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.
State what is meant by a nucleon. [1]
A nucleon is either the proton or neutron in a nucleus.
Outline the structure of nucleons in terms of quarks. [2]
A proton is made of two up and one down quarks. [1]
A neutron is made of one up and two down quarks. [1]
Outline what is meant by “Hadron”, “Meson”, “Baryon” and “Lepton”.
Hadron: A particle made of two or more quarks
Meson: A particle made of one quark and one anti-quark
Baryon: A particle made of three quarks
Lepton: A fundamental particle that does not undergo strong interactions
State what is meant by an antiparticle. [1]
An antiparticle has the same mass of its own particle but opposite quantum number.
Some particles are identical to their antiparticles. Discuss whether the neutron and the antineutron are identical. [2]
A neutron (ddu) has baryon number +1 but an antineutron (ddu) has baryon number -1. [1]
Hence, they are different. [1]
Explain, in terms of the number of nucleons and the forces between them, why argon-36 is stable and argon-39 is radioactive.
They have the same number of protons but different number of neutrons. [1]
The electric force between protons is repulsive but the nuclear force between neutrons and protons is attractive. [1]
The nuclear force in Ar-36 balances the coulomb force therefore it is stable. [1]
The excess neutrons in Ar-39 increases the nuclear energy level of the nucleus, leading to an imbalance of forces which makes it less stable. [1]
State what is meant by the term decay constant.
Decay constant is probability of decay of nucleus per unit time.
Identify the type of fundamental interactions associated with “photons” and “pi mesons” respectively. [2]
Photon is the exchange particle of electromagnetic interaction. [1]
Pi meson is the exchange particle of strong interaction. [1]
State why π+ mesons are not considered to be elementary particles. [1]
It is because π+ mesons are composed of more than one quark.
State what is meant by an exchange particle. [2]
A virtual particle, such as W boson, [1] that mediates the interaction between two other particles. [1]
State the name of a particle that is its own antiparticle. [1]
Photon or Z boson.
State a reason why the kaon K0 (ds) cannot be its own antiparticle. [1]
The strangeness of K0 is +1. The strangeness of the antiparticle of K0 is -1. So, they are different.
State what is meant by an elementary particle. [1]
A particle that is not made of any smaller constituents.
State to which class of elementary particles the electron belongs. [1]
Leptons
Outline two properties of strangeness. [2]
Strangeness is always conserved in strong interaction [1], but not always conserved in weak interaction. [1]
State two reasons why it is not possible for a particle to consist of two up quarks only. [2]
- A particle of two up quarks would have charge of +4/3 but the charge of a (non-elementary) particle can only be an integer or 0.
- A particle of two up quarks would have baryon number of 2/3 but the baryon number of a (non-elementary) particle can only be 1, -1 or 0.
