Radioactivity

Question 1

Why are some nuclei unstable

Answer 1

The number of neutrons inside it - too few or too many can affect the stability of

Question 2

How do you predict which nucleus will decay next

Answer 2

You can’t, it is random

Question 3

How is ionising radiation formed

Answer 3

When unstable nuclei decay

Question 4

What does ionising radiation cause

Answer 4

Atoms to gain or lose electric charge, forming ions

Question 5

What can we predict about the decay of a radioactive material

Answer 5

The PROBABILITY that a certain proportion of a radioactive material will decay in a given time

Question 6

What are the three types of ionising radiation

Answer 6

1. Alpha (α)
2. Beta (β)
3. Gamma (γ)

Question 7

What are alpha particles

Answer 7

Fast moving helium nuclei (helium atoms with no electrons) that are thrown out of the unstable nuclei when they decay

Question 8

What is the range and ionising power of alpha, beta and gamma

Answer 8

Alpha - short range, high ionising power
Beta - mid range, mid ionising power
Gamma - long range, low ionising power

Question 9

How far can alpha particles move in air and through paper and why

Answer 9

Air - a few cm
Paper - a few mm

The range is low because they interact with atoms along their path, therefore rapidly giving up their energy

Question 10

What is a beta- particle

Answer 10

Fast moving electrons that are ejected by a decaying nucleus.

Question 11

How is a beta- particle ejected from the nucleus considering there are no electrons in a nucleus

Answer 11

In an unstable nucleus, a neutron can split into a proton and electron. The proton stays in the nucleus but the electron is ejected

Question 12

What is the purpose of radioactive decay

Answer 12

For a nucleus to get a balance of protons and neutrons to allow it to be stable

Question 13

How much heavier are alpha particles than beta particles

Answer 13

8,000

Question 14

What is the relative charge of a beta- particle

Answer 14

-1

Question 15

What is the relative charge of a beta+ particle

Answer 15

+1

Question 16

Why do beta particles have a longer range than alpha, and why does this have an affect

Answer 16

They interact less frequently with matter in their paths because they are smaller and carry less charge

Question 17

How far can beta particles travel through air and aluminium

Answer 17

Air - long distances
Alumulumu - 1-2 mm

Question 18

What are gamma rays

Answer 18

Electromagnetic waves with very short wavelengths

Question 19

What is the mass and charge of gamma radiation

Answer 19

Mass = 0
Charge = 0

Question 20

What can you use to detect ionising radiation (2)

Answer 20

1. Photographic film
2. A Geiger-Muller tube

Question 21

What is a Geiger-Muller tube

Answer 21

A tube that contains a gas that becomes ionised when radiation hits it, causing an electrical current which allows a counter to click up one.

It is used to find out the number of radioactive particles present

Question 22

How else can we represent alpha particles

Answer 22

He (helium) or 4
He
2

Question 23

What is the charge of an alpha particle

Answer 23

+2

Question 24

What is the charge of a beta particle

Answer 24

-1

Question 25

What is the nuclear equation for alpha decay

Answer 25

-4 from the mass number -2 from atomic number This will then form a new element. We must then add the helium at the end as a product

Question 26

What would be the alpha-decay equation for uranium-238

Answer 26

U -> Th + He Th - thorium. We use this because the mass number loses 4 and the atomic number loses 2

Question 27

What is the nuclear equation for beta decay

Answer 27

The atomic number (small) goes up by 1 but the mass number (big) does not go up. Then an electron is added to the end e.g. C -> N + e

Question 28

What letter is used to represent an electron

Answer 28

0 e -1 The mass number is zero but it has a charge of -1 so the atomic number is -1

Question 29

What is the nuclear equation for gamma radiation

Answer 29

Nothing is changed because gamma rays are purely energy E.g. Th - > Th + γ(gamma)

Question 30

What is the equation for neutron emission

Answer 30

One is taken off the mass number but zero is taken off the atomic number. Then a neutron (n) is added to the end

Question 31

What is the activity of a radioactive sample measured in

Answer 31

becquerels (Bq)

Question 32

What happens to the activity of a radioactive sample as time goes on

Answer 32

It decreases

Question 33

Are beta particles electrons from inside or outside the nucleus

Answer 33

Inside

Question 34

What are 3 background sources of radioactivity in space

Answer 34

Comic rays Solar radiation Cosmic microwave background (CMB)

Question 35

What are 3 background radiation sources from the earth

Answer 35

1. Radon gas 2. Gamma radiation from naturally occurring isotopes like uranium and thorium 3. Rocks and soil (radioactive elements in the earth’s crust)

Question 36

Design an experiment for determining the penetrating power of different radiation types

Answer 36

Put a Geiger-muller tube behind some materials/ further away from the radiation source, then test if it detects it or not. Then move on to the next radiation source. REPEAT. REMEMBER TO CHECK FOR BACKGROUND RADIATION AND SUBTRACT THIS FROM ALL READINGS.

Question 37

Design an experiment for investigating the ionising power of different types of radiation

Answer 37

It is the opposite to the distance one - because if it has a high ionising power it will ionise the particles around it so will not travel a far distance. REMEMBER TO CHECK FOR BACKGROUND RADIATION FIRST AND SUBTRACT THIS FROM READINGS