Radioactive Decay

Question 1

What is radioactive decay?

Answer 1

A random process. In a sample of radioactive material, we don’t know, and cannot predict, which nucleus will decay next

Question 2

Where does alpha decay usually happen? And what happens? What is its atomic mass and proton number?

Answer 2

In large nuclei
loses 2p and 2n
4 mass no.
2 proton no.
(-4 mass, -2 proton)

Question 3

What is beta decay? What is its proton number na mass number? What happens in a reaction?

Answer 3

A fast moving, high energy, electron emitted from the nucleus
0 mass no.
-1 proton no.
Gains 1p, loses 1e
(=mass, +1 proton)

Question 4

What is gamma decay? What is its proton and mass number?

Answer 4

Excess energy is emitted as energy
Doesn’t change the element
0 mass no.
0 proton no.
(=mass, =proton)

Question 5

What is neutron decay? What is its mass no. And proton no. ?

Answer 5

Where a nucleus emits a neutron
Won’t change the element (only its mass no.)
1 mass no.
0 proton no.
(-1 mass, =proton)

Question 6

What’s the mass and charge of the subatomic particles?

Answer 6

Proton = 1 mass, +1 charge
Neutron = 1 mass, 0 charge
Electron = 1/2000 mass, -1 charge

Question 7

What is half life

Answer 7

Time taken for half the nuclei in the sample to decay

Question 8

What will drop by 50% in 1 half life?

Answer 8

Count rate
Activity
No. of undecayed nuclei
Mass of undecayed sample
%remaining

Question 9

How to find an accurate half life from a graph

Answer 9

Draw a line from halfway down the no. of undecayed atoms and draw access until it reaches the curve.
Draw the line down to the x axis.
Calculate the difference between the lines.
Repeat this, halving each time until you run out of space.
Find the mean average of the differences.

Question 10

How is carbon-14 used to date artefacts?

Answer 10

The amount of c-14 shows how long ago it was living, the higher the % left, the more recent

Doesn’t work with rocks or fossils as they have no c-14

Question 11

What are the two safety precautions when using radioactive material in experiments?

Answer 11

Limit exposure time and increases distance between yourself and the radioactive material

Question 12

What does a Geiger-Müller counter measure?

Answer 12

The amount of radiation

Question 13

Which type of decay is the most/least ionising and why?

Answer 13

Alpha decay = most, biggest charge
Gamma decay = least, no charge

Question 14

What’s the atomic mass and charge of the three types of decay?

Answer 14

Alpha = 4 mass, 2+ charge
Beta = 1/2000 mass, -1 charge
Gamma = 0 mass, 0 charge

Question 15

How far does alpha, beta and gamma particles travel in the air?

Answer 15

Alpha = few cm
Beta = a meter
Gamma = several km

Question 16

What do alpha, beta and gamma particles pass through?

Answer 16

Alpha = air
Beta = most things including air, paper and body
Gamma = most things including aluminium and led

Question 17

What can’t alpha, beta and gamma particles pass through?

Answer 17

Alpha = most things including paper, card, metal, skin, smoke
Beta = thick aluminium & led sheeting
Gamma =. Very thick layer of led or concrete

Question 18

What is the energy of alpha, beta and gamma particles?

Answer 18

Alpha = low
Beta = medium
Gamma = high

Question 19

What is the definition of activity in terms of radiation?

Answer 19

No. Of decays happening per second

Question 20

What is the definition of count rate in terms of radiation?

Answer 20

No. Of detected decays per set amount of time

Question 21

What is the definition of bequerel in terms of radiation?

Answer 21

Unit of activity, e.g an acting of 50Bq means 50 decays per second

Question 22

Where does background radiation come from?
Put the 8 sources into order of most to least

Answer 22

1. Air (33.6%)
2. Medical (21%)
3. Ground/Buildings (16%)
4. Food and drink (15.6%)
5. Cosmic (13%)
6. Nuclear weapons (0.4%)
7. Air travel (0.3%)
8. Nuclear reactors (0.1%)

Question 23

What are 6 examples of uses of radiation?

Answer 23

Smoke alarms
Radiotherapy for thyroid cancer
Sterilisation of medical equipment
Kidney scans
Lung scans
Pesticides in the environment

Question 24

What’s the purpose of radiation safety measures

Answer 24

Radiation safety measures ae designed to increase your distance from the source and / or decrease your exposure time

Question 25

What is contamination?

Answer 25

unwanted radioisotopes in or on
an object

Question 26

What is exposure?

Answer 26

Near to a radioactive source

Question 27

What are three safety precautions of a nuclear power station?

Answer 27

Control rods, coolant, moderator

Question 28

Purpose and design of control rods:

Answer 28

Made of boron or cadmium
Reduce or stop chain reactions
Lowered to absorb neutrons

Question 29

What’s the purpose and design of the moderator?

Answer 29

Made up of graphite or water
Slow down neutrons
Fission of uranium atom works better with slow neutrons (makes the reaction more efficient)

Question 30

What’s the purpose and design of the coolant?

Answer 30

Made of CO2 or water
Cool down the reactor to protect from damage

Question 31

What is nuclear fission

Answer 31

Fission means split.
Nuclear fission is the split of the nucleus.
In a nuclear reactor we split uranium nuclei (or plutonium or even thorium).
To split a uranium-235 nucleus we add an extra neutron, making the nucleus unstable, causing it to split.
This produces new, smaller nuclei and ENERGY.

Question 32

What’s nuclear fusion?

Answer 32

Small nuclei join together, releasing energy