6) Radioactivity Flashcards
What is the mass of positrons?
The same mass as electrons
Who discovered the nucleus?
Rutherford
What did Rutherford conclude?
A positively charged mass in the centre of an atom repelled particles
What did Rutherford fire?
Alpha particles
What happens when atoms absorb EM radiation?
Electrons move to a higher energy level further from the nucleus
What happens when atoms emit EM radiation?
Electrons drop to a lower energy level closer to the nucleus
What is the proton number (Z)?
Total number of protons
What is the nucleon number (A)?
Total number of protons and neutrons
What are the isotopes of hydrogen?
Protium
Deuterium
Tritium
What are specific isotopes of an element called?
Nuclides
How does an unstable nucelus become more stable over time?
By randomly emitting ionising radiation
What is the process of randomly emitting ionising radiation called?
Radioactive decay
How often is decay?
Decay is spontaneous
What are the 3 types of ionising radiation?
Alpha
Beta
Gamma
When does gamma radiation happen?
When an excited nucleus releases energy
How is gamma radiation produced?
By gamma decay
What does a neutron decay to form in beta-minus decay?
A proton and electron
What does a proton decay to form in beta-plus decay?
A neutron and positron
What happens to the products of beta decay?
They are ejected from the nucleus
What does alpha radiation release?
Helium nuclei (alpha particles)
What does alpha radiation do to the mass of the nucleus?
Decreases by 4 atomic units (2 protons and 2 neutrons)
How can radioactivity be detected?
Photographic film
Geiger-Muller tube
Cloud chamber
How do photographic films show radiation?
A bright spot appears where ionising radiation hits the film
How does a cloud chamber show radiation?
A chamber full of alcohol vapour condenses on ionising radiation leaving a trail of radiation
How does a Geiger-Muller tube show radiation?
1) Radiation enters tube full of low pressure gases
2) It ionises atoms in gas, knocking electrons out of atoms
3) Gas can now conduct electricity and completes an electric circuit
4) Current produces clicking noise
5) Count-rate is number of decays recorded each second
What are beta particles?
Electrons
How ionising are alpha particles?
Highly ionising but easily stopped (paper)
How ionising is beta radiation?
Fairly ionising but stopped by aluminium foil
What is beta plus radiation the emission of?
A positron
What is beta minus radiation the emission of?
An electron
How ionising is gamma radiation?
Weakly ionising but only stopped by centimetres of lead or concrete
What is gamma radiation used for?
Sterilisation
Exploring internal organs
How is gamma radiation used to explore internal organs?
We can trace radiation’s weakly ionising movement around the body
Gamma radiation has a short-half life meaning the radiation vanishes quickly
What is alpha radiation used for?
Smoke detectors
How is alpha radiation ued in smoke detectors?
1) Radioactive material fires alpha aprticles at smoke detector
2) If smoke comes bwteen radioactive material and smoke detecotr, less alpha particles reach detector setting off smoke alarm
What is beta radiation used for?
Paper production
How is beta radiation used in paper production?
1) Beta particles are fired through paper to make sure it is the right thickness
2) If thickness changes more or less beta particles reach detector stopping production
What is the most penetrating type of radiation?
Gamma
How does nuclear fission happen?
1) Neutron collides with large nucleus and is absorbed, creating an unstable nucleus
2) Nucleus splits into fragments releasing energy and more neutrons
3) These neutrons then collide with other nuclei
4) Energy released is used to boil water which rotates a turbine which turns a generator, producing electricity
What is the most common fuel soruce of nuclear fission?
Uranium-235
Where does nuclear fission usually happen?
Nuclear reactors
What do moderators control?
The speed at which neutrons travel in a reactor
How does speed of neutrons affect nuclear fission?
Slower moving neutrons are more likely to trigger a fission reaction
What do control rods control?
The number of neutrons in a reactor
They absorb neutrons to slow the rate of reaction
How does removing control rods affect the rate of reaction?
Rate of reaction increases
What uses the chain reactions of nuclear fission to create explosions?
Atom bombs
What happens in nuclear fusion?
Two small nuclei are fused together to create a larger nucleus
How do stars generate their energy?
Through the fusion of hydrogen and helium nuclei
Why can’t scientists create sustainable energy using nuclear fusion?
Hydrogen must be heated to over 100 million degrees C
What does nuclear fusion require?
Very high temperatures and pressure`
What must be the same on each side when writing nuclear equations?
Atomic number
Mass number
How does the element change in gamma decay?
The element does not change
0 protons or neutrons are lost
How does the element change if nuclear fusion?
Protons remain the same
4 nucleons are relseased for chain reactions
What does 1 atom decay to form in nuclear fission?
2 new atoms
Some neutrons
What happens in beta decay?
A neutron decays to form an electron and a proton
How does the element change in alpha decay?
4 nucleons are lost in the form of an alpha particle
2 protons are lost so the intial atom becomes a different element
What does electrons being ‘excited’ mean?
They absorb energy and rise to a higher energy level
What happens if electrons are excited enough?
They can escape the atom
What happens if electrons are not excited enough?
They de-excite and emit radiation to lose energy
What does ultraviolet absorbed by oxygen produce?
Ozone
How are X-rays, UV and visible light generated?
When electrons in atoms lose energy and change their state in the atom
What is emitted from the nucleus of atoms when the structure of the nucleus changes?
Gamma rays
What is the process of an atom losing one of its outer electrons called?
Ionisation
What can ionising radiation do?
Break molecules into small particles called ions
What does cell damage from ionising radiation cause?
Mutations leading to cancer and organ failure
What is the process of scientists checking each other’s work called?
Peer review
What is a half-life?
The average time taken for the number of radioactive nuclei to halve
What is the activity of a radioactive substance measured in?
Becquerels (Bq)
How does the half life of an element change as the radioactivty decreases?
Half lives are constant
How do you measure count rate to work out a substance’s half life?
Geiger counter
What are sources of background radiation?
Rocks
The Sun
Food
Radon gas
Why are rocks radioactive?
Rocks like granite contain small amounts of uranium salts
How can we reduce our exposure to radioactive materials?
Shielding
Storage in lead/steel boxes
Rubber gloves, wash hands
No food or drink
How does the age of a radioactive substance affect danger?
New radioactive substances are the most dangerous
Why is iodine-123 suitable for treating cancer cells?
It has a short half life (13.2 hours)
Doesn’t damage many healthy cells
Why is iodine-131 used in medical tracers for the thyroid gland?
Long enough half life (8 days) to monitor how well gland cuntions
Harm is limited as patient does not need extra doses
How is radiation used in radiotherapy?
High doses of radiation can kill mutated cells (cancers) but also harms healthy cells
What are cons of radiotherapy?
Can kill healthy cells- radiation sickness
Patients feel very unwell
What are pros of radiotherapy?
High doses can kill mutated cells
Longer, healthier lives
What is contamination?
When radioactive atoms or molecules get onto other materials
What is irradiation?
When something is exposed to radiation on its outside
What effects how harmful contamination is?
The type of radiation atoms emit
How can we reduce irradiation?
Standing behind lead or storing radioactive materials in lead-lined boxes
What are the 2 types of exposure to radiation?
Contamination
Irradiation
Why is alpha radiation so dangerous to the body?
It cannot penetrate skin so stays inside the body
What are tracers used to do?
Track blood flow around the body
What type of radiation do tracers usually emit?
Gamma rays
WHat does PET stand for?
Positron Emission Tomography
Why do radioactive isotopes used in PET scanning have to be produced near the hospital?
They have a short half-life and will decay
What is emitted in PET scanning?
Positrons
What is the radius of an atom?
1 x 10^-10m
What is the equation for the level or radiation due to a substance?
total level of radiation - level of background radiation = substance radiation
What is the safest form of radiation outside of the body?
Alpha as it cannot enter the body
