P7 - Radioactivity✔️ Flashcards
What is a radioactive substance?
Atoms of a radioactive substance each have a nucleus that is unstable - which can become stable or less unstable by emitting alpha,beta or gamma radiation
What does it mean if a substance is decaying?
An unstable nuecleus is described as decaying when it emits radiation - no one can tell when an unstable nucleus will decay as it happens without anything being done to the nucelus
Why did Geiger and marsdens experiment with alpha particles take place in a vacuum chamber?
To prevent air molecule absorbing the alpha particles
How did Geiger and marsden experiment with alpha particles?
They set up the apparatus in a vacuum chamber with a detector (consisting of a microscope focused on a Small glass plane) and each time an alpha particle hit the plate, a spot of light was observed - the detector was moved to different positions and the number of spots of light observed were recorded
What were the results from Geiger an marsdens experiment? what did Rutherford conclude?
most of the alpha particles passed straight through the metal foil - he concluded that there is a positivley charged nucleus at the centre of every atom much smaller then the atom because most alpha particles passed straight through the atom without reflection- and most of the atoms mass was located at the centre, rest was empty space
How did Niel Bohr adapt the nuclear model?
Adapted the model by suggesting that electrons orbit the nucelus at specific distances - called energy levels
What did the work of James Chadwick result in?
Provided the evidence to show the existence of neutrons within the nucleus
What was the plum puding model?
Earlier model of the nucleus with positively charged matter spread about (as in a pudding) and electron burried inside (like plum in the pudding) - rutherfords discovery meant that the plum puding model was no longer accepted
What are isotopes?
Are atoms of the same element with different number of neutrons
Features of an alpha particle?
Made up of two protons plus two neutrons - relative mass is 4 and its relative charge is +2 and is identical to a helium nucleus
What happens when a unstable nucleus emits an alpha particle?
-is atomic number goes down by 2 and its mass goes down by 4
-the mass and the charge of the nucelus are both reduced
What is a beta particle and how is a beta particle created and emitted?
An electron emitted by a nucelus that has too many neutrons compared with its protons - a neutron in the nucleus changes into a proton and a beta particle (ie and electron) is instanly emitted
Features of a beta particle?
-relative mass of a beta particle is effectivley zero
-relative charge is -1
What happens to an unstable nucleus when a beta particle is emitted?
-atomic number goes up by 1 and its mass is unchanged(neutron changes into proton)
-the charge of the nucleus is increased, mass of nucelus is unchanged
What is gamma radiation?
An electromagnetic radiation from the nucelus of an atom - it is uncharged and has no mass and is able to penetrate far into materials and travel far in air - weakly ionising
Symbol for alpha radiation?
α
Symbol for beta radiation?
β
What material is needed to absorb gamma radiation?
Thick sheets of lead or meters of concrete
What material is needed to absorb beta radiation?
sheet of aluminium around 5mm
What material is needed to absorb alpha radiation?
Sheet of paper
How can you tell when a radioactive substance will decay?
You can’t - radioactive decay is entirley random, so you can’t predict exactly which nucleus in a sample will decay next
Define half-life?
The time it takes for the amount of radiation emitted by a source to halve - can be used to make predictions about radioactive sources - its activity is measured in becquerels, Bq
What would it mean if a source had a short half-life?
Means the activity falls quickly becuase the nuclei are very unstable and rapidly decay - these sources are dangrous due to the high amount of radiation they emit
What would it mean if a source had a long half-life?
Means the activity falls slowly becuase most of the nuclei don’t decay for a long time - can be dangrous because nearby areas are exposed to radiation for millions of years
Define background radiation?
Is the low-level radiation that’s around us all the time - result of naturally occurring isotopes which are all around us
Give an example of background radiation caused by the enviorment?
Radiation from space, which is known as cosmic rays mostly from the sun - however the earths atmosphere protects us from most the radiation
Give an example of background radiation caused by human activity?
Radiation due to fallout from nuclear explosions or nuclear waste
What is background radiation measured in?
Measured in sileverts (Sv) - 1 Sv is equal to 1000 millisieverts (mSv)
What does irradiation mean?how can it be limited?
Exposure to radiation is called irradiation - can be reduced by keeping sources in lead-lines boxes, standing behind barriers and using remote controlled arms
How can we be contaminated by radiation?how can it be prevented?
Contaminating atoms might get into yout system, and then decay releasing radiation which could cause you harm - gloves and tongs should be used when handling sources
Which radioactive sources are most dangrous outside the body?
Beta and gamma sources are the most dangerous - because they can penetrate the body and get to delicate organs
Why is alpha radiation outside the body not that dangerous?
Alpha can not penetrate the skin and is easily blocked by a small air gap
Why is alpha radiation dangerous inside the body?
Alpha sources are very dangerous because they do all their damage in a very localised area so it is more contamination rather then irradiation
Why are beta and gamma sources not that dangerous inside the body?
Beta radiation is absorbed over a larger area and some passes out the body - gamma radiation mostly pass out the body and has lower ionising power so it is not as dangerous
Give three risks of using radiation?
- can enter living cells and ionise atoms and molecules - can lead to tissue damage
- lower doses can cause mutations in the cells, which is cancer
- higher doses kills cells completely - radiation sickness
Explain how gamma sources are usually used in medical traces?
- radioactive isotopes can be injected into people - their progress around the body can be followed using an external detector
- iodine-123 - used to check if the thyroid gland is taking in iodine
Why is gamma a suitable type of radiation for medical uses?
Gamma radiation passes out of the body without causing much ionisation - will have a short half-life so the radioactivity inside the patient quickly disapears
How can gamma rays be used to kill cancer - explain the process?
Higher enough dosage, able to kill cancer cells but not too damaging to living cells is directed carefully at the site of the cancer - there is quite a bit of damage to living cells which can leave the patient feeling very ill
How can beta radiation be used to kill cancer cells?
Radiation-emitting implants (usually beat-emitters) can be put next to or inside tumours
Issues and benefits with using radiation for medical purposes?
- traces can cause cancer - but can diagnose life-threatening conditions
- prolonged exposure to radiotherapy poses future risks - many choose it to still get rid of the cancer completely
Define nuclear fission?
Type of nuclear reaction that is used to release energy from large, unstable atoms by splitting them into smaller atoms
What happens during nuclear fission?
When the atom splits it forms two new lighter elements that are roughly the same size - and have same energy in their kinetic energy store - two or three neutrons are also released when an atom splits
How can a chain reaction occur from nuclear fission?
When two or three neutrons are released from the atom spliting they can be absorbed by another nucleus (if they are moving slow enough) - can cause more fission to occur
Explain how gamma rays are released from nuclear fission?
The energy not transferred to the kinetic energy stores of the products is carried away by gamma rays
Explain how nuclear fission can be used to generate electrcity?
Energy carried away by gamma rays, and in the kinetic energy stores of the remaining free neutrons can be used to heat water, making steam to turn turbines and generators
How is the amount of energy released by nuclear fission controlled?
changing how quickly the chain reaction can occur - by using control rods which are lowered and raised inside a nuclear reactor, to absorb neutrons - which slows down the chain reation and controls the amount of energy released
How do nuclear weapons work?
Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion
Define nuclear fusion?
Collision of two light nuclei at high speed which fuse to create a larger, heavier nucleus - does not have as much mass as the two seperate light nuclei because some energy is released as radiation
Why is it hard to utilise nuclear fusion to produce energy?
The temperature and pressure needed for fusion are so high that fusion reactors and hard and expensive to build
