Nuclear Physics

Question 1

Describe the basic structure of an atom

Answer 1

nucleus containing protons and neutrons, around which electrons orbit in fixed energy levels/shells

Question 2

Describe the plum pudding model of the atom

Answer 2

Sphere of positive charge with negative electrons embedded in it

Question 3

What charges do protons, neutrons and electrons carry?

Answer 3

Protons = positive
Neutrons = no charge
Electrons = negative

Question 4

Why do atoms have no overall charge?

Answer 4

Equal numbers of positive protons and negative electrons

Question 5

What is the radius of an atom?

Answer 5

around 1x10^-10m

Question 6

What is ionisation?

Answer 6

Process which adds or removes electrons from an atom

Question 7

What is the mass number of an element?

Answer 7

Number of protons + number of neutrons

Question 8

Which particle do atoms of the same element always have the same number of?

Answer 8

protons

Question 9

What are isotopes?

Answer 9

Atoms of the same element (same number of protons) with different numbers of neutrons

Question 10

What were the two main conclusions from the alpha particle scattering experiment?

Answer 10

• most of the mass of an atom is concentrated in the nucleus
• nucleus is positively charged

Question 11

What are the three types of nuclear radiation?

Answer 11

alpha, beta and gamma

Question 12

Which type of nuclear radiation is the most ionising?

Answer 12

alpha

Question 13

What is the range in air of alpha, beta and gamma radiation?

Answer 13

a few cm, 1m and unlimited, respectively

Question 14

what are the equation symbols for alpha and beta particles?

Answer 14

4 0
a and β
2 -1

Question 15

What is meant by the half-life of a radioactive source?

Answer 15

time taken for half the unstable nuclei to decay or the time taken for the count rate to halve

Question 16

What is radioactive contamination?

Answer 16

unwanted presence of substances containing radioactive atoms on or in other materials

Question 17

Where does background radiation come from?

Answer 17

rocks
cosmic rays
fallout from nuclear weapons testing
nuclear accidents

Question 18

Why are gamma-emitting sources used for medical tracers and imaging?

Answer 18

gamma rays pass through the body without causing much damage to cells

Question 19

What is nuclear fusion?

Answer 19

when two light nuclei join to make a heavier one

Question 20

How does nuclear fission occur?

Answer 20

an unstable nucleus absorbs a neutron, it splits into two smaller nuclei, and emits two or three neutrons plus gamma rays

Question 21

Why is Rutherford’s alpha scattering experiment so important?

Answer 21

It led to the discovery of the nucleus and changed the model of the atom

Question 22

Complete the sentence on the alpha scattering experiment: Most of the alpha particles passed straight through …

Answer 22

therefore the atom is mostly empty space

Question 23

Complete the sentence on the alpha scattering experiment: Some of the alpha particles are deflected …

Answer 23

therefore the central nucleus is where charge is concentrated

Question 24

Complete the sentence on the alpha scattering experiment: A very small number are backscattered/have a large angle scattering …

Answer 24

Nucleus is very small + massive (lots of mass) as well as being where charge is concentrated

Question 25

Definition of an energy level

Answer 25

- exists at a particular distance from the nucleus and contains electrons with a certain defined energy (all the same)

Question 26

What happens to the energy levels the further they are from the nucleus?

Answer 26

They have higher energy

Question 27

Can electrons move between energy levels?

Answer 27

Yes, by gaining/losing exactly the right amount of energy

Question 28

What is nuclear radiation?

Answer 28

Particles of energy (photons) emitted (given out) by an unstable nucleus

Question 29

What does an alpha particle consist of?

Answer 29

2 protons and 2 neutrons

Question 30

What is the charge of an alpha particle?

Answer 30

+2

Question 31

What is the range in air of an alpha particle?

Answer 31

a few cm

Question 32

Penetration of alpha particles

Answer 32

stopped by a sheet of paper (layer of dead skin cells on outside)

Question 33

Ionising power of alpha particles

Answer 33

very high

Question 34

What do beta particles consist of?

Answer 34

fast electron (close to speed of light)

Question 35

Charge of beta particle

Answer 35

-1

Question 36

Range in air of beta particle

Answer 36

10s of cm

Question 37

beta particle penetration of materials

Answer 37

stopped by couple of mm of Al

Question 38

Ionising power of beta particle

Answer 38

quite ionising

Question 39

What does a gamma ray consist of?

Answer 39

high frequency energy photon

Question 40

charge of gamma ray

Answer 40

0

Question 41

Range in air of gamma ray

Answer 41

near infinite

Question 42

Gamma ray penetration of materials

Answer 42

reduced by v thick lead or several feet of concrete

Question 43

ionising power of gamma ray

Answer 43

low

Question 44

Neutron consists of

Answer 44

a neutron

Question 45

charge of a neutron

Answer 45

0

Question 46

Which types of radiation are uncharged?

Answer 46

neutron and gamma

Question 47

which type of radiation consists of positively charged particles?

Answer 47

alpha

Question 48

Which type of radiation consists of negatively charged particles?

Answer 48

beta

Question 49

Which type of nuclear radiation does not ionise substances?

Answer 49

neutron

Question 50

Which type of nuclear radiation has the greatest ionising effect?

Answer 50

Alpha

Question 51

Which type of nuclear radiation travels the furthest in air?

Answer 51

neutron

Question 52

Definition of activity

Answer 52

The total number of radioactive events (alpha, beta, gamma or neutron radiation) taking place per second

Question 53

Definition of count rate

Answer 53

Number of radioactive events picked up by the detector per second

Question 54

Which is bigger, activity or count rate, and why?

Answer 54

Activity is bigger - not all radiation enters the detector - some radiation passes through without ionising - not picked up

Question 55

Units for activity and count-rate (they are the same)

Answer 55

Becquerel (Bq)

Question 56

How is count rate detected?

Answer 56

With a Geiger counter

Question 57

Definition of half-life

Answer 57

The time taken for the activity of a sample to drop to half of the original value

Question 58

Place the types of radiation in order of most to least damaging if someone is irradiated by it

Answer 58

Most: gamma beta alpha (stopped by skin)

Question 59

Place the types of radiation in order of most to least damaging if someone is contaminated by it

Answer 59

Most: alpha (all of the radiation/energy absorbed by the body) beta gamma

Question 60

Definition of fission

Answer 60

the process during which a large unstable nucleus splits to form 2 smaller fragment nuclei and neutrons

Question 61

What is a chain reaction in fission?

Answer 61

A single reaction causes further reactions in this case by releasing neutrons which trigger further fission events. Usually chain reactions result in a very rapid increase in the rate of release of energy - this needs to be controlled to be safe

Question 62

Definition of fusion

Answer 62

The process by which 2 light nuclei join together producing a more massive nucleus and lots of energy

Question 63

Advantages of fusion reactors

Answer 63

- The fuel (hydrogen) is present in sea water - the product in an inert, harmless gas - Helium - BUT it is very difficult

Question 64

Nuclear fusion in the sun

Answer 64

Hydrogen fuses to form helium