Topic 4 - Atomic Structure

Question 1

Isotopes and radiation?

Answer 1

1. All elements have different isotopes, but there are usually only one or two stable ones.
2. The other unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable. This process is called radioactive decay.

Question 2

Whare is alpha radiation?

Answer 2

1. Alpha particles are helium nuclei.
2. Alpha radiation is when an alpha particle is emitted from the nucleus.
3. They don’t penetrate very far into materials and are stopped quickly - they can only travel a few cm in air and are absorbed by a sheet of paper.
4. They are strongly ionizing.

Question 3

What is a beta particle?

Answer 3

1. A beta particle is a fast-moving electron released by the nuceleus.
2. They are moderately ionising. They penetrate moderately far into materials before colliding and have a range in air of a few metres.
3. For every beta particle emitted, a neutron in the nucleus turns into a proton.

Question 4

What are gamma rays?

Answer 4

1. Gamma rays are waves of electromagnetic radiation released by the nucelus.
2. They penetrate far into materials without being stopped and will travel a long distance in air.
3. They are weakly ionising because they tend to pass through
   rather than collide with atoms. Eventually they hit something and do damage.
4. They can be absorbed by thick sheets of lead or metres of concrete.

Question 5

Halflife definition?

Answer 5

1. Halflife is the time taken for the number of radioactive nuclei in an isotope to half.

Question 6

Risks of radiation?

Answer 6

1. Radiation can enter living cells and ionise atoms and molecules within them. This can lead to tissue damage.
2. Lower doses tend to cause minor damage wihtout killing the cells. This can give rise to mutant cells which divide uncontrollably. This is cancer.
3. Higher doses tend to kill cells completely, causing radiation sickness.

Question 7

How do medical tracers use radiation?

Answer 7

1. Certain radioactive isotopes can be injected into people and their progress around the body can be followed using an external detector. A computer converts the reading to a display showing where the strongest reading is coming from.
2. One example is the use of iodine-123, which is absorbed by the thyroid gland just like normal iodine-127, but it gives out radiation which can be detected to indicate whether the thyroid gland is taking in iodine as it should.
3. Isotopes taken into the body like this are usually gamma, so that the radiation passes out of the body without causing much ionisation. They should have a short halflife so the radioactivity inside the patient quickly disappears.

Question 8

How does radiotherapy use radiation?

Answer 8

1. Since high doses of ionising radiation will kill all living cells, it can be used to treat cancers.
2. Gamma rays are directed carefully and at just the right dosage to kill the cancer cells without damaging too many normal cells. Radiation-emitting implants can also be put next to or inside tumors.
3. However, a fair bit of damage is inevitably done to normal cells, which makes the patient feel very ill.

Question 9

What is nucelar fission?

Answer 9

1. Nuclear fission is a type of nuclear reaction used to release energy from large and unstable atoms by splitting them into smaller atoms.

Question 10

How does nuclear fission occur?

Answer 10

1. Spontaneous fission rarely occurs, usually the nucleus has to absorb a neutron before it will split.
2. When the atom splits it forms two new lighter elements that are roughly the same size.
3. Two or three neutrons are also released when an atom splits, and if any of these neutrons are moving slow enough to be absorbed by another nucleus, they can cause more fission to occur. This is a chain reaciton.
4. The energy not transferred to the kinetic energy store of the products is carried away by gamma rays.

Question 11

How do you control energy released by fission?

Answer 11

1. The amount of energy produced by fission in a nuclear reactor is controlled by changing how quickly the chain reaction can occur.
2. This is done by using control rods, which are lowered and raised inside a nucelar reactor to absorb neutrons, slow down the chain reaction and control the amount of energy released.

Question 12

What does unctonrolled chain reactions lead to?

Answer 12

1. Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion - this is how nuclear weapons work.

Question 13

What is nuncelar fusion?

Answer 13

1. Nuclear fusion is the opposite of nuclear fission.
2. It is the joining of small nuclei.

Question 14

How does nuclear fusion work?

Answer 14

1. In nuclear fusion, two light nuclei collide at high speed and fuse to create a larger, heavier nucleus.
2. The heavier nucleus produced by fusion does not have as much mass as the two separate, light nuclei did. This is because some of the mass of the lighter nuclei is converted into energy and released.
3. Fusion releases a lot of energy, more than fission for a given mass of fule.
4. So far, scientists havent found a way of using fusion to generate energy for us to use. The temperatures and pressures needed for fusion are so high that fusion reactors are really hard and expensive to build.

Question 15

What happens during alpha decay?

Answer 15

1. When an atom emits an alpha particle, its atomic number reduces by 2 and its mass number reduces by 4
2. The charge of the nucleus decreases

Question 16

What happens during beta decay?

Answer 16

1. When beta decay occurs, a neutron in the nucleus turns into a proton and releases a fast-moving electron
2. The number of protons in the nucleus has increased by 1, so the positive charge of the nucleus increases
3. The mass doesn’t change, the atomic number increases by 1

Question 17

What happens through gamma rays?

Answer 17

1. Gamma rays are a way of getting ride of excess energy from a nucleus
2. This means there is no change to the atomic mass or atomic number of the atom

Question 18

How does radioctive decay work?

Answer 18

1. Radioactive decay is entirely random. This means you cant predict exactly which nucleus in a sample will decay next, or when any of them will decay
2. However, you can find out the time it takes for the amount of radiation emitted by a source to halve, this is known as the half-life. It can be used to make predictions about radioactive sources, even though their decays are random

Question 19

How can halflife be used?

Answer 19

1. It can be used to find the rate at which a source decays - its activity
2. Activity is measured in becquerelels, Bq (1 Bq is one decay per seacond)

Question 20

How does the radioactivity of a source change over time?

Answer 20

1. The radioactivity of a source decreases over time
2. Each time a radioactive nucelus decays to become a stable nucleus, the activity as a whole will decrease
3. A short half life means the activity falls quickly, because the nuclei are very usntable and rapidly decay
4. Sources with a short half-life are dangerous because of the high amount of radiation they emit at teh start, but they quickly become safe
5. A long half life meanst he activity falls more slowly because most of the nuclei dont decay for a long time - the source just sits there, releasing small amounts of radiation for a long time
6. This can be dangerous because nearby areas are exposed to radiation for millions of years

Question 21

What is background radiation?

Answer 21

1. Background radiation is the low-level radiation that is around us all the time

Question 22

What does background radiation come from?

Answer 22

1. Radioactivity of naturally occuring unstable isotopes which are all around us e.g. air, food, rocks
2. Radiation from space, which is known as cosmic rays. These come mostly from the sun
3. Radiation due to human activity e.g. fallout from nuclear explosions or nuclear waste

Question 23

What is irradiation?

Answer 23

1. Irradiation is exposure to radiation
2. Objects near a radioactive source are irradiated by it
3. Irradiating something does not make it radioactive
4. Keeping sources in lead-lined boxesm standing behind barrirs or being in a different room are ways of reducing the effects of irradiation

Question 24

What is contamination?

Answer 24

1. Contamination is radioactive particles getting onto objects
2. If unwated radioactive atoms get onto or into an object, the object is said to be contaminated
3. These contaminating atoms might then decay, releasing radiation which could cause you harm
4. Contamination is especially dangerous because radioactive particles could get inside your body
5. Use gloves and tongs when handling sources, to avoid getting particles stuck to your skin or under your nails. You could also wear protective suits to stop you from breathing in radioactive particles

Question 25

What radiation is is most dangerous outside the body?

Answer 25

1. Outside the body, beta and gamma sources are the most dangerous 2. This is because beta and gamma can penetrate the body and get to the oragans 3. Alpha is less dangerous because it cant penetrate the skin and is easily blocked by air

Question 26

What radiation is is most dangerous inside the body?

Answer 26

1. Inside the body, alpha sources are the most dangerous, because they do all their damage in a very localised area 2. Alpha is also the most ionising, so it causes the most tissue damage 3. Beta sources are less damaging inside the body as radiation is absorbed over a less localized area 4. Gamma sources are the least dangerous inside the body as they mostly pass straight out - they have the lowest ionising power

Question 27

How do electrons more within the atom?

Answer 27

1. If they gain energy by absorsbing EM radiation (photon) they can jump to a higher energy level 2. If they release EM radiation, the move to a lower energy level that is closer to the nucleus