Unit 1 Radioactivity

Question 1

What is the history of the structure of the atom?

Answer 1

The structure of the atom began as the (J.J) Thompson Plum Pudding Model (1903) - sphere of positive charge with negative electrons scattered throughout.

Question 2

What were the three observations from the ‘Rutherford Alpha Particle Scattering experiment’?

Answer 2

-Most of the fast, highly charged alpha particles went whizzing straight through undeflected. This was an expected result for all of the particles of the plum pudding model was correct.
-A few of the alpha particles were slightly deflected through very large angles. This was not expected.
-Approximately 1 in 8000 of the alpha particles were deflected backwards or back-scattered. This was definitely not as expected.

Question 3

What are the three explanations for the results from Rutherford’s experiment?

Answer 3

-The fact that most alpha particles went through in a straight line suggested that most of the atom was empty space (99% vacuum).
-A small number being deflected, and an even smaller amount coming back to the source (1 in 8000), suggested that there is positive material in the centre of the atom (the nucleus) which repels the positive alpha particles.
-The back scattered alpha particles also indicated that the majority of the mass is concentrated in a very small but massive (lots of mass - not size) region called the nucleus.

Question 4

Why does an atom have no overall charge?

Answer 4

Same number of positive protons and negative electrons. They therefore cancel out each other’s charge.

Question 5

What is the definition of mass and atomic number?

Answer 5

Mass number- the number of protons and neutrons in the nucleus

Atomic number- the number of protons in the nucleus.

Question 6

What are nucleons?

Answer 6

Particles belonging to the nucleus of an atom (protons and neutrons collectively).

Question 7

What is the definition of an isotope?

Answer 7

Isotopes of an element are atoms which have the same atomic number but different mass number.

Question 8

What does an atom being ‘radioactive’ mean?

Answer 8

Their nuclei change or decay (or disintegrate) by spitting out radiation, in the form of particles or electromagnetic waves in order to reach a more stable state.

Question 9

Where does most background radiation come from?

Answer 9

Sources such as cosmic rays from outer space along with rocks and soil some of which contain radioactive elements such as radon gas.

Radioactive waste from nuclear fission power plants and radioactive fallout from nuclear weapons testing also contributes to background radiation.

Question 10

How can the measured activity from a radioactive source be corrected?

Answer 10

By subtracting the background activity.

Question 11

What are the three types of radiation and what do they consist of?

Answer 11

Alpha radiation- emitted from unstable atoms with large nuclei. Each alpha particle is a helium nucleus consisting of two protons and two neutrons emitted from the unstable parent nucleus

Beta radiation- emitted from a nuclei where the number of neutrons is much larger than the number of protons. A beta particle is a fast moving electron released from the unstable parent nucleus.

Gamma radiation- does not consist of particles but of very high-energy electromagnetic waves emitted from the unstable parent nucleus.

Question 12

What are the RAM and ionising power of the three types of radiation?

Answer 12

Alpha- RAM=4 and it has a strong ionising power.

Beta- RAM= 1/1840 and it has a weak ionising power.

Gamma- RAM=0 and it has the weakest ionising power.

Question 13

What is the penetrating effect of each type of radiation and what can they be stopped by?

Answer 13

Alpha- it has a very low penetrating effect and can be stopped by a few cm of air or thin paper.

Beta- it can penetrate and can be stopped by thin aluminium or other metal.

Gamma- it is extremely penetrating and can be reduced by thick lead or concrete.

Question 14

How does the mass and atomic number change in alpha, beta and gamma decay?

Answer 14

Alpha decay- mass number reduces by 4 and atomic number reduces by 2.

Beta decay- mass number stays the same and atomic number increases by 1.

Gamma decay- mass and atomic number stay the same.

Question 15

What are ions?

Answer 15

Ions are charged atoms (or molecules). Atoms become ions when they lose (or gain) electrons.

Question 16

Why can radiation be extremely harmful to the human body?

Answer 16

Radiation can cause ionisation and can be very harmful to the human body because the energy from the radiation is absorbed by living cells. The radiation can remove electrons from atoms (ionisation) and produce radiation burns, destroys living cells and damage the genetic material of the cell.

Question 17

Why are alpha and beta particles dangerous if they get in to the body?

Answer 17

Alpha- they cannot penetrate the skin so will not be able to leave the body if they get in.

Beta- they can penetrate the skin and can cause damage to the cells (shielding is necessary).

Question 18

What are the general safety precautions when handling a radioactive source?

Answer 18

• Wear protective clothing such as lead lined gloves or a lead apron (shielding)
• Keep the source as far away as possible by using tongs (distance)
• Keep exposure time as short as possible (time)
• Keep radioactive materials in lead lined containers (shielding)

Question 19

What is the definition of ‘half life’?

Answer 19

The half life of an isotope is the time taken for the activity to fall to half of its original value.

The half life of a radioactive substance is a specific and constant value - can be short (a matter of seconds) or long (several days or even thousands of years).

Question 20

What are the medical uses of radioactivity?

Answer 20

Sterilising syringes, location of tumours, monitoring the function organs and identifying Circulation problems:

-A patient can be given a drink, or an injection, which contains a small quantity of radioactive material (a tracer) which emits gamma rays. The radioactive material will move around the body and its movement can be tracked and monitored using a gamma camera which detects the gamma radiation outside the body.
This helps to locate circulation problems and tumours as well. Tumours can be located because they absorb more of the radioactive isotope than the other parts of the body. Gamma radiation is usually used as it does not cause much ionisation in the body. The isotope used must also have a short half-life (normally a few hours only) so that the radiation levels will drop quickly within the patient.

Treatment of tumours:

-Gamma radiation from a Cobalt-60 isotope can be used to treat tumours by killing the cancerous cells.

Sterilisation of medical equipment:

-Surgical equipment, hospital dressings and plastic syringes can be sterilised (killing off germs and bacteria) by exposing them to gamma radiation. This saves the damage that can be caused when boiled water is used to sterilise. The radiation can also pass through paper and plastic so sterilising can even be carries out after packaging.

Question 21

What are the industrial uses of radioactivity?

Answer 21

Carbon dating:

All living organisms contain some carbon-14.
When the organism is still alive, the ratio of carbon-12 to carbon-14 remains constant. Once the organism dies, the amount of carbon-14 decreases as the radioactive isotope decays.
Comparing the amount of carbon-14 present in a sample with the amount in a living organism allows calculation of the age of the sample.
Fortunately, carbon-14 has a long half-life of approximately 5700 years and so decays slowly.
This method was used to date the Dead Sea Scrolls

Thickness control:

A machine is used to adjust the pressure on rollers. Beta radiation is used to monitor the thickness of a sheet of paper or aluminium.
An emitter is placed on one side of the sheet and a detector on the other. As the sheet moves past, the activity detected will be the same as long as the thickness remains unchanged. This is continually monitored and if the activity changes (increases or decreases) a signal is sent to the rollers to change the pressure (decreases or increases) until the sheet returns to the correct thickness.

A beta source with a very long half-life is used
because it is important that the amount of radiation emitted stays fairly constant so that any changes in the count rate are due to thickness changes only, it also means that the radioactive source does not need to be frequently replaced.

An alpha source is unsuitable because it would not pass through any of the sheets.

A gamma source could be used but it would only be useful for very dense metals such as thick sheets of lead.

Locating leaks in underground pipes:

Leaks in underground pipes carrying oil, water or gas can be located by putting a gamma ray emitting radioactive isotope into the fluid in the pipe. An increase in the signal will be detected when the detector is just above the leak.
The gamma radiation can easily pass through the ground. This means that it is not necessary to dig up large areas of ground to find the leak.
The radioactive material, used as the tracer, for locating leaks must:
1. Emit radiation that is able to penetrate the ground- needs to be GAMMA RAYS
2. Not have a very long half-life - a few hours or days is ideal so that it remains long enough to be detected but not so long that it becomes a dangerous safety hazard.

Non-destructive Testing:

Industrial radiography is a method of non-destructive testing where many types of manufactured components can be examined to verify the internal structure and integrity of the specimen without breaking into the object.
Gamma radiation sources are used to inspect a variety of materials. The vast majority of radiography concerns the testing and grading of welds on pressurized piping, pressure vessels and pipelines. Other tested materials include concrete, machined parts and plate metal. Non-metal components such as ceramics used in the aerospace industries are also regularly tested.

Question 22

What are the agricultural uses of radioactivity?

Answer 22

Agricultural Uses:

Treatment of fresh food-

Gamma Radiation of food has many opponents but it could clearly be a valuable option in countries with hot climates where refrigeration is not always possible.
The following information has been obtained from the Food Standards Agency website (www.food.gov.uk):

Irradiation is a technique used in food production. It can be used to kill bacteria that cause food poisoning, such as salmonella, campylobacter and E. Coli. It also helps to preserve food and reduce food waste.

During irradiation, food is exposed to electron beams, X-rays or gamma rays. The effect is similar to other preservation methods, such as pasteurisation or cooking. The appearance and texture of the food changes less during irradiation than other preservation methods.

Irradiated food has been exposed to radiation but does not become radioactive itself.

Safety of irradiated food:

Decades of research worldwide have shown that irradiation of food is a safe and effective way to:
* kill bacteria in foods
* extend the shelf life of food
In 2011, the European Food Safety Authority reviewed the evidence and confirmed again that food irradiation is safe.

How irradiation changes food-

Irradiation changes food in similar ways as other preservation techniques,
such as cooking, caming and pasteurisation. Some viamins may be
reducel bur this happens whenever foods are preserved or stored long.
term. There is no evidence that any of the changes caused by food irradiation are a risk to the health of consumers.

The law covering food irradiation states that irradiation can only be used Where it is of benefit to the consumer. A company that wants to irradiate a food product has to be able to show that the benefits of irradiation outweigh any negative aspects.

An example of the benefits of irradiation is reducing the risk of foodborne illness.

This will vary between different foods and will mean that the use of food irradiation is more suitable to some foods than others.

How irradiation works-

FSA EXPLAINS
When food is irradiated, it absorbs energy. This absorbed energy kills the bacteria that can cause food poisoning in a similar way that heat energy kills bacteria when food is cooked. They can also delay fruit ripening and help stop vegetables from sprouting.

Once the irradiation treatment has stopped, the food quickly loses this absorbed energy in the same way that cooked food quickly cools down.

Question 23

How do smoke alarms work using alpha radiation?

Answer 23

One type of smoke detector uses Americium-241, a source of alpha radiation, to detect smoke. The alpha radiation ionises the air particles inside the smoke detector. This allows a small electric current to flow through the air. If there is a fire, smoke particles go into the detector and are hit by alpha radiation which then causes them to drop. The drop in current is detected by the smoke detector which then sets off the alarm.

Question 24

What is the definition of ‘nuclear fission’?

Answer 24

Nuclear Fission is the splitting of a large nucleus into two lighter nuclei with the release of energy.

Question 25

How does nuclear fission produce energy?

Answer 25

Fission usually comes about as a result of the large nucleus (e.g. Uranium-235 or Plutonium-239) absorbing a neutron and then splitting which produces two smaller nuclei. At the same time energy is released and two or three fast neutrons are also emitted. These are known as the fission neutrons which go on to produce further fissions and subsequently create a chain reaction.

Question 26

What is a ‘controlled’ nuclear fission’?

Answer 26

In a nuclear power station, steps are taken to ensure that, on average, just one of the fission neutrons goes on to produce further fission.

The heat produced in the reaction is used to turn water into steam and drive a turbine to generate electricity

Question 27

How much fuel is required in fission?

Answer 27

The amount of nuclear fuel (e.g. Uranium) required is significantly less than other fuels such as coal, oil and gas which therefore reduces transport costs. There is also no CO2 produced in the nuclear fission process and therefore it does not contribute to global warming.

Question 28

What are the dangers with nuclear fission?

Answer 28

A major disadvantage of all fission processes is that the fission fragments are almost always highly radioactive. This type of radioactive waste is extremely dangerous with a long half-life, and expensive measures must be taken to store it until the level of activity is sufficiently small. In some cases, this means the waste must be stored deep underground, in a vitrified (glass-like) state, for tens of thousands of years - danger is that the containers may leak and cause underground water pollution.

Question 29

What are the arguments for and against Nuclear Fission?

Answer 29

FOR:
-The fission reaction can produce vast amounts of electricity with no CO2 production and hence no contribution to global warming.
-Has a much higher energy density compared with coal, oil and gas.
-Provides employment opportunities.

AGAINST:
-Major incidents in fission power plants at Chernobyl (Ukraine) in 1986 and Fukushima (Japan) in 2011 have caused huge economic, health and environmental damage to the surrounding area.
-Many people are concerned about living close to nuclear power plants and the storage facilities used for radioactive waste (NIMBY- Not In My Back Yard).
-The mining, transport and purification of the uranium ore releases large amounts of CO2 into the atmosphere which contributes to global warming.

Question 30

What is the definition of ‘nuclear fusion’?

Answer 30

Two light nuclei, such as hydrogen, combine to form a heavier nucleus, such as helium, with the release of energy.

Question 31

Describe the process of nuclear fusion

Answer 31

This is the process whereby two light nuclei collide and combine together to form a heavier nucleus. As hydrogen nuclei are positive they will only combine if they are travelling at high speeds. These high speeds are produced by making the light nuclei mixture very hot to start with. Temperatures of approx. 150 million degrees celcius are required. These high temperatures are difficult to achieve on Earth but this is the process which goes on in stars like our Sun. At these very high temperatures a 4th state of matter exists called PLASMA.

Question 32

How does nuclear fusion take place in the Sun?

Answer 32

In the sun, hydrogen isotopes known as tritium (or hydrogen-3) and deuterium (hydrogen-2) collide and combine to create a new nucleus, helium-4. This causes the release of a vast amount of energy.
(Scientist hope to use the same reaction to carry out Nuclear Fusion on Earth).

Question 33

What is the equation for Nuclear Fusion?

Answer 33

2 3 4 1
H + H —– He + n + energy
1 1 2 0

Question 34

How much energy does nuclear fusion create compared to chemical reactions and nuclear fission?

Answer 34

Fusing nuclei together in a controlled way releases four million times more energy per kg than a chemical reaction such as burning coal, oil or gas. Compared with fission it releases four times as much energy per kg of fuel.

Question 35

Where can the deuterium and tritium hydrogen isotopes be obtained from?

Answer 35

They can be easily obtained from sea-water and are nearly inexhaustible.

Question 36

Give two benefits of what nuclear fusion produces

Answer 36

-The fusion reaction does not emit CO2 into the atmosphere
- Its only major by-product is helium which is an inert, non-toxic gas.

Question 37

What are the main problems that are preventing Nuclear Fusion from taking place on Earth at the moment?

Answer 37

1. Containment- it is very difficult to contain the plasma at a high enough temperature without causing damage to the surrounding materials in the reactor.
2. Confinement time- it is challenging to contain the plasma for a sufficiently long enough time for the fusion reaction to take place.

There is currently a prototype fusion reactor at the Culham Oxfordshire Research Centre called JET (Joint European Torus). JET began in 1983 but has so far been unsuccessful at efficiently producing enough energy from the fusion process.

Question 38

Describe ITER

Answer 38

A new fusion reactor project called ITER
(International Thermonuclear
Experimental Reactor) is being built in southern France and like JET it will use a magnetic confinement chamber to hold the
plasma in place. Completion is scheduled for 2025.

There are 35 nations collaborating to build the world’s largest tokamak, a magnetic fusion device that has been designed to prove the feasibility of fusion as a large-scale and carbon free source of energy.
The scientists and engineers at ITER hope for the fusion reactor to:
* Produce a net energy and generate up to 500MW of fusion power.
* Maintain fusion for long periods of time.