they approach the speed of light. Either of these effects (increased velocity or increased mass) will increase the radius of the circle and so the path will be a spiral.
(The particles move in a spiral, because a current of electrons or ions, flowing perpendicular to a magnetic field, experiences a force perpendicular to its direction of motion. The charged particles move freely in a vacuum, so the particles follow a spiral path.)
The radius will increase until the particles hit a target at the perimeter of the vacuum chamber. Various materials may be used for the target, and the collisions will create secondary particles which may be guided outside of the cyclotron and into instruments for analysis. The results will enable the calculation of various properties, such as the mean spacing between atoms and the creation of various collision products. Subsequent chemical and particle analysis of the target material may give insight into nuclear transmutation of the elements used in the target.


Cyclotron radiation

 Cyclotron radiation is electromagnetic radiation emitted by moving charge d particles deflected by a magnetic field. The Lorentz force on the particles acts perpendicular to both the magnetic field lines and the particles' motion through them, creating an acceleration of charged particles.


FUNCTIONS:

Cyclotrons have a single electrical driver, which saves both money and power, since more expense may be allocated to increasing efficiency.
Cyclotrons produce a continuous stream of particles at the target, so the average power is relatively high.
The compactness of the device reduces other costs, such as its foundations, radiation shielding, and the enclosing building.


 

 













Advantages of the cyclotron:

  • Cyclotrons have a single electrical driver, which saves both money and power, since more expense may be allocated to increasing efficiency.
  • Cyclotrons produce a continuous stream of particles at the target, so the average power is relatively high.
  • The compactness of the device reduces other costs, such as its foundations, radiation shielding, and the enclosing building.





















Limitations of the cyclotron

The magnet portion of a 27" cyclotron. The gray object is the upper pole piece, routing the magnetic field in two loops through a similar part below. The white canisters held conductive coils to generate the magnetic field. The D electrodes are contained in a vacuum chamber that was inserted in the central field gap.
The spiral path of the cyclotron beam can only "sync up" with klystron-type (constant frequency) voltage sources if the accelerated particles are approximately obeying Newton's Laws of Motion. If the particles become fast enough that relativistic effects become important, the beam gets out of phase with the oscillating electric field, and cannot receive any additional acceleration. The cyclotron is therefore only capable of accelerating particles up to a few percent of the speed of light. To accommodate increased mass the magnetic field may be modified by appropriately shaping the pole pieces as in the isochronous cyclotrons, operating in a pulsed mode and changing the frequency applied to the dees as in the synchrocyclotrons, either of which is limited by the diminishing cost effectiveness of making larger machines. Cost limitations have been overcome by employing the more complex synchrotron or linear accelerator, both of which have the advantage of scalability, offering more power within an improved cost structure as the machines are made larger.

 

 



Use of the cyclotron

For several decades, cyclotrons were the best source of high-energy beams for nuclear physics experiments; several cyclotrons are still in use for this type of research.
Cyclotrons can be used to treat cancer. Ion beams from cyclotrons can be used, as in proton therapy, to penetrate the body and kill tumors by radiation damage, while minimizing damage to healthy tissue along their path.
Cyclotron beams can be used to bombard other atoms to produce short-lived positron-emitting isotopes suitable for PET imaging

There are basically two applications for the cyclotron. It's a particle accelerator, and, though it can be adapted to accelerate any charged particle, it is most frequently applied to accelerate positive charges. Protons are frequently the choice. We use the cyclotron in the physics lab, and in medicine.
In the medical area we are developing the cyclotron as a proton treatment source. More medical facilities are being set up with the cyclotron providing accelerated protons to irradiate tissue. The proton, unlike gamma rays, has a depth of penetration that can be finely tuned (by "tuning" the cyclotron) to limit damage to other tissues.
The cyclotron is also used to create radioactive materials that are used as radiation sources which can be implanted. The radioactive materials can also be used as tracers in medical work ups and in research, and also to provide "luminosity" in some imaging because of the way tissue takes up these selected materials. These mostly short-lived radionuclide's are "big business" in medical and biophysics.
In the physics laboratory, we use the cyclotron to create particle streams that we then slam into targets. This is the continuation of research to investigate the quantum mechanical world. The cyclotron can be used to "feed" another or other accelerators to get higher energies and a "bigger bang" in the world of collisions.

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