Radioactivity Flashcards
State 4 types of radiation
Alpha
Beta
Gamma
Neutron
State 3 subatomic particles
Proton
Neutron
Electron
For alpha radiation describe
What it is made of
Its ionising power
Its penetrating power
Its range in air
Made of two protons and 2 nutrons
It has a high ionising power
It is stopped by skin or paper
It can travel a few cm in air
For Beta radiation describe
What it is made of
Its ionising power
Its penetation power
It’s range in air
It is made of an electron
It has medium ionising power
It can be stopped by a few mm of Aluminium
It as a range of a few meters in air
For Gamma radiation describe
What it is made of
Its ionising power
Its penetation power
It’s range in air
It is made of an electromagnetic wave
It has low ionising power
It is stopped by thick lead or many meters of concrete
It has an infinite range in air
State 3 natural sources of background radiation
- Cosmic rays (from space)
- Radon gas
- Radioactive rocks
What safety precautions do you need to take when handling a radioactive source
- Wear a labcoat and gloved to prevent contamination
- Aways point the source away from you
- Never look into the opening of the source
- If not handing the source make sure you stand at least one meter away
- Keep the radioactive source in a lead lined box when not in use
Describe how a geiger counter detects radiation
A geiger counter contains a gas filled tube and a central electrode. When radiation enters the tube it ionises the gas, alowing it to conduct an electric current.
This current flow is detected by the counter which causes it to click and record the count rate
State two man made sources of background radiation
- Medical procedures
- Nuclear power stations
Describe the nuclear model of the atom
Who proposed this model of the atom and when?
The nuclear atom contains a dense positively charged nucleus made up of protons and neutrons and electrons orbitng around the outside.
It was proposed by Ernest Rutherford in 1911, and the idea of neutrons was added into the model in 1932.
Label each of these parts of the atom
a. Electron
b. Neutron
c. Proton
Define the term electron shell
What happens when electrons move from one shell to another
An electron shell is a fixed energy level within the atom. Electrons in an atom can only have certain amounts of energy, which corresponds to the shells
When an electron absorbs energy it can jump up from one energy level to another. When the electron moves back down to its original shell (energy level) this energy is released as an electromagnetic wave.
Describe the plum pudding model of the atom
Who proposed this model and when?
The plum pudding model consists of a spherical cloud of positive charge which contains negative electrons embedded within it
This model was proposed by JJ Thompson in 1904
Describe the rutherford gold foil experiment
Enerst Rutherford got two scienctists who worked under him, Geiger and Marsden, to conduct an experiment where alpha particles were fired at a thin sheet of gold foil.
A ring of detectors was placed around the gold foil and the alpha particles which emerged were detected
They found that most of the alpha particles passed straight through the foil and the some of them were scattered by large angles
State 3 findings of the Rutherford gold foil experiment and explain the conclusions that were drawn from each one.
Most of the alpha particles passed straight through the gold foil - this shows that most of the atom is made up of empty space
Some particles were deflected by large angles - this shows that most of the mass of the atom is in the nucleus, otherwise only small deflections would be detected
A few particles bounced straight back - this proved that the nucleus was positive, if it was negative particles on a direct collision would stick to the nucleus.
What are the charge and mass of a proton?
Charge: +1e
Mass: 1u
What is the charge and mass of an electron?
Charge: -1e
Mass: 0u (1/2000 u)
What is the charge and mass of a neutron?
Charge: 0
Mass: 1u
What do the two numbers in an atomic symbol mean?
The top number is the mass number this tells you the number of protons and neutrons added together
The bottom number is the atomic number, this tells you the number of protons in the nucleus
How do you calculate the number of neutrons in the nuclus?
Mass number - Atomic number
Describe what an isotope is
Isotopes are elements with the same atomic number but different mass numbers.
This occurs becuase the atoms have the same number of protons but different numbers of neutrons.
What are the rules that are used when working out nuclear equations?
The mass numbers must be the same on either side of the equation when they are added together
The atomic numbers must be the same on either side of the equation when they are added together
Complete this nuclear equation for alpha decay
Complete this equation for beta decay
Rank the three main types of nuclear radiation in terms of penetrating power
Gamma - most penetrating (stopped by several cm of lead or thick concrete)
Beta - Medium penetration (stopped by a few mm of aluminium)
Alpha - Least penetrating (stopped by skin or paper)
Rank the three types of nuclear radiation in terms of their range in air
Gamma - longest range in air (many kilometers)
Beta - medium range in air (a few meters)
Alpha - shortest range in air (a few centimeters)
How is penetrating power measured?
Penetrating power is measured in terms of the type and thickness of material that it takes to stop the radiation from getting through completely
How does ionisation occur?
Which types of radiation are ionising?
Ionisation is when an electron is knocked off of an atom by radiation, leaving a positively charged ion
Alpha, Beta and Gamma are all inoising types of radiation
What do you see if radiation passes through a magnetic field?
Explain how physicists use this effect to visulaise particles
If radiation passes through a magnetic field might curve if it is a charged particle.
Alpha particles curve in a wide arc
Beta paticles curve in a narrow arc
Gamma particles do not curve at all as they are uncharged
Physicists put a cloud chamber inside a magnetic field and then look at the pattern made by the charged particles, the direction and radius of the curve can tell you which type of particle it is
Explain why the activity of a radioactive sample falls over time
Every radioactive atom in a sample has the same chance of decaying at any given time.
After some time has passed some of the atoms have decayed so there are fewer atoms left that could decay. This means that as the number of atoms reduces, so does the number of decays every second, so the activity of the sample drops
Define the term half life
This is the amount of time it takes for half of the radioactive isotopes in a sample to decay
What is the half life of this sample?
Explain how to find it.
To work out the half life of a sample you halve the starting number of atoms (or starting activity) draw a line along to the curve and then down to read the x-axis. You then halve it again and measure the time taken for it to halve a second time. The average of this can be taken to give a more accurate value of the half life.
Explain why radioactivity is a random process
Each atom in a sample has exactly the same probability of decaying in a fixed time. As it is a probability we cannot predict exactly when each of the decays will occurs, making it a random process.
Explain how to calculate the proportion of radioactive isotopes remaing in after a given time
Example calculation: A substance has a half life of 3 years. What proportion of the isotope will be remaining after 15 years.
- Work out the number of half lives that have passed in the time
To do this divide the total time by the time of one half life.
- Start with the number 1 (a whole) and divide it by 2 for each half life that has passed
Example:
The number of half lives that has passed is 15/3 = 5 half lives
To find the proportion remaining divide 1 by 2 5 times, giving an answer of 1/32 remaining
