1. STARTER
If a company has 1 million phones and sells half of the stock every day, how long does it take to sell all the stock?
20 days
A piece of paper is 0.5 mm, how many times would it need to be folded to reach the moon?
(348, 400 km to the moon from earth)
41 times is more than enough
How come?

2. Learning objectives
Review what is meant by isotope and how this is radioactive. (D)
Understand the ‘random’ nature of radioactive decay. (C)
State and explain what is meant by ‘half-life’. (B)
Draw key conclusions from graphs of radioactive decay. (A)
Keywords:
Proton Isotope
Neutron Half-life
Electron Count
Stable/Unstable
NOTICES: …………….

3. THEY ARE ISOTOPES OF THE CARBON ATOM
Recap of …. Isotopes
Carbon 12 C 6
?????
Carbon 13 C 6
?????
Carbon 14 C 6
????? ? ? ?
What is being shown above?
THEY ARE ISOTOPES OF THE CARBON ATOM
Isotopes are atoms of the same element with different numbers of neutrons. The isotopes of an element have the same number of protons.
The nuclei of some isotopes are unstable. They can split up or ‘decay’ and release radiation. Such isotopes are called radioactive isotopes or radioisotopes. When a radioactive isotope decays, it forms a different atom with a different number of protons.

4. What do these isotopes decay into?
TASK – Isotopes of what?
What do these isotopes decay into?
Plutonium
240 Pu 94
Uranium
236 U 92 1) -
Alpha
Decay =
Carbon 14 C 6
Nitrogen 14 N 7 - = 2)
Beta
Decay
Ceasium
137 Cs 55
Barium
137 Ba 56 3) - =
Beta
Decay

5. RECAP: What are our 3 types of radiation?α β γ

6. CLASS ACTIVITY HOW MANY FLIPS UNTIL ALL COINS SHOW HEADS?
You each have 3 coins.
When told you must spin or flip your 3 coins.
Tell the teacher when asked how many (if any landed) on heads and put these to one side.
When told spin/flip your remaining coins telling the teacher which landed on heads and putting these to one side.
Repeat until we stop.
1p coin -
Do we expect that some coins will turn up heads each time we spin/flip the coins?
Can we predict how many will be heads on each turn?
Is it more likely there will be more heads when we have more coins?
Also less heads when we have less coins?

7. CLASS ACTIVITY Time (no. spins/flips) No. of Heads 1 2 3 4 5 6 7 8 910 11 12 13
You each have 3 coins.
When told you must spin or flip your 3 coins.
Tell the teacher when asked how many (if any landed) on heads and put these to one side.
When told spin/flip your remaining coins telling the teacher which landed on heads and putting these to one side.
Repeat until we stop.

8. CLASS ACTIVITY What does this graph show?
RIGHT CLICK ON GRAPH
-> EDIT DATA
-> INPUT THE DATA COLLECTED FROM YOUR CLASS.
IT WILL UPDATE APPROPRIATELY
RIGHT CLICK ON GRAPH
-> EDIT DATA
-> INPUT THE DATA COLLECTED FROM YOUR CLASS.
IT WILL UPDATE APPROPRIATELY
What does this graph show?
What detailed statement can you make from the graph?

9. Random???? What does random mean?
Unexpected, unusual, odd ….etc
‘Happening without method’
Random….we know it is going to happen just not exactly when.
What things can you think of that are ‘random’
RADIOACTIVITY

10. RADIOACTIVITY Do we know when a nucleus is going to decay?
Can we predict how many nuclei are going to decay at any time?
Can we expect more nuclei to decay when there are more unstable nuclei in a sustance?
Also less decays when there are less unstable nuclei?
RIGHT CLICK ON GRAPH
-> EDIT DATA
-> INPUT THE DATA COLLECTED FROM YOUR CLASS.
IT WILL UPDATE APPROPRIATELY

11. RADIOACTIVITY & HALF-LIFE
You are going to keep track of radioactive decay of a bunch of nuclei
You will need to do this in pairs
TIME (SECONDS)
No.OF DECAYS 1 2 3 4 5 6 8 11 15
Note how many nuclei decay with time – we will then plot this on graph 2 2 2 1 1 1 1 1 1

12. TASK – TIMING DECAY START Some more left RIGHT CLICK ON GRAPH
-> EDIT DATA
-> INPUT THE DATA COLLECTED FROM YOUR CLASS.
IT WILL UPDATE APPROPRIATELY

13. DO WE NEED TO RUN THAT AGAIN??
‘THOUGHT SO’
‘ONE MORE TIME’

14. TASK – TIMING DECAY START Some more left RIGHT CLICK ON GRAPH
-> EDIT DATA
-> INPUT THE DATA COLLECTED FROM YOUR CLASS.
IT WILL UPDATE APPROPRIATELY

15. TIMING DECAY - RESULTS

16. TIMING DECAY – USING DATA
We want to plot how much activity is left in our radioactive substance, so there is one more thing to do our data.
80 -
decays =
77 -
decays =
WE STARTED WITH 80 UNSTABLE RADIOACTIVE NUCLEI
75 -
decays =
We therefore need to start with 80 and minus the decays that occurred each second.

17. WHAT CONCLUSION CAN WE DRAW FROM OUT GRAPH?
Radioactive decay
WHAT CONCLUSION CAN WE DRAW FROM OUT GRAPH?
A GRAPH LIKE THIS CAN TELL US THE ‘HALF-LIFE’ OF A RADIOACTIVE SUBSTANCE

18. What is meant by ‘half-life’?
REMEMBER:
The nuclei of radioactive atoms are unstable. They break down and change into a completely different type of atom. This is called radioactive decay. For example, carbon-14 decays to nitrogen-14 when it emits beta radiation.
What is meant by ‘half-life’?
The ‘half-life’ of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
OR…….
the time it takes for the count rate from a sample containing the isotope to fall to half its starting level

19. Reading half-life graphs
How do we read half-life from our graphs? 60
What is the half-life of the substance shown in the graph? 50 40
4 days
Number of radioactive nuclei 30
What is the second half-life of the substance shown in the graph? 20 10 2 4 6 8 10 12 14
9 days
Time (Days)

20. Reading half-life graphs
Compare and contrast the two graphs

21. Reading half-life graphs
Short half-life, more active sample 60 50 40
Number of radioactive nuclei 30 20 10 1 2 3 4 5 6 7 8
Days

22. Reading half-life graphs
Long half-life, less active sample 60 50 40
Number of radioactive nuclei 30 20 10 5 10 15 20 25 30 35 40
Days

23. In a single elimination tournament…
After each round, half of the teams are eliminated.
This is similar to the half-life of a radioactive element.
Day1
Day 3
Day2
Day 5
Day 4

24. After one “half life”, 50% of the material has decayed
It did not disappear, but it did turn into a different element because of alpha, beta, or gamma decay.
Radioactive materials decay
from the “Parent” material
into the “Daughter Product”.
Daughter Product
Original
“Parent” Material

25. Each half-life, the amount of atoms gets cut in half.

26. One half-life.

27. Two half-lives.

28. Three half-lives.

29. Four half-lives.

30. Don’t worry about the last atom
Don’t worry about the last atom. You start with so many trillions that you never really get there.
(It will just decay and then they’re all gone.)

31. 100% parent 0% daughter 0 half lives
Since you don’t know how many atoms you started with, a ratio between parent to daughter will tell you how many half-lives have gone by.
100% parent
0% daughter
0 half lives

32. One half-life.
50% parent
50% daughter
1 half-life

33. Two half-lives.
25% parent
75% daughter
2 half-lives

34. Three half-lives.
12.5% parent
87.5% daughter
3 half-lives

35. Four half-lives.
6.25% parent
93.75% daughter
4 half-lives

36. Summary
The half-life of a radioactive isotope is the average time it takes for he number of nuclei of the isotope in a sample to halve.
The activity of a radioactive source is the number of nuclei that decays per second.
The number of radioactive isotopes and the activity decrease by half every half-life.

37. Review Questions
1) A Radioactive substance consists of unstable nuclei that emit nuclear radiation to become stable. 2) Isotopes are atoms of the same element with different number of neutrons. When isotopes decay their nuclei split and release energy. 3) Half-life refers to the time taken for a nuclear samples activity to reduce by half.. 4) 32 days (4 half-lives) 5) 3.5 days (accept )