EQ's

Question 1

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?

Answer 1

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

Question 2

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?

Answer 2

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

Question 3

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.

Answer 3

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

Question 4

Suggest why people are opposed to the use of nuclear power

[2 marks]

Answer 4

There is a risk of a reactor meltdown

There could be problems with the safe long-term disposal of the hazardous radiocative waste

Question 5

Suggest why an isotope with a large percentage mass and long half-life may provide a large contamination risk

[2 marks]

Answer 5

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

Question 6

Suggest why an isotope with a short half-life may provide a high contamination risk

[2 marks]

Answer 6

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

Question 7

What is the difference between radioactive contamination and irradiation?

[2 marks]

Answer 7

Contamination is when an unwanted radioactive substance is present on or inside an object

Irradiation is when an object is exposed to ionising radiation

Question 8

Give two reasons why gamma radiation is used to sterilise food

[2 marks]

Answer 8

To kill bacteria

To prolong shelf life

Question 9

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?

Answer 9

When gamma rays pass through food, they just deposit energy, so the food does not become radioactive

Question 10

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.

Answer 10

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

Question 11

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

Answer 11

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

Question 12

Explain how nuclear fusionleads to the release of energy

[2 marks]

Answer 12

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

Question 13

Explain what makes radioactive decay random

[2 marks]

Answer 13

You cannot predict which nuclei is going to decay

You cannot predict when the nuclei is going to decay

Question 14

Even though there may be a risk, doctors frequently use radioactive substances for medical diagnosis and treatments.
Suggest why

[1 mark]

Answer 14

The benefits of using the radiation may outweigh the risk

Question 15

Explain the risk to a patient of using a radioactive substance as a medical tracer.

[2 marks]

Answer 15

The radioactive substance will emit radiation which cause ionisation

This may harm healthy cells by causing cell damage

Question 16

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]

Answer 16

To prevent the transfer of the radioactive material to your hands

Which will cause irradiation over a long period of time

Question 17

Explain the ideal properties of a radioactive source for medical diagnosis

[4 marks]

Answer 17

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

Question 18

How does the use of control rods ensure that the chain reaction within a nuclear reactor is controlled?

[3 marks]

Answer 18

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

Question 19

Explain what is meant by a chain reaction in nuclear fission

Answer 19

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

Question 20

What is the difference between induced and spontaneous nuclear fission

[2 marks]

Answer 20

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

Question 20

Explain what is meant by nuclear fission

[2 marks]

Answer 20

The splitting of a heavy, unstable nucleus to form two daughter nuclei and 2-3 neutrons

This reaction releases energy

Question 21

Suggest three advantage of the fuel used in a fusion reactor compared with a fuel used in a fission reactor

[3 marks]

Answer 21

They are easy to obtain and extract from seawater

They release more energy

They produce little radioactive waste

also available in large amounts

Question 22

What is the energy released from a nuclear fuel inside a reactor used for?

[1 mark]

Answer 22

To generate electricity

also to heat water

Question 23

Describe how the energy produced in nuclear fission is used to generate electricity

[3 marks]

Answer 23

The energy is used to heat up water
This produces steam
The steam drives a turbine which turns a generator

Question 24

Why does lowering control rods reduce the amount of energy released by nuclear fuel?

[2 marks]

Answer 24

The control rods absorb the neutrons
So there are fewer neutrons
And the chain reaction slows down

Question 25

Suggest two reasons why scientists want to creat nuclear fission reactors

[2 marks]

Answer 25

They provide another source of energy

They produce no radioactive waste