Hazards and uses of radioactive emissions and of background radiation

Aprenda jogando

Responda a estas perguntas para ganhar energia, depois pesque e explore. Sem precisar de conta.

Para educadores: slides de aula, resumos de revisão prontos para usar de Hazards and uses of radioactive emissions and of background radiation (Science, Physics) — use na sua aula ou rode o tópico como atividade interativa de turma que seus aprendizes jogam como um jogo ao vivo.

Notas de aula

Background Radiation

Background radiation is around us all of the time and comes from both natural and man-made sources.
Natural sources include rocks and cosmic rays from space.
Man-made sources include fallout from nuclear weapons testing and nuclear accidents.
The level of background radiation and the radiation dose a person receives can be affected by their occupation and/or location.
Some areas of the world have higher background radiation because they are closer to sources of radiation.
All living things emit a small amount of radiation — the amount within a banana is tiny and not at all dangerous.
Background count rate must be subtracted from measured count rates to give the corrected count rate.

Radiation Dose and Regulation

The amount of radiation received by a person is called the dose, measured in sieverts (Sv).
One sievert is a very big dose and would cause acute radiation poisoning.
People normally receive about 3 mSv (0.003 Sv) in one year.
The UK limit for nuclear industry employees is 20 mSv in one year.
A dosemeter (radiation badge) is worn by radiographers and anyone working with radiation to track the dose they receive.
Exposure is regulated because ionising radiation can damage cells and tissues.

Dangers of Radiation

Ionising radiation can damage human cells and tissues, causing tissue damage and mutations.
High-energy radiation such as gamma rays and X-rays can damage healthy tissue if not properly targeted.
If atoms in a DNA strand are ionised, the DNA can be damaged; the cell may die or the DNA may be mutated when it reforms.
If a mutated cell replicates, a tumour may form — this is cancer, a significant danger of radiation exposure.
Acute radiation exposure can cause skin burns and reduce white blood cells, lowering the immune system and making a person more susceptible to infections.

Handling Radiation Safely

Radioactive sources should be kept in a shielded container when not in use, such as a lead-lined box.
Sources should be handled with gloves and tongs to increase the distance from the body.
Protective clothing may be worn to prevent the body becoming contaminated.
The time a radioactive source is used for should be limited.
After using a source, hands should be washed, and the date and time of use recorded.

Contamination and Irradiation

Contamination is the unwanted presence of materials containing radioactive atoms on other materials — the material becomes radioactive.
Contamination often happens due to a radiation leak, and is almost always a mistake or accident.
Irradiation is the process of exposing a material to α, β or gamma radiation; it does not make the material radioactive.
Irradiation can kill living cells, so it is used to sterilise surgical equipment and food.
Contamination is more dangerous than irradiation because it causes continuous exposure to radiation.
Contamination is especially dangerous if a source gets inside the body, irradiating internal organs as it moves through.
Lead-lined suits reduce irradiation by absorbing radiation, while airtight suits prevent contamination by stopping radioactive atoms entering the body.

Half-Life and Risk

The half-life is the time taken for the activity of a radioactive source to decrease to half of its original value.
Different isotopes have very different half-lives: francium-218 is about 1 millisecond, polonium-210 about 140 days, and uranium-235 about 700 million years.
A short half-life means nuclei decay quickly, emitting a lot of radiation in a short time — a greater risk of irradiation.
If only a small amount is used, a short half-life is advantageous because the material quickly loses its radioactivity.
A long half-life means a sample decays slowly but stays radioactive for a very long time — a greater risk of contamination.
Radioactive waste with a long half-life is buried underground to prevent release into the environment.

A half-life graph

Medical Tracers

A tracer is a radioactive isotope used to track the movement of substances, such as blood, around the body.
Gamma emitters are usually used because gamma rays are highly penetrating and can pass out of the body to be detected externally, creating an internal image.
Iodine-131 is an example of a radioactive tracer.
Gamma rays are less ionising than some other radiation, so harm to the patient is minimised.
The amount of isotope used is kept to a minimum to reduce exposure.
Isotopes are chosen with short half-lives of around a few hours — long enough for the procedure but not so long as to cause long-term harm.
Because of short half-lives, isotopes must be produced nearby or they would decay too much before reaching the hospital.

PET Scanning

In PET scanning, positrons are emitted by the decay of the tracer.
The positrons travel a small distance and annihilate when they interact with electrons in the tissue.
This annihilation produces a pair of gamma rays (gamma photons) which can be detected outside the body.
PET scanners are used to diagnose cancer and determine the location of a tumour.

Radiotherapy

Radiotherapy is the treatment of cancer using radiation (chemotherapy uses chemicals).
Radiation can kill living cells, and some cells — such as bacteria and cancer cells — are more susceptible than others.
During external radiotherapy, beams of gamma rays are directed at the tumour; gamma is used because it can penetrate the body to reach the tumour.
The beams are moved around to minimise harm to healthy tissue while still targeting the tumour.
Surrounding healthy tissue is often shielded to avoid damage.
During internal radiotherapy, small pellets of radioactive material are inserted into the tumour, exposing it directly to radiation.

Other Uses of Radiation

α particles are used in smoke detectors: they ionise the air to create a current, and when smoke blocks the α emitter the current stops and the alarm triggers.
β particles are used to measure the thickness of thin materials such as paper, cardboard or aluminium foil.
β is used because it is partially absorbed — if α were used it would all be absorbed, and if gamma were used almost all would pass through with no detectable difference.
As material gets thicker, more β particles are absorbed and fewer reach the detector; if it gets thinner, the opposite happens, allowing thickness to be kept constant.
Gamma radiation is used to sterilise medical equipment because it is the most penetrating, irradiating all sides of instruments — even through packaging.
Food can be irradiated to kill microorganisms, making it last longer and reducing food-borne infections.
Radiation is also used to determine the age of ancient artefacts.

Evaluating Risk and Peer Review

The hazards of radioactive material differ according to the half-life involved.
The use of radiation in medicine carries risk, but the benefits can outweigh the risks — the risks from radiation are smaller than the risks of leaving a condition untreated.
When evaluating risk, compare the potential dangers with the benefits, using given data.
Some people worry about the safety and nutritional value of irradiated food.
Scientific communities must be independent of government influence so their conclusions are trusted.
Restaurants must clearly mark meals containing irradiated ingredients so people can make informed choices.
Peer review is important when publishing findings on radiation risk.

Slides

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

CADASTRE-SE — GRÁTIS ENTRAR

Questões de prática

Prévia grátis — 8 de 63 perguntas. Cadastre-se para ver todas.

1.What is meant by the term 'background radiation'?
Easy
- ARadiation that is present in the environment all of the time
- BRadiation emitted only by nuclear power stations
- CRadiation given to a patient during a medical scan
- DRadiation that is deliberately released during a nuclear accident
2.Which of the following are sources of background radiation? (select all that apply)
Medium
- ARocks
- BCosmic rays from space
- CFallout from nuclear weapons testing
- DA medical tracer injected into a patient
- EA smoke detector in a home
3.All background radiation is man-made.
Easy
True or false?
4.Which of the following is a man-made source of background radiation?
Easy
- ARadon gas from rocks
- BCosmic rays from space
- CFallout from nuclear weapons testing
- DFood and drink
5.Which statement correctly describes contamination?
Medium
- AThe unwanted presence of materials containing radioactive atoms on other materials
- BThe process of exposing a material to α, β or gamma radiation
- CThe time taken for the activity of a radioactive source to halve
- DThe amount of radiation received by a person
6.Irradiating a material makes that material radioactive.
Easy
True or false?
7.Which of the following is the correct definition of irradiation?
Medium
- AThe process of exposing a material to α, β or gamma radiation
- BThe unwanted presence of radioactive atoms on a material
- CThe time taken for the activity of a source to halve
- DThe amount of radiation a person receives
8.Match each term to its correct definition.
Medium
- Contamination
- Irradiation
- Half-life
- The process of exposing a material to α, β or gamma radiation
- The time taken for the activity of a radioactive source to halve
- The unwanted presence of materials containing radioactive atoms on other materials

Mais perguntas

9.Why is gamma radiation the most suitable type of radiation for sterilising medical equipment?
Medium
- AIt is the most penetrating, so it can irradiate all sides of the instruments
- BIt is the least penetrating, so it stays on the surface
- CIt is the most ionising, so it kills bacteria quickly
- DIt has the shortest half-life of all radiation types
10.Which type of radiation is used in a smoke detector?
Medium
- Aα
- Bβ
- CGamma
- DX-rays
11.Which type of radiation is most suitable for monitoring the thickness of aluminium foil?
Medium
- Aα
- Bβ
- CGamma
- DX-rays
12.A longer half-life is always safer for a medical tracer.
Easy
True or false?
13.Which of the following isotopes would be most suitable for use as a medical tracer inside the human body?
Medium
- AAn α emitter with a half-life of 160 days
- BA gamma emitter with a half-life of 6 hours
- CA β emitter with a half-life of 28 years
- DAn α emitter with a half-life of 432 years
14.Which of the following are correct about β radiation? (select all that apply)
Medium
- Aβ radiation is a fast-moving electron
- Bβ radiation is stopped by a sheet of paper
- Cβ radiation is moderately penetrating
- Dβ radiation is used in smoke detectors
- Eβ radiation is the most penetrating type of radiation
15.Which of the following statements about the risks of using radiation in medicine is correct?
Medium
- AThe risks of using radiation in medicine always outweigh the benefits
- BThe benefits of using radiation in medicine can outweigh the risks
- CRadiation is used in medicine only when there is no risk at all
- DRadiation is never used in medicine because of the risks
16.Radiation can kill living cells, and some cells such as bacteria and cancer cells are more susceptible to radiation than others.
Easy
True or false?
17.Which of the following are possible effects of ionising radiation on the human body? (select all that apply)
Medium
- ADamage to DNA that may lead to a mutation
- BA reduced number of white blood cells
- CSkin burns similar to severe sunburn
- DThe body becoming permanently radioactive
- EAn increase in the number of red blood cells
18.Match each radiation safety measure to the risk it is designed to reduce.
Medium
- Keeping the source in a lead-lined box
- Using tongs to move the source
- Limiting the time the source is used
- Wearing an airtight suit in a leak area
- Reduces irradiation by absorbing radiation
- Increases distance, reducing irradiation
- Reduces the total dose received
- Prevents radioactive atoms entering the body
19.Which of the following statements about the properties of β radiation make it suitable for monitoring the thickness of aluminium foil? (select all that apply)
Medium
- Aβ particles are partially absorbed by the foil
- Bβ particles are highly ionising and stop in air
- CThe thicker the foil, the fewer β particles pass through
- Dβ particles are the most penetrating type of radiation
- EA detector on the other side measures the β particles that get through
20.Place the following steps in the correct order for using a radioactive source safely in a school experiment.
Medium
- Put on gloves and use tongs
- Remove the source from its lead-lined container
- Carry out the experiment quickly
- Return the source to its shielded container
- Wash hands after the experiment
21.A patient receives a radiation dose of 0.003 Sv in a year from background radiation. What is this dose in millisieverts (mSv)?
Medium
- A0.003 mSv
- B3 mSv
- C3000 mSv
- D0.000003 mSv
22.Which of the following are reasons why gamma radiation is used to sterilise medical equipment? (select all that apply)
Medium
- AGamma is the most penetrating type of radiation
- BGamma can irradiate all sides of the instruments
- CGamma is the most strongly ionising type of radiation
- DInstruments can be sterilised without removing the packaging
- EGamma is stopped by a sheet of paper
23.A radioactive tracer is injected into a patient's bloodstream. Which of the following is the most important reason for choosing an isotope with a short half-life of a few hours?
Medium
- AIt will emit a very high dose of radiation during the procedure
- BIt will decay away quickly, reducing long-term exposure
- CIt will make the patient permanently radioactive
- DIt will allow the tracer to be stored for many years
24.Which of the following statements about the half-life of a radioactive isotope are correct? (select all that apply)
Medium
- AA short half-life means the nuclei decay very quickly
- BA long half-life means the isotope remains radioactive for a long time
- CA short half-life always makes an isotope safe to handle
- DA long half-life presents a risk of contamination for a longer time
- EHalf-life is the time for the activity to double
25.Match each unit or term to its correct description.
Medium
- Sievert (Sv)
- Millisievert (mSv)
- Dosimeter
- Half-life
- Unit of radiation dose
- One thousandth of a sievert
- Device worn to monitor radiation exposure
- Time for activity to halve
26.Irradiating food makes the food radioactive.
Easy
True or false?
27.The radiation source used is not an α emitter. How can you tell from the data?
Medium
- AThe count rate decreases as distance increases
- BThe count rate is still measurable at 1.5 m
- CThe count rate is highest at 0.1 m
- DThe background count rate is 13 counts per minute
28.Which of the following are concerns that some people have about irradiated food? (select all that apply)
Hard
- AThe food might become radioactive
- BThe nutritional value might be reduced
- CThe food might be unsafe to eat
- DIrradiated food cannot be stored as long
- EThe process might change the taste
29.A tracer used in a PET scan emits positrons. What happens to the positrons inside the body?
Hard
- AThey travel a small distance and annihilate with electrons, producing gamma rays
- BThey are absorbed by the bones and emit X-rays
- CThey decay into α particles that are detected outside the body
- DThey pass straight through the body without interacting
30.A hospital stores a gamma-emitting tracer with a half-life of 6 hours. A fresh batch is produced 30 hours before it is needed. What fraction of the original activity remains when it is used?
Medium
- A1/5
- B1/16
- C1/32
- D1/64
31.A sealed packet of surgical instruments is passed through a beam of gamma radiation before being sent to the operating theatre. Which statement about the instruments afterwards is correct?
Medium
- AThey have become radioactive and must be stored in a lead-lined box.
- BThey are not radioactive but any micro-organisms on them have been killed.
- CThey are not radioactive and micro-organisms on them are unaffected.
- DThey have become radioactive but only for a few hours.
32.A worker in a nuclear facility wears a dosemeter on their chest. What is the purpose of the dosemeter?
Medium
- ATo absorb radiation before it reaches the worker's body
- BTo measure the amount of radiation the worker has received
- CTo make the worker's body radioactive so it can be monitored
- DTo detect the half-life of the source being handled
33.A hospital is choosing a gamma-emitting isotope to inject into a patient so that blood flow through the kidney can be imaged. Which of the following properties make an isotope suitable? (select all that apply)
Medium
- AIt emits gamma radiation that can penetrate out of the body
- BIt has a half-life of a few hours
- CIt has a half-life of several years
- DIt emits α radiation
- EThe amount injected is kept to a minimum
34.If a radioactive source is accidentally spilled onto a laboratory bench, the bench surface itself becomes radioactive.
Easy
True or false?
35.A factory uses a β source and a detector to check the thickness of aluminium foil as it is rolled out. The detector reading suddenly drops. What does this indicate and how should the machine respond?
Hard
- AThe foil has become thinner, so the rollers should be tightened
- BThe foil has become thicker, so the rollers should be loosened
- CThe foil has become radioactive, so the line should be stopped
- DThe source has a longer half-life than expected, so it should be replaced
36.Match each radiation application to the property of the radiation that makes it suitable.
Medium
- Smoke detector
- Thickness gauge for aluminium foil
- Sterilising packaged medical equipment
- α particles ionise air and are blocked by smoke
- β particles are partially absorbed by thin material
- Gamma rays are the most penetrating and reach all sides
37.A patient receives a dose of 0.003 Sv from natural background radiation in a year. A radiotherapy patient receives a localised dose of 60 Sv to a tumour. Which statement best compares the risk to the two patients?
Hard
- AThe radiotherapy patient faces far greater risk of tissue damage at the tumour because the dose is much larger
- BBoth patients face identical risk because any radiation exposure is equally harmful
- CThe background patient faces greater risk because their whole body is exposed
- DThe radiotherapy patient faces no risk because the radiation only targets the tumour
38.Place the following steps in the correct order to find the corrected count rate from a radioactive source at a given distance.
Medium
- Measure the background count rate with the source removed
- Measure the count rate from the source at the chosen distance
- Subtract the background count rate from the measured count rate
- Repeat the source measurement to reduce the effect of random variation
39.The student's results show that the corrected count rate falls as distance from the source increases. Which conclusion is best supported?
Medium
- AThe radiation is absorbed more strongly by the air at greater distances
- BThe source is decaying rapidly during the experiment
- CThe detector becomes less sensitive over time
- DThe background radiation increases with distance
40.Table: Isotope X has a half-life of 6 hours and emits gamma. Isotope Y has a half-life of 5.3 years and emits gamma. Both are considered for use as tracers injected into a patient. Which is more suitable and why?
Medium
- AX, because it decays to a safe level within hours of the procedure
- BY, because it stays active long enough to be detected
- CX, because gamma emitters cannot be detected outside the body
- DY, because a longer half-life always means a lower dose to the patient
41.Complete the sentence about the two types of sources of background radiation.
Easy
Background radiation comes from ____ sources and ____ sources.
42.Name the unit used to measure radiation dose.
Medium
43.A person normally receives about 0.003 Sv of radiation in one year. How many millisieverts (mSv) is this?
Medium
44.What is the name given to the treatment of cancer using radiation?
Medium
45.Complete the sentence about the half-life of a medical tracer.
Medium
A medical tracer should have a half-life of around a few ____.
46.A radioactive tracer has an initial activity of 800 counts per second. Its half-life is 4 hours. Calculate the activity after 20 hours.
Medium
47.Complete the sentences about half-life and risk using the words provided.
Easy
If an isotope has a short half-life, the nuclei will decay very ____. If a large amount is used, the levels of radiation emitted could make handling the isotope extremely ____. If an isotope has a long half-life then a sample of it will decay ____. Sources with long half-life values present a risk of ____ for a much longer time.
48.The student corrected her results to take account of background radiation. The uncorrected count rate at 0.1 m was 324 counts per minute. What is the value of the background count rate?
Medium
49.A radioactive tracer has an activity of 4000 counts per second when produced. Its half-life is 6 hours. Calculate the activity after 24 hours, in counts per second.
Medium
50.A person working in the nuclear industry is allowed to receive a dose of 20 mSv in one year. Express this dose in sieverts (Sv).
Medium
51.Complete the sentence about radiation dose.
Easy
The amount of radiation received by a person is called the dose and is measured in ____.
52.Calculate the corrected count rate at 0.5 m, in counts per minute.
Medium
53.Explain why contamination is more dangerous than irradiation.
Hard
54.Suggest two precautions that hospital staff might take when working with radioactivity.
Medium
55.Explain why the beams in external radiotherapy are moved around the patient during treatment.
Hard
56.Explain why scientific communities investigating the safety of irradiated food need to be independent of government influence.
Hard
57.A radioactive source with a very long half-life is spilled in a laboratory and contaminates the floor. Explain why this contamination is a serious hazard.
Hard
58.A person normally receives about 0.003 Sv of radiation in one year. How many millisieverts (mSv) is this?
Medium
- A2 mSv
- B4 mSv
- C3 mSv
- D5 mSv
59.A radioactive tracer has an initial activity of 800 counts per second. Its half-life is 4 hours. Calculate the activity after 20 hours.
Medium
- A22 counts per second
- B28 counts per second
- C31 counts per second
- D25 counts per second
60.The student corrected her results to take account of background radiation. The uncorrected count rate at 0.1 m was 324 counts per minute. What is the value of the background count rate?
Medium
- A15 counts per minute
- B13 counts per minute
- C14 counts per minute
- D12 counts per minute
61.A radioactive tracer has an activity of 4000 counts per second when produced. Its half-life is 6 hours. Calculate the activity after 24 hours, in counts per second.
Medium
- A275 counts per second
- B250 counts per second
- C225 counts per second
- D300 counts per second
62.A person working in the nuclear industry is allowed to receive a dose of 20 mSv in one year. Express this dose in sieverts (Sv).
Medium
- A1.02 Sv
- B0.02 Sv
- C-0.98 Sv
- D2.02 Sv
63.Calculate the corrected count rate at 0.5 m, in counts per minute.
Medium
- A166 counts per minute
- B220 counts per minute
- C202 counts per minute
- D184 counts per minute

Flashcards

What is background radiation?

Radiation that is present in the environment around us all of the time, coming from both natural and man-made sources.

Name the two types of sources of background radiation.

Natural sources and man-made sources.

Give two natural sources of background radiation.

Rocks (and other materials in the ground) and cosmic rays from space.

Give two man-made sources of background radiation.

Fallout from nuclear weapons testing and nuclear accidents.

Why do some areas of the world have higher background radiation than others?

Because they are closer to sources of radiation, for example rocks that release radioactive radon gas.

What two factors can affect the level of background radiation and radiation dose a person receives?

Their occupation and/or their location.

What is radiation dose measured in?

Sieverts (Sv). 1000 millisieverts (mSv) = 1 sievert (Sv).

What is the typical radiation dose a person receives in one year?

About 3 mSv (0.003 Sv).

What is the UK yearly radiation dose limit for nuclear industry employees?

20 mSv in one year.

What is a dosemeter (radiation badge) used for?

It is worn by people who work with radiation to keep track of the amount of radiation they are receiving.

What is contamination?

The unwanted presence of materials containing radioactive atoms on other materials, often caused by a radiation leak.

What is irradiation?

The process of exposing a material to α, β or gamma radiation. Irradiating a material does not make it radioactive.

Why is contamination potentially more harmful than irradiation?

Contamination causes continuous exposure to radiation, and is especially dangerous if the source gets inside the body and irradiates internal organs.

How is lead shielding used to protect against irradiation?

Lead-lined suits (or lead shielding) absorb most of the radiation that would otherwise hit the person, reducing their exposure.

How is an airtight suit used to protect against contamination?

It stops radioactive atoms from getting onto or inside the person's body.

Which type of radiation is used in smoke detectors and why?

α radiation, because it is the strongest ioniser and is absorbed by smoke, which stops the current and triggers the alarm.

Which type of radiation is used to measure the thickness of materials such as paper or aluminium foil, and why?

β radiation, because it is partially absorbed by the material, so the amount passing through changes as the thickness changes.

Why is β radiation chosen for thickness gauging rather than α or gamma?

α would be completely absorbed (none would get through) and gamma would mostly pass through, so the detector could not sense a change in thickness.

Why is gamma radiation used to sterilise medical equipment?

It is the most penetrating radiation, so it can irradiate all sides of the instruments, even through their packaging.

What is a medical tracer?

A radioactive isotope that is used to track the movement of substances, such as blood, around the body.

Which type of radiation is usually used for a medical tracer and why?

Gamma, because it is highly penetrating and can pass out of the body to be detected, allowing an internal image to be created.

Give an example of a radioactive isotope used as a medical tracer.

Iodine-131.

Why are tracers chosen with short half-lives of around a few hours?

Long enough to carry out the procedure, but not so long that the isotope remains in the body and causes long-term harm.

Why must isotopes used in PET scans be produced nearby?

Because their short half-life means they would decay too much to be usable by the time they reached the hospital.

What is radiotherapy?

The treatment of cancer using radiation, where beams of gamma rays are directed at the tumour to kill the cancer cells.

Why are the gamma ray beams moved around during radiotherapy?

To minimise harm to healthy tissue while still aiming the radiation at the tumour.

What happens during internal radiotherapy?

Small pellets of radioactive material are inserted into the tumour, exposing it directly to radiation.

What is the half-life of a radioactive isotope?

The time it takes for the activity of a radioactive source to decrease to half of its original value.

Why do sources with short half-lives present a greater risk of irradiation?

A short half-life means the source has a high activity, so it emits a high rate of radiation in a short time.

Why do sources with long half-lives present a greater risk of contamination?

They remain radioactive for a very long time, so they must be controlled, shielded and stored for longer to prevent them spreading.

Why is radioactive waste with a long half-life buried underground?

To prevent it from being released into the environment while it remains radioactive.

What is the main risk to health from ionising radiation?

It can damage DNA in cells, causing mutations that may lead to cancer, and can also cause tissue damage.

Give two acute effects of a large radiation exposure.

Skin burns (like severe sunburn) and a reduction in white blood cells, which lowers the immune system and increases susceptibility to infection.

Give two precautions for handling radioactive sources safely.

Keep the source in a shielded (lead-lined) container when not in use, and handle it with tongs and gloves to increase distance from it.

Why is radiation used in medicine despite the risks?

The benefits outweigh the risks — the danger from the radiation is smaller than the danger of leaving the condition untreated.

Why must scientific communities studying radiation safety be independent of government influence?

So their findings are unbiased and trustworthy, allowing the public to rely on the conclusions.

Why is it important that irradiated ingredients are clearly marked on restaurant menus?

So people can make an informed choice about what they eat, based on their own concerns or beliefs.

Unlock all 63 questions, flashcards & more

Crie uma conta grátis para ver todas as perguntas, os slides, flashcards e resumos de revisão deste tópico.

CADASTRE-SE — GRÁTIS ENTRAR

Provas anteriores

A prática com provas anteriores deste tópico chega em breve.

Em breve