Particle accelerators and detectors -Short Answers

Question 1Particle accelerators may be used to

accelerate protons. If the energy of the accelerated protons is high enough then, when these protons collide with stationary protons, different types of particles of large mass may be produced

(a) Explain why high energies are required to produce particles of large mass

Question 1 Cont (b) The diagram shows the basic structure of a

cyclotron in which protons are accelerated

Point on the diagram above to show the(i) magnets and their polarity [1](ii)points where the alternating electric potential difference

is applied[1](c)Outline why the frequency of the alternating electric

potential difference is made equal to the frequency of orbit of the protons

Question 1 Cont The diagram shows the basic structure of a

cyclotron in which protons are accelerated

(c) Outline why the frequency of the alternating electric potential difference is made equal to the frequency of orbit of the protons

Question 1 Cont The diagram shows the basic structure of a

cyclotron in which protons are accelerated

(d)Explain the effect of the increasing energy of the protons on their frequency of orbit and state how this effect is dealt with in the cyclotron.

Question 1 Cont The diagram shows the basic structure of a cyclotron in

which protons are accelerated

(e) Protons of much higher energy than those produced in a cyclotron can be produced in a synchrotron. In a particular experiment protons leave a synchroton with energy 28 GeV. They enter a bubble chamber where some of them collide with stationary protons. Deduce that the energy available to produce other particles from these collisions is about 7 GeV.

Question 1The diagram shows the basic structure of a

cyclotron in which protons are accelerated

(f) Suggest, based on the answer to (e) and conservation of momentum, why it is better

to arrange for two protons of total energy 28 GeV, moving in opposite directions, to collide.

Question 2a)(i)Describe the operating principle of

the bubble chamber [2] (ii)Outline how two particle properties

or characteristics are measured using a bubble chamber [2]

   (b)The proportional wire spark chamber

has now replaced the bubble chamber Outline two advantages of this

detector compared to the bubble chamber [2]

Question 3

A drift tube accelerator has an alternating potential difference of 50kV, with a frequency of 10 MHz applied to a row of tubular electrodes Calculate the length of the drift tube if electrons are to arrive at the right time to be accelerated in the next gap

Question 4

• The synchrotron at Fermilab has a diameter of 20 km Estimate the magnetic flux density needed to move a proton beam of 350 GeV

•

Question 5A cyclotron is operated as an oscillator

frequency of 15 MHz and has a dee radius of 050m

 Calculate the magnetic flux density

needed to accelerate protons in the cyclotron

Determine the kinetic energy of the proton in MeV

Question 6

Calculate the strength of a magnetic field use in a cyclotron in which a deuteron makes 15 x 107 revolutions per second

Question 7

Calculate the total energy and the wavelength of a proton that has kinetic energy of 30 GeV

Question 8

A drift tube accelerator has an alternating potential difference of 30 kV, with a frequency of 15 MHz applied to a tow of tubular electrodes Calculate the lengths of the first drift tube if electrons are to arrive at the right time to be accelerated in the next gap?

Question 9 At CERN, protons are injected into a 200m Diameter 28

GeV synchrotron ring with an energy of 50 MeV The tube is filled with protons which are injected with proton current of 100 MA for 6 uS There are 14 acceleration point spaced evenly around the ring with a potential difference between the electrodes of each accelerator of 4 kV The final energy of the proton is 28 GeV. If relavistive effects are ignored:

a) Calculate the speed of the protons at injectionb) Determine the time it takes to go around the ring at

this speedc) Calculate the momentum of the proton at injectiond) Determine the number of protons that were injectede) Deduce by how much the energy of proton increases

in each revolution of the synchrotronf) Estimate the number of times a proton must go

around the accelerator to obtain its final maximum energy

Question 10An ion gun in an evacuated container consists of 2

parallel conducting plates separated by a distance of 20 cm A potential difference of 50 kV is applied across the plates Protons enter between the plates and drift with negligible speed into a region between the plates The negative plate has a small hole where protons can be ejected

(a)Calculate the electric field strength between the plates

 (b)Determine the energy of the protons that are

ejected through the hole of the negative plate

(c) Deduce that the speed of the protons ejected through the hole is approximately 31 x 10-6 ms’

 (d) Describe why the apparatus is evacuated