P7 New Flashcards
What is an isotope ? And what does it have the same of compared to the normal element ?
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 )
What is radioactive decay ?
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
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 ?
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
What is ionising radiation ?
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
What are alpha particles ?
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
What are beta particles ?
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
What are gamma rays ?
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
In what form are nuclear equations written in ? And whats the golden rule for nuclear equations ?
Atom before decay —> atom after decay + radiation emmited
The total mass and atomic number must be equal on both sides
What does alpha decay do to the charge and mass of the nucleus ?
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
What does beta decay do to the charge of the nucleus ?
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
What do gamma rays do to the charge or mass of the nucleus ?
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
What does a Geiger-Muller tube and counter do?
It records the count rate - the number of radiation reaching it per second
Because radioactive decay is totally random, what can’t you predict ?
You can’t predict when a nucleus will decay or when a nucleus in a sample will decay next
What can half-life be used to find ?
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 )
What is half life ?
The half-life is the time taken for the number of radioactive nuclei in a isotope to half
Each time a radioactive nucleus decays to become a stable nucleus…
The activity as a whole will decrease
What does the activity of an isotope never reach ?
Zero
What does a short half-life mean ?
A short half-life means that the activity falls quickly, because the nuclei are very unstable and rapidly decay
What does a long half-life mean ?
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
What is activity ?
It is the rate at which a source decays
What is backround radiation ?
Backround radiation is the low-level radiation that’s around us all the time
Where does backround radiation come from ?
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
What is radiation dose ?
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
What is exposure to radiation called ? And how can you reduce the effects of exposure to radiation ?
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
What is contamination ? And how can these contaminating atoms cause you harm ?
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
What are the most dangerous sources of radiation outside the body ?
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
What are the most dangerous sources of radiation inside the body ?
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
What are the risks when using radiation ?
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
Why are gamma sources usually used in medical tracers ?
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
What is radiotherapy ? And hwo does it work?
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
What is nuclear fission ?
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
What happens when the atom splits in nuclear fission ?
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
How can fission be used to benefit companys ?
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
How can the amount of energy produced by fission in a nuclear reactor be controlled ?
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
What is nuclear fusion ?
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
What did dalton do ?
He described atoms as solid spheres and said that different spheres made up dofferent elements
What did JJ thomson do ?
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
What did Rutherford do ?
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
What did Bohr do?
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
How were protons found out ?
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
Who found out the neutrons ?
Chadwick
How much times smaller is the radius of a nucleus compared to the radius of an atom ?
The radius is about 10,000 times smaller than the radius if an atom
