P6 Flashcards
Describe the charge of the atom
An equal number of protons and electrons, to Crete an overall charge of 0
What are ions
Different number of electrons
What are isotopes?
Different number of neutrons , but same element (atomic number)
What is an unstable nucleus?
Has too much energy and must get rid of it
What is a radio active substance?
A substance that becomes stable by emitting radiation
What does is mean to be ‘unstable’?
Too many protons and /or neutrons in a nucleus to be nicely held together.
What are the 3 different forms of radiation, and their charge?
Alpha ➡️ 2+
Beta➡️ 1-
Gamma➡️ 0
Describe alpha radiation
A particle
2 protons and 2 neutrons
Heavily ionising
Stopped by paper/skin
Very slow because is heavy
Up to few cm range
Describe beta radiation:
A fast moving electron
Stopped by thin aluminium
Moderately ionising
Fast
Up to 1m
Describe gamma radiation
A wave
High energy electromagnetic waves
Travels at the speed of light
Lightly ionising
Stopped by thick lead
Unlimbered range in air
What is ionisation?
Makes ions within the body, this is bad because those damages cells become highly reactive and replicate within the body creating tumours .
Why is penetrating power the opposite of ionising power?
If you penetrate though substances , you simply pass them- you don’t ionise them
Why does beta experience a greater deflection than alpha in an electromagnet field?
F=M✖️ A
Alpha has greater mass and will therefore result in a smaller acceleration
What is a Geiger counter?
A instrument used to detect and measure ionising radiation.
What decides the radioactivity a source can emit?
The heavier , the more likely it is to emit all three types
What happens during gamma decay?
The nucleus stays the same but inky loses energy
What happens during alpha decay?
The nucleus loses two protons and two neutrons, therefore the new nucleus has a lower amount of protons and neutrons
4
2
What happens during beta decay?
A neurones turns into one electron and one proton. It keeps the proton in the nucleus, but let’s go of an electron.This decreases the number of neutrons by 1, and increases the number of protons by 1.
0
-1
Can you predict when a single unstable nucleus will decay?
No radioactive decay is a random process
What is half life?
The time taken for half of the unstable nuclei in a radioactive substance to decay.
Time taken for activity to half
What is activity?
The number of nuclei that decay every second
How do you solve mass after half life ?
Time ➗half life =n
Amount ➗ 2^n
How do you solve half life from a graph?
Go to mass ➗2
Find it on graph,
Do it again : should be the same value
How many neutron and protons are in
12 X
6
bottom number = protons
Top number = protons +neutrons (mass number)
6 protons
6 neutrons
In what format are isotopes written?
‘Name’-‘mass number’
- to distinguish between isotopes
How would you wrote the nuclear equation of yeh alpha decay of a nucleus of uranium - 238
- Uranium 238 goes first (completely separate from the alpha side
- Immediately after an arrow
- On the right hand side write the alpha particle charge
- Complete the equation
How do you calculate net decline as a ratio?
Decrease in activity ➗ original activity
Leave as a fraction
How do you plot activity on a graph?
Divide the mass by 2
Now use the NEW mass to divide by 2
Plot each increment keeping the half life the same
How are electrons arranged in atoms?
Electrons occupy energy levels , the different energy levels, are are different distances.
The lowest energy level is closest to the nucleus
How do atoms absorb electromagnetic radiation?
Electrons in low energy levels, move up to a higher energy level by gaining energy
(The electrons excite to higher energy levels)
*electrons can be excited by absorbing electromagnetic radiation
What are photons ?
Particles of light
Do atoms electrons absorb all EM radiation?
No the incident EM radiation must be of an exact certain frequency (difference of energy level between shells)
Describe excitation
1️⃣A single photon is absorbed entirely by a single electron
2️⃣the energy of the photon is directly proportional to the frequency of EM radiation
3️⃣if the energy of the photon exactly matches the difference in energy between the two levels , the electron will excite to a higher energy level
What happens when atoms emit electromagnetic radiation?
As only a certain number of electrons are allowed to exist at any given energy level (2,8,8)
Therefore the electrons that have excited to higher energy levels, will de-excite to return to original energy levels.
As they de-excite , they emit energy as photons agian
How do electrons de-excite
As de-excites may return to it’s original energy level . It can do this at once or in steps. Each time it de-excites , it emits the energy in the form of a photon of a given frequency.
The emitted photons are of lower energy, then that was absorbed
What is an unstable nuclei?
A nucleus that has too much energy , due to an imbalance between the number of protons to neutrons
What happens when a small nuclei is unstable VS when a large nuclei is unstable?
A small nuclei wil undergo radioactive decay.
Whereas a big nuclei will undergo nuclear fission (it would take too much time to get rid of energy)
What is the definition of nuclear fission ?
The splitting of a larger parent nucleus into two smaller daughter nuclei, with the release of energy and neutrons
Draw out a nuclear fission event
neutron required to start the reaction
What is “nuclear waste “?
The two smaller daughter nuclei produced in the reaction are themselves unstable, and since they are unstable. However as they are small they become stable by undergoing radioactive decay
What is a chain reaction?
A process in which neutrons are realised during a fission event , to go on to produce further fission events.
What is a controlled chain reaction?
A reaction where only one neutron from each fission event is able to produce another fission event
What are control rods?
Carbon rods , that absorb the surplus neutrons and only let one go, so that energy is generated at a steady rate,
What is an uncontrolled chain reaction ?
Where every neutron from each fission event goes on to produce further fission events.
Energy is released at an exponential rate
What are “fissionable isotopes” ?
- not all heavy nuclei can be made unstable by adding neutrons.
Fissionable isotopes are are stable, but can be made unstable by adding neutrons
What are the isotopes of uranium, and which can be fissionable?
U-235 (fissionable )
U-238 (non-fissionable )
What is enriched uranium
Natural =
99% non-fissionable U-238
1% fissionable U-235
Enriched uranium =
97% non-fissionable U-238
3% fissionable U-235
*must be used in the nuclear power plant
What is the definition of “nuclear fusion “?
The joint of two small parent nuclei into a larger daughter nucleus , with the release of energy
What are the advantages of nuclear fusion ?
No radioactive waste is produced.
The fuel required is readily available in water (more sustainable)
Nuclear fusion produced a lot more energy than fission, per kg
What are the disadvantages of nuclear fusion?
Building a fusion reactor is not viable , as more energy is required to make the nuclei overcome their repulsive forces, than is related from fusion
Where does energy come from in fission and fusion ?
There is a difference in made between parent and daughter nuclei (parent has more mass)
*no change in mass number
Mass then transformed into energy
What is Einstein’s energy equation ?
