Chapter 24 - Particle Physics

Question 1

Alpha scattering experiment

Answer 1

• A narrow beam of photons (with the same Ek were fired at a thin sheet of gold foil)
• The alpha particles were scattered and detected on a zinc sulfide screen mounted on the end of a microscope
• Each alpha particle created a tiny speck of light so they counted the amount of particles scattered through different angles per minute

Question 2

Alpha scattering experiment observations

Answer 2

If the plum pudding model were correct all of the alpha particles would have passed straight through

• Around 1 in every 2000 particles were scattered
• Around 1 in every 10000 was deflected at an angle >90

Question 3

Alpha scattering experiment findings

Answer 3

Most of the atom was empty space (most passed through)
The atom had a concentration of mass (some deflected at angles >90)
The atom had a concentration of positive charge (some deflected)
The nucleus must have a size of around 10^-14 m

Question 4

Charge of a nucleus formula

Answer 4

Q = +/- Ze

where Z is the atomic number

Question 5

Why were alpha particles scattered

Answer 5

Because of the electrostatic repulsion with the electric field of the nucleus, they wouldn’t actually hit the nucleus

Question 6

Kinetic energy formula from the alpha scattering experiment

Answer 6

Ek = Qq/4πε0d

where Q, q are the two charges and d the distance to the nucleus

Question 7

Size of a nucleus

Answer 7

Around 10^-15 m

Question 8

Size of an atom

Answer 8

Around 10^-10m

Question 9

Isotopes

Answer 9

Nuclei of the same element that have the same amount of protons but a different amount of neutrons

Question 10

Atomic labelling system

Answer 10

A
X
Z

where A is the nucleon number (protons + neutrons) and P is the proton number

Question 11

Atomic mass unit (u) definition

Answer 11

One twelfth of the mass of a neutral carbon-12 atom

Question 12

Atomic mass unit (u)

Answer 12

(1.661 x 10^-27)kg

Protons and neutrons can be treated as having a mass of 1 u and electrons 0

Question 13

Radius of a nucleus formula

Answer 13

R = r0 A^1/3

where r0 is the minimum radius of a nucleus and A the nucleon number

Question 14

r0

Answer 14

around 1.2 x 10^-15

Question 15

Finding density of a nucleus

Answer 15

Mass is nucleon number x u
Volume is 4/3 π r^3
ρ = m/V

Question 16

Antimatter

Answer 16

Every particle has a corresponding antiparticle that will completely annihilate each other if they meet, converting the two masses to photons
Have the same mass and opposite charge of the particle
Generally shown by the particle’s symbol with a bar above

Question 17

Strong nuclear force

Answer 17

Experienced by nucleons, range around 10^-15m

Repulsive over a short distance, attractive a larger one

Question 18

Electromagnetic force

Answer 18

Experienced by static and moving charged particles, relative strength 10^-3 compared to strong nuclear, infinite range

Question 19

Weak nuclear force

Answer 19

Responsible for beta decay, relative strength 10^-6 compared to strong nuclear, range around 10^-18m

Question 20

Gravitational force

Answer 20

Experienced by all particles with mass, relative strength 10^-40 compared with strong nuclear, infinite range

Question 21

Fundamental particles

Answer 21

Have no internal structure and can’t be broken down further

Question 22

Fundamental quarks

Answer 22

up. down, top, bottom, charm, strange

Question 23

Fundamental non-quark particles

Answer 23

electron, muon, tau and their anti-particles

Question 24

Hadrons

Answer 24

Particles and anti-particles that are affected by the strong nuclear force.

Can also decay by the weak nuclear force and are affected by the EM force if charged

e.g. protons, neutrons, mesons

Question 25

Leptons

Answer 25

Particles and antiparticles that are not affected by the strong nuclear force. Experience the EM force if charged

e.g. electron, tau, muon

Question 26

Up quark

Answer 26

u, charge +2/3 e

Question 27

Down quark

Answer 27

d, charge -1/3 e

Question 28

Strange quark

Answer 28

s, charge -1/3 e

Question 29

Proton quarks

Answer 29

uud

Question 30

Neutron quarks

Answer 30

udd

Question 31

Baryons

Answer 31

Hadrons made up of three quarks

Question 32

Mesons

Answer 32

Hadrons made of a quark and an anti-quark

Question 33

Neutrino

Answer 33

No charge, mass less than a millionths that of an electron
Up to 100 million per cubic metre
Electron, tau, muon neutrinos and anti-neutrinos
Symbol nu and the other symbol in subscript

Question 34

Beta minus decay

Answer 34

Neutron -> proton + electron + electron anti-neutrino

1 1 0 -
0 n –> 1 p + -1 e + νe

Question 35

Beta plus decay

Answer 35

Proton -> neutron + positron + electron neutrino

1 1 0
1 p –> 0 n + +1 e + νe

Question 36

Beta minus quarks

Answer 36

0 -

d –> u + -1 e + νe

Question 37

Beta plus quarks

Answer 37

0 -

u –> d + +1 e + νe

Question 38

What is conserved in beta decay?

Answer 38

Charge, nucleon number, proton number

Question 39

Strong nuclear force attractive and repulsive distances

Answer 39

< 3fm - attractive

< 0.5fm - repulsive