Chapter 6.4 - Nuclear and Particle Physics

Question 1

Alpha particle scattering experiment and what it proved

Answer 1

A stream of alpha particles were emitted at a piece of gold foil. Most of the particles went straight through, but some were reflected back. This meant that matter must be mostly empty space with small, dense positively charged pockets (the nucleus)

Question 2

fm

Answer 2

femtometer - 10^-15m

Question 3

Standard notation for an atom

Answer 3

^A_ZX

Where

A is mass number

Z is proton number

Question 4

Radius of a nucleus

Answer 4

R = r₀A^1/3

where

r₀ is a constant

A is the mass number

Question 5

Value of r₀

Answer 5

1.4 fm

Question 6

Strong nuclear force

Answer 6

The force that holds the nucleus together against the repulsion of the electrostatic repulsion

Question 7

How the strong force varies with distance

Answer 7

Repulsive < 0.5 fm

Attractive enough to overcome electrostatic repulsion at < 3 fm

Question 8

Hadron

Answer 8

Particles that feel the strong nuclear force (made of quarks)

Question 9

What is the only stable hadron

Answer 9

Proton

Question 10

Lepton

Answer 10

Fundamental particles that don’t feel the strong force but do feel the weak nuclear force

Question 11

Examples of hadrons (2)

Answer 11

proton, neutron

Question 12

Examples of leptons (2)

Answer 12

Electron, neutrino

Question 13

Antiparticle and its properties

Answer 13

Every particle has an antiparticle with the same properties, except it will have the opposite charge

Question 14

Pair production

Answer 14

When energy is transformed into a particle and an antiparticle

Question 15

How a gamma ray might create antimatter

Answer 15

A high energy photon can turn into a electron and a positron via pair production. The energy of the photon (hf) is transformed into the mass of the two produced particles (leftover energy is put to their kinetic energy)

Question 16

Annihilation

Answer 16

When a particle meets its antiparticle the mass of both is converted into energy in the form of two photons

Question 17

Quark

Answer 17

The building block of hadrons

Question 18

Quark composition of a proton

Answer 18

uud

Question 19

Quark composition of a neutron

Answer 19

udd

Question 20

up quark charge

Answer 20

+2/3

Question 21

down quark charge

Answer 21

-1/3

Question 22

strange quark charge

Answer 22

-1/3

Question 23

β^- decay

Answer 23

Occurs in a neutron rich atom. Neutron decays to a proton, electron and antineutrino. (d –> u)

Question 24

β⁺ decay

Answer 24

Occurs in a proton rich atom. Proton changes into a neutron and emits a positron and a neutrino, (u–>d)

Question 25

Radioactive decay

Answer 25

When a nucleus stabilises by releasing particles/energy in various forms

Question 26

Properties of radioactive decay

Answer 26

It is spontaneous and random

Question 27

What is meant by spontaneous and random

Answer 27

There is no way to know when a nucleus will decay. It can't be predicted

Question 28

Alpha radiation

Answer 28

A helium nucleus

Question 29

β radiation

Answer 29

An electron

Question 30

γ radiation

Answer 30

A gamma ray

Question 31

ν (nu)

Answer 31

Symbol for neutrino

Question 32

Range of β⁺ radiation

Answer 32

Effectively 0 since it will almost instantly be annihilated by an electron

Question 33

How to investigate radioactivity

Answer 33

Place a material between a radioactive source and a geiger-muller tube and record the count rate over a period of time. Repeat with different materials

Question 34

where α emmision occurs

Answer 34

Heavy nuclei

Question 35

when γ radiation is emitted

Answer 35

When a nucleus has too much energy (often after alpha or beta decay)

Question 36

Activity

Answer 36

The number of nuclei that decay each second

Question 37

Decay constant

Answer 37

The rate at which a material will decay

Question 38

Equation for activity

Answer 38

decay constant \* undecayed nuclei

Question 39

Half life

Answer 39

The average time taken for half of the undecayed nuclei to decay

Question 40

Experiment to determine half life of an isotope

Answer 40

Calculate the background radiation rate first using a geiger-muller counter. Fill a bottle with uraniuam salt and protactinium-234. Shake the bottle so they mix and then wait for them to seperate again. Once they have seperated take measurements by measuring the count for 10 seconds. Repeat this measurement every say 30 seconds. Plot a graph and determine half life from it

Question 41

Equations for half life, nuclei and activity

Answer 41

Just use common sense exponential maths

Question 42

How carbon dating works

Answer 42

Living things take in carbon-14 from the atmosphere and all living things will have the same ratio of carbon-12 to carbon-14. When something dies the carbon-14 decays and is not replenished so the ratio will start to decrease. Therefore how long ago something died (e.g. paper from wood) can be determined. The half life of carbon-14 is about 6000 years so it is not suitable for very long ago (e.g. dinosaurs like if u wanted to know when a stegosaurous died or something like that maybe a pterodactyl idk)

Question 43

Mass defect

Answer 43

The difference in mass between a nucleus and the sum of the masses of all its protons and neutrons if they were seperated

Question 44

Binding energy

Answer 44

Equals the mass defect (E=mc²)

Question 45

Graph of binding energy per nucleon against nucleon numbner

Answer 45

Goes up steeply then peaks and slowly decreases. Peaks at Iron

Question 46

How to calculate energy released from a fission/fusion reaction

Answer 46

It is equal to the change in binding energy

Question 47

How fission reactors work

Answer 47

Rods of uranium rich in ²³⁵U undergo nuclear fission, producing energy and emitting high energy neutrons. These neutrons go on to collide with other uranium atoms causing them to undergo fission and so on, in a chain reaction. The emitted neutrons are travelling to fast to cause fission so they are slowed down by a moderator such as water. To make sure that the chain reaction remains steady and does not get out of control, control rods made of boron are lowered into the case. These absorb some of the neutrons so that there are not enough to cause the reaction to get out of control. The heat from the reaction is then used to heat water and make steam, which powers a turbine and then a generator

Question 48

Environmental impact of nuclear waste

Answer 48

Radioactive waste can take a long time to decay to safe levels Natural distasters pose a risk to nuclear plants (e.g. Fukishima)

Question 49

How nuclear fusion reactions work

Answer 49

Light nuclei under very high temperatures (much higher than in fission) combine and form a heavier nucleus and release lots of energy