Nuclear And Particle Physics Flashcards
(24 cards)
Why would you expect ^4He and ^16O to have a larger binding energy per nucleon than the nuclides surrounding it in the nuclide chart?
Each of these has a “magic number” of both protons and neutrons, completely filling their nuclear shell and making them more stable.
Why do alpha particles have a much larger Relative Biological Effectiveness than beta particles
They are heavy ionising particles that leave all their energy in a small volume which causes clustered damage that is difficult to repair. Beta particles are very light and penetrate much further, depositing their energy in a larger area
Which are the two dominant processes through which the beta particles lose energy when traversing a sheet of lead
Bremsstrahlung and Ionisation
What is the difference between X-rays and Gamma rays?
X-rays originate from transitions between the energy levels of atomic electrons. Gamma rays originate from transitions between different nuclear states.
In a nuclear fission reactor, what is the role of the moderator
Neutrons from one nuclear fission are needed to induce subsequent fissions and they are emitted with large kinetic energy. Since the absorption cross section is larger for low energy neutrons their energy should be reduced to increase the yield of the reaction. This is done by a moderator with which the neutrons interact and lose their kinetic energy. This is often water.
In a nuclear fission reactor, what is the role of the control rods?
Each fission results in on average more than one neutron that can induce subsequent fissions. This would lead to an exponentially growing reaction rate unless some of the neutrons are removed from the process. The control rods are made of a material with high neutron capture cross section and can be inserted and removed to control the rate of the process.
Why can the use of heavy water can increase the energy yield in a nuclear fission bomb?
Water is an efficient neutron moderator since the hydrogen atoms in it have a similar mass as the neutrons and hence there is a large transfer of kinetic energy to them in collisions. However, some of the neutrons may be absorbed by the hydrogen to form deuterium and hence they are lost from the process. Deuterium has a much smaller neutron absorption cross section and hence using D_2O is better for the neutron economy of the process.
Why does the use of a tamper increase the energy yield in a nuclear fission bomb?
A tamper is a heavy material surrounding the core of the bomb that by its inertial will delay the disintegration of the fissile material. Hence it enables the reaction to continue longer, increasing the energy release.
What is the origin of the long-lived radioactive contamination from a fusion bomb?
The fusion process in a hydrogen bomb is ignited by a conventional fission bomb. Hence the long-lived contamination comes from that primary bomb or from any tamper that may be used.
State the defining property of Hadrons
Hadrons are made of quarks and interact strongly, eg proton, pion
State the defining property of Leptons
Leptons are fundamental fermions that feel the weak force and, if charged the electromagnetic force, but not the strong force. Eg electron, muon and neutrinos
State the defining property of Mesons
Mesons are quark and anti-quark pairs (not necessarily the same flavour) eg pion and kaon.
State the defining property of Baryons
Baryons are bound states with 3 quarks or anti-quarks. Eg proton and neutron
State the defining property of Bosons
Bosons are particles with integer spin. Eg W^[+-], Z, Gamma and the Higgs boson
State the defining property of Fermions
Fermions are particles with half-integer spin. Eg quarks and leptons.
Give one quantity that Is conserved in the strong and EM interaction but not the weak interaction
Quark flavour
Give one example of one discrete transformation under which the strong and EM interaction is unchanged but the weak interaction isn’t.
Parity (P), charge conjunction (C) and the combination CP are conserved in the strong and EM interaction but not the weak interaction
How does the Higgs boson relate to the Brout-Englert-Higgs field
The Higgs boson is the quantisation of the BEH field
Describe beta-minus decay
A neutron turns into a proton emitting an electron and an antineutron
Define half-life
The half-life of a radioactive isotope is the time taken for half of the radioactive nuclei in a sample to decay
How is the binding energy related to stability?
The higher the binding energy per nucleon the more stable the nucleus.
What is nuclear fission?
Fission is the splitting of a heavy nucleus into two lighter nuclei, releasing energy and often free neutrons
What is nuclear fusion?
Fusion is the joining of two light nuclei to form a heavier nucleus, releasing energy.
What are the conditions needed for fusion?
Extremely high temperatures and pressures are needed to overcome the electrostatic repulsion between nuclei
