Radioactivity

Question 1

What is radioactive decay?

Answer 1

Some isotopes have an unstable nucleus
To become stable, the nucleus gives out radiation
This process is radioactive decay

Question 2

Can radioactive decay be predicted?

Answer 2

No, it is a completely random process and scientists cannot predict when it will occur

Question 3

Activity

Answer 3

The rate at which a source of unstable nuclei decay

Question 4

How do we measure activity and what’s the unit?

Answer 4

Using a Geiger-Muller tube
Becquerel (Bq)

Question 5

What is the count rate in a Geiger-Muller tube?

Answer 5

Number of decays recorded each second by a detector
Ie the number of radioactive emissions picked up
But scientists can’t say for certain when this will happen

Question 6

Alpha particles

Answer 6

A type of radiation
Consists of 2 neutrons and 2 protons
The same as a helium nucleus

Question 7

Beta particles

Answer 7

A type of radiation
1 electron which is ejected from a nucleus at a very high speed when a neutron changes into a proton and electron

Question 8

Gamma ray

Answer 8

Type of electromagnetic wave
Is radiation from the nucleus

Question 9

Neutron radiation

Answer 9

Sometimes given off by an unstable nucleus, also a type of radiation

Question 10

Properties of alpha particles

Answer 10

Large
Travels around 5cm in the air before stopping due to air particles
Stopped with a single sheet of paper
Strongly ionising - produces lots of ions when hitting an atom

Question 11

Properties of beta particles

Answer 11

Travels around 15cm in the air
Stopped by a sheet of aluminium
Quite strongly ionising

Question 12

Properties of gamma rays

Answer 12

Can travel several metres in the air before stopping
Has to be stopped by several cm of lead
Weak ionising

Question 13

Ionising power

Answer 13

When radiation collides with atoms, that can cause atoms to lose electrons and form positive ions

Question 14

Nuclear equations

Answer 14

Shows us what happens when a radioactive nucleus decays

Question 15

Alpha decay equations

Answer 15

The atomic number decreases by 2
The mass number decreases by 4
Creates helium atom with a mass of 4 and number of 2

Question 16

Beta decay equations

Answer 16

The atomic number increases by 1
The mass number does not change
Produced an electron with atomic number -1

Question 17

Why does the atomic number in a beta decay increase by 1?

Answer 17

Because the neutron becomes a proton, increasing the atomic number

Question 18

Risks of ionising radiation

Answer 18

Can penetrate skin cells, if it hits the DNA in the nucleus can cause a mutation and thus cancer

Question 19

Uses of radiation in medicine as a tracer

Answer 19

Can be used as X-rays ro visualise damage to find tumours/ arthritis etc
To find problems in the thyroid gland which absorbs iodine. Drinking radioactive iodine then detecting the gamma rays that are emitted to see if too much/little has been absorbed

Question 20

Count rate vs activity

Answer 20

Activity = rate at which unstable nuclei decay
Count rate = rate at which radioactive emissions are detected, effected by background radiation

Question 21

What determines an isotope’s instability?

Answer 21

If it has too many or too few neutrons

Question 22

Why is radioactive decay random?

Answer 22

A radioactive source has so many nucleus it’s impossible to predict when a particular one decays

Question 23

Gamma decay equations

Answer 23

No change to atomic number or mass number

Question 24

Half life

Answer 24

Because a nuclei’s radioactive decay is random,
Scientists can’t state when individual nucleus decay
So we find time taken for half of the nuclei in a source to decay

Question 25

If nuclei have a short half life what does that show?

Answer 25

It is an unstable isotope As it has to give out more radioactivity to achieve stability

Question 26

Half life in terms of count rate

Answer 26

Time it takes for count rate/ activity of the sample to fall to half of its initial rate

Question 27

How to find half life from a graph?

Answer 27

Find where half of the decays are on y axis Draw lines from the y axis to the time using the graph at the x axis

Question 28

Irradiation

Answer 28

Exposing an object to nuclear radiation Can be either alpha, beta, gamma, neutrons

Question 29

How can irradiation be used?

Answer 29

Sterilising medical equipment that can’t be heated normally

Question 30

How does sterilisation of medical equipment work?

Answer 30

Place equipment in plastic wrapper to stop bacteria entering Place near a radioactive isotope, releasing gamma radiation Use protection from lead shield then withdraw it to expose the equipment to gamma waves

Question 31

Ionising radiation risk

Answer 31

Can hit the atoms in our cells and form ions Causing mutation in DNA and thus uncontrolled division = cancer

Question 32

How to be protected from alpha radiation?

Answer 32

Gloves

Question 33

How to be protected from beta or gamma radiation?

Answer 33

Lead apron

Question 34

If the levels of radiation are too high how else can we be protected?

Answer 34

Lead screen and lead glass Use a radiation monitor to avoid contact with radioactive isotopes

Question 35

Radioactive contamination

Answer 35

When unwanted radioactive isotopes end up on materials Causing the isotopes to decay and emit ionising radiation

Question 36

Why is alpha radiation dangerous when inside the body?

Answer 36

Crash into living cells Damage DNA = mutation

Question 37

Is gamma radiation dangerous to humans?

Answer 37

Not too bad as it usually pases right through

Question 38

Peer review

Answer 38

Studies are published on affects of things eg radiation to be checked by other scientists

Question 39

Background radiation

Answer 39

Radiation around us all the time

Question 40

Sources of background radiation

Answer 40

Radioactive rock eg granite Cosmic rays from space (high energy particles) due to supernovas Nuclear weapon testing fall out Accidents at power stations

Question 41

What affects exposure to background radiation?

Answer 41

Location eg places with a lot of granite Occupation eg cabin crew with a lot of cosmic rays

Question 42

What is radiation dose measured in?

Answer 42

Sieverts (Sv)

Question 43

Radioactive isotopes as a medical tracer

Answer 43

Check how much iodine has been absorbed by the thyroid glands by swallowing radioactive iodine, decaying Bone scans to visualise tumours off damage by arthritis

Question 44

What must a medical tracer be like?

Answer 44

Must pass out body (not alpha) Not strongly ionising = damage Not decay into another isotope Short half life so not present for a long time

Question 45

Radiotherapy

Answer 45

Destroying cancer with ionising radiation

Question 46

How does radiotherapy work externally ?

Answer 46

External source of ionising radiation Gamma rays pass into body and destroy tumour from

Question 47

Risks of external radiotherapy

Answer 47

Damages healthy tissue

Question 48

How does radiotherapy work internally?

Answer 48

Radioactive rods put inside the body

Question 49

Benefits of internal radiotherapy

Answer 49

Radiation precisely targets tumour No damage to healthy tissue

Question 50

What are the stages of nuclear fission?

Answer 50

Unstable nucleus absorbs a neutron Nucleus split to form smaller daughter nuclei, gamma, neutrons The neutrons are absorbed by other unstable nucleus Repeats

Question 51

Nuclear chain reaction

Answer 51

Nuclear fission When unstable nucleus absorbs neutron which releases more neutrons to be absorbed by nucleus Causing a large amount of energy to be released

Question 52

Controlled chain reaction

Answer 52

Scientists controlling nuclear fission to release energy in a nuclear reactor

Question 53

What causes a nuclear bomb?

Answer 53

Uncontrolled nuclear fission

Question 54

Nuclear fusion

Answer 54

2 light nuclei such as hydrogen join to create a heavier nucleus This mass of the nuclei converted to energy, released as radiation

Question 55

What can nuclear fusion do?

Answer 55

Release energy in stars