7 Nuclear Physics

Question 1

when an electron moves from a higher energy state to a lower energy state…

Answer 1

photons are emitted

Question 2

describe the emission spectra

Answer 2

an electron transfer to a lower energy level and emit photon

Question 3

Isotopes tend to be more unstable because

Answer 3

they have an imbalance of protons and neutrons

Question 4

state and define the two main characteristic of radioactive decay

Answer 4

1. spontaneous: not influenced by external factors
2. random: cannot predict the time of decay

Question 5

Explain the relationship between penetrating power and ionizing ability.

Answer 5

Alpha = most ionising = lose energy quickly = least penetrating, can be stopped by paper/skin

Question 6

explain this Z-N diagram

Answer 6

For Z<20, proton number = neutron number → stable

For Z>20, neutron-proton ratio increases because as proton number increases, the electrostatic repulsion becomes very strong and more neutron is required to ‘shield’ the protons from each other and bind the nucleons together → unstable

Question 7

examples of radiation detectors

Answer 7

• Photographic film
• Geiger-Muller (GM) tubes

Question 8

describe beta-minus decay

Answer 8

n → p + e-

Question 9

describe beta-plus decay

Answer 9

p → n + e+

Question 10

α particles are emitted by nuclei that

Answer 10

have too many nucleons

Question 11

define half life

Answer 11

the time taken for the undecayed nuclei to halve

Question 12

define mass defect (Δm)

Answer 12

the difference in mass between separated and combined nucleons
(mass ⇒ binding energy)

Question 13

convert mass defect to binding energy

Answer 13

ΔE = Δm x 931.5 (MeV)

Question 14

convert MeV to J

Answer 14

1 e = 1.6 x 10^-19 C
1 eV = 1.6 x 10^-19 J
1 MeV = 1.6 x 10^-13 J

Question 15

define nuclear fission

Answer 15

an unstable atom absorbs neutrons and becomes unstable → the nucleus splits into two daughter nuclei; releases energy

Question 16

What happens to the binding energy after fission/fusion
1) per nucleon
2) total

Answer 16

binding energy per nucleon increases as the nuclei becomes more stable.
→ total binding energy also increases

Question 17

why do lighter nuclei undergo fusion while heavier nuclei undergo fission?

Answer 17

small mass → less protons → attractive nuclear forces between nucleons > repulsive electrostatic forces between protons → fuse
(vice-versa for large mass)

Question 18

advantages of fusion

Answer 18

Reactants readily available in ocean; no harmful by-product

Question 19

Moderator

Answer 19

slows down neutrons so they can be captured by a U-235 nucleus

Question 20

Heat Exchanger

Answer 20

heat water to steam to be used to turn turbines and produce electricity

Question 21

Chain reaction

Answer 21

A self-sustaining nuclear reaction where U-235 fission releases more neutrons and trigger more fissions… this is when the rate of neutron production ≥ the rate of neutron lost

Question 22

what is quark?

Answer 22

fundamental particles that make up other subatomic particles such as protons and neutrons

Question 23

define baryon

Answer 23

consists of 3 quarks;
baryon number = 1

Question 24

what are the quark configurations of proton and neutron?

Answer 24

proton: uud
neutron: udd

Question 25

why does proton have the longest half-life of all baryons?

Answer 25

lightest baryon → most stable

Question 26

list the 4 fundamental interaction forces in order of strengths

Answer 26

strong > electromagnetic > weak > gravity

Question 27

which interaction force is responsible for the radioactive decay of atoms?

Answer 27

weak

Question 28

define exchange particles

Answer 28

virtual particles that mediate the a fundamental force between interacting particles

Question 29

Explain how atomic spectra provide evidence for the quantisation of energy in atoms.

Answer 29

E=hf=h(c/λ), since atomic spectra consists of discrete wavelengths, atoms must contain discrete/quantised energy levels

Question 30

describe the absorption spectra

Answer 30

1. Electrons absorb photons and become ‘excited’
2. Electrons de-excite and re-emit the photons but in all directions, so these wavelengths appear black in the direction of the observer.

Question 31

define radioactive decay

Answer 31

an unstable atomic nucleus becomes more stable by emitting a particle (alpha, beta) or a wave (gamma)

Question 32

state the nature of the 3 radiation

Answer 32

alpha = He nucleus (2p, 2n)

beta = high speed electron

gamma = EM radiation

Question 33

what materials stop the 3 types of radiation

Answer 33

alpha = paper

beta = thin aluminum foil

gamma = thick lead

Question 34

define background radiation

Answer 34

low level of radiation in our surroundings at all times

Question 35

state the sources of background radiation

Answer 35

radon gas, rocks, food, cosmic rays

Question 36

determine the background radiation

Answer 36

where the line plateaus

Question 37

β- particles are emitted by nuclei that

Answer 37

have too many neutrons

Question 38

β+ particles are emitted by nuclei that

Answer 38

have too many protons

Question 39

γ particles are emitted by nuclei that

Answer 39

have too much energy

Question 40

define the activity of a redioactive substance

Answer 40

number of decays per second

A = dN/dt = - λN

Question 41

define binding energy (ΔE)

Answer 41

the energy to separate the nucleons in a nucleus

Question 42

Calculate the binding energy per nucleon, in MeV, for K-40 (19 protons)
Nuclear mass = 39.953548 u
Mass of one neutron = 1.008665 u
Mass of one proton = 1.007276 u

Answer 42

1. ∆m = nuclear - (p+n)
2. convert u to kg!!
3. ∆E = ∆mc²
4. ∆E per nucleon (divide by 40)
5. convert J to MeV!!
   → ∆E per nucleon = 8.594 MeV

Question 43

Draw the graph of mass number against binding energy per nucleon, including the main features

Answer 43

mass

Question 44

define nuclear fusion

Answer 44

two small nuclei join to produce a larger nucleus; release energy

Question 45

In nuclear fission/fusion, how is the mass of the product compared to the mass of the reactant? Why?

Answer 45

mr > mp because part of the mass of the reactant is converted into energy.

Question 46

In the graph of mass number (A) against B.E. per nucleon, what does the steeper graident for smaller A show?

Answer 46

fusion releases more energy (B.E.per nucleon increases more)

Question 47

difficulty in making a fusion reactor

Answer 47

Very difficult to create heat and pressure that exists in the sun → need to input more energy than what comes out

Question 48

Control Rod

Answer 48

absorbs neutrons to control the rate of reaction

Question 49

Enrichment

Answer 49

increasing the % of U-235 ( more reactive/fissionable isotope) in a fuel used in a nuclear power station

Question 50

Critical Mass

Answer 50

the minimum mass of nuclear fuel needed to sustain a chain reaction

Question 51

why does nuclear fusion need high temperature?

Answer 51

need lots of energy to overcome the electrostatic repulsion between positively charged nuclei

Question 52

define meson

Answer 52

a quark and an antiquark pair

Question 53

what is lepton?

Answer 53

fundamental particles that cannot be broken down further (eg. electron)

Question 54

how do you determine whether a particle interaction can occur?

Answer 54

check if QBLS are conserved
Q = charge
B = baryon number
L = lepton number
S = strangeness

Question 55

The strong force applies only to particles made up of

Answer 55

quarks

Question 56

The electromagnetic force only applies tp

Answer 56

particles with charge

Question 57

The gravitational force only applies to

Answer 57

particles with mass

Question 58

quark confinement states…

Answer 58

it is impossible to observe a free quark in isolation because more particles will be created when you try to separate a pair of quarks

Question 59

draw the Feymann diagram for beta-plus decay

Question 60

Mg-27 nuclei decay by β- to form Al-27. Explain why there’s a difference between the energy released in the decay and the total kinetic energy of beta particles and gamma rays.

Answer 60

another particle (anti-nutrino) is emitted

Question 61

Fluorine (18,9) can be created when a proton traveling at high speed interacts with an oxygen nucleus (18,8). Explain why the proton must be traveling at high speed for this process to occur.

Answer 61

+ve nucleus repels proton;
proton must be close to nucleus for nuclear force to be effective (high electric potential energy);
so the proton needs high initial kinetic energy

Question 62

range of wavelength for visible light

Answer 62

380 to 700 nm