Topic 4 - Atomic Structure

Question 1

What is the radius of an

atom?

Answer 1

1x10^-10m

Question 2

How big is the nucleus compared to the atom?

Answer 2

10 000x smaller

Question 3

What is the

isotope of an element?

Answer 3

an atom with the same number of protons but a different number of neutrons

Question 4

What is

radioactive decay?

Answer 4

an unstable isotope decaying into other elements and giving out radiation as it tries to become more stable

Question 5

What are the

three types of radiation you need to know?

Answer 5

• alpha
• beta
• gamma

Question 6

What is

ionising radiation?

Answer 6

radiation that knocks electrons off atoms, creating positive ions

Question 7

What is the

ionising power of a radiation source?

Answer 7

how easily it can knock electrons off atoms

Question 8

What is

alpha radiation?

Answer 8

when an alpha particle is emitted from the nucleus

Question 9

What does an

alpha particle

consist of?

Answer 9

two neutrons and two protons

Question 10

What are some characteristics of

alpha radiation?

think:
- penetratability
- ionisation
- absorbance

Answer 10

• they don’t penetrate very far into materials and are stopped quickly - they can only travel a few cm in air
• they are strongly ionising
• they are absorbed by a sheet of paper

Question 11

How does

alpha radiation work in smoke detectors?

Answer 11

It ionises air particles, causing a current to flow. If there is smoke in the air, it binds to the ions - meaning the current stops and the alarm sounds.

Question 12

What does a

beta particle

consist of?

Answer 12

a fast-moving electron

these have virtually no mass and a charge of -1

Question 13

What are some characteristics of

beta radiation?

think:
- penetratability
- ionisation
- absorbance

Answer 13

• they penetrate moderately far into materials before colliding and have a range in air of a few metres
• they are moderately ionising
• they are absorbed by a sheet of aluminium (around 5mm)

Question 14

What is a use of

beta radiation?

Answer 14

testing the thickness of sheets of metal

Question 15

What does

gamma radiation

consist of?

Answer 15

waves of electromagnetic radiation

Question 16

What are some characteristics of

gamma radiation?

think:
- penetratability
- ionisation
- absorbance

Answer 16

• they penetrate far into materials without being stopped and will travel a long distance through air
• this means they are weakly ionising because they tend to pass through rather than collide with atoms
• they can be absorbed by thick sheets of lead or metres of concrete

Question 17

What does a

geiger-muller tube and counter record?

Answer 17

the number of radiation counts reaching it per second

Question 18

Define

activity.

and state what this is measured in.

Answer 18

the rate at which a source decays

becquerels, Bq - 1Bq = 1 decay per second

Question 19

Define

half-life.

Answer 19

the time taken for the number of radioactive nuclei in an isotope to halve

Question 20

What is

background radiation?

Answer 20

the low-level radiation that’s around us all the time

Question 21

Where does

background radiation

come from? (3 places)

Answer 21

• radiactivity of naturally occuring unstable isotopes which are all around us
• radiation from space (cosmic rays), these come mostly from the sun, the Earth’s atmosphere protects us from much of this
• radiation due to human activity

Question 22

What is a

radiation dose?

and what is this measured in?

Answer 22

the risk of harm to body tissues due to exposure to radiation

sieverts, Sv

background radiation is small, so millsieverts are often used

Question 23

Define

irradiation.

Answer 23

exposure to radiation

Question 24

How could you

reduce the effects of irradiation?

(4 ways)

Answer 24

• keep sources in lead-lined boxes
• stand behind barriers
• be in a different rom
• use remote-controlled arms

Question 25

# Define contamination.

Answer 25

**unwanted radioactive atoms** geting onto or into an object

Question 26

# How could you reduce the risk of contamination? | (2 ways)

Answer 26

- use **gloves** and **tongs** when handling sources - wear a **protective suit** to avoid **breathing in** particles

Question 27

# Why are beta and gamma sources the most dangerous outside the body?

Answer 27

they can penetrate the body and get to the delicate **organs** ## Footnote alpha **can't penetrate the skin** and is easily blocked by a **small air gap**

Question 28

# Why is alpha radiation most dangerous inside the body?

Answer 28

it does all of its damage in a **very localised area** ## Footnote **beta** sources are **less damaging** as radiation is absorbed over a **wider area** and some **passes out** of the body altogether **gamma** sources are the **least dangerous** as they mostly **pass straight out**

Question 29

# What are some risks to using radiation?

Answer 29

radiation can **enter living cells** and **ionise atoms and molecules** within them, this can lead to **tissue damage** ## Footnote **lower doses** tend to cause **minor damage** without **killing** the cells, this can give rise to **mutant cells** which **divide uncontrollably** **higher doses** tend to **kill cells completely**, causing **radiation sickness** (keading to vomiting, tiredness and hair loss) of a lot of cells **all get blatted at once**

Question 30

# How does radiotherapy work?

Answer 30

Gamma rays are **directed carefully** and at just the right **dosage** to kill the **cancer cells** without damaging too many **normal cells**. ## Footnote A **fair bit of damage** is **inevitably** done to **normal cells**, which makes the patient feel **very ill**.

Question 31

# What is nuclear fission?

Answer 31

a type of **nuclear reaction** that is used to **release energy** from large unstable atoms by **splitting them** into smaller atoms

Question 32

# How does nuclear fission work? | (6 steps)

Answer 32

1. The nucleus **absorbs a neutron**. 2. The atom splits into **two new lighter** elements that are roughly the same size. 3. **Two or three neutrons** are also released when an atom splits. 4. If any of these neutrons are moving **slow** enough to be **absorbed** by another nucleus, they can cause **more fission** to occur. 5. The energy not transferred to the kinetic energy stores of the particles is carried away by **gamma rays**. 6. This energy can be used to **heat water**, making steam to turn **turbines** and **generators**.

Question 33

# How is the energy produced by fission in a nuclear reactor controlled?

Answer 33

By using **control rods** to change how quickly the **chain reaction** can occur. ## Footnote These are lowered and raised inside a nuclear reactor to **absorb neutrons**, **slow down** the chain reaction and **control** the amount of energy released.

Question 34

# How does nuclear fusion work?

Answer 34

two **light nuclei collide** at high speed and **join** to create a **larger**, heavier nucleus ## Footnote the **heavier** nucleus produced by fusion does not have as much **mass** as the two **seperate**, light nuclei did, some of the mass of the light nuclei is converted to **energy** and released

Question 35

# What are the positives and negatives of nuclear fusion? | (1+, 2-)

Answer 35

+fusion releases **a lot** of energy (**more** than fission for a given mass of fuel) -scientists haven't found a way of using fusion to generate energy for us to use -the **temperatures** and **pressures** needed for fusion are so **high** that fusion reactors are really **hard** and **expensive** to buil