Radioactivity- 6

Question 1

What did Ernest Rutherford do that proved the plum pudding model wrong?

Answer 1

Conducted an experiment where he fired positively charged subatomic particles (alpha particles) through gold foil. He discovered that while most went through, some bounced back which is how he discovers the positively charged nucleus and electrons moving around it while most of the atom being empty space.

Question 2

Proton

Answer 2

Location- nucleus
Relative charge +1
Relative mass 1

Question 3

Neutron

Answer 3

Location: nucleus
Relative charge: 0
Relative mass: 1

Question 4

Electron

Answer 4

Location: shells
Relative charge: -1
Relative mass: 0/ 1 over 1835

Question 5

If the atom absorbs energy:

Answer 5

The electron can move to a higher orbit (outer shells)

Question 6

When an electron returns to a lower orbit

Answer 6

the atom emits energy as electromagnetic radiation (visible light of a particular wavelength.)

Question 7

Ionising radiation

Answer 7

Radiation that causes electrons to escape an atom.

Question 8

Main source of background radiation

Answer 8

Radon gas

Question 9

Other radiation

Answer 9

Food and drink
buildings and ground
Cosmic rays
Medical (gamma+ xrays)
Nuclear

Question 10

How is radioactivity of a source measured?

Answer 10

Geiger- Müller tube
Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow.
This tube can either be connected to a counter to count the pulses of current or can produce a click each time radiation is detected.
The count rate is the number of clicks per second or minute.

Question 11

What do scientists need to do before measuring the radiation of a source?

Answer 11

Measure the background radiation several times and calculate the mean then subtract this from their reading of the radiation of a source.

Question 12

Half life

Answer 12

The average time it takes for the number of radioactive nuclei in an isotope to halve

Question 13

Alpha decay

Answer 13

He
Atomic mass (top number decreases) by 4
Atomic number (bottom number) decreases by 2

Question 14

Beta decay

Answer 14

e
Atomic mass (top number) stays the same
Atomic number (bottom number) increases by 1

Question 15

Positron (beta plus) decay

Answer 15

e
Atomic mass (top number) stays the same 
Atomic number (bottom number) decreases by 1

Question 16

How does nuclei lose energy when subatomic particles in the nucleus are rearranged

Answer 16

As gamma radiation

Helps to make nuclei more stable

Question 17

Half life of isotope uranium-235

Answer 17

700 million years

Question 18

Half life of isotope carbon-14

Answer 18

5730 years

Question 19

Half life of isotope caesium-137

Answer 19

30 years

Question 20

Half life of isotope radon-222

Answer 20

3.8 days

Question 21

The more stable nuclei a sample contains, the lower its —

The half life of an isotope is also a measure of how long it takes for the activity to —

Answer 21

Activity

Halve

Question 22

What can small amounts of ionising radiation over long periods of time cause?

Answer 22

Damage DNA inside the cell and cause mutations

Cancer

Question 23

How are risks of radiation contamination reduced in hospitals

Answer 23

Storing radioactive sources in lead-lined containers
Distance from a source (using tongs)
Shielding from the source
Minimising time in the presence of a source

Question 24

What happens when someone is irradiated

Answer 24

They’re exposed to alpha, beta or gamma radiation from nearby radioactive materials. Once a person moves away the irradiation stops

Question 25

What happens when someone is contaminated

Answer 25

They get particles of radioactive material on their skin or in their body. They’ll be exposed to radiation as the unstable isotopes in the material decay. This will continue until the material has decayed or until the source of contamination is removed but this isn’t always possible. Water and soils can be contaminated and spread through the food chain.

Question 26

Plum pudding model

Answer 26

Positively charged pudding

Question 27

Radius of nucleus and atom

Answer 27

Nucleus: 1 times 10^-15 m | Atom : 1 times 10^-10 m

Question 28

``` Alpha particles How many protons and neutrons Relative mass How many electrons Charge How far will they travel in air How ionising What are they stopped by ```

Answer 28

``` 2 protons and 2 neutrons Relative mass of 4 No electrons so charge is +2 Written as a or ^42He Travel a few cm in air as they lose energy quickly Very ionising Stopped by sheet of paper ```

Question 29

``` What are beta particles Relative mass Charge Where do the electrons that are beta particles come from How far will they travel in air How ionising What are they stopped by ```

Answer 29

``` High energy, high speed electrons Relative mass is 1/1835 Charge is -1 They come from the nucleus of atoms when a neutron transforms to a proton. Beta particles don’t ionise the atom as they leave them. Travel a few metres in air Moderately ionising Stopped by 3mm thick aluminium because they’re less ionising than alpha particles so lose less energy ionising particles they encounter- so they have more energy to travel through thicker materials. Gains 1 electron B- or ^0 -1 e ```

Question 30

What are positrons Mass Charge

Answer 30

``` High energy high speed particles Same as electrons 1/1835 Charge +1 Lose 1 electron B+ or. ^0 +1 e ```

Question 31

``` What are gamma rays What are their charge How far do they travel in air How ionising What are they stopped by ```

Answer 31

``` High frequency electromagnetic waves Don’t have an electric charge Travel a few km in air Weakly ionising Stopped by lead few cm thick ```

Question 32

Isotopes of the same element

Answer 32

Same atomic number (bottom number) number of protons | Different mass number (top number) if different numbers of neutrons

Question 33

How is a positive ion formed

Answer 33

An atom has the same number of protons and electrons so has no charge. If an atom loses an electron, it then has one more proton than it electron so has an overall positive charge. When an atom gains an electron the overall charge is negative because there’s one more electron than proton and electrons have a negative charge.