Unit 6 - Radioactivity Flashcards
What is particle theory?
A model that helps explain the properties of solids, liquids and gases.
When does a chemical reaction happen?
When different atoms in a substance beacons joined in different ways.
Which scientist found out that atoms contain subatomic particles?
J.J Thomson
What was the model that Thomson created?
The Plum Pudding model
What was the plum pudding model?
One positively charged material with negative charge electrons scattered through it.
What is an alpha particle?
A positively charged subatomic particle
What did Earnest Rutherford do?
He fired alpha particles at some gold foil in a vacuum vessel and noticed that: most particles traveled through undeflected, some were deflected by small amounts.
Why did Rutherford think that the alpha particles would go straight through the foil?
Gold is very malleable and he used gold foil 3-5 . He didn’t think that very thin foil could bounce back heavy alpha particles.
Explain the theory of why the particles bounced back of Rutherford experiment
The alpha particles bounced back because the atoms have a very dense nuclear core that contained all the positive charge of the atom and most of the mass of the atom. Positive repels positive
Why did most of the alpha particles from Rutherford experiment go straight through?
Most of an atom in empty space
What are nucleons?
Smaller particles in the nucleus. (Protons and neutrons)
What does relative mass mean?
It is an easier way of comparing masses of subatomic particles
What is the relative mass of each subatomic particle.
Proton = 1 Neutron = 1 Electron = 0
What is the relative charge of each subatomic particle?
Proton = +1 Neutron = 0 Electron = -1
What is the atomic number?
The number of protons in an element
What is the mass number?
The mass of the nucleus - protons + neutrons
What is an isotope?
Atoms of a single element that have different numbers of neutrons.
Give example of carbon isotopes
Carbon-12, carbon-13, carbon-14
What are electron shells?
The certain orbits that the electrons can exist in
What causes tubes to light up and change colours?
The tubes light up when an electrical voltage makes electron move within atoms of gas. They change colour when a different gas is used.
What is electronic configuration?
The distribution of electrons of an atom.
How do atoms emit visible light?
If an atom absorbs energy from an electrical current, an electron can move to a higher orbit (more outer shell). When the electron returns to a lower orbit, the atom merits the energy as visible light of a particular wavelength.
Which shells can the electrons move between?
Any, it depends on the amount of energy that the atom has absorbed.
What is emission spectrum?
The spectrum of frequencies of electromagnetic radiation emitted from an atom. (The different colours emitted)
What is the absorption spectrum?
The different frequencies of visible light that is absorbed by the element when light passes through it.
What is the relation between the emitted and absorbed wavelengths of a gas?
The wavelengths absorbed are the same as the wavelengths it emits.
What is ionising radiation?
When radiation causes electrons to escape.
What is ionisation?
When an atom gains so much energy that one or more of the electrons can escape from the atom altogether. Or it gains electrons to make the charge negative.
What is a positive ion?
When ionisation occurs causing the atom to have a positive charge.
How is a diagram of an ionised atom drawn?
The atom structure after ionisation with square brackets and the charge in the top right corner.
What is background radiation?
A low level of ionising radiation from space and naturally radioactive substances
What is the main source of background radiation?
Radon gas
How is radon gas produced?
By small amounts of uranium in rocks
Why does the amount of radon gas differ around the country?
Some rocks and building stones have different amounts of radon
Besides radon gas, give 2 other sources of background radiation
Food and hospital ( x-rays, gamma ray scans)
What are cosmic rays?
High energy charged particles that stream out of the sun and stars. They are a form of radiation.
How can radioactivity be detected?
Using photographic film that becomes darker when more radiation reached it.
How do people who work with radiation stay safe?
They wear film bandages to check the amount of radiation they have been exposed to
Besides photographic film, what can also be used to measure the radioactivity?
A Geiger muller tube ( Geiger counter with a counter attached)
How does a Geiger counter work?
Radiation passing through the tube ionises the argon gas inside it and allows a short pulse of current. The counter makes a click every time radiation is detected,
What is the count rate?
The number of clicks per second or minute.
How does the count rate help to measure the radiation of a source?
They measure the background radiation first and calculate a mean. Then they subtract this from the radiation of the source
What makes a substance radioactive?
When the nucleus is unstable so it can easily change or decay
What happens during any radiation?
The nucleus is unstable so it begins to decay. This causes radiation to be emitted so the nucleus becomes more stable as it looses energy. It is a random process.
What are the 3 types of radiation?
Alpha, beta and gamma
What is an alpha particle?
An atom that has the nucleus of helium (2 protons and 2 neutrons) There are no electrons so it has a positive charge of 2.
What are beta particles?
High energy and speed electrons. A charge of -1
What are positrons?
High energy and speed particles with the same mass as electrons but a charge of +1
What are gamma rays?
High frequency electromagnetic waves with no charge. Travel the same speed as light.
What can an unstable nucleus emit? (5)
Beta particles (electrons), positrons, gamma rays, alpha particles, neutrons
What does penetrate mean?
Pass through
Why are alpha particles good at ionising?
They are emitted at high speeds and they have a high relative mass so they transfer a lot of energy.
Why are alpha particle not very penetrating?
Every time they ionise an atom, they lose energy, since they produce many ions in a short distance, they lose energy quickly.
Why do beta particles penetrate much further than alpha particles?
They are much less ionising
What are the different matters that stop each of the radiations?
Alpha = cm in air or a sheet of paper Beta = m in air of 3mm thick aluminium Gamma = km in air or few cm thick of lead
How can decay of an atom make it become a different element?
The number of protons is altered so the atomic number changes
What happens in beta- decay?
A neutron becomes a proton so an electron is fired as a neutron has a charge of 0. The mass number stays the same but the atomic number increases
What happens during beta+ decay
A proton becomes an neutron so a positron is fired because the charge of a proton is positive. The atomic number decreases but the mass number stays the same
When is alpha or beta radiation used?
When the nucleus is unstable and tries to become stable
When is gamma radiation used?
When the atom has excess energy
What does a nuclear equation show?
What happens during radioactive decay
What must be the same in nuclear equations?
The charge and the mass
What are becquerels? (Bq)
The units that are used for the number of nuclear decays per second.
Is radioactive decay predictable?
No, it’s random
What is a half-life?
The time taken for half the unstable nuclei in a sample of radioactive isotope to decay.
Does to activity of radioactive decay increase or decrease as time increases?
Decrease
What makes the activity lower in a nuclei?
When it is more stable
Why is some food irradiated with gamma rays?
To make the food safer to eat and make it last longer
What does irradiate mean
To expose something to radiation
How are surgical instruments sterilised besides heating it
They are sealed into bags and irradiated with gamma rays
Give 3 uses of radioactivity?
Killing microorganisms
Checking thickness
Tracers
How can a radioactive isotope be used as a tracer?
A gamma source is added to water to find leaks underground. When there’s a leak, the water flows into the earth. A Geiger muller tube following the path of the pipe detects a higher level of radiation.
How can radioactive isotopes be used to check the thickness?
For paper, it is squeezed between rollers. The thickness depends on the force. A beta radiation source fires out beta particles which are detected on the other side of the paper by a detector. If it’s too thick, less beta particles are detected and the count rate has decreases so the rollers apply more force and vice versa.
What is the radioactive isotope that most smoke alarms contain?
Americium-241
How does a smoke alarm work?
A smoke alarm contains an electrical circuit with two plates and a gap between them. An americium-241 source is as the negative plate. The alpha particles that it gives off ionise the air molecules so they have a positive charge and move to the negative plate. When there is smoke between the gap, it slows down the movement and the detector detects less ions so the alarm goes off.
What can large amounts of ionising radiation cause?
Tissue damage like reddened skin
What can a small amount of ionising radiation for a long period of time cause?
Damage to DNA (mutations) which can cause cancer
If the radiation dose is low, how harmful is it?
Not very damaging because some of the mutations are able to repair themselves
Why is the source of radiation always handled with tongs?
The intensity of radiation is highest here
How can the risk of a radiation source be reduced?
Pointing the source away from people and storing them in a lead-lined container
Give 4 ways medical staff working with radioactive sources decrease their risk of danger
Increase the distance between them and the source
Shielding the source
Minimising the time they spend exposed
Monitoring their exposure amount with dosimeter badges
When would a patient be exposed to radiation for treatment
If the benefits outweighs the dangers, the minimum dose is used
What type of radioactive sources are used for medical treatment
Ones with short half-lives to minimise the exposure time
How is someone irradiated?
When they are exposed to alpha, beta or gamma radiation from nearby radioactive materials, could be from an accident. When they move away, irradiation stops
When does someone become contaminated?
If particles of radioactive materials get on their skin or inside their body. The unstable isotopes will decay causing the person to be exposed to radiation. It will only only stop if the isotopes have fully decayed or if it is removed
Why does contamination of long half-life isotopes have greater hazards?
If they contaminate water, the contamination can spread through the food chain.
The effects last longer
What does radiation transfer?
Energy
What are the other 2 types of nuclear reactions used as a source of energy on a large scale?
Nuclear fission
Nuclear fusion
Why are nuclear fuels useful for naval ships and submarines?
They store a lot more energy per kilogram than any type of fuel
Give 3 positives of nuclear fuels
They don’t burn, they don’t need air to release energy, they don’t produce carbon dioxide
What is nuclear energy used for in power stations?
To generate electricity
Give one way uranium is better that other non renewables
At our current rate of use, it should last over 200 years which is much longer than any other
What is a negative of conventional power stations?
They produce carbon dioxide which contributes to climate change and pollution
Why can nuclear power stations be expensive?
They produce radioactive waste which can last for millions of years and is expensive to treat.
How is radioactive waste treated?
It is sealed into concrete or glass and buried
Why are power stations expensive to decommission?
Parts of it become radioactive as it is used
Why have 12 countries in Europe voted to ban nuclear power stations?
They don’t think the benefits outweigh the dangers
Which isotope collects in the brain?
Technetium-99m
Where does iodine-123 get absorbed?
Thyroid gland
Where is krypton-81m gas absorbed?
Lungs
What isotope is found in the kidneys?
Iodine-125
What can be attached to white blood cells to investigate infections?
Indium-111
Why are radioactive materials good to diagnose medical conditions?
You don’t need to cut the body
What do radioactive tracers emit?
Gamma rays
How can tracers be taken? (4)
Injected into the bloodstream
Swallowed
Inhaled
Injected directly into an organ
How are the locations of the tracers located?
Using gamma cameras
How do tracers diagnose internal bleeding?
They are injected into the blood. The bleeding will block the tracers causing it to build up with gamma rays which are detected.
How are tracers used for tumours?
They are attached to glucose molecules. Tumours take up glucose faster and the gamma cameras pick up more gamma rays there.
How to PET scanners work?
The tracers build up where there are problems. The tracer then emits a positron which when it hits an electron, they are both destroyed and 2 gamma rays are emitted in opposite directions. The PET scanner moves round the body and builds an image
Why do isotopes used in tracers have a short half life?
So the body is affected as little as possible
Why are isotopes used in tracers made at the hospital?
They have a short half life and need to be radioactive for medical use
How does internal radiotherapy work?
A beta emitter like iodine-131 is placed inside the body by the tumour. The patient stays in a room alone while the source is in place.
How does external radiotherapy work?
Beams of gamma rays, x-rays or protons are directed at the tumour from outside the body. Several lower strength beams may be directed at different angles so it is only the tumour affected
Why are cancer cells more suitable to be killed by radiation?
They divide more rapidly than most other cells
What happens in nuclear fission?
A uranium-235 nucleus absorbs a neutron and immediately splits into 2 identical daughter nuclei (radioactive). 2 or more neutrons are released. They are all moving at high speeds due to a lot of energy. There is also heat made. The neutrons will then hit other uranium-235 nuclei which become unstable and release neutrons.
What type of reaction is nuclear fission?
Uncontrolled nuclear chain reaction.
What is the fuel made into in nuclear reactors?
Fuel rods
What slows down the neutrons in a nuclear reactor and why?
In the reactor core, the rods are inserted into holes in a material called a moderator (water, graphite or heavy water - isotope of hydrogen-). This is to increase the chance of the neutrons being absorbed by another uranium-235 nucleus.
How do the control rods work in a nuclear reactor?
They move up an down to change the amount of the fuel rods that are exposed to the neutrons. They absorb 2 of the neutrons so fission doesn’t occur too fast. To stop the reaction, the rods are fully lowered.
How is a reactor core used to generate electricity?
It is transferred to a coolant which is pumped through the reactor. The coolant is water, gas or liquid metal. The hot coolant is pumped to a heat exchanger where it is used to make steam which turns a turbine and makes a generator produce electricity.
What are the key points to remember when working out fission questions?(2)
The first neutron that hits the nucleus
The extra 3 neutrons that are emitted
When does nuclear fusion occur?
When small nuclei combine to form larger ones
Why is the total mass of the new nucleus less than the smaller 2 combined?
Some mass is converted into energy
What fusion reaction is the main source for stars?
When hydrogen nuclei combine to form helium
What is electrostatic repulsion?
When the same charged subatomic particle repel each other.
What is the name for hydrogen-2 and hydrogen-3?
Deuterium and tritium
Why are there extremely high pressures in the center of the sun?
It has a very strong gravitational field
In order for the nuclei to fuse in the sun, they need to be extremely close, how is this done?
The high pressure and strong GF force the nuclei close together
What 2 things make the nuclei more likely to hit?
The nuclei being forced close together and the high energy as they move fast
How do the nuclei in nuclear fusion hit each other
The high energy can overcome the electrostatic repulsion
Why is it very hard to carry out nuclear fusion on earth? (3)
It needs to be faster, hotter and a higher temperature than the sun.
What is nuclear fusion?
Combining of nuclei, a nuclear reaction where lighter nuclei combine to form a heavier product with the release of enormous amounts of energy
What are the products of deuterium and tritium fusion? (3)
Energy, neutron and helium
Give a positive of nuclear fusion of fission
There are far less problems with disposing the radioactive waste as the helium is not radioactive.
