P7 New

Question 1

What is an isotope ? And what does it have the same of compared to the normal element ?

Answer 1

An isotope is a different form of the same element
Isotopes have the same atomic number (same amount of protons) but a different mass number (as they have more/less neutrons )

Question 2

What is radioactive decay ?

Answer 2

It is when a unstable isotope tends to decay into other elements and give out radiation to try and become more stable. This process is called radioactive decay

Question 3

Radioactive substances give out one or more types of ionising radiation from their nucleus

What are the 3 main types of ionising radiation ? And what else can they release as they rebalance their atomic and mass number ?

Answer 3

The 3 main types of ionising radiation is alpha, beta and gamma radiation

They can also release neutrons when they decay, as they try to rebalance their atomic and mass numbers

Question 4

What is ionising radiation ?

Answer 4

Ionising radiation is radiation that knocks electrons off atoms, creating positive ions.

The ionising power of a radiation source is how easily it can do this

Question 5

What are alpha particles ?

Answer 5

Alpha particles are helium nuclei so 2+ and mass number 4
They have a mass number of 4 and a atomic number of 2 as they have 2 protons and 2 neutrons
When a atom emits alpha particles it looses 2 electrons and 2 neutrons

They dont penetrate very far into materials and are stopped quickly - they are absorbed by a sheet of paper and they can only travel a gew cm in the air

Because of their size they are very ionising

Question 6

What are beta particles ?

Answer 6

A Beta particle is simply a fast-moving electron released by the nucleus

Beta particles have virtually no mass and a charge of -1

They are moderatly ionising - they penetrate moderatly far into a material before colliding and they can travel in air for a few metres. Also they can be absorbed by a thin sheet of aluminium (around 5mm)

For every beta particle emmited, a neutron in the nucleus has turned into a proton

Question 7

What are gamma rays ?

Answer 7

Gamma rays are EM waves with a short wavelength that are released by the nucleus

They penetrate far into materials without being stopped and travel a long distance through air
This means that they are weakly ionising as they tend to pass through atoms rather than collide with them bu eventually they hit something and do damage

They are absorbed by thick sheets of lead or metres of concrete

Question 8

In what form are nuclear equations written in ? And whats the golden rule for nuclear equations ?

Answer 8

Atom before decay —> atom after decay + radiation emmited

The total mass and atomic number must be equal on both sides

Question 9

What does alpha decay do to the charge and mass of the nucleus ?

Answer 9

When an atom emits alpha particles, it’s atomic mass decreases by 2 and it’s mass number decreases by 4. The charge also decreases.

In nuclear equations the alpha particles are written as the helium nuclei

Question 10

What does beta decay do to the charge of the nucleus ?

Answer 10

Beta particles is an electron created and emitted by a nucleus which has too many neutrons compared to protons. A neutron turns into a proton, emitting a beta particle at high speeds instantly from the nucleus.

The number of protons has increased by one so this increases the positive charge of the nucleus (the atomic number)

And because the nucleus has lost a neutron and gained a proton during beta decay, the mass number stays the same as there is still the same amount of particles it’s just that one changed into a positive particle so for e.g. if u have 2 protons and 2 neutrons and if one changes into a proton u still have 4 particles but there is just 3 protons and only one neutron

Question 11

What do gamma rays do to the charge or mass of the nucleus ?

Answer 11

Gamma rays are a way of getting rid of excess energy from a nucleus

This means that there is no change to the mass number or atomic number

Question 12

What does a Geiger-Muller tube and counter do?

Answer 12

It records the count rate - the number of radiation reaching it per second

Question 13

Because radioactive decay is totally random, what can’t you predict ?

Answer 13

You can’t predict when a nucleus will decay or when a nucleus in a sample will decay next

Question 14

What can half-life be used to find ?

Answer 14

Half-life can be used to find the rate at which a source decays - it’s activity

Activity is measured in becquerels, Bq ( where 1 Bq is 1 devay per second )

Question 15

What is half life ?

Answer 15

The half-life is the time taken for the number of radioactive nuclei in a isotope to half

Question 16

Each time a radioactive nucleus decays to become a stable nucleus…

Answer 16

The activity as a whole will decrease

Question 17

What does the activity of an isotope never reach ?

Answer 17

Zero

Question 18

What does a short half-life mean ?

Answer 18

A short half-life means that the activity falls quickly, because the nuclei are very unstable and rapidly decay

Question 19

What does a long half-life mean ?

Answer 19

A long half-life means that the activity (which is the rate of which the source decays) falls more slowly as most the nuclei dont decay for a long time.

The source just sits there, releasing small amounts of radiation over a long time - dangerous becuase nearby areas will be exposed to radiation for millions of years

Question 20

What is activity ?

Answer 20

It is the rate at which a source decays

Question 21

What is backround radiation ?

Answer 21

Backround radiation is the low-level radiation that’s around us all the time

Question 22

Where does backround radiation come from ?

Answer 22

1) radioactivity of naturally occuring unstable isotopes which are all around us - in air, in food, rocks etc

2) radioation from space, which is known as cosmic rays and these mostly come fron the sun. Although the earths atmosphere protects us from it mostly

3) radiation due to human activity, e.g. fallout from nuclear explosions or nuclear waste but this represents only a small amount of backround radiation

Question 23

What is radiation dose ?

Answer 23

It tells you the risk of harm to body tissues due to exposure to radiation
Its measured in Sieverts

Radiation dose depends on how long you spent exposed to the radiation and how harmful the radiation is to your body

Your radiation dose depends on where you live or if you have a job that invloves radiation

Question 24

What is exposure to radiation called ? And how can you reduce the effects of exposure to radiation ?

Answer 24

Irridiation

For example we are always being irradiated by backround radiation sources and also irridaiting something does not make it radioactive

You can reduce irradiation by keeping sources in lead-lined boxes

Question 25

What is contamination ? And how can these contaminating atoms cause you harm ?

Answer 25

Contamination is radioactive particles getting onto objects
If unwanted radioactive atoms get onto or into an object, the object is said to have been contaminated

These contaminating atoms might then decay, releasing radiation which can then cause you harm
And its very bad if you breathe these particles in so you should wear protective clothing when handling radioactive sources

Question 26

What are the most dangerous sources of radiation outside the body ?

Answer 26

Beta and gamma are the most dangerous as they can penetrate the body and get into delicate organs inside your body. Alpha is less dangerous because it can’t penetrate the skin and is easily blocked by a small air gap

Question 27

What are the most dangerous sources of radiation inside the body ?

Answer 27

Inside the body, alpha sources are the most dangerous as they do all their damage in a localised area. So contamination, rather than irradiation, is the major concern when working with alpha sources. And also alpha is the most ionising.

Beta sources are less damaging than alpha as the radiation from beta is absorbed over a wider area and some even passes out the body all together. Gamma is even less damaging in the body as is mostly just passes straight out and they have the lowest ionising power

Question 28

What are the risks when using radiation ?

Answer 28

1) radiation can enter living cells and ionise atoms and molecules within them - this can kead to tissue damage

2) lower doses tend to do minor damage to the cells without killing them. But this can lead to them becoming mutant cells which divide uncontrollably. Which is cancer

3) higher doses tend to kill cells completely, causing radiation sickness - which leads to vomiting, tiredness and hair loss, onlt if a lot if the cells get killed at once

Question 29

Why are gamma sources usually used in medical tracers ?

Answer 29

Certain radiocative isotopes can be injected into people or swalloed so that their progress around the body can be followed by using an external detector

For example, iodine -123 which is absorbed by the thyroid gland just like normal iodine 127, but iodine 123 (unstable isotope) gives out radiation which can be detected to indicate whether the thyroid gland is taking in iodine as it should .

Isotopes that are usually taken into the body are Gamma so that the radiation can also pass out the body without causing much ionisation. Also they should have a short-half life so that the
radioactivity quickly disappears

Question 30

What is radiotherapy ? And hwo does it work?

Answer 30

It is when you treat cancer with radiation
Since high doses of ionising radiation will kill all living cells, it can be used to kill cancer

Gamma rays are directed and at the right dosage to kill the cancer cells withiut killing too much normal cells which will make the patient very sick but it would be worth it in the end

Question 31

What is nuclear fission ?

Answer 31

Nuclear fission is a nuclear reaction that is used to release energy from large and unstable atoms by splitting them up into smaller atoms

Unforced fission rarely happens as a nucleus has to absorb a neutron before it will split

Question 32

What happens when the atom splits in nuclear fission ?

Answer 32

When the atom splits it forms 2 new lighter elements that are roughly the same size
2 or 3 neutrons are also released when a atom splits and if any of these neutrons are moving slow enough to be absorbed by antoher nucleus then they can cause more fission to occur. This is a chain reaction

Question 33

How can fission be used to benefit companys ?

Answer 33

The energy carried away by gamma rays and in the kinetic energy stores of the remaining free neutrons and other decay products, can be used to heat water making steam to turn tubines and generators

Question 34

How can the amount of energy produced by fission in a nuclear reactor be controlled ?

Answer 34

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

Question 35

What is nuclear fusion ?

Answer 35

Nuclear fusion is the opposite of nuclear fission

In nuclear fusion, two light nuclei collide at high speed and join (fuse) to create a larger, heavier nucleus. For example, hydrogen nuclei can fuse to produce a helium nucleus but the heavier nucleus produced by fusion does not have as much mass as the two separate nuclei did as some of the mass of the lighter nuclei got converted into energy and then released

Fusion releases a lot of energy (more than fission for a given mass of fuel)
The temperature and pressure needed for fusion to occur is so high that fusion reactors are really hard and expensive to build

Question 36

What did dalton do ?

Answer 36

He described atoms as solid spheres and said that different spheres made up dofferent elements

Question 37

What did JJ thomson do ?

Answer 37

He said that atoms couldn’t be solid spheres. His measurements of charge and mass concluded that an atom must have contained even smaller negatively charged particles called electrons. His theory was the plum pudding model. The plum pudding model showed the atom as a ball of positive charge with electrons stuck in it

Question 38

What did Rutherford do ?

Answer 38

He showed that the plum pudding model was wrong

He shot alpha particles at a thin sheet of gold and he expected the particles to pass straight through or be slightly deflected because of the positive charge being spread out across the atom ‘plum pudding model’ but while most the particles went through the empty space, some of them were deflected more than expected and some even deflected backwards so the plum pudding model couldn’t be correct.

He created the nuclear model of the atom where he said that there is a positively charged nucleus at the centre where most of the mass is concentrated and there is a cloud of electrons that surround the nucleus

So the alpha particles pass through the empty space, or if near positive nucleus it would get deflected or if alpha particles hit the nucleus straight on then the particles get reflected backwards

Question 39

What did Bohr do?

Answer 39

Scientists realised that there couldn’t be a cloud of electrons around the nucleus as they would be attracted to the nucleus and this would cause the atom to collapse

So Bohr suggested that the electrons are arranged in shells that orbit the positive nucleus and are all at a fixed position away from the nucleus

Question 40

How were protons found out ?

Answer 40

Rutherford said that the nucleus could be divided into smaller particles which have the same charge as a hydrogen nucleus. These particles were called protons

Question 41

Who found out the neutrons ?

Answer 41

Chadwick

Question 42

How much times smaller is the radius of a nucleus compared to the radius of an atom ?

Answer 42

The radius is about 10,000 times smaller than the radius if an atom