Separate Physics - 6.4

Question 1

What is the size of an atom?

Answer 1

Very small – a radius of about 1x10^-10 m

Question 2

Describe the basic structure of an atom

Answer 2

A positively charged nucleus (protons and neutrons) orbited by negatively charged electrons

Question 3

What is the radius of the nucleus

Answer 3

1/10’000^th the radius of an atom (but contains most of the mass)

Question 4

Describe electrons within energy levels

Answer 4

Electrons are arranged at different distances (energy levels) from the nucleus

Question 5

How can electron arrangements change?

Answer 5

• Absorption of electromagnetic radiation (higher energy level)
• Emission of electromagnetic radiation (lower energy level)

Question 6

What is the overall electrical charge of an atom?

Answer 6

No overall charge – electron and proton numbers are equal

Question 7

How many protons do an atom of the same element have?

Answer 7

The same number

Question 8

What is the atomic number?

Answer 8

The number of protons in an atom

Question 9

What is the mass number?

Answer 9

The number of protons and neutrons in an atom

Question 10

Draw the modern model of an atom

Answer 10

Question 11

What is an isotope?

Answer 11

Atoms of the same element with different numbers of neutrons

Question 12

What happens to an atom if it loses one or more outer electron(s)?

Answer 12

It becomes a positive ion

Question 13

Before the discovery of the electron, what were atoms thought to be (as suggested by Dalton)?

Answer 13

Tiny spheres that could not be divided

Question 14

What was the Plum Pudding model?

Answer 14

The atom was suggested to be a ball of positive charge with negative electrons embedded in it

Question 15

What did Rutherford’s scattering experiment show?

Answer 15

The mass of the atom was concentrated in the centre (nucleus) and it was charged

Question 16

How did Bohr adapt the nuclear model as suggested by Rutherford?

Answer 16

Bohr suggested electron orbit the nucleus at specific distances (energy levels)

Question 17

What can the positive charge of a nucleus be subdivided into?

Answer 17

Protons

Question 18

20 years after the nucleus became scientifically accepted, what did James Chadwick identify?

Answer 18

Neutrons (explaining the imbalance between atomic number and atomic mass)

Question 19

Some atomic nuclei are unstable – what can the nucleus emit (and in doing so become more stable)?

Answer 19

Radiation – a random process of radioactive decay of the unstable nuclei

Question 20

What is ‘activity’ in terms of nuclear radiation?

Answer 20

The rate at which a source of unstable nuclei decays

Question 21

How is nuclear ‘activity’ measured?

Answer 21

In becquerels (Bq) where 1 Bq is 1 decay per second

Question 22

What can a Geiger-Muller tube record?

Answer 22

The count-rate (the number of radiation decays reaching the device per second)

Question 23

What types of ionising nuclear radiation are there?

Answer 23

• Alpha
• Beta
• Gama

Question 24

Describe alpha (α) radiation (structure, penetration, absorption and ionising strength)

Answer 24

• 2 neutrons and 2 protons (like a helium nucleus)
• They don’t penetrate very far (a few cm in air) and are absorbed by a piece of paper
• They are strongly ionising

Question 25

Describe beta (β) radiation (structure, penetration, absorption and ionising strength)

Answer 25

* A fast moving electron (virtually no mass) * Penetrate a few metres in air and are absorbed by a 5mm sheet of aluminium * Moderately ionising

Question 26

Describe gamma (γ) radiation (structure, penetration, absorption and ionising strength)

Answer 26

* Waves of electromagnetic radiation * Penetrate far into materials and are absorbed by thick sheets of lead or metres of concrete * Weakly ionising

Question 27

As well as alpha, beta and gamma radiation what else can radiative substances release?

Answer 27

Radioactive substances can release neutrons (as they rebalance their atomic and mass numbers)

Question 28

What can nuclear equations represent?

Answer 28

Radioactive decay

Question 29

How can an alpha particle be represented?

Answer 29

Question 30

How can a beta particle be represented?

Answer 30

Question 31

What can nuclear radiation emission change in a nucleus?

Answer 31

The mass or the charge

Question 32

What happens to Rn²¹⁹ when it experiences alpha decay?

Answer 32

\*Mass and charge both decreased

Question 33

What happens to C¹⁴ when it experiences beta decay?

Answer 33

\*Mass remains but charge increased

Question 34

What would be the nuclear equation for the decay of Uranium-238?

Answer 34

Question 35

What happens to the mass or charge of a nucleus when it experiences gamma emission?

Answer 35

The mass and charge remain the same

Question 36

How can the process of radioactivity be described?

Answer 36

Random

Question 37

What happens to the radioactivity of a source over time?

Answer 37

It decreases

Question 38

What is half-life?

Answer 38

The time taken for the number of nuclei of a radioactive isotope to halve (or the count rate to halve)

Question 39

What is the half-life of the following sample:

Answer 39

Question 40

What does a short half-life mean?

Answer 40

The activity falls quickly due to rapid decay?

Question 41

What does a long half-life mean?

Answer 41

The activity falls slowly due to slow decay?

Question 42

Higher Q. How can net decline be calculated

Answer 42

1. Find the activity after each half-life 2. Divide the final activity by the initial 3. Multiply by 100 to make a percentage

Question 43

What is radioactive contamination?

Answer 43

The unwanted presence of materials containing radioactive atoms on other materials

Question 44

What is the hazard of radioactive contamination?

Answer 44

The hazard is due to the decay of the contaminating atoms

Question 45

What is irradiation?

Answer 45

Exposing an object to nuclear radiation (the object itself does not become radioactive)

Question 46

Why is radioactive contamination so dangerous?

Answer 46

Radioactive particles could get inside the body

Question 47

Outside of the body what radioactive sources are most dangerous?

Answer 47

Beta and Gamma

Question 48

Inside the body what radioactive source is most dangerous?

Answer 48

Alpha

Question 49

What precautions should be taken around hazardous radioactive materials?

Answer 49

* Wearing gloves / using tongs * Protective suits * Breathing apparatus * Limiting exposure time

Question 50

Separate Q. What two sources of background ration are there?

Answer 50

Natural sources and man-made sources

Question 51

Separate Q. List examples of natural background radiation

Answer 51

* Food * Rocks * Cosmic rays from space

Question 52

Separate Q. List examples of man-made background radiation

Answer 52

* Fallout from nuclear weapons * Nuclear accidents

Question 53

Separate Q. What can affect the level of background radiation?

Answer 53

Occupation / location (e.g. pilots experience higher levels than office workers)

Question 54

Separate Q. What is a radiation dose measured in?

Answer 54

Sieverts (Sv)

Question 55

Separate Q. How many millisieverts is a sievert?

Answer 55

1000

Question 56

Separate Q. What risks are there when using radiation?

Answer 56

Radiation can enter living cells and ionise atoms leading to tissue damage

Question 57

Separate Q. What risks are involved with lower doses of radiation?

Answer 57

Minor damage to cells can lead to mutations (and cancers)

Question 58

Separate Q. What risks are involved with high doses of radiation?

Answer 58

Higher doses kill cells completely causing radiation sickness

Question 59

Separate Q. What are medical tracers?

Answer 59

Gamma isotopes are injected / swallowed and detected which can show problems (e.g. iodine-123)

Question 60

Separate Q. What is radiotherapy

Answer 60

High doses of ionising radiation can kill cancerous cells (directing gamma rays to specific points)

Question 61

Separate Q. What is nuclear fission?

Answer 61

The splitting of a large unstable nucleus (such as uranium or plutonium)

Question 62

Separate Q. How can the likelihood of ‘spontaneous fission’ be described?

Answer 62

Rare

Question 63

Separate Q. For fission to occur, what must the unstable nucleus absorb?

Answer 63

A neutron

Question 64

Separate Q. What happens to a nucleus undergoing fission?

Answer 64

It splits into two smaller nuclei (roughly the same size) and emits two or three neutrons, gamma rays and energy

Question 65

Separate Q. What do all fission products have?

Answer 65

Kinetic energy

Question 66

Separate Q. What might the neutrons of a fission reaction cause?

Answer 66

A chain reaction

Question 67

Separate Q. How are controlled chain reactions utilised?

Answer 67

Nuclear reactors

Question 68

Separate Q. How are uncontrolled chain reactions utilised?

Answer 68

Nuclear weapons

Question 69

Separate Q. What is nuclear fusion?

Answer 69

The joining of two light nuclei (forming a heavier nucleus)

Question 70

Separate Q. What can happen to some of the mass of two light nuclei during nuclear fusion?

Answer 70

It can be converted into the energy of radiation