Radioactivity Flashcards
JJ Thompson Plum Pudding model
-discovered that electrons could be removed from atoms
-suggested ‘plum pudding’ model
-atoms are spheres of positive charge with tiny electrons stuck in them
Ernst Rutherford Nuclear model
-fired beam of alpha particles at thin gold foil
-expected most particles to travel straight through some deflected back
-realised most of mass was concentrated in a tiny positively charged nucleus at centre
Niels Bohr Bohr Model
-suggested that electrons were in fixed orbits at set distances from nucleus
-called energy levels
-electrons can only exist in these shells and no where else
What happens when an inner electron moves up to a higher shell?
-absorbs EM radiation with the right amount of energy.
-when it moves up, it moves into an empty or partialy full shell
What happens when an inner electron moves down to a lower shell?
-Once it has gone up a level, the electron will quickly fall back
-Will emit the same amount of energy it absobred
-energy carried away by EM radiation
What happens to the energy levels as you move further from the nucleus?
-they get closer together
-means an excited electron falling from the third energy level to the second would release less energy than the same from second to first
-means frequency of the generated radiation decreases as you get further
What is released when electrons move between energy levels?
-Visible light
-changes within nucleus itslef produce high frequency, high energy gamma rays
What is an isotope?
An isotope of an element are atoms with the same number of protons but a different number of neutrons
What do unstable isotopes do?
They decay into other elements and give out radiation as they try to become more stable
What are Alpha particles?
-are a helium nuclei (two neutrons and two protons)
-emitted from the nucleus
-can only travel a few cm in air
-absorbed by a thin sheet of paper
-because of their size, they are strongly ionising
What are Beta minus particles?
-beta minus particle is just a fast moving electron released by the nucleus
-both moderately ionising
-beta minus have can travel a few metres in air
-absorbed by a sheet of aluminium 5mm thick
What are Beta plus particles?
-beta plus particle is a fast moving positron (antiparticle of electron). has the same mass just a positive charge
-moderately ionising
-have a smaller range, because when they hit an eletron the two destroy each other and produce gamma rays
What is annihilation?
-When a beta plus particle hits an electron, they destroy each other
-produces gamma rays
-used in PET scanning
What are gamma rays?
-waves of EM radiation released by the nucleus after it undergoes nuclear rearrangement
-penetrate far into materials and travel a long distance through air
-they are weakly ionising as they pass through rather than collide with atoms
-can be absorbed by thick sheets of lead or metres of concrete
In nuclear equations, Alpha decay….
-decreases charge and mass of the nucleus
-mass number decreases by 4
-atomic number decreases by 2
In nuclear equations, Beta minus decay….
-increases the charge of the nucleus
-mass number doesn’t change
-atomic number increases by 1
In nuclear equations, Beta plus (positron) emission….
-decreases charge of the nucleus
-mass number doesn’t change
-atomic number decreases by 1
In nuclear equations, neutron emission….
-decreases the mass of the nucleus
-the mass number stays the same
-the atomic number stays the same
In nuclear equations, gamma rays….
-Don’t change the charge or mass of the nucleus
-they are a way of getting rid of excess energy from an atom
SP6d Background radiation
A) What is background radiation?
B) What are some sources of background raidiation
A) Background radiation is:
- The low level radiation thats around us all the time
- The radioactivity of naturally occurring unstable isotopes all around us
B) Some sources include;
- Radon gas. This is the main source that is produced by rocks that contain small amounts of uranium. Radon gas diffuses into the air and can build up in houses with poor ventilation.
- Certain foods naturally contain small amounts of radioactive substances.
- High-energy, charged particles stream out of the Sun and other stars. They are known as cosmic rays & are a form of radiation.
what is radiation due to human activity?
-fallout of nuclear explosions or radiation from nuclear waste etc.
-This represents a tiny proportion of the total background radiation
How can activity be measured
- with a Geiger-Muller tube which clicks each time it detects radiation
- can be attached to a counter, which displays num. of clicks per second (count rate)
- measured in becquerels (Bq)
- 1 Bq = 1 decay per second
Difference between irradiation and contamination
-EXPOSURE to radiation is called IRRADIATION
-RADIOACTIVE PARTICLES getting onto objects is called CONTAMINATION
what is irradiation?
-Objects near a radioactive source are irradiated by it.
-Means they are exposed to it (e.g background radiation)
-Irradiating something does not make it radioactive
how to prevent irradiation on an object/human?
-keeping sources in a lead-lined box
-standing behind barriers
-being in a different room
-medical staff who work with irradiation wear photographic film badges to monitor exposure
what is contamination?
-when unwanted radioactive atoms get onto an object, the object is contaminated
-these contaminating atoms might decay, releasing radiation which could cause harm
why is contamination especially dangerous?
-as radioactive particles could get inside your body
-this releases radiation inside your body
how to stop or prevent contamination?
-once a person is contaminated, contamination must be removed fully or all radioactive atoms must decay before they are safe again
-gloves and tongs should be used when handling sources to avoid particles getting stuck in skin or under your nails
SP6i Dangers of radioactivity
what is the most and least dangerous radiation outside the body?
-beta and gamma radiation
-as they can penetrate the body and get to the organs
-alpha is less dangerous, because it can’t penetrate the skin
SP6i Dangers of radioactivity
what is the most and least dangerous radiation inside the body?
-alpha are the most dangerous
-as they are strongly ionising, they do all their damage in a very localised area
-means contamination is the main concern when working with alpha sources
SP6i Dangers of radioactivity
A) Describe the dangers of ionising radiation
B) Describe how radiation is handled in hospitals
A) Small amounts of ionising radiation over a long period of time can damage the DNA inside a cell. This damage is called a mutation.
- DNA contains the instructions controlling a cell, so some mutations can cause the cell to malfunction and can cause cancer.
- However not all mutations are harmful and cells are often capable of repairing damage if dosage is low.
B) Medical staff working with radioactive sources have their exposure limited in a number of ways, including increasing distance, shielding themselves and minimise time spent with the source.
- Siome patients may be exposed to a dose of radiation for medical diagnoses or treatment.
SP6h Using radioactivity
How is alpha radiation used?
A) Smoke Alarms
- A smoke alarm contains a source of alpha particles, usually a radioactive isotope called americium-241.
- The detector has an electrical circuit with an air gap between 2 electrically charged plates. The americium-241 sources releases alpha particles, which ionise molecules in the air.
- These ions are attracted to plates with an opposite charge & so allow a small electrical current to flow.
- As long as this current is flowing, the alarm will not sound. When smoke gets into the air gap the smoke particles slow down the ions.
- This causes the current flowing to decrease, the alarm sounds if the current drops below a certain level.
SP6h Using radioactivity
How are gamma rays used?
A) Killing microorganisms
- Food can be irridated with gamma rays to kill bacteria, making it safer to eat + it can be stored longer.
- Surgical instruments need to be sterilised to kill microorganisms. Some instruments such as plastic syringes cannot be sterilised using heat, so they are sealed into bags and irridated with gamma rays, which can penetrate the bag & equipment.
B) Radioactive detecting
- Radioactive isotopes can be used as tracers. For example, gamma rays can be added to a water source to detect for leaks in the pipes.
- Where there is leaks there will be an increase in gamma radiation, which can be found using a Geiger-Muller
SP6h Using radioactivity
How are beta particles used
A) Checking Paper Thickness
- There will be a detector that counts the rate at which beta particles get through the paper from a source on one side.
- When the paper is too thin, more beta particles penetrate the paper and the detector records this increase.
- A computer senses that the count rate has risen and reduces the force applied to the roller to make the paper thicker.
Why is irradiation a good method of sterilisation?
-As, unlike boiling, it doesn’t involve high temp.
-Allows fresh fruit or plastic instruments to be sterilised without damage
SP6j Radioactivity in medicine
Describe how patients can be diagnosed using gamma rays
- A radioactive tracer, which emits gamma rays, is put into the patient. Tracers often contain a radioactive isotope attatched to molecules that will be taken up by particular organs in the body.
- The tracer is usually injected into the bloodstream, the location of the tracer is detected using gamma cameras. Tracers can be used to find sources of internal bleeding.
- Gamma cameras can also be used to locate tumours. The tracer is made using radioactive glucose molecules because very active cellsm such as cancer cells, will take in more glucose.
SP6j Radioactivity in medicine
Describe how patients can be diagnosed using positrons
- The tracer emits a positron. When this meets an electron, both it and the electron, are destroyed and 2 gamma rays are emitted in opposite directions.
- The detector in a PET scanner moves around the patient, building up a set of images showing where different amount of gamma radiation are coming from.
SP6j Radioactivity in medicine
Describe how;
A) Internal radiotherapy
B) External radiotherapy
can be used to treat a patient.
A) Internal radiotherapy uses a beta emitter such as iodine-131 placed inside the body, within or very close to a tumour.
- This does not always require surgery - the patient stays in a room while the source is in place.
B) Most radiotherapy is external radiotherapy, which uses beams of gamma rays, X-rays or protons directed at the tumour from outside the body.
- Several lower strength beams may be directed at the tumour from different directions so that only the tumour absorbs a lot of energy & the surrounding tissues are harmed as little as possible.
How does nuclear fission chain reaction work?
- A slow moving neutron is fired at a large, unstable nucleus (uranium-235)
- The neutron is absorbed by the nucleus, making the atom more unstable, causing it to split
- When U-235 atom splits, it forms two new lighter elements (daughter nuclei) and energy is released
- Each time a uranium atom splits up, it also spits out multiple neutrons, which hit other unstable U-235 atoms, repeating the cycle
Why can a neutron be absorbed by the nucleus?
Because it has a neutral charge, meaning it is not repelled by the positive charge of the nucleus
What does a control rod do?
-Limits the rate of fission by absorbing excess neutrons
-Creates a steady rate of nuclear fission, where each fission produces another fission
What does a moderator do?
Slow down fast moving neutrons, allowing a chain reaction to take place
What does a fuel rod do?
-they contain the unstable radioactive isotope (U-235)
-needed to make thermal neutrons
What are thermal neutrons?
Slow moving neutrons, capable of maintaining a chain reaction when with an abundance of them
SP6l Nuclear fission
Describe how electricity is generated from nuclear fission
- Energy released from the reactor core is transferred to a coolant, which is pumped through the reactor.
- The coolant can be water, a gas or a liquid metal. The hot coolant is pumped to a heat exchanger where it is used to make steam.
- The steam drives a turbine, which turns a generator to produce electricity.
How do meltdowns happen?
-When a chain reaction in a nuclear reactor is left to continue unchecked
-large amounts of energy is released in a short time, creating many new fissions following each fission
-this causes a runaway reaction which could lead to a meltdown
How does nuclear fusion work?
-when two light nuclei collide at high speed and fuse to create a larger, heavier nucleus
-hydrogen nuclei can fuse to produce a helium nucleus
Why does the nucleus formed in nuclear fusion not have the same mass as the two lighter nuclei?
As some of the lighter nuclei is converted into energy and released in the form of gamma rays.
Why does fusion only happen at really high pressures and temperatures?
-because the positively charged nuclei have to get very close to fuse, as they have to overcome the repelling force of electrostatic attraction
Why should we want fusion reactors?
As they would only produce helium, meaning that they could solve our energy crisis
How does a nuclear power station work?
1) energy released by fission is transferred to thermal energy store of moderator
2) this is then transferred to the thermal energy store of the coolant
3) then to the thermal energy store of cold water passing through a boiler
4) causes the water to boil and energy transferred to the kinetic energy store of steam
5) this energy is transferred to the kinetic energy store of a turbine and then to the kinetic energy store of a generator
6)This energy is then transferred away from generator electrically
Advantages of nuclear power
- fairly safe way of generating electricity
- very reliable energy source
- reduces the need for fossil fuels as nuclear fission does not release greenhouse gases
- huge amounts of energy can be generated from a relatively small amount of nuclear material
- Nuclear fuels store alot more energy per kg than any other material.
- Nuclear fuels also don’t burn, so air is not a requirement to release energy.
Disadvantages of nuclear power
- Overall cost of nuclear power is high due to initial cost of the power plant and final decommisioning
- Public perception is very negative
- Carries the risk of meltdowns
