Radioactivity Flashcards
What is the activity of an unstable nucleus?
Activity I’d the rate at which a source of unstable nuclei decays
What is the unit of radioactive activity?
Becquerel
What is count-rate?
The number of radioactive decays per second for a radioactive source
What is an example of a detected that may be used to measure count-rate?
Geiger-muller tube
What is the nature of radioactive decay like?
Random, which nuclei decays and when is determined only by chance and it’s impossible to predict which nuclei will decay and when
What is a half-life of a radioactive isotope?
The time it takes for the number of unstable nuclei in a substance to halve and the time it takes for the count rate from a sample to fall to half its initial level
What are the advantages of nuclear power for generating electricity?
Nuclear fuels don’t produce carbon dioxide, the fuel is readily available so would reduce strain on the fossil fuel supplies, less nuclear fuel has to be used to produce the same amount of energy as burning fossil and doesn’t contribute to global warming
What are some disadvantages of using nuclear power to generate electricity?
Unpopular - public perceive nuclear power as very dangerous, security risks as the radioactive substances can be useful for terrorists, expensive to commission and decommission the stations and risk of nuclear accidents
What is nuclear fission?
The splitting of large, unstable nuclei to form smaller more stable nuclei
What usually needs to happen to induce fission?
The unstable nuclei must absorb a neutron and spontaneous fission
What is emitted in a fission reaction?
Two smaller nuclei, two or three neutrons, gamma rays and energy
What is the name of common fissile nuclei?
Uranium-235
What are the three main components of the core a nuclear reactor?
Moderator, fuel and control rods
What takes place during a chain reaction in a nuclear reactor?
An unstable nucleus absorbs a neutron, the nucleus undergoes fission releases 2 or 3 further neutrons and these induce more fission which results in a chain reaction
What is the consequence of an uncontrolled chain reaction?
The rate of fission events become to high and results in the production of too much energy and this can lead to a nuclear explosion
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 and the lower the rods are inserted, the slower the rate of fission
What is the role of the moderator in a nuclear reactor?
To slow down the neutron so they are travelling at speeds which allowing them to be absorbed by fissile nuclei and cause fission
How is electricity produced in a nuclear power station?
The reactions release thermal energy, the thermal energy is used to boil water and then produce steam and this steam is then used to turn a turbine which starts the generator
What is nuclear fusion?
When two light nuclei join to produce a heavier nucleus and release energy
What are the name of isotopes of hydrogen which are commonly used in nuclear?
Deuterium and tritium
Which releases more energy, nuclear fusion or fission?
Nuclear fusion
What is the difficulty of generating energy through nuclear fusion?
Fusion requires very high temperatures which in itself requires large quantities of energy, currently the production of fusion results in a net loss of energy
What is an example of where fusion occurs?
In the sun (stars use fusion as their energy source)
Why does nuclear fusion require so much energy?
Both nuclei are positive therefore a lot of energy is required to overcome the electrostatic repulsion between the two nuclei
What are the four types of nuclear radiation?
Alpha and beta particles, gamma rays and neutrons
What is meant by background radiation?
Radiation that is always present and it’s in very small amounts and so not harmful
What are sources of background radiation?
Rocks, cosmic rays from rays, nuclear weapons testing and nuclear accidents
How do you measure and detect background radiation?
Photographic film and Geiger-Müller counter
How is photographic film used to measure radiation?
A photographic film turns dark when it absorbs radiation, this is useful for people who work on radiation as the more radiation they are exposed to, the darker the film becomes therefore the workers know when they have been exposed to too much radiation
How is Geiger-Muller tubes used to measure radiation?
When the Geiger-Muller tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation, the frequency of the pulse depends on how much radiation is present, a high frequency would mean the tube is absorbing a large amount of radiation
What constitutes an alpha particle?
Two protons and neutrons and it’s the same as a helium nucleus
What is the range of an alpha particle?
A few centimetres
What is block beta radiation?
A thin sheet of aluminium and several metres of air
What will Bloch gamma radiation?
Several centimetres of lead and few metres of concrete
Which type of radiation is most ionising?
Alpha radiation
Which type of radiation is least ionising?
Gamma radiation
How does gamma emission affect mass/charge of an atom?
Both mass and charge remain unchanged
What is the plum-pudding model of the atom?
A sphere of positive charge, with the negatively charged electrons distributed evenly throughout it
Prior to the discovery of the electron, what was believed about the atom?
believed to be indivisible
Which experiment led to the plum-pudding model being discarded?
Rutherfords alpha-scattering experiment
What is the name given to the currently accepted model model of the atom?
The Bohr model
What is Rutherfords experiment like?
Alpha particles were fired at a thin sheet of gold foil, most particles went straight through, some particles were deflected by small angles and few particles were deflected by large angles
What are the conclusions of Rutherfords experiment?
Most of the atom is empty space, the nucleus has a positive charge and most of the mass is concentrated in the nucleus
What happens in the process of beta plus decay?
A proton turns into a neutron and a positron
What is the process called when a neutron changes into a proton and an electron?
Beta minus decay
When alpha decay occurs, what happens to the atomic number and the mass number of the atom?
The atomic number decreases by 2, the mass number decreases by 4 and new element is made since the atomic number has changed
What effect does beta minus decay have on the mass number and atomic number of an atom?
The mass number stays the same as the total number of neutrons and protons hasn’t changed and the atomic number increases since there is one more proton
What is the approximate radius of an atom?
1x10^-10 metres
What are the three subatomic constituents of an atom?
Protons, neutrons and electrons
Where is most of the mass of an atom concentrated?
In the nucleus
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
1/10,000
What are the arrangements of the subatomic particles?
Protons and neutrons are found in the atom’s nucleus and electrons are found in discrete energy levels around the nucleus
What type of charge does the nucleus of an atom have?
Positive charge
What two ways can an atoms electron arrangement can be changed?
Absorbing or emitting EM radiation
How can an atoms electron arrive change when it absorb EM radiation?
Electrons move to higher energy levels and they move away from the nucleus
How can atoms electron arrangement change when it emits EM radiation?
Electrons move to a lower energy level and they move towards the nucleus
How does the ratio of electrons to protons in an atom result in the atom having no overall charge?
The number of protons is equal to the number of electrons and they have equal and opposite charges so charge cancels
What do all forms of the same element have in common?
Number of protons
What is an isotope of an atom?
same number of protons but different number of neutrons
What property differs between isotopes of an atom?
The mass of an atom
How do atoms Turks into positive ions?
The lose one or more of their outer electrons and electrons are negatively charged so the resultant charge of the atom is positive
