Radioactivity and Particles

Question 1

What is meant by the term half-life?

Answer 1

Time take for radioactivity to halve

Question 2

What is the purpose of the moderator in reactors in nuclear power stations?

Answer 2

1) slow down neutrons
2) increase rate of fission
3) increase absorption of neutrons by fuel

Question 3

What happens in a nuclear reactor when the control rods are removed?

Answer 3

1) rate of reaction increases
2) more neutrons collide with uranium as fewer neutrons are absorbed by the control rods
3) temperature increases

Question 4

What is the formula of alpha radiation?

Answer 4

a a-4 4
X —> Y + A
z z-2 2

Question 5

What is an alpha particle?

Answer 5

A helium nucleus (2 protons and 2 neutrons)

Question 6

What happens in Beta decay?

Answer 6

A neutron changes into a proton plus an electron. The proton stays in the nucleus and the electron leaves.

Question 7

What is the formula for beta radiation?

Answer 7

a a 0
X —> Y + B
z z-1 -1

Question 8

What piece of equipment can be used to detect radiation?

Answer 8

Geiger-Muller counter or photographic film

Question 9

How can scientists use radioactivity to find the age of a piece of rock?

Answer 9

1) there is a known activity of rocks when formed
2) measure the activity now
3) compared activity now to original activity
4) determine the number of half lives that have elapsed
5) calculate the age from reference to half life

Question 10

What are Gamma rays?

Answer 10

Very high frequency electromagnetic waves

Question 11

Order the ionising power of different types of radiation from most ionising to least

Answer 11

1) alpha
2) beta
3) gamma

Question 12

Order the penetrating power of different types of radiation from most penetrating to least

Answer 12

1) gamma
2) beta
3 alpha

Question 13

What is the range of alpha radiation in air?

Answer 13

A few cm

Question 14

What is the range of beta radiation in air?

Answer 14

Several 10s of cm

Question 15

What is the range of gamma radiation in air?

Answer 15

Virtually infinite

Question 16

What stops alpha radiation?

Answer 16

Paper

Question 17

What stops beta radiation?

Answer 17

A few mm of aluminium

Question 18

What stops gamma radiation?

Answer 18

A few cm of lead

Question 19

What is meant by the term fission?

Answer 19

Splitting of a nucleus

Question 20

What are sources of background radiation?

Answer 20

1) radiation from rocks/buildings/radon gas
2) cosmic radiation/radiation from the sun
3) radiation from medical sources
4) nuclear waste/accidents
5) some foods (bananas)

Question 21

What is the activity of a sample of radioactive decay measured in?

Answer 21

Bq (becquerel) - 1 count per second - 1 Bq

Question 22

How is radioactivity used in medical tracers?

Answer 22

1) a source which emits gamma radiation is injected into the skin
2) radiation is penetrating so is able to escape from the body and is detected by gamma cameras
3) the computer converts the reading to an on-screen displays showing where the radiation is being emitted from so the doctor can monitor the performance of various organs
4) radioactive material has to have a short half life so it decays before doing significant damage to the patient

Question 23

Why is a source of alpha radiation not used in medical tracers?

Answer 23

1) would have insufficient range as not very penetrating
2) would be absorbed by patient
3) more ionising than gamma rays

Question 24

How is radiation used in radiotherapy?

Answer 24

1) barrow beam of gamma rays is directed at an area of tissue (e.g. a tumour) that needs to be destroyed
2) done from a variety of different angles so as not to destroy the healthy surrounding tissue

Question 25

Describe carbon dating

Answer 25

1) carbon dating can only be used on marrer that was once living 2) the same proportion of C-14 is found in the atmosphere and in living things 3) when organisms dies the C-14 becomes trapped inside of them and begins to decay so it’s radioactivity decreases over time 4) compared proportion of C-14 in dead tissue to living tissue and you can tell how many half lives have passed and hence estimate the age

Question 26

How do smoke detectors work?

Answer 26

1) radiation from an alpha source ionises the air inside the detector 2) a voltage applied to a pair of electrodes causes a small ionisation current to flow between them 3) when smoke enters the detector the alpha particles are blocked by the larger smoke particles and the ionisation current fails triggering an alarm to go off

Question 27

How can nuclear fission lead to a chain reaction?

Answer 27

1) neutrons released 2) neutrons slowed by moderator 3) can be absorbed by other uranium nuclei 4) causing further fissions

Question 28

Why is shielding needed in nuclear reactors?

Answer 28

1) reactor material is radioactive 2) radiation ionises cells 3) radiation is very penetrating

Question 29

What effect does the emission of a beta particle have on a nucleus?

Answer 29

Neutron changes into a proton

Question 30

Why can radioactive sources be dangerous?

Answer 30

1) can not be seen 2) can damage cells 3) can cause cancer

Question 31

How can the risks of working with radioactive sources be reduced?

Answer 31

1) reduce exposure time 2) handle with tongs 3) use shielding 4) wear film badge to monitor exposure

Question 32

How can ionising radiation cause harm?

Answer 32

1) can damage cells 2) can cause mutation 3) can cause cancer

Question 33

Why is it dangerous to live near rocks that release radon?

Answer 33

1) radon is heavier than air 2) collects in building 3) breathe into lungs 4) radioactive

Question 34

What is fusion?

Answer 34

The joining of two atomic nuclei to form a different nucleus

Question 35

Where does nuclear fusion happen naturally?

Answer 35

The sun

Question 36

Why is fusion better than fission?

Answer 36

Doesn’t create waste

Question 37

What are the differences between nuclear fission and nuclear fusion?

Answer 37

1) in nuclear fission the nucleus is split into two nuclei | 2) in fusion two nuclei are joined together to form one nucleus

Question 38

How do control rods control nucleus reactions?

Answer 38

They absorb some of the neutrons

Question 39

What is meant by the term unstable?

Answer 39

Substance is radioactive so will emit radioactive particles or gamma rays

Question 40

What does shielding do in a nuclear reactor?

Answer 40

Absorbed dangerous radiation

Question 41

What does the coolant do in a nuclear reactor?

Answer 41

Removes energy from the reactor

Question 42

What is the role of a fuel rod in a nuclear reactor?

Answer 42

Contains uranium for fission

Question 43

What type of energy is released in a fission reaction?

Answer 43

Kinetic energy

Question 44

Explain the role of the moderator in a fission reaction

Answer 44

1) slows neutrons | 2) so neutrons can be absorbed by uranium

Question 45

Explain in terms of neutrons what is meant by the term controlled nuclear fission

Answer 45

1) each fission of a nucleus is caused by a single neutron 2) each fission releases more than one neutron 3) excess neutrons can speed up the reaction 4) more fissions releases excess energy 5) control rods absorb neutrons 6) control rods regulate the rate of fission

Question 46

Describe nuclear fission and how the chain reaction is controlled

Answer 46

1) nucleus absorbs neutron 2) splits into two daughter nuclei 3) extra neutrons releases 4) kinetic energy released 5) releases neutrons hit further nuclei 6) moderator slows down the neutrons 7) control rods absorb neutrons 8) control rods help prevent ‘runaway’ chain reaction

Question 47

What is meant by the term fission products?

Answer 47

1) particles formed after fission | 2) neutron and daughter nuclei

Question 48

Why is it important to contain fission products for such a long time?

Answer 48

1) they are still radioactive | 2) they have a long half life

Question 49

Why is it dangerous to remove most of the control rods from a reactor?

Answer 49

1) fewer neutrons would be absorbed 2) fission rate would increase 3) too much energy produces 4) meltdown of core/reactor

Question 50

why are beta particles used to detect the thickness of an aluminium sheet?

Answer 50

1) alpha particles would be stopped before they reached the detector as they do not penetrate enough 2) gamma rays would be too penetrative so would not be affected by changes in thickness 3) some beta particles will pass through the foil 4) thinner aluminium absorbs fewer beta particles

Question 51

what happens to the nucleus of an atom when it undergoes beta decay?

Answer 51

1) proton number increases by 1 | 2) neutron number decreases by 1