P7. Radioactivity Flashcards
Give an approximation for the radius of an atom
1 x 10-¹⁰ metres
What are the three subatomic constituents of an atom?
- Proton
- Neutron
- Electron
Where is the most of the mass of an atom concentrated?
In the nuleus
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10000
Describe the arrangement of protons, neutrons and electrons in an atom
The protons and neutrons are found in the atom’s nucleus
The electrons are found in discrete energy levels around the nucleus
What type of charge does the nucleus of an atom have? Why?
Positive charge
The nucleus contains protons and neutrons
Protons have a positive charge
Neutrons have no charge
Give two ways that an atom’s electron arrangement can be changed
- Absorbing electromagnetic radiation
- Emitting electromagnetic radiation
Explain how an atom’s electron arrangement changes when it absorb EM radiation
Electrons move further away from the nucleus
They move to a higher energy level
Explain how an atom’s electron arrangement changes when it emits EM radiation.
Electrons move closer to the nucleus
They move to a lower energy level
How does the ratio of electrons to protons in an atom result in the atom having of no overall charge?
The number of protons is equal to the number of electrons
Protons and electrons have equal and opposite charges, so charges cancel
What do all forms of the same element have in common?
They all have the same number of protons
What is the name given to the number of protons in an atom?
Atomic Number
What is an atom’s mass number?
The total number of protons and neutrons in the atom
What is an isotope of an atom?
An atom of an element that has a different number of neutrons, but the same number of protons
How do atoms turn into positive ions?
They lose one or more of their outer electrons
Electrons are negatively charged, so the resultant charge of the atom is positive
What may lead to a significant model being changed or replaced?
The discovery of a new experimental evidence which doesn’t agree with the existing theory
How did the plum-pudding model describe the atom?
A ball of positive charge, with negatively charged electrons distributed evenly through
Prior to the discovery of the electron, what was believed about the atom?
The atom was believed to be indivisible
Which experiment led to the plum-pudding model being discarded?
Rutherford’s alpha-scattering experiment
What is the name given to the currently accepted model of the atom?
The Bohr Nuclear Model
State the conclusions of the Alpha-Scattering experiment.
Most of the mass of the atom is concentrated at the centre in the nucleus
The nucleus is positively charged
What reinforces a scientific theory?
When experimental results agree with the hypothesised theoretical calculations and theories
What did James Chadwick’s experiments on the atom prove?
The existence of neutrons
Why do unstable nuclei give out radiation?
Unstable nuclei undergo decay to become more stable
As they release radiation their stability increases
What is the name of the process in which an unstable nucleus gives out radiation to become more stable?
Radioactive decay
Define the activity of an unstable nucleus
Activity is the rate of decay of a source of unstable nuclei
What is the unit of radioactive activity?
Becquerel (Bq)
What is a count-rate?
The number of radioactive decays per second for a radioactive source
Give an example of a detector that may be used to measure count-rate
Geiger-Muller Tube
State four types of nuclear radiation
- Alpha particles
- Beta particles
- Gamma rays
- Neutrons
What are the constituents of an alpha particle?
Two protons and two neutrons
It is the same as a helium nucleus
What is the range of an alpha particle through air?
A few centimetres (normally in the range of 2-10cm)
What will stop beta radiation from passing through a point?
A thin sheet of aluminium
Several metres of air
What will stop gamma radiation from passing through a point?
Several centimetres of lead
A few metres of concrete
Which type of radiation is most ionising?
Alpha radiation
Which type of radiation is least ionising?
Gamma radiation
State any changes to mass or charge that occur due to the emission of a gamma ray
Both mass and charge remain unchanged
Describe the nature of radioactive decay
Random
Which nuclei decays and when is determined only by chance
It is impossible to predict which nuclei will decay and when
Define the half-life of a radioactive isotope
The time it takes for the number of unstable nuclei in a substance to halve
The time it takes for the count rate from a sample to fall to half its initial level
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials
What is irradiation?
The process of exposing a material to nuclear radiation
The material does not become radioactive
Why is important for the results of studies on the effects of radiation to be published and shared with other scientists?
To allow the findings to be independently checked
This is known as peer review
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations are attempted
How many millisieverts equal 1 sievert?
1000 millisieverts = 1 sievert
Why might the radiation dosage that different people experience differ?
Some occupations involve working with radiation
Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
What factor determines how dangerous a particular radioactive isotope is?
The half-life of the isotope
Why are isotopes with long half-lives particularly harmful?
They remain radioactive for much longer periods of time
They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long
What is nuclear fission?
The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons)
Give an example of a fissionable isotope?
Uranium - 235
What usually needs to happen to induce fission?
The unstable nuclei must absorb a neutron
Spontaneous fission (where no neutron absorption occurs) is rare
Alongside two smaller nuclei, what else is emitted in a fission reaction?
Two or three neutrons
Gamma rays
Energy
What form of energy do all fission products have?
Kinetic energy
What takes place during a chain reaction in a nuclear reactor?
An unstable nucleus absorbs a neutron
The nucleus undergoes fission and releases 2 or 3 further neutrons
These induce more fission, which results in a chain reaction
What is the consequence of an uncontrolled chain reaction?
The rate of fission event becomes too high and results in the production of too much energy
This can lead to a nuclear explosion
What are the three main components of the core a nuclear reactor?
- Fuel rods
- Control rods
- Moderator
What is the role of the moderator in a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
How is the chain reaction in a fission reactor kept under control?
Control rods are positioned in between the fuel rods
The rate of fission is controlled by moving these rods up and down
The lower the rods are inserted, the slower the rate of fission
What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?
Fissile Nuclei
What is nuclear fusion?
The joining of two light nuclei to produce a heavier nuclei and release energy
Which releases more energy, nuclear fission or nuclear fusion
Nuclear fusion
Explain the difficulty of generating energy through nuclear fusion
Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them
Explain why nuclear fusion is currently not a viable way to produce energy on Earth
With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss
