ATOMIC STRUCTURE Flashcards
What is the mass number?
Protons and neutrons
What is the atomic number?
Protons/electrons
What is an isotope?
Same atomic number and charge
Different mass number (neutrons)
What happens if an isotope is unstable?
It tends to decay into other elements and give out radiation as they try to become more stable (radioactive decay)
What can be the products of radioactive decay?
Neutrons (trying to stabilise)
Alpha, beta and gamma radiation
What is an alpha particle?
Like a helium nuclei
Two protons and two neutrons
What is alpha radiation?
When an alpha particle is emitted from the nucleus
What are the characteristics of alpha radiation?
Don’t penetrate very far into materials and are stopped quickly
Strongly ionising
What can alpha radiation be stopped by?
Skin/sheet of paper
What is a beta particle?
A fast-moving electron
No mass and a charge of -1
What are the characteristics of beta radiation?
Penetrate moderately far into materials before colliding
Moderately ionising
What can beta radiation be stopped by?
Sheet of aluminium (around 5mm)
What happens during beta radiation?
For every electron emitted, a neutron is turned into a proton
What are gamma rays?
Waves of electromagnetic radiation released by the nucleus
What are the characteristics of gamma rays?
They penetrate far into materials without being stopped
Weakly ionising (pass through rather than collide with atoms)
What can gamma rays be stopped by?
Thick sheets of lead or concrete
What are nuclear equations?
They show radioactive decay
Mass and atomic number have to balance
How do you set out nuclear equations?
atom before decay —> atom after decay + radiation emitted
What happens during alpha decay (nuclear equation)?
An atom emits an alpha particle so it’s mass number reduces by 4 and it’s atomic number reduces by 2
Which number is mass and atomic?
Mass number
then
Atomic number
What happens to the charge of an atom after alpha decay?
The charge decreases because it lose two protons (+)
What happens during beta decay?
A neutron in the nucleus turns into a proton and releases a fast-moving electron (beta particle)
What happens to the charge of an atom after beta decay?
A neutron has been turned into a proton so the charge increases
What happens to the mass and atomic number of an atom after beta decay?
The atomic number increases because one new proton has been made
The mass number stays the same because a proton has been made and a neutron has been lost
What do gamma rays do during decay?
They get rid of excess energy from a nucleus so no change to atomic or mass number of an atom
How can radiation be measured?
By using a Geiger-Muller tube and counter to record count-rate
What is half life?
The time it takes for the number of radioactive nuclei in an isotope to halve
What happens each time a radioactive nucleus decays to become stable?
The activity will decrease
What can half life be used to find?
The rate at which a source decays (1 becquerel Bq = 1 decay per second)
What does a short half life mean?
Activity falls quickly because nuclei are very unstable and rapidly decay (dangerous because emit high amounts of radiation)
What does a long half life mean?
Activity falls more slowly because most of the nuclei don’t decay for a long time (can be dangerous because nearby areas exposed to radiation for years)
What is background radiation?
Low level radiation that’s around us all the time
REMEMBER TO SUBTRACT FROM RESULTS
What are cosmic rays?
Radiation from the sun
What are examples of naturally occurring radiation?
Rocks
Food
Building materials
Air
What is an example of radiation due to human activity?
Fallout from nuclear explosions or waste
How many Sv = mSv
1Sv = 100mSv
What is radiation dose measured in?
Sv (sieverts)
What does radiation dose tell you?
The risk of harm to body tissues due to exposure to radiation
What is irradiation?
Exposure to radiation
How can you stop irradiation occurring?
Keep sources in lead-lined boxes
Stand behind barriers
Be in a different room
Use remote controlled arms
When is an object considered contaminated?
If an unwanted radioactive atom gets onto or into an object
How do you stop contamination occurring?
Wear gloves
Use tongs
Protective suits
Why are beta and gamma radiation the most dangerous outside the body?
Because they can penetrate the body and get to delicate organs
(Alpha cannot penetrate the skin)
Why is alpha radiation the most dangerous inside the body?
Because they cannot pass back out through the skin and do damage in very localised areas
Why is beta and gamma radiation least damaging inside the body?
Because they can pass out of the body and have lowish ionising power
Why is radiation a risk to humans?
It can enter living cells and ionise atoms and molecules which can lead to tissue damage (can kill cells)
How can radiation be used as medical tracers?
Injected or swallowed
External detector can monitor their progress around the body (usually gamma and never alpha)
What radiation should be used in medical tracers?
Gamma so can exit the body without causing much damage
Short half life so radiation quickly disappears
How can radiation be used to treat cancer?
Gamma rays directed carefully and at just the right dosage to kill cancer cells without damaging too many normal cells
What is nuclear fission?
Nuclear reaction that is used to release energy from large and unstable atoms
What happens during nuclear fission?
Atom splits to form two new lighter elements
Two or three neutrons are also released which can cause more fission to occur if they are absorbed by another nucleus
What happens to the energy not transferred to the kinetic energy stores during nuclear fission?
It is carried away by gamma rays
What is nuclear fusion?
The joining of two small nuclei
What happens during nuclear fusion?
Two light nuclei collide at high speed and fuse together to create a larger heavy nucleus
What happens to the mass during nuclear fusion?
Some mass of the lighter nuclei is converted into energy therefore the heavier nucleus weighs less than the two nuclei before
Which releases more energy: fission or fusion?
Fusion
What is the order of the model of the atom?
Atomic model - Dalton
Plum pudding model - Thomson
Nuclear model - Rutherford
Planetary model - Bohr
