TOPIC 6 Radioactivity (Extra apart from School made) Flashcards
What is the structure of an atom?
Positively charged nucleus with protons and neutrons
Surrounded by orbits of negatively charged electrons
OVERALL NEUTRAL CHARGE
Where is most of the mass in an atom found?
In the nucleus
How big is the nucleus of an atom compared to the size of the atom?
100,000 times smaller.
What is an isotope?
An atom of the some element with different mass (nucleon) number but the same atomic (proton) number.
How is an isotope different to an element, in terms of its subatomic particles?
An isotope will have more or less neutrons than the element.
What are the charges of: protons, neutrons and electrons?
Proton: +1
Neutron: 0
Electron: -1
What makes electrons move between shells?
Losing or gaining the right amount of energy (electro magnetic)
Gaining energy- move AWAY from nucleus
Losing energy- moving TOWARDS the nucleus
How do atoms form positive ions?
Losing a certain amount of outer shell electrons.
eg: +2 charge has lost 2 electrons
What is background radiation?
Ionising radiation, at a low, safe level from space and naturally radioactive substances in the environment.
What produces background radiation around us? (Mention Main source)
Radon gas (Main) Cosmic rays Food and drink Buildings Naturally in soil, seas etc
How can radiation be detected (2 methods)?
Geiger-Müller Tube
Radiation dosimeter
How does a Geiger-Müller Tube work?
Contains a counting circuit and space full of particles
Radioactive substance enters and bumps into a particle, releasing an electron
The electron is attracted to the positive counting circuit , creating a measurable current
What 3 types of radiation do unstable nuclei emit?
Alpha
Beta (+/-)
Gamma
Can we predict when unstable nuclei will decay?
No, it is a random process
What type of radiation are alpha, beta and gamma radiation?
Ionising radiation
What is the charge on an alpha particle?
+2
What is the mass on an alpha particle?
What type of atom is an alpha particle the same as?
4 mass units
Helium atom (mass=4, proton number= 2)
How ionising is an alpha particle?
Highly ionising
During Alpha Decay, how does:
- the mass number change
- the atomic number
Mass number- decrease by 4
Atomic number- decrease by 2
What is the charge on a beta particle?
-1
What is the mass of a beta particle?
1
—
1850 mass units
What happens during beta minus decay?
A neutron changes to a proton and a high speed electron is ejected from the nucleus
0 e
-1
What happens to the atom during beta minus decay (subatomic particles)?
Atomic number increases by 1
Mass umber doesn’t change
What happens during beta plus decay?
Proton becomes a neutron and a positron (positive charge)
What happens during beta plus decay (subatomic particles)?
Decreases the atomic number by 1
Leaves mass number unaffected
What happens during gamma decay (subatomic particles)?
Both atomic and mass number remain unaffected.
What is activity?
How many decays happen per second (rate of decay)
What is activity measured in?
Becquerels
What is 1 Bq mean?
1 nuclear decay per second
What is the half time?
What is the acronym to remember this?
The time for activity of a sample to half
TASH
Which has a higher activity:
Substance with a shorter half life
Substance with a longer half life
Shorter half life- quickest to half it’s life
How is radioactivity used for the diagnosis and treatment of cancer?
- Tracers using a beta emitter during INTERNAL RADIOTHERAPY like iodine-131 placed inside body/close to tumour
- EXTERNAL RADIOTHERAPY - beams of gamma rays directed at tumour from outside of body
- Lower strengths beams from around tumour to harm tissue around it as little as possible
How is radioactivity used to irritate food?
- Gamma Rays kill bacteria
- Allows food to be stored for longer/safe to eat
-Surgical Equipment is also irradiated using heat from gamma rays (sterilise)
How do smoke detectors use radioactivity?
H
How is radioactivity used to monitor the thickness of paper?
- Paper is made by squeezing wood pulp between rollers
- Squeeze harder for thinner paper
- Beta particle detector is used- if it penetrates the paper, count rate is higher and rollers apply less pressure
How is radioactivity used to detect leaking pipes?
- Gamma source is added to water in pipes underground
- When leaking, the water flows into the surrounding Earth
- Geiger-Müller Tube follows pipe’s path and detect where pipe is leaking (higher radiation)
What is contamination?
When someone gets particles of radioactive material on their akin/inside their body.
This can also happen to water or soil
What is irradiation?
When someone is exposed to alpha, beta or gamma radiation from nearby sources. The irradiation stops when they move away.
How are radioactive sources handled by people working with them?
With tongs, to increase the distance from the body
How are radioactive sources stored, where people work?
eg: Hospital- Always stored in boxes lined with lead
How are people dealing with radioactive substances monitored?
By wearing a dosimeter badge- measures levels of radiation
How are cancer patients protected from harm by radiation?
The lowest possible dose is used
The patient is exposed for the minimum amount of time
What is a tracer? (medicine)
Usually a substance that is used by the body (eg: glucose) attached to a radioactive substance.
Why are tracers used?
Different parts of the body absorb different types of tracers.
This helps to diagnose problems in different areas of the body.
Give an example of a tracer and it’s use.
Any from:
Technetium-99 - attached to drug that collects in the brain
Iodine-123 - absorbed by thyroid gland
Krypton-81m - inhales to investigate lung function
Iodine-125 - made into a compound excreted by the kidneys
Indium-111 - attached to whit blood cells to locate infection
What are gamma cameras used for?
Used to detect highest area of radiation
eg: internal bleeding, tumour
How are positrons used in medicine (hint: tracers)?
1) Tracer is injected into patient
2) Tracer emits POSITRONS.
3) When each positron interacts with an electron, both are destroyed
4) This causes 2 gamma rays to be emitted in opposite directions
5) These gamma rays are detected by a PET scanner, which moves around the patient + detects the rays produced
How does a PET scan show active areas of an organ?
Active areas of the organ take up more tracer and appear BRIGHTER.
How does internal radiotherapy work?
- Beta emitter like iodine-131 placed in body/very close to tumour
- Doesn’t always require surgery-p but the patient must be alone while the source is in place
How does external radiotherapy work?
- Beams of gamma rays, X-Rays or protons directed at tumour from outside the body
- Several loser strength beams may be directed from different angles too
- Tissue absorbs less, tumour absorbs more
Why do levels of radioactivity decrease over time?
More unstable nuclei decay = the activity of a radioactive source will also decay
Why are the nuclei formed after a fission reactions slightly lighter than the nucleus from before?
The nuclei have broken up in smaller nuclei and lost some mass as energy.
List 3 PROS of nuclear power stations/energy
Any 3 from:
- Store a lot more energy by kg than any other fuel
- Don’t need air to release energy
- Don’t produce CO2
- Estimated to last longer than other fuels
- Designed for safety
List 3 CONS of nuclear power stations/energy.
Any 3 from:
- Produce waste that will remain radioactive for millions of years
- Waste is expensive to treat
- Parts of power stations come radioactive as it is used- expensive to decommission
- Accidents - risk to people
- Many people believe nuclear power stations are bad
What is nuclear fission?
The process of splitting a nucleus
Releases large amounts of energy
Used in nuclear power stations
Which two isotopes are usually used in nuclear reactors as fuel?
Uranium-235 or plutonium-239
Both have relatively large nuclei- easy to split when hit by neutrons
What are the stages of nuclear fission?
- Isotope hit by a neutron
- Splits into 2 smaller daughter nuclei (radioactive)
- Three more neutrons are released
- Energy is released- kinetic and thermal
- This process continues - CHAIN REACTION
What is nuclear fusion?
A nuclear reaction, in which lighter nuclei are combined together to form heavier product nuclei, with the release of enormous amounts of energy
What happens during nuclear fusion?
Isotopes (eg: of Hydrogen) fuse together and release energy and a neutron
Where do stars use nuclear fusion?
In their core
Which isotopes do stars use for nuclear fusion?
Hydrogen isotopes (eg: Tritium, Deuterium)
What does the temperature need to be like for nuclear fission to occur?
- Really high temperatures (millions of degrees)
- If not, particles will collide and rebound - ELECTROSTATIC REPULSION (protons in nucleus repel)
- If high enough, the particles have enough kinetic energy to overcome their repulsion and fuse
What should the density be like for nuclear fusion to occur?
High density
-At the core, gravitational fields are higher, making collisions more likely to happen
How does a chain reaction occur (nuclear fission)?
1) A slow- moving neutron is fired at an unstable, large nuclei- often uranium-235. The neutron is absorbed by the nucleus. This makes the atoms more unstable, leading it to split up again.
2) When U-235 splits, it forms two lighter elements and energy is released.
3) These daughter nuclei can be lots of different products but all of them are radioactive.
4) Each times uranium atom splits up, it also spits out 2 or 3 neutrons, which hit more uranium nuclei and so on….. causing a chain reaction.
What’s special about the neutrons in a chain reaction?
They contain a lot of energy
At what speed must neutrons be at to cause a chain reaction?
What are these neutrons called
Slow speed
Thermal neutrons
How are the speed of neutrons in a reactors controlled?
Uranium fuel rods are placed in a moderator (eg:graphite) to slow down the fast-moving neutrons
What do control rods do in a reactor?
Limit the rate of fission by absorbing excess neutrons.
They are placed in between the fuel rods and raised and lowered to control the chain reaction, crating a steady state of nuclear fission.
What would happen if the chain reaction ina nuclear reactor was left unchecked?
Large amounts of energy would be released in a wry short a,punt of time.
Many new fissions will follow each fission- runaway reaction- explosion.
How does a nuclear reactor function (different parts/stages)?
1) They are powered by NUCLEAR REACTORS- create controlled chain reactions.
2) Energy released by fission is transferred to the thermal energy store of the MODERATOR, then the thermal energy store of the COOLANT, then to the thermal energy store of the cold water passing through the BOILER.
Water boils- energy is transferred to kinetic energy of the steam
3) Energy is transferred to the kinetic energy store of the TURBINE and to the kinetic energy store of the generator.
The energy is transferred away from the GENERATOR electrically.
