EQ's Flashcards
Techentium-99m is an important isotope in medical imaging.
The half-life of technetium-99m is 6 hours.
A fresh sample of technetium-99m is prepared in a hospital.
What fraction of this sample will have decayed after 18 hours?
So the question is NOT asking you how much will be remaining but how much will have decayed!!! So that will be original - remaining to find out how much has been decayed
1h-l = 6 hours
18/6 = 3
= 3 half lives
(1/2)3=1/8 remaining
so 8/8 - 1/8 = 7/8 has decayed (8/8 = 1)
Answer = 7/8
A sample of technetium of mass 128 mg is prepared on March
3rd at midday.
The half-life of technetium is 6 hours
How much of this technetium will be remaining on March
5th at the same time?
It’s asking about how much is remaining
1 h-l = 6 hours
2 days = 48 hours
48/6= 8 half lives
= (1/2)8= 1/256 remaining
= 1/256 x 128= 0.5 mg remaining
Answer= 0.5 mg
To estimate the age of rocks, scientists sometimes compare the amount of potassium-40 the amount of argon-40 they contain.
They assume that, when the rock was just formed, it contained no argon .
Potassium-40 has a half-life of 1.3 × 109 years, and it decays to form argon-40, which is stable.
The ratio of potassium-40 to argon-40 in a particular rock is 1:1.
Estimate the age of the rock.
This question is basically about net decline ratios (o.g.:remaining)
for this one, if the ratio if 1:1 and the half-life is 1.3 × 109 years
After 1 half-life (1:1) the potassium has halved once (1/2)1 which is a net decline ratio of 1o.g:1 remaining (remember)
So the answer is 1.3 × 109 years old ( a half life)
Answer =1.3 × 109 years
Suggest why people are opposed to the use of nuclear power
[2 marks]
There is a risk of a reactor meltdown
There could be problems with the safe long-term disposal of the hazardous radiocative waste
Suggest why an isotope with a large percentage mass and long half-life may provide a large contamination risk
[2 marks]
It has a great mass
It has a long half life which menas that it takes longer to decay and will remain in the environment for longer
Suggest why an isotope with a short half-life may provide a high contamination risk
[2 marks]
It has a short half life, which menas it has a high activity
So it decays quickly and so will release radiation into the environment at a faster rate
What is the difference between radioactive contamination and irradiation?
[2 marks]
Contamination is when an unwanted radioactive substance is present on or inside an object
Irradiation is when an object is exposed to ionising radiation
Give two reasons why gamma radiation is used to sterilise food
[2 marks]
To kill bacteria
To prolong shelf life
A friend is concernedabout eating apples and other food which have been sterilised using gamma rays.
How would you explain to them that there was no need to worry?
When gamma rays pass through food, they just deposit energy, so the food does not become radioactive
In a hospital, a radiographer might take dozens of X-rays per day.
Write down two ways in which they protect themselves against the harmful effects of radiation.
Maximise their distance from the X-ray beams and the source of radiation
Use the appropriate shielding to absorb the X-rays travelling towards them
A rock has a count rate of 80 Bq
After half an hour, the count rate is 23 Bq
Calculate the half-life of the rock
1) 80/2= 40
2) 40/2= 20
To get from 80 to around 20Bq is 2 half lives
If 2h-l = 30mins
1 h-l = 15mins
=15 minutes
Answer = 15 minutes
Explain how nuclear fusionleads to the release of energy
[2 marks]
Two light nuclei join to form a heavier nucleus- the combined mass of the reactants is greater than the mass of the product
This is because the mass was converte into energyd and released as radiation
Explain what makes radioactive decay random
[2 marks]
You cannot predict which nuclei is going to decay
You cannot predict when the nuclei is going to decay
Even though there may be a risk, doctors frequently use radioactive substances for medical diagnosis and treatments.
Suggest why
[1 mark]
The benefits of using the radiation may outweigh the risk
Explain the risk to a patient of using a radioactive substance as a medical tracer.
[2 marks]
The radioactive substance will emit radiation which cause ionisation
This may harm healthy cells by causing cell damage
Wearing polythene gloves doesn’t prevent your hands from being irradiated
Suggest why you should still wear these gloves when handling radioactive materials
[2 marks]
To prevent the transfer of the radioactive material to your hands
Which will cause irradiation over a long period of time
Explain the ideal properties of a radioactive source for medical diagnosis
[4 marks]
It should emit gamma radiation which is weakly ionising
This will cause less cell damage
It should have short half-life
This means that it will not remain in the body for a long period of time and so will cause less cell damage
+ highly penetrating so it can be detected outside of the body and will penetrate the skin and not remain in the body
How does the use of control rods ensure that the chain reaction within a nuclear reactor is controlled?
[3 marks]
Control rods absorb the neutrons within the reactor
The control rods are lowered further if the rate of the reaction becomes too high
The control rods reduce the number of fission neutrons which go on to cause further fission reactions
Explain what is meant by a chain reaction in nuclear fission
A neutron hits a heavy and unstable nucleus and are absorbed by it, causing the nucleus to split into two daughter nuclei and 2-3 neutrons
These neutrons then go on hit other unstable nuclei and the process repeats in a secondary fission reaction
What is the difference between induced and spontaneous nuclear fission
[2 marks]
Spontaneous fission is random
Induced fission is controlled where we allow a neutron to hit a heavy, unstable nucleus and cause it to rapidly undergo fission
Explain what is meant by nuclear fission
[2 marks]
The splitting of a heavy, unstable nucleus to form two daughter nuclei and 2-3 neutrons
This reaction releases energy
Suggest three advantage of the fuel used in a fusion reactor compared with a fuel used in a fission reactor
[3 marks]
They are easy to obtain and extract from seawater
They release more energy
They produce little radioactive waste
also available in large amounts
What is the energy released from a nuclear fuel inside a reactor used for?
[1 mark]
To generate electricity
also to heat water
Describe how the energy produced in nuclear fission is used to generate electricity
[3 marks]
The energy is used to heat up water
This produces steam
The steam drives a turbine which turns a generator
Why does lowering control rods reduce the amount of energy released by nuclear fuel?
[2 marks]
The control rods absorb the neutrons
So there are fewer neutrons
And the chain reaction slows down
Suggest two reasons why scientists want to creat nuclear fission reactors
[2 marks]
They provide another source of energy
They produce no radioactive waste
