Chapter 25 Radioactivity

Question 1

What is the charge of an alpha particle?

Answer 1

2+

Question 2

What is a beta particle?

Answer 2

A fast moving electron

Question 3

What is gamma radiation?

Answer 3

High frequency photons

Question 4

What and how are different types of radiation affected by charge?

Answer 4

Gamma is unaffected
Beta - is attracted by a positive charge
Beta + is attracted by a negative charge
Alpha is affected by a negative charge

Question 5

What absorbs alpha (what is its range) and why?

Answer 5

It has a short range because it easily ionises surrounding particles. Paper or air absorbs them fine.
It is a large particle so it collides with other particles easily

Question 6

What absorbs beta particles and what is its range?

Answer 6

It is less ionising than the alpha particle. They have a much longer range in air and a few mm of aluminium stops it

Question 7

How ionising is gamma, what is its range and why?

Answer 7

It is not very ionising at all. A few cm of lead will absorb it but an infinite amount of lead could also still allow it through. The graph of absorption per thickness is exponential.

Question 8

What can ionising radiation do to the body?

Answer 8

It can cause damage to living cells and dna mutation

Question 9

How must radiation sources be handles?

Answer 9

With tongs

Question 10

Describe the equation for alpha decay

Answer 10

A particle with a mass of A and proton number of Z decays into a particle with a mass of A-4 and a proton number of Z-2

Question 11

What causes beta decay?

Answer 11

The weak nuclear force

Question 12

What is the equation for gamma decay?

Answer 12

X ==> X + γ

Question 13

What does random mean when it comes to decay?

Answer 13

It means that we cannot predict when a nucleus is about to decay
Each nucleus within the sample has an equal chance of decaying

Question 14

What does spontaneous mean when it comes to decay?

Answer 14

The decay is not affected by the presence of other nuclei

The decay is not affected by external factors such as pressure

Question 15

Even through decay is random and spontaneouse we can…

Answer 15

still predict the way that the overall substance decays

Question 16

What is the half life?

Answer 16

This is the time it takes for half the nuclei in a sample to decay

Question 17

What affects the half life?

Answer 17

The activity of the nuclei

Question 18

What is the activity?

Answer 18

This is the amount of decays in a sample per second

Question 19

What is the activity affected by?

Answer 19

The number of nuclei

The decay constant

Question 20

What is the equation for activity?

Answer 20

A = λ x N
A = Activity
λ = Decay constant
N = Number of nuclei

Question 21

What is the unit for activity?

Answer 21

bq (becquerel)

The decays per second

Question 22

What is the decay constant?

Answer 22

It is the probability that a nucleus will decay

Question 23

What is the unit for the decay constant?

Answer 23

S^-1

Question 24

What is the decay equation?

Answer 24

N = N0e^(-λt)

Question 25

What is an alternative to the decay equation that also involves activity?

Answer 25

A = A0e^(-λt)

Question 26

What is the simplified decay equation at the half life? and when is it used?

Answer 26

e^(λ t-half) = 2

Question 27

How does carbon dating work?

Answer 27

When an organism dies, It stops consuming carbon-14. The ratio of carbon-12 to carbon-14 from a sample of a living material is used and and compared to a dead sample. The amount of carbon-14 is calculated by analysing the activity of a sample of carbon. Activity is proportional to the number of undecided carbon-14 nuclei

Question 28

Describe the process for atmospheric carbon

Answer 28

High speed protons from cosmic rays collide with atom in the upper atmosphere to produce neutrons which collide with nitrogen-14 nuclei and form carbon-14 which emit beta-minus particles and become nitrogen 14 again so the amount of nitrogen-14 in the atmosphere is repleished

Question 29

What are the limitation of carbon dating and why?

Answer 29

Assumptions are made that the ratio of carbon-14 to carbon-12 has remained constant. This ratio is also affected by CO2 levels and solar flairs
Because the amount of carbon-12 to carbon-14 is low, the count from a sample is very low

Question 30

Why cant carbon dating be used on rocks?

Answer 30

Because the rocks were never living and the half life is too short. Other elements are used to date rocks

Question 31

What is the process of rock dating?

Answer 31

Rubidium-87 emits a beta- particle and transform into a strontium-87. The half life is about 49 billion years.

Question 32

What is the maximum time that carbon dating is affective to?

Answer 32

50,000 years