7.5 Cyclotron

Question 1

A cyclotron is a type of what??

Answer 1

A particle accelerator

Question 2

What is a particle accelerator?

Answer 2

A device that accelerate charged particles and direct them using electric and magnetic fields.

Question 3

The set up of the cyclotron must be in what?

Answer 3

A vacuum

Question 4

What is required to set up a cyclotron?

Answer 4

2 electrode, alternating pd supply, magnetic field perpendicular to plates/electrodes

Question 5

What is the equation for the frequency of charged particles circling in a magnetic field?

Answer 5

2(pi)f = Bq/m

Question 6

What is special about the electrodes/plates?

Answer 6

They’re hollow to allow charged particle entrance

Question 7

How does a cyclotron work?

Answer 7

• Charged particles are emitted and accelerated towards the oppositely charged electrode/plate
• The electrodes are charged due to supplied alternating pd,this means that an electric field is created accelerating a charged particle towards oppositely charged plate.
• The charged particle enters the electrode and by the means of the magnetic field it makes a semi circle to return to the gap
• Being in the gap requires pd to be alternated so that the charged particle can be attracted towards the opposite plate and thus accelerated by the electric field
• Momentum of the charged particle will be greater so that the radius of the semi circle to return will be greater . After doing the 180 degrees the charged particle will leave
• This is constant until the radius of the path is great enough to leave on of the electrodes through a gap

Question 8

What must the frequency of pd be in a cyclotron? And why

This is in terms of frequency of revolutions of charged particle

Answer 8

Since the charged particles only describe half a revolution before pd needs to be alternated. So it means the pd must be alternated every 18p degrees. This means the frequency of pd must be twice the frequency of revolution of charged particles.

Question 9

What is the magnitude of energy gained when accelerated through the electric field (gap)

Answer 9

Full of between the plates

Question 10

What charge must be the particles used in a cyclotron?

Example

Answer 10

Positive charge

E.g.protons

Question 11

Why do many cyclotrons have a limit to accelerating particles?

Answer 11

As the accelerating only lasts while mass is constant

Question 12

Why is this a problem?

Answer 12

The momentum would change so the synchronism with frequency will change

Question 13

What was made to overcome this problem?

Answer 13

Synchro-cyclotrons

Question 14

How do synchro-cyclotrons work to overcome change in mass?

Answer 14

The frequency of pd is lowered in such a manner as to keep accelerating charged particles as their mass increases

Question 15

Why cannot electrons be used in a cyclotron?

Answer 15

As their mass is too small, hence they will change mass too quickly and so the alternating pd wont be able to be synchronised. This means electrons would slow down defeating the effect

Question 16

Why wouldn’t neutrons work in a cyclotron?

Answer 16

They wouldn’t accelerate in the electric field

Question 17

Example of where a cyclotron is used in the real world

Answer 17

Proton beam therapy

Question 18

Why are charged particles accelerated in a cyclotron?

Answer 18

To reach the electrode/plate of opposite charge

Question 19

Why did charged particles return to the gap after entering the electrode.

Answer 19

Lack of electric field means it is moving at constant velocity. The velocity is said to be the second finger (the direction of movement of particle )and it is always at 90 to magnetic field. So this means the force will always be towards the middle, hence the particle will move in a circle, accelerating constantly making a U turn.

Question 20

Why does the momentum increase?

Answer 20

Greater acceleration between plates each time they meet the gap means momentum is greater

Question 21

How is an electron volt energy?

Answer 21

E = QV and Ek = 1/2 mv^2

QV = 1/2mv^2

eV = 1/2mv^2

When e = charge of electrons

Question 22

How can we work out energy of electron when we have the charge and pd ?

Answer 22

Pd x Charge

V×e

Question 23

What is an electron volt?

Answer 23

The amount of energy an electron will gain when accelerated through a pd of 1 V

Question 24

Charge of electron?

Answer 24

1.6x 10^-19

Question 25

When calculating the frequency of the pd that is synchronized with charged particle arrival what do we need to do?

Answer 25

2(pi)f = BQ/m

Then multiply frequency by 2

Question 26

How to work out the amount of circles a charged particle will make in order to reach x energy?

Answer 26

At the crossing the charge particle gains an energy equal to pd between. We work out energy gained per revolution (pd x 2 ) and do x/by it to get circles.