Nuclear Physics

Question 1

Describe the plum pudding model

Answer 1

a sphere of positive charge, with small areas of negative charge evenly distributed throughout

Question 2

What did Rutherford’s scattering show?

Answer 2

the existence of the nucleus

Question 3

What was observed in Rutherford’s scattering experiment?

Answer 3

• most alpha particles passed straight through the foil with no deflection
• a small amount of particles were deflected by a large angle
• very few particles were deflected back by more than 90 degrees

Question 4

what does most alpha particles passed straight through the foil with no deflection show?

Answer 4

most of the atom was empty space

Question 5

what does a small amount of particles were deflected by a large angle show?

Answer 5

The centre of the atom is positively charged, as the particles were repelled from the center and deflected.

Question 6

what does very few particles were deflected back by more than 90 degrees show?

Answer 6

the centre of the atom was very dense

Question 7

range in air for alpha particles

Answer 7

2 - 10cm

Question 8

range in air for beta particles

Answer 8

around 1cm

Question 9

range in air for gamma particles

Answer 9

infinite range: follows inverse square law

Question 10

ionising power for alpha particles

Answer 10

highly ionising

Question 11

ionising power for beta particles

Answer 11

weakly ionising

Question 12

ionising power for gamma particles

Answer 12

very weakly ionising

Question 13

which radiation are deflected by electric and magnetic fields

Answer 13

only alpha and beta is deflected by electric and magnetic fields

Question 14

what is absorbs alpha radiation?

Answer 14

paper

Question 15

what is absorbs beta radiation?

Answer 15

aluminium (around 3mm)

Question 16

what is absorbs gamma radiation?

Answer 16

several meters of concrete or several inches of lead

Question 17

what are some ways to use gamma radiation?

Answer 17

• as detectors
• to streilise surgical equipment
• in radiation therapy

Question 18

how is gamma used as a detector?

Answer 18

A radioactive source with a short half-life, which emits gamma radiation, can be injected into a patient, and the gamma radiation can be detected using gamma cameras to help diagnose patients.

Question 19

how is gamma used to streilise surgical equipment?

Answer 19

gamma radiation will kill any bacteria present on the equipment

Question 20

how is radiation therapy used in radiation therapy?

Answer 20

is used to kill cancerous cells in a targeted region of the body, such as a tumor

– it will also kill any healthy cells in that region

Question 21

what is the inverse square law equation?

Answer 21

I = k / x^2

Question 22

what is the inverse square law?

Answer 22

Intensity is inversely proportional to the square of the distance from its source.

Question 23

How could you work with ionising safely?

Answer 23

• using long-handled tongs
• storing the source in a lead-lined container
• keeping the source as far away as possible
  -never pointing the source towards others

Question 24

how to measure radiation taking into accound the background radiation?

Answer 24

corrected count = total count rate - background count

Question 25

what are some sources of background radiation?

Answer 25

- radon gas, which is released from rocks - artificial sources, caused by nuclear weapons testing and nuclear weapons. - cosmic rays enter the Earth's atmosphere from space - rocks, containing naturally occuring radioactive isotopes

Question 26

radioactive decay

Answer 26

a random process, meaning you can't predict when the next decay will occur.

Question 27

decay constant

Answer 27

the probability of a nucleus decaying per unit time

Question 28

activity

Answer 28

the number of nuclei that decay per second A=λN

Question 29

half-life

Answer 29

time taken for the number of nuclei to halve

Question 30

half life equation

Answer 30

T1/2 = ln2 / λ

Question 31

how can half-life of a radioactive nucleus be used?

Answer 31

- carbon dating objects - medical diagnosis

Question 32

carbon dating of objects

Answer 32

- nuclei with a long half-life such as carbon-14 can be used to date organic objects - this is done by measuring the current amount carbon-14 and comparing it to the initial amount.

Question 33

Sources of background radiation?

Answer 33

Radon gas, rocks, cosmic rays, medical uses, nuclear industry.

Question 34

What induces nuclear fission?

Answer 34

Slow thermal neutrons.

Question 35

Materials used as moderators?

Answer 35

heavy water.

Question 36

Moderator function?

Answer 36

Slows neutrons so they can be absorbed by fissile nuclei.

Question 37

Control rods function?

Answer 37

Absorb neutrons to control reaction rate.

Question 38

Control rod materials?

Answer 38

Boron

Question 39

Coolant function?

Answer 39

Transfers heat from core to heat exchanger.

Question 40

How is nuclear fuel handled?

Answer 40

Remotely, using shielding.

Question 41

Types of waste?

Answer 41

Low-level, intermediate, high-level waste.

Question 42

How is radioactive waste stored?

Answer 42

Sealed containers, long-term geological storage

Question 43

What is mass defect?

Answer 43

The difference between the mass of separated nucleons and the actual mass of the bound nucleus

Question 44

What is induced fission?

Answer 44

Fission caused by absorption of a neutron by a heavy nucleus, making it unstable and split into daughter nuclei plus neutrons.

Question 45

Why are thermal (slow) neutrons effective at inducing fission?

Answer 45

low neutrons have a higher probability of being captured by certain fuel nuclei

Question 46

How is an emergency shutdown achieved?

Answer 46

Control rods are fully inserted into the core to absorb neutrons and stop the chain reaction quickly.

Question 47

What distinguishes high-level waste from low-level waste?

Answer 47

High-level: highly radioactive, long-lived → needs deep, secure storage; low-level: short-lived, lower activity, can be nearer-surface disposed.

Question 48

Name key storage/processing steps for high-level waste

Answer 48

- Remote removal - cooling ponds (allow heat/radioactivity to decline) reprocessing (remove usable isotopes) vitrification - encasing in steel casks - deep geological storage.

Question 49

Give one major benefit and one major risk of nuclear power

Answer 49

Benefit: large energy yield with no greenhouse gas emissions in operation. Risk: radioactive waste longevity and potential for catastrophic accidents

Question 50

Equation for determining radius with electron diffraction.

Answer 50

sinx = 1.22λ / 2R

Question 51

value for the constant R0

Answer 51

1.4 * 10^-15

Question 52

finding nuclear radius?

Answer 52

* calculating the distance of closest approach of a charged particle * The point at which the particle stops and has no kinetic energy is its distance of closest approach

Question 53

equation for closest aproach

Answer 53

Eelec =1/4πε0 * Q1Q2/r

Question 54

Induced fission

Answer 54

* firing a thermal neutron into the uranium nucleus causing it to become extremely unstable. * Thermal neutrons induce fission . * The products of fission are two daughter nuclei and at least one neutron. *The neutrons released during fission go on to cause more fission reactions forming a chain reaction.

Question 55

critical mass

Answer 55

minimum mass of fuel required to maintain a steady chain reaction.