Physics Chapter 7 Flashcards
Radioactive decay is said to be “random” and “spontaneous”. Outline what is meant by each of these terms. (2)
Random: it cannot be predicted which nucleus will decay.
Spontaneous: the decay cannot be influenced in any way.
State what is meant by the binding energy of a nucleus.
It is the energy released when a nucleus breaks into its constituent nucleons /
It is the energy needed to break a nucleus into its constituent nucleons.
Describe what is meant by radioactive decay. (2)
It is the process when an unstable nucleus randomly releases energy (1)
by emitting α particles / β particles / γ rays. (1)
Explain the function of the moderator in a nuclear reactor. (3)
Moderators are used to slow down the neutrons emitted by fissions. (1)
When the neutrons are slowed down, they have higher chance of (1) colliding with the U-235 nuclei. (1)
So more fissions can occur.
Outline how energy released in the nuclear reactor is transformed to electrical energy. [3]
The KE of the neutrons is transferred to thermal energy in the heat exchanger. [1]
It turns the water in the heat exchanger to moving steam. [1]
The KE of the steam converts to the KE of the turbine in the generator. [1]
The KE of the turbine converts to electrical energy in the generator.
State what is meant by mass defect. [1]
Mass defect is the difference in mass between a nucleus and all its constituents.
State what is meant by the term isotope and nuclide.
Isotope: isotopes are the nuclei of the same proton number but different mass number/neutron number. [1]
Nuclide: a nuclide is a nucleus or an atom characterised by its constituents [1]
Define radioactive half-life. (1)
It is the time for the activity of a radioactive sample to decrease by half./
It is the time for the number of undecayed nuclei of a radioactive sample to decrease by half.
Outline why uranium ore needs to be enriched before it can be used in a nuclear reactor. [3]
The amount of U-238 is much higher than U-235 in uranium ore. [1]
U-235 is fissile but U-238 absorbs neutrons which reduces nuclear reaction rate. [1]
So the concentration of U-235 has to be increased to ensure fission. [1]
Compare the processes of nuclear fusion and nuclear fission.
Nuclear fusion: it is a process that two nuclei combine [1]
to form new nuclei of greater mass. [1]
Nuclear fission: it is a process that a nucleus splits [1]
into two nuclei of smaller mass. [1]
Define the term unified atomic mass unit.
It is the 1/12 of the mass of a C-12 atom.
Define the term unified atomic mass unit.
It is the 1/12 of the mass of a C-12 atom.
Radioactive decay is said to be a random process. State what is meant by random decay. [2]
It cannot be determined which particular nucleus will decay. [1]
It cannot be determined when a nucleus will decay. [1]
State what is meant by ionization. (1)
It is a process that an atom/molecule gains or loses electrons.
Outline why a beta particle has a longer range in air than an alpha particle of the same energy. [3]
A beta particle is a fast moving electron which is lighter than an alpha particle. [1]
A beta particle has a smaller charge than an alpha particle [1]
Hence, a beta particle is less likely to interact with air molecules [1] and lose energy. Therefore, its range is longer.
