Radioactive Decay Flashcards
What is radioactive decay?
A random process. In a sample of radioactive material, we don’t know, and cannot predict, which nucleus will decay next
Where does alpha decay usually happen? And what happens? What is its atomic mass and proton number?
In large nuclei
loses 2p and 2n
4 mass no.
2 proton no.
(-4 mass, -2 proton)
What is beta decay? What is its proton number na mass number? What happens in a reaction?
A fast moving, high energy, electron emitted from the nucleus
0 mass no.
-1 proton no.
Gains 1p, loses 1e
(=mass, +1 proton)
What is gamma decay? What is its proton and mass number?
Excess energy is emitted as energy
Doesn’t change the element
0 mass no.
0 proton no.
(=mass, =proton)
What is neutron decay? What is its mass no. And proton no. ?
Where a nucleus emits a neutron
Won’t change the element (only its mass no.)
1 mass no.
0 proton no.
(-1 mass, =proton)
What’s the mass and charge of the subatomic particles?
Proton = 1 mass, +1 charge
Neutron = 1 mass, 0 charge
Electron = 1/2000 mass, -1 charge
What is half life
Time taken for half the nuclei in the sample to decay
What will drop by 50% in 1 half life?
Count rate
Activity
No. of undecayed nuclei
Mass of undecayed sample
%remaining
How to find an accurate half life from a graph
Draw a line from halfway down the no. of undecayed atoms and draw access until it reaches the curve.
Draw the line down to the x axis.
Calculate the difference between the lines.
Repeat this, halving each time until you run out of space.
Find the mean average of the differences.
How is carbon-14 used to date artefacts?
The amount of c-14 shows how long ago it was living, the higher the % left, the more recent
Doesn’t work with rocks or fossils as they have no c-14
What are the two safety precautions when using radioactive material in experiments?
Limit exposure time and increases distance between yourself and the radioactive material
What does a Geiger-Müller counter measure?
The amount of radiation
Which type of decay is the most/least ionising and why?
Alpha decay = most, biggest charge
Gamma decay = least, no charge
What’s the atomic mass and charge of the three types of decay?
Alpha = 4 mass, 2+ charge
Beta = 1/2000 mass, -1 charge
Gamma = 0 mass, 0 charge
How far does alpha, beta and gamma particles travel in the air?
Alpha = few cm
Beta = a meter
Gamma = several km
What do alpha, beta and gamma particles pass through?
Alpha = air
Beta = most things including air, paper and body
Gamma = most things including aluminium and led
What can’t alpha, beta and gamma particles pass through?
Alpha = most things including paper, card, metal, skin, smoke
Beta = thick aluminium & led sheeting
Gamma =. Very thick layer of led or concrete
What is the energy of alpha, beta and gamma particles?
Alpha = low
Beta = medium
Gamma = high
What is the definition of activity in terms of radiation?
No. Of decays happening per second
What is the definition of count rate in terms of radiation?
No. Of detected decays per set amount of time
What is the definition of bequerel in terms of radiation?
Unit of activity, e.g an acting of 50Bq means 50 decays per second
Where does background radiation come from?
Put the 8 sources into order of most to least
- Air (33.6%)
- Medical (21%)
- Ground/Buildings (16%)
- Food and drink (15.6%)
- Cosmic (13%)
- Nuclear weapons (0.4%)
- Air travel (0.3%)
- Nuclear reactors (0.1%)
What are 6 examples of uses of radiation?
Smoke alarms
Radiotherapy for thyroid cancer
Sterilisation of medical equipment
Kidney scans
Lung scans
Pesticides in the environment
What’s the purpose of radiation safety measures
Radiation safety measures ae designed to increase your distance from the source and / or decrease your exposure time
What is contamination?
unwanted radioisotopes in or on
an object
What is exposure?
Near to a radioactive source
What are three safety precautions of a nuclear power station?
Control rods, coolant, moderator
Purpose and design of control rods:
Made of boron or cadmium
Reduce or stop chain reactions
Lowered to absorb neutrons
What’s the purpose and design of the moderator?
Made up of graphite or water
Slow down neutrons
Fission of uranium atom works better with slow neutrons (makes the reaction more efficient)
What’s the purpose and design of the coolant?
Made of CO2 or water
Cool down the reactor to protect from damage
What is nuclear fission
Fission means split.
Nuclear fission is the split of the nucleus.
In a nuclear reactor we split uranium nuclei (or plutonium or even thorium).
To split a uranium-235 nucleus we add an extra neutron, making the nucleus unstable, causing it to split.
This produces new, smaller nuclei and ENERGY.
What’s nuclear fusion?
Small nuclei join together, releasing energy
