Nuclear Flashcards
What causes nuclear instability?
1) The neutron count is excessively high
2) The neutron count is insufficient
3) The total count of nucleons (protons and neutrons) becomes overly large, rendering the nucleus too hefty
4) An overabundance of energy is present within the nucleus
What are the main three types of radioactive decay?
Beta+ decay, Beta- decay and Alpha decay
Describe briefly the process of Beta- decay
Involves a neutron transforming into a proton, during which an electron and an antineutrino are emitted.
Describe briefly the process of Beta+ decay
Sees a proton converting into a neutron, with the emission of a positron and a neutrino
Describe briefly the process of Alpha decay
entails the emission of an α particle, which is essentially a helium nucleus
What is binding energy?
The nuclear binding energy is the energy that is required to disassemble a nucleus into its component protons and neutrons
What is meant by the ‘mass defect’?
Nuclei are observed to have a mass that is slightly less than the total mass of their individual protons and neutrons. This difference in mass is known as the mass defect (Δm)
What is Einstein’s famous equation?
E=mc2 , The mass defect is converted into energy during the formation of a nucleus
Describe nuclear fission
Certain heavy and unstable nuclei, such as uranium, can spontaneously split into two smaller nuclei, a process referred to as nuclear fission. This process typically results in the formation of smaller, more stable nuclei, along with the release of a few neutrons.
What are the two types of nuclear fission?
Spontaneous fission - occurs without any external intervention
Induced fission - initiated by absorbing an external neutron into the nucleus
Why is the energy release during fission reactions significant?
Because the resulting daughter nuclei have:
-A higher binding energy per nucleon,
indicating greater stability
-A reduced overall mass
The difference in mass is converted into energy, following Einstein’s equation (E = mc2).
Why do nuclei become unstable?
As nuclei grow in size, they become more unstable. The vast and complex structures of giant nuclei make them prone to spontaneous vibrations and distorted shapes, which further contribute to their instability.
Giant nuclei are more likely to undergo spontaneous fission.
An increase in nucleon numbers exacerbates instability.
This inherent instability naturally limits the maximum number of protons and neutrons that can coexist within a nucleus, effectively capping the number of elements that can exist.
What is nuclear fusion?
Nuclear fusion is the process where lightweight atomic nuclei merge to form a heavier nucleus, simultaneously releasing a large amount of energy.
What are the three key points of fusion?
1)Fusion combines lighter nuclei to create
heavier ones
2)High temperatures and pressures are
essential to overcome the electrostatic forces
repelling the nuclei.
3)Fusion reactions predominantly occur in the
plasma state, a high-energy phase of matter
present within stars.
What is significant about energy released during fusion?
The energy liberation in fusion is substantial due to the fact that the resulting nucleus:
-Exhibits a stronger nuclear binding energy per
nucleon compared to the reactants.
-Has a slightly lower total mass than the sum of
the original reacting nuclei.
This mass difference is converted into energy
What are some advantages of fusion power?
-No long-lived radioactive waste produced
-Abundance of fuel sources, such as hydrogen
What are the disadvantages of fusion power?
Achieving a self-sustaining fusion reaction that generates a net energy output is currently beyond our reach due to:
-The need for extremely high temperatures,
exceeding 100 million °C, to achieve hydrogen
isotope fusion.
-The complexity in designing and maintaining
confinement systems capable of containing the
resultant plasma state.
What is a nuclear reactor and what does it do?
Nuclear reactors produce energy through nuclear fission reactions. This process involves the splitting of the nuclei of heavy atoms, such as uranium.
Describe briefly how a reactor works
Within reactors, rods containing the uranium isotope U-235 are subject to fission when they absorb neutrons. Each fission event generates additional neutrons, heat energy, and radioactive by-products. Each neutron released by the fission reaction is able to go on to cause further fission with other U-235 nuclei.
What is a moderator and how does it work?
Moderators enable controlled fission. To initiate fission, neutrons must travel at a specific speed. A moderator within the reactor decelerates the neutrons to this necessary speed. Common materials used as moderators include water and graphite. Once moderated, neutrons can trigger further fission reactions given an adequate supply of fissile fuel, leading to a self-sustaining nuclear chain reaction.
What is critical mass and why does it play a vital role in a nuclear reactor?
Critical mass refers to the minimal amount of fuel required to maintain a chain reaction. Below this threshold, the reaction will diminish. Reactors are designed with a fuel quantity surpassing this critical mass to guarantee a constant fission process. Nevertheless, unchecked fission can release energy too rapidly, posing explosion risks. Thus, reactors employ mechanisms to manage these reactions.
What are control rods and what do they do?
Control rods regulate fission rates. Neutron-absorbing materials form control rods, which adjust fission rates within the reactor core. This modulation affects the reactor’s power output.
To increase the rate of fission, rods are retracted; to decrease it, rods are inserted. An automatic system can promptly insert rods fully to shut down the reactor if necessary.
How is heat removed and electricity generated in a nuclear reactor?
The fission process generates heat, which is carried away by a coolant fluid circulating within the reactor. This thermal energy is then used to produce steam that powers turbines, generating electricity.
What are the pros and cons of nuclear reactors?
Nuclear power provides a continuous, low-carbon energy source but carries risks, including potential radioactive waste leaks and reactor meltdowns. Secure, long-term isolation of radioactive materials is essential. Moreover, the construction of nuclear facilities is intricate and expensive, and local opposition to reactor sites can pose additional challenges. Decision-makers must consider these issues when authorising nuclear reactors.
Describe and explain how a constant rate of fission is maintained in a reactor by considering what events or sequence of events may happen to the released neutrons
Neutrons from fission first collide with the moderator—commonly water or graphite—to lose energy over roughly 50 collisions until they reach thermal speeds. At this energy, they are more likely to be absorbed by uranium-235, causing a subsequent fission and releasing more neutrons. For the chain reaction to remain constant, on average, one neutron from each fission must induce another fission, achieving a critical condition. However, not every neutron contributes: some may escape the reactor core, be absorbed by uranium-238, or be absorbed by the control rods. Control rods, composed of neutron-absorbing materials, are adjusted to capture excess neutrons. This feedback mechanism maintains the reaction rate at a steady, critical level.
What is a moderator in a nuclear reactor?
A moderator is a material, such as water or graphite, used to slow down fast neutrons to thermal speeds through successive collisions, increasing the likelihood that they will be absorbed by the fuel (typically uranium-235) to sustain fission.
What role do control rods play in a nuclear reactor?
Control rods, made from materials that absorb neutrons, are inserted or withdrawn from the reactor core to regulate the number of neutrons available for fission. This adjustment helps maintain the reactor at a critical state, ensuring a constant fission rate. (e.g Boron is a great example of neutron absorbing material)
What does ‘critical condition’ mean in the context of a nuclear reactor?
A reactor is said to be in a critical condition when, on average, each fission event produces exactly one neutron that causes another fission. This balance ensures a steady, self-sustaining chain reaction.
What is a thermal neutron?
A thermal neutron is a neutron that has been slowed to low energies by the moderator, increasing its probability of being absorbed by fissile material such as uranium-235, thereby inducing further fission.
What is meant by a chain reaction in a nuclear reactor?
A chain reaction in a nuclear reactor refers to the process whereby each fission event produces neutrons that go on to cause further fission events, sustaining the nuclear reaction at a constant rate when the reactor is critical.
What is the feedback mechanism in the context of reactor control?
The feedback mechanism involves the adjustment of control rods based on the reactor’s neutron flux. By absorbing excess neutrons, the control rods help regulate the chain reaction, ensuring the reactor remains in a stable, critical state.
How do uranium-235 and uranium-238 differ in their roles in a nuclear reactor?
Uranium-235 is a fissile material that readily undergoes fission when absorbing a thermal neutron, whereas uranium-238, which is more abundant, can absorb neutrons but typically does not fission with thermal neutrons; instead, it may capture neutrons to form heavier elements or scatter neutrons, thus affecting the overall chain reaction.
what is induced fission?
splitting of nucleus into two smaller nuclei brought about by bombardment
What is a Thermal neutron?
neutrons that have low energies or speeds
What makes a self sustaining reaction?
fission reaction gives out neutrons
neutrons (from fission) cause further fissions
self-sustaining when one fission leads to (at least) one
further fission
