Particle Physics

Question 1

What force holds electrons in orbit?

Answer 1

Electrostatic force.

Question 2

How is an ion created?

Answer 2

If a particle loses or gains electrons.

Question 3

What determines whether an atom is of the same element as another?

Answer 3

If they have the same amount of protons.

Question 4

Isotope:

Answer 4

Diff. number of neutrons, same amount of protons..

Question 5

What does the mass no. show?

Answer 5

Amount of protons and neutrons/ amount of nucleons (A).

Question 6

What does the atomic number show?

Answer 6

Number of protons (bottom left number).

Question 7

Specific charge:

Answer 7

charge per unit mass.

Question 8

What is the point of the strong nuclear force?

Answer 8

Overcomes electrostatic force and holds protons together by overcoming force of repulsion within the nucleus.

Question 9

3 notes on SNF:

Answer 9

• range of 3-4fm for attraction.
• same effect between 2 protons as it does between 2 neutrons or a proton and a neutron.
• Attractive down until 0.5fm when it becomes repulsive to prevent collisions between neutrons and protons.

Question 10

Describe alpha particle structure:

Answer 10

2 protons 2 neutrons.

Question 11

Describe beta particle:

Answer 11

fast moving electrons, caused atomic number to increase by 1 as neutron changes to a proton as a result.

x –> Y + beta particle + anti-neutrino. (proton to neutron creates new element Y)

Question 12

Describe gamma waves:

Answer 12

No mass or charge and is usually emitted from high energy atoms after a beta or alpha emission.

Question 13

What speed do all EM waves travel at?

Answer 13

3 * 10^8

Question 14

Describe nature of EM waves:

Answer 14

Emitted from a charged particle when it loses energy. An electric wave and magnetic wave that move in phase and oscillate at 90 degrees to each other.

Question 15

What 2 circumstances are EM waves emitted?

Answer 15

1) Fast moving electron is stopped.
2) Electron moves from higher to lower energy level.

Question 16

Define photon:

Answer 16

A packet of EM waves - E= hf.

Question 17

Give equation for power of a beam:

Answer 17

P = nhf where n is the number of photons passing a fixed point per second.

Question 18

What happens during a PET scan?

Answer 18

Positron emitting isotope is injected into the patient and when some reaches the brain it emits positrons that annihilate electrons and release gamma photons which are detected by computers.

-2 photons released to conserve momentum.

Question 19

Describe antiparticles:

Answer 19

-same mass, opposite charge.
-if it meets its corresponding particle it annihilates and the mass is converted into energy as photons.

Question 20

Describe pair production:

Answer 20

A photon with enough energy passing by a nucleus or electron suddenly changes into a particle antiparticle pair.

Question 21

Define electron volt:

Answer 21

Energy transferred when an electron is moved through a potential difference of 1 volt.

Question 22

Equation relating rest energy of particle to photon produced in annihilation and pair production?

Answer 22

hf = rest energy.
2hf = 2*rest energy.

hf= 2 rest energy

the minimum energy must meet this requirement as if it is not at least the rest energy a photon cannot be created / cannot turn into particle antiparticle pair.

Question 23

What can be used to detect path of alpha and beta particles?

Answer 23

Cloud chamber - very cold and saturated. Particles leave visible trail of droplets.

Question 24

Exchange particle for electromagnetic force?

Answer 24

Virtual photons -virtual because we can’t detect them directly. symbol is lambda.

This only acts on charged particles.

Question 25

Why is weak nuclear force ‘weak’?

Answer 25

Must be weaker than SNF otherwise it would affect stable nuclei.

Question 26

What is the exchange particle of the WNF? How are they different to photons?

Answer 26

W boson - have a non-zero rest mass, very short range of about 0.001 fm, can have a charge.

Question 27

Describe Beta plus decay:

Answer 27

proton changes to a neutron and a beta plus particle and neutrino is released.

Question 28

Describe electron capture:

Answer 28

Proton in a proton rich nucleus changes to a neutron as a result of weak interaction with inner -shell electron.
The electron changes to a neutron.

Question 29

Why was neutrino believed to have existed?

Answer 29

To conserve energy in beta decay.

Question 30

How are particles and antiparticles created in the atmosphere and in artificial environments?

Answer 30

Cosmic rays (protons or nuclei) collide with gas atoms in the atmosphere and create particle antiparticle pairs.

Collide head on with protons in particle accelerators.

Question 31

Describe muon, pion and kaon.

Answer 31

Muon - 200 times heavier than electron (basically a heavy electron)
Pion - rest mass greater than muon but less than proton.
Kaon - Rest mass greater than pion but still less than proton.

Question 32

What is the difference between Hadrons and Leptons?

Answer 32

Hadrons can interact via strong interaction whereas Leptons do not use the strong interaction.

Hadrons tend to decay through the weak interaction apart from the proton as it is stable.

Question 33

What is the similarities and difference between Baryons and Mesons?

Answer 33

Baryons eventually all decay into protons.
Mesons do not include protons in their decay.

They both interact through strong interaction and are both composed of quarks and antiquarks.

Question 34

What do leptons and antileptons produce when they interact?

Answer 34

Hadrons.

Question 35

Difference between muon neutrino and electron neutrino?

Answer 35

Muon neutrinos are produced from muon decay - when they interact with baryons they produce only muons.
Electron neutrinos create electrons in baryon interactions.

Question 36

2 Lepton rules:

Answer 36

1) When a neutrino interacts with a hadron, it produces a charged lepton
2)In muon decay, it changes into a muon neutrino and an electron is created to conserve charge.

Question 37

What do strange particles decay through?

Answer 37

Weak force. They are created in twos. Strangeness can be changed by plus or minus 1.

Although, strangeness is only conserved in the strong interaction.

Question 38

Describe quarks for mesons and baryons:

Answer 38

Mesons are quark antiquark pair.
Baryons are three quarks or three antiquarks - sigma particle is only strange baryon.

Question 39

What happens to the quarks in beta minus decay?

Answer 39

An down quark changes to an up quark to create a proton from a neutron.