6.4 Nuclear & Particle Physics

Question 1

what was the alpha particle scattering experiment?

Answer 1

Ernest Rutherford fired a beam of fast moving alpha particles at a thing gold foil to see how the alpha particles were deflected, the detector was a zinc sulphide screen that would produce a faint flash of light whenever an alpha particle hit it

Question 2

what were the deductions from the alpha particle scattering experiment?

Answer 2

• the vast majority of the mass of the atom is contained within a small volume called the nucleus
• the nucleus has a positive charge
• the nuclear distance is considerably smaller than the diameter of the atom, meaning that the atom is mostly empty space

Question 3

what was the evidence in the experiment that showed there was a very dense nucleus?

Answer 3

most of the mass must be in the nucleus since he fast alpha particles (with high momentum) are deflected by the nucleus

Question 4

what was the evidence in the experiment that showed the nucleus was positive?

Answer 4

some of the alpha particles were deflected through large angles, so the centre of the atom must have a large, positive charge to repel them, Rutherford named this the nucleus

Question 5

what was the evidence in the experiment that showed that the atom is mostly made up of empty space?

Answer 5

most of the fast, charged alpha particles went straight through the foil, so the atom is mainly empty space

Question 6

what is the charge and mass of a proton (in terms of e for charge and u for mass)?

Answer 6

+1 charge

mass = 1

Question 7

what is the charge and mass of a neutron (in terms of e for charge and u for mass)?

Answer 7

0 charge

mass = 1

Question 8

what is the charge and mass of a electron (in terms of e for charge and u for mass)?

Answer 8

-1 charge

mass = 1 / 1840 (negligible)

Question 9

what is the defintion of nucleon number?

Answer 9

no. of protons and neutrons inside the nucleus (also known as the mass number)

Question 10

what are isotopes?

Answer 10

isotopes contain the same no. of protons and electrons but different no. of neutrons

Question 11

what is mass number equal to?

Answer 11

no. of protons and neutrons

Question 12

what is atomic number equal to?

Answer 12

just no. of protons

Question 13

what is the strong nuclear force?

Answer 13

the strong nuclear force acts between nucleons and holds the nucleus together against the electrostatic attraction repulsion of the protons

Question 14

is the strong nuclear force attractive or repulsive?

Answer 14

(trick question) it is BOTH, it is attractive to about 3 x 10^-15 and 0.5 x 10^-15m, it is a repulsive force between nucleons for distances of separation up to around 0.5x10^-15m, it is a SHORT RANGE force - it doesn’t act over large distances

Question 15

how much bigger is the diameter of the whole atom compared to the diameter of the nucleus?

Answer 15

roughly 10,000 times greater

Question 16

what is the relationship between the radius of a nucleus and the nucleon number?

Answer 16

R (radius) is proportional to the cube root of the nucleon number A, comes from the equation R = RoA^1/3

Question 17

what will a graph of radius of nucleus against nucleon number look like (think about the relationship)?

Answer 17

exponential, starts steep then decreasing gradient until it plateaus

Question 18

what will a graph of radius of nucleus against cube root of nucleon number look like (think about the relationship)?

Answer 18

constant gradient, straight line upwards

Question 19

what is the equation that links radius of a nucleus to nucleon number?

Answer 19

R = Ro x A^1/3
where Ro = a constant (1.4 x 10^-15)
R = nuclear radius
A = nucleon number

Question 20

what is greater atomic density or nuclear density?

Answer 20

nuclear density is much greater than atomic density

Question 21

what are the two equations needed to calculate nuclear density? to get to ρ = 3Mn / (4πro^3)?

Answer 21

ρ = m / v
and assuming v = 4/3πr^3, subbing in R^3 = Ro^3A from R = Ro x A^1/3 gets you to a simplified formula to work out the mean density of the nucleus: ρ = 3Mn / (4πro^3)

Question 22

what are fundamental particles?

Answer 22

fundamental particles are particles that cannot be broken down into smaller components (e.g electrons, quarks)

Question 23

what are hadrons?

Answer 23

hadrons are particles consisting of a combination of quarks to give a net zero or whole number change, neutrons and protons are hadrons - hadrons are particles that feel the strong force and weak force e.g protons and neutrons

Question 24

what are leptons?

Answer 24

lepton are fundamental particles, electrons and neutrinos are leptons - leptons are particles that feel the weak force and not the strong force, e.g electrons and neutrinos

Question 25

what are quarks?

Answer 25

quarks are components of hadrons and have a fractional electric charge, to date, they are believed to be fundamental particles, there are different types of quark, for example, up, down and strange quarks

Question 26

what are neutrinos?

Answer 26

a neutrino is a fundamental particle (lepton) with almost no mass and zero charge, each neutrino has an antimatter partner called an antineutrino

Question 27

what is the weak nuclear force?

Answer 27

the weak nuclear force is felt by both quarks and leptons, it can change quarks from one type to another or leptons from one type to another or leptons from one type to another and is responsible for beta decay

Question 28

what is an antiparticle?

Answer 28

an antiparticle is a particle of antimatter that has the same rest mass (mass at zero speed) but, if charged, the equal and opposite charge to its corresponding particle, for example the positron (e+) is the antiparticle of the electron (e-) - every known particle has its own ‘opposite particle’ of antimatter particle called an antiparticle

Question 29

what are the two classifications of particles?

Answer 29

hadrons and leptons

Question 30

are hadrons fundamental?

Answer 30

no - they can be broken down into quarks

Question 31

what quarks are in a proton?

Answer 31

uud - two up and one down making the charge +1, 2/3 +2/3 - 1/3 = 1

Question 32

what quarks are in a neutron?

Answer 32

udd, one up and two down making the charge 0, 2/3 - 1/3 - 1/3 = 0

Question 33

what charge does an up quark have?

Answer 33

+2/3

Question 34

what charge does a down quark have?

Answer 34

-1/3

Question 35

what does each lepton also have?

Answer 35

a neutrino which is also fundamental particle, and which is produced in beta decay

Question 36

what is special about neutrinos?

Answer 36

they have ZERO MASS and ZERO CHARGE

Question 37

what is the Baryon number of quarks?

Answer 37

1/3

Question 38

what does the squiggly line above a particle denote?

Answer 38

an antiparticle

Question 39

what is the charge and name of a proton’s antiparticle?

Answer 39

antiproton, charge = -1

Question 40

what is the charge and name of a neutron’s antiparticle?

Answer 40

antineutron, charge = 0

Question 41

what is the charge and name of an electron’s antiparticle?

Answer 41

positron, charge = +1

Question 42

what is the charge and name of a neutrino’s antiparticle?

Answer 42

antineutrino, charge = 0

Question 43

what is radioactive decay?

Answer 43

radioactive decay is the spontaneous and random decay of an unstable nucleus into a more stable nucleus by the emission of an α, β or γ radiation

Question 44

what is the nature, mass, charge and symbol of an alpha particle?

Answer 44

• helium atom, made up of 2 protons and 2 neutrons
• mass = 4u
• charge = +2e
• symbol = α

Question 45

what is the nature, mass, charge and symbol of a beta-minus particle?

Answer 45

• electron
• mass = 1/1840 (negligible)
• charge = -e
• symbol = β-

Question 46

what is the nature, mass, charge and symbol of a beta-plus particle?

Answer 46

• positron
• mass = 1/1840 (negligible)
• charge = +e
• symbol = β+

Question 47

what is the nature, mass, charge and symbol of a gamma ray?

Answer 47

• high freq. electromagnetic radiation
• mass = zero
• charge = zero
• symbol = γ

Question 48

what happens in beta minus decay in terms of numbers of protons and neutrons?

Answer 48

a neutron is converted to a proton which produces an electron and an electron anti-neutrino

Question 49

what happens in beta plus decay in terms of numbers of protons and neutrons?

Answer 49

a proton is converted to a neutron which produces a positron and an electron neutrino

Question 50

which radiation is the most penetrating out of alpha, beta and gamma?

Answer 50

gamma, beta then alpha

Question 51

which radiation is the most ionising out of alpha, beta and gamma?

Answer 51

alpha, beta then gamma

Question 52

what is beta minus decay?

Answer 52

in beta minus decay a neutron in the nucleus breaks down into a proton under the influence of the weak nuclear force, and a beta minus particle (an electron) and an electron anti-neutrino are emitted

Question 53

what is beta plus decay?

Answer 53

in beta plus decay a proton in the nucleus breaks down into a neutron under the influence of the weak nuclear force, and a beta plus particle (a positron) and an electron neutrino are emitted

Question 54

what is the quark change when a nuclei undergoes beta minus decay?

Answer 54

udd changes into uud

neutron into proton

Question 55

what is the quark change when a nuclei undergoes beta plus decay?

Answer 55

uud changes into udd

proton into neutron

Question 56

what is the equation in terms of the quark model for beta minus decay?

Answer 56

d —> u + e + ̅ν

Question 57

what is the equation in terms of the quark model for beta plus decay?

Answer 57

u —> d + e + v

Question 58

what are the names of the nuclei after it has undergone alpha decay?

Answer 58

daughter nuclei from parent nuclei

Question 59

can you get pure gamma decay?

Answer 59

no - gamma radiation frequently accompanies either α or β decay, but never occurs as purely a gamma decay

Question 60

what happens to the rate of activity of a radioactive sample over time (the rate at which unstable nuclei decay)?

Answer 60

the rate decreases over time because there are fewer unstable nuclei

Question 61

what is the equation that links activity to no. of undecayed nuclei?

Answer 61

A = λN
where A = activity
λ = decay constant
N = no. of undecayed nuclei

Question 62

what is activity in terms of a radioactive source?

Answer 62

activity, A, is the number of nuclear decays (the number of gamma rays emitted) per unit time, an activity of one decay per second is called one becquerel Bq

Question 63

what is the decay constant?

Answer 63

λ, the decay constant is the probability that an individual nucleus will decay per unit time, given by λ = A / N and has units (s^-1)

Question 64

what is the definition for half life?

Answer 64

the half-life (t1/2) is defined as the mean time taken for the activity of a source, or the no. of undecayed nuclei present, to halve

Question 65

what is the equation for the half life of an isotope?

Answer 65

t1/2 = ln(2) / λ

Question 66

what are the two exponential equations, one for activity and no. of undecayed nuclei?

Answer 66

A = Ao x e^-λt
N = No x e^-λt
where A = activity, Ao = initial activity
N = no. of undecayed nuclei, No = initial no. of undecayed nuclei, λ = decay constant, t = time spent decaying

Question 67

outline an experiment to investigate the absorption of α-particles, β and γ radiation

Answer 67

• you can investigate the penetrating power of alpha, beta and gamma radiation using a Geiger-Muller tube and counter to detect the radiation passing through sheets of different materials placed between the tube and the radioactive source
• the background radiation count rate (the number of ionising events detected per second or per minute when no radioactive source is nearby) must be first measured and then subtracted from all recorded count rates. Use paper and aluminium foils and pieces of lead of different thickness to investigate what thickness of each material stops each type of radiation

Question 68

how does carbon dating work?

Answer 68

the ratio of carbon 14 to non-radioactive carbon 12 in dead organic matter decreases with time, so the ratio of activity of no. of carbon-14 nuclei in a dead organic sample compared to a living sample can be used for dating

Question 69

what are the two limitations of carbon dating?

Answer 69

• Because the quantity of carbon-14 is very small count rates are correspondingly small and after a few half lives may be indistinguishable from the background count rate
• the ratio of carbon-14 to carbon-12 in the air and in all living things is assumed to be constant, that is there has been no variation over time, this may not be true if there has been changes in the rate at which carbon-14 is produced in the atmosphere

Question 70

what is Einstein’s mass energy equation?

Answer 70

E = mc^2

Question 71

what is annihilation?

Answer 71

annihilation is the process in which a particle and its antiparticle interact and their combined mass is converted to energy via E = mc^2 (photons are released)

Question 72

what is pair production?

Answer 72

pair production is the process of creating a particle-antiparticle pair from a high-energy photon (like from annihilation)

Question 73

what has greater mass, the total mass of the separated nucleons or the total mass of the nucleons?

Answer 73

total mass of the separated nucleons has MORE ENERGY than the total mass of the nucleons

Question 74

why is there a difference between the mass of the separate nucleons and the mass of the whole nucleus?

Answer 74

this arises from the fact that all the nucleons are bound together by the strong nuclear force, this means work has to be done to separate the nucleons, so the separated nucleons gain potential energy and by Einstein’s mass-energy equation they then have more mass

Question 75

in radioactive decay, how is energy released? in what form?

Answer 75

energy is released in the form of the kinetic energy of the fast moving alpha or beta particles, and may also be released as gamma ray photons

Question 76

what is the origin of the energy released in radioactive decay?

Answer 76

the origin of this energy is the conversion of some of the masses of the particles involved into energy

Question 77

what is the opposite of pair production?

Answer 77

annihilation (and vice versa)

Question 78

what can the instability of a nucleus be caused by?

Answer 78

• too many neutrons
• too few neutrons
• too much energy in the nucleus
• too many nucleons in total (too heavy)

Question 79

can you ever get a free quark on its own?

Answer 79

no - you cannot get a free quark on its own, you cannot separate quarks, if you tried to the energy put in would just get converted into more quarks and antiquarks, you just get pair production

Question 80

when energy is converted to mass what is the ratio between matter and antimatter produced?

Answer 80

equal amounts of matter and antimatter

Question 81

outline an experiment to determine the half-life of an isotope such a protactinium

Answer 81

(see page 215 for diagram or page 74 in revision guide)

• use a protactinium generator, a bottle containing a uranium salt, the decay products of uranium (including protactinium-234) and two solvents, which separate out into layers
• shake the bottle to mix the solvent together
• wait for the liquids to separate, the protactinium-234 will be in solution in the top layer, and the uranium salt will stay in the bottom layer, then you can put the Geiger-Muller tube at the top layer to measure the activity of the protactinium-234
• as soon as the liquids separate, record the count rate (how many counts in 10 secs), re-measure the count rate at sensible intervals (e.g every 30 seconds)
• once you’ve collected your data, leave the bottle to stand for at least ten mins, then take the count rate again, this is the background count rate corresponding to background radiation (you could also do this at the beginning of the experiment, before shaking the bottle)
• subtract this value from your measured count rates, then plot a graph of count rate against time, it should look like an exponential downwards on decreasing gradient, you can use your graph to work out the half-life by looking at how long it takes for the count rate (or activity) to halve

Question 82

what does alpha decay occur in?

Answer 82

very heavy nuclei like uranium and radium, the nuclei of these atoms are too massive to be stable

Question 83

what doe beta minus decay occur in?

Answer 83

neutron-rich nuclei, where they have many more neutrons than protons in their nucleus

Question 84

how can you calculate the binding energy per nucleon?

Answer 84

binding energy / nucleon number

Question 85

what is the mass defect?

Answer 85

the difference in mass between the mass of a nucleus and the total mass of its separate nucleons (extra mass)

Question 86

what is the mass defect in a decay reaction equal to?

Answer 86

this extra mass (mass defect) is equivalent to the binding energy of a nucleus and is released as energy

Question 87

what is the definition of binding energy?

Answer 87

binding energy of a nucleus is the minimum energy required to separate the nucleus (protons and neutrons) into its constituent parts

Question 88

what does the graph of binding energy per nucleon against nucleon number look like? what does it mean?

Answer 88

you get a curve, a high binding energy per nucleon means more energy is needed to remove nucleus from the nucleus so in other words the most stable nuclei occur around the maximum point on the graph at around iron (Fe 56)

Question 89

what does fusion do in terms of binding energy per nucleon?

Answer 89

increases the binding energy per nucleon which means lots of energy is released during fusion

Question 90

what does fission do in terms of binding energy per nucleon?

Answer 90

fission is when large nuclei split in two, the nucleon numbers of the two new nuclei are smaller than the original nucleus , which means there is an increase in the binding energy per nucleon, so energy is also released during nuclear fission but much more is produced in fusion

Question 91

what is alpha absorbed by?

Answer 91

absorbed by paper of a few cm of air

Question 92

what is beta-minus absorbed by?

Answer 92

absorbed by 3mm of aluminium

Question 93

what is beta-plus absorbed by?

Answer 93

annihilated by electron - so virtually no range

Question 94

what is gamma absorbed by?

Answer 94

absorbed by many cm of lead, or several m of concrete

Question 95

when balancing decay equations, what must be conserved?

Answer 95

charge and nucleon number

Question 96

gamma radiation is emitted from what type of nuclei?

Answer 96

a nuclei with an excess of energy, an ‘excited’ nuclei

Question 97

what can the binding energy per nucleon graph be used to estimate?

Answer 97

the energy released from nuclear reactions

Question 98

what is induced nuclear fission?

Answer 98

induced nuclear fission occurs when a nucleus absorbs slow-moving neutrons and the resulting unstable nucleus undergoes a fission reaction to split into two smaller nuclei and a small number of neutrons, releasing energy

Question 99

what is a chain reaction?

Answer 99

a chain reaction is the sequence of nuclear reactions produced when an induced nuclear fission reaction triggers more than one further fission reaction

Question 100

what is a control rod?

Answer 100

a control rod is a rod that can be lowered up and down into the core of a nuclear reactor, absorb neutrons and slow down the chain reaction, they are usually made of boron (to control rate of fission)

Question 101

what is a moderator?

Answer 101

a moderator is a substance used in nuclear reactor which slows down neutrons so that they have a greater change of being absorbed by the fissile nuclear fuel (aids reaction), they are usually made of graphite but can be water too

Question 102

what does the word fission actually mean?

Answer 102

splitting up or breaking into parts/components

Question 103

what does the diagram look like for a fission reactor?

Answer 103

see page 221 textbook

Question 104

what are the three types of nuclear waste?

Answer 104

high level, intermediate level

Question 105

what are the three types of nuclear waste?

Answer 105

high level, intermediate level, low level

Question 106

what is high level nuclear waste?

Answer 106

produces large amounts of radiation, includes fuel rods removed from the core and waste resulting from the reprocessing of this fuel

Question 107

what is intermediate level nuclear waste?

Answer 107

intermediate level nuclear waste is material which has become radioactive because it has been in a nuclear reactor, for example the reactor’s metal cladding

Question 108

what is low level nuclear waste?

Answer 108

low level waste nuclear waste include items which are only slightly radioactive due to becoming contaminated with small amounts of radioactivity, such as cleaning materials and protective clothing

Question 109

why does high level nuclear waste need shielding?

Answer 109

high level waste produces heat as a result of the rapid decay of some of the short lived isotopes, so it needs cooling for a few years, as well as shielding to block radioactive emissions over many thousands of years while the longer half-life isotopes decay

Question 110

what are two main advantages of nuclear fusion?

Answer 110

• no radioactive waste products are formed by the fusion process (unlike with fission)
• there is a virtually unlimited supply of the raw materials, about 1% of seawater molecules have a deuterium atom in them (deuterium and tritium are the two isotopes used in fusion)

Question 111

what is nuclear fusion?

Answer 111

when two light nuclei can combine to create a larger nucleus

Question 112

why is a high temp and high pressure required for nuclear fusion?

Answer 112

fusion requires a high temp and pressure to give the nuclei enough kinetic energy to overcome to electrostatic repulsion and be close enough to fuse with with the nuclear strong force

Question 113

what are the problems associated with building and decommissioning nuclear power plants?

Answer 113

because of all the necessary safety precautions, building and decomissioning is very time-consuming and expensive

Question 114

why is a lot of energy released in nuclear fusion?

Answer 114

a lot of energy is released during nuclear fusion because the new, heavier nucleus has a much higher binding energy per nucleon (and so a lower total mass), the energy released helps to maintain the high temperatures needed for further fusion reactions

Question 115

why is nuclear fusion not currently a source of energy?

Answer 115

not efficient, any apparatus than it can induce fission requires much more electrical energy than it could produce, too expensive

Question 116

where does nuclear fusion often occur in naturally?

Answer 116

stars like our Sun