Nuclear and Particle Physics

Question 1

What is a Lepton?

Answer 1

Leptons are fundamental particles, that cannot be broken down into smaller constituents. They only experience the weak nuclear force. Examples: electron, muon, tau.

Question 2

Define a Hadron

Answer 2

Hadrons are particles made up of quarks. They are split into a further subcategory of baryons and mesons.

Question 3

What is a Baryon? Give examples

Answer 3

A baryon consists of three quarks. Examples: proton - uud and neuton - udd.

Question 4

What is a Meson? Give examples

Answer 4

A meson consists of a quark and antiquark. Examples: pion and kaon.

Question 5

Suggest why it took a long time to find experimental evidence for the top quark

Answer 5

• Top quark is very heavy.
• Large amount of energy required
• Availability of antimatter is poor
• Difficulty of storing antimatter

Question 6

What is Thompsons Plum Pudding model?

Answer 6

Electrons in a sea of positive charge.

Question 7

Explain what happened to the particles in the alpha particle scattering?

Answer 7

Most particles went straight through. Some deflected at a large angle. Few repelled back towards the source.

Question 8

What were the conclusions of Alpha Particle scattering?

Answer 8

Most of the atom in empty space. The nucleus has a positive charge. Most of the mass in concentrated in the nucleus.

Question 9

What happens to electrons in an electric field?

Answer 9

They are accelerated by the field, moving in the positive direction. KE they gain depends on the p.d they move through. KE = qV

Question 10

How is a cathode ray produced?

Answer 10

Thermionic emission.

Question 11

How does a linear accelerator work?

Answer 11

• Electrons move in a straight line as electrode is equally attractive in all directions.
• Alternating voltage changes as the electron exits tube, repelling it and it is attracted to positive potential.
• Speed increases so tubes get progressively longer.
• Alternating voltage has uniform frequency.

Question 12

Theory of relativity.

Answer 12

The apparent mass increase becomes significant at speeds approaching light speeds - relativistic speeds.

Question 13

What does a cyclotron require?

Answer 13

Magnetic field, so charged particles will feel a centripetal force. Electric field so polarity of D can be switched to accelerate particles.

Question 14

Derive an equation for cyclotron frequency.

Answer 14

f=1/T T=2πr/v v = ωr
r=mv/Bq
T = 2πmv/Bqv
f=Bq/2πm

Question 15

What is a synchrotron?

Answer 15

A machine that accelerates charged particles around a fixed circular path.

Question 16

How does a synchrotron keep a fixed circular path?

Answer 16

Increasing the magnetic field strength in line with the momentum. r=mv/Bq

Question 17

How do quarks interact?

Answer 17

Strong nuclear force.

Question 18

each quark has a baryon number of

Answer 18

+1/3

Question 19

Mesons have

Answer 19

a quark and antiquark, so have a baryon number of zero

Question 20

Strange quarks have a strangeness of

Answer 20

-1