Fusion is the process when
two SMALL NUCLEI join to form a LARGER NUCLEI with the production of ENERGY
Fission
Fission is the process when two large nuclei split to
form two smaller nuclei with the production of energy. This can occur
spontaneously or due to a collision with a neutron. Often extra neutrons are
produced.
Chain Reaction
When neutrons split nuclei by fission and extra neutrons are produced which can split further nuclei. Large quantities of energy are produced.
Reducing
exposure to ionising radiation.
There are 3 groups of category to reduce harm caused by
radiation:
MONITOR
SHIELD
DISTANCE
Monitor
includes things like wearing radiation badges or EPUs, timing how long you are
exposed to radiation, checking with radiation counters any contamination on
clothes.
Shielding
is placing layers of absorbers between you and the source, BEWARE, goggles and
a lab coat are great at protecting against alpha but have no effect on gamma.
Only thick layers of lead would offer protection against gamma.
Distance. Radiation obeys the inverse square law, as you double the distance from a source the level you are exposed to decreases by ¼ . Using tongs is an effective method of keeping your distance from a source.
To give you an idea of the radiation dose that would occur with radiotherapy, here is my mum’s dose. I know that she’d have been happy to share this with you as a learning experience. I really miss you mum x
Here are some videos and powerpoint shows that I’ve made for the NPA but the outcomes are the same as those in N5 Physics. Thanks to John Sharkey for the use of the Virtual Flash Physics (Int 2) and to Julian Hamm of furryelephant for the animations of ionising an atom.
After watching the video can you mix and match the effects of the radiation. There are a few booboo’s such as given below and I say we put a beta particle instead of a beta source in the cloud chamber! But as I’ve already spent a day on this I had better move on!
NB In the video above I know totally that photographs were taken well before 1896, the first being taken in 1826. Henri Becquerel discovered that Uranium, a naturally radioactive element fogs photographic film.
I hope that I am not breaking any rules, but these great resources no longer appear to be online. Can’t believe they are 20 years old!
The first photos show the background count rate, a reading of counts taken over a 1 minute period. The source is then taken out at 9:00 am and a count taken between 9:00 and 9:01, readings are then taken every 15 mins.
half life Questions A print out for those who would like a copy of the National 5 Chemcord revision questions on half life. Here are the questions written out: HALF LIFE QUESTIONS
What is meant by the half life of a radioactive substance?
The activity of a source drops from 1000 kBq to 125 kBq in 9 days. Calculate the half life of the source.
The activity of a source drops from 4800 kBq to 150 kBq in 10 days. Calculate the half life of the source.
The activity of a source drops from 720 MBq to 45 MBq in 20 years. Calculate the half life of the source.
The activity of a source drops from 4096 kBq to 1 kBq in 2 days. Calculate the half life of the source.
The activity of a source drops from 448 kBq to 3.5 kBq in 17.5 years. Calculate the half life of the source.
A source has an activity of 1800 kBq and a half life of 2 days. What is its activity 10 days later?
A source has an activity of 576 MBq and a half life of 30 years. What is its activity 180 years later?
A source has an activity of 2400 kBq and a half life of 8 s. What is its activity 32 s later?
A source has an activity of 3200 kBq and a half life of 5.3 days. What is its activity 37.1 days later?
A source has an activity of 800 kBq after being stored for 4 days. If the half life is 1 day, what was its initial activity?
A source has an activity of 1800 kBq after being stored for 72 s. If the half life is 24 s, what was its initial activity?
A source has an activity of 40 kBq after being stored for 10 years. If the half life is 2 years, what was its initial activity?
A source has an activity of 30 kBq after being stored for 2 days. If the half life is 8 h, what was its initial activity?
A source has an activity of 40 MBq and a half life of 15 s. How long will it take for its activity to drop to 625 kBq?
A source has an activity of 25 MBq and a half life of 8 days. Approximately how long will it take for its activity to drop to below 1MBq?
A source has an activity of 320 MBq and a half life of 1000 years. Approximately how long will it take for its activity to drop to 500 kBq?
A background count rate of 20 counts per minute is measured in the absence’ of a source. When the source is present the count is 140 counts per minute initially, dropping to 35 counts per minute after 15 days. What is the half life to of the source?
If the background count is 28 counts per minute and the count with a source drops from 932 to 141 counts per minute in 24 h, what is the half life of the source?
If the background count rate is 24 counts per minute and the count rate with a source present drops from 4120 to 25 counts per minute in 2 days, what is the half life of the source?
In an experiment with a radioactive source, the count rate corrected for background radiation was measured and the following results obtained.
Time
in minutes
Corrected
Count Rate
in c.p.m.
0
1
2
3
4
5
100
58
32
18
10
5.6
a) Plot a graph to show these results.
b) Estimate the half life of the source from these results.
22. In an experiment with a source, carried out in an area where there is a high background radiation, the following results were obtained.
Time (s)
Count Rate
(c.p.m.)
0
30
60
90
120
150
180
210
240
270
300
88
72
60
52
44
39
36
34
32
29
30
a) Plot a graph to show these results.
b) Estimate the background count rate.
c) Estimate the half life of the source from these results.
ANSWERS
time taken for the activity to decrease by half
3 days
2 days
5 years
4h
2.5 years
56.25kBq
9 MBq
l50 kBq
25 kBq
12.8 MBq
14.4 MBq
1.28 MBq
1920 kBq
90s
32 to 40days
9500 years
5 days
8 h
73. 4h
For Questions 2-6 (to find t ½ when Ao and A known)
Step
Summarise
Starting with the original activity keep halving until you reach the final activity
COUNT THE ARROWS. This is the NUMBER of half lives.
Use the formula t½= time÷No. of t ½
Don’t forget to write out the time.
For Questions 7-10 (to find the final activity when t and t ½ are known) Step
Summarise
Use the formula to find the number of half lives (this will be the number of arrows) No. of t ½ = time÷ t½
Starting with the original activity keep halving until you reach the final activity
COUNT THE ARROWS. This is the NUMBER of half lives.
Don’t forget to write out the units for final activity.
For Questions 11-14 (to find Ao when A, t ½ and time are known)
Steps
Summarise
Use the formula to find the number of half lives (this will be the number of arrows) No. of t ½ = time÷ t½
DOUBLE the final activity for the number of t ½ eg If you have 4 half lives double the final activity 4 times. NB DO NOT MULTIPLY BY 4
The alternative is to MULTIPLY the final activity by 2n (2 to the power n where n is the number of half lives)
The number at the end of the arrows is your original activity, don’t forget to add the units.
For Questions 15-17
Step
Summarise
Starting with the original activity keep halving until you reach the final activity
Count the Arrows
Use the formula time = t½ × No. of t ½
Experiment to Measure Half Life
The activity of a radioactive source decreases time. However the rate of decrease slows with time. Because of this, and because the decay of individual atoms is random and unpredictable, theoretically a radioactive source will never completely lose all of its activity. The time taken for half of the atoms in a radioactive sample to decay is a constant for that source called the half-life of the source. So the half-life of a radioactive source is the time period during which the activity of the source falls to half of its original value. The half-life of some sources is as low as a fraction of a second; for others it is many thousands of years.
Finding the half-life of a radioactive source
Apparatus: Geiger-Muller tube, Scaler counter or ratemeter, Source (eg.sealed protactinium-234 radioactive source and drip tray).
Instructions:
Use the Geiger-Muller tube and scaler counter to measure the background count rate.
Record this value.
Set up the apparatus shown in the diagram.
Measure and record values of count rate and time interval for a suitable time period.
Correct all your measurements for background by taking the background count off all other measured count rates..
Plot a graph of COUNT RATE or ACTIVITY against TIME.
Find the half life from the graph
Half life and safety
To measure the half-life of a radioactive source, the level of the background radiation is first measured. Then the count rate with the radioactive source present is measured over a suitable period of time using a suitable detector such as a Geiger-Muller tube connected to a scaler. A graph of the count rate (with the source present), corrected for background radiation, is plotted.A suitable count rate value is chosen, say 80 counts per minute, and the time at which the source had this count rate, t1, is marked as above. In a similar way the time t2 at which the count rate is half the previous value, 40 counts per minute, is found. The half-life of the source is the time period t2 -t1. Any starting value can be chosen, the time period for the count rate to halve in value will always be the same.
EXAMPLE
In six years, the activity of a radioactive isotope drops from 200 kBq to 25kBq. Calculate the half-life of the isotope.
SOLUTION: original activity = 200 kBq
⇓
Activity after 1 half-life = ½ ×200 kBq = 100 kBq
⇓
Activity after 2 half-lives = ½ × 100 kBq = 50 kBq
⇓
Activity after 3 half-lives = ½ × 50kBq = 25 kBq
So 6 years represents 3 half-lives, thus one half-life is 2 years.
Safety with radiation
There are several safety precautions that must be taken when handling radioactive substances.
Always handle radioactive substances with forceps. Do not use bare hands.
Never point radioactive substances at anyone.
Never bring radioactive substances close to your face, particularly your eyes.
Wash hands thoroughly after using radioactive substances especially after using open sources or radioactive rock samples.
Unauthorised people must not be allowed to handle radioactive substances. In particular, in the United Kingdom, no one under 16 years of age may handle radioactive substances.
In addition there are several safety precautions relating to the storage and monitoring of radioactive substances.
Always store radioactive substances in suitable lead-lined containers.
As soon as source has been used, return it to its safe storage container, to avoid unnecessary contamination.
Keep a record of the use of all radioactive sources.
The equivalent dose received by people can be reduced by three methods:
shielding;
limiting the time of exposure;
increasing the distance from the source.
Stay safe and keep under your annual dose of 2.2 mSv!
Here are the results from the Protactinium Generator Experiment. Your task is to correct for background (take the background count per second away from the count rate) and then plot a graph of count rate (cps) against time (s). Remember the count rate was taken every 10 s but shows the value of the count rate (for one second)
Background count rate (c.p.m.) 48.0, 46.0, 42.0
Average background count rate (c.p.m.) 45.3
Average background per second (c.p.s.) work it out!
Time
Count rate
(s)
(cps)
0
80.3
10
73.9
20
67.3
30
60.5
40
55.2
50
49.6
60
45.7
70
41.5
80
37.4
90
34.1
100
31.3
110
28.5
120
25.9
130
23.9
140
21.7
150
19.4
160
17.6
170
16
180
14.9
190
13.4
200
12.3
210
11.2
220
10.2
230
9.2
240
8.4
250
7.5
260
6.9
270
6.4
280
5.7
290
5.3
300
4.7
Indium 116 Half Life
Here are the results for the Indium-116 half life experiment. Warning, do not plot a graph in 15 minute intervals or you will have more difficulty finding the half life. Make the scale ten minute intervals.
You can track the experiment yourself through the link below
Instructions:
