Nuclear fission IB DP Physics Study Notes - 2025 Syllabus
Nuclear fission IB DP Physics Study Notes
Nuclear fission IB DP Physics Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Physics syllabus with Students should understand
that energy is released in spontaneous and neutron-induced fission
the role of chain reactions in nuclear fission reactions
the role of control rods, moderators, heat exchangers and shielding in a nuclear power plant
the properties of the products of nuclear fission and their management.
Standard level and higher level: 4 hours
Additional higher level: There is no additional higher level content.
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 1
- IB DP Physics 2025 SL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
- IB DP Physics 2025 HL- IB Style Practice Questions with Answer-Topic Wise-Paper 2
Nuclear reactions
∙The first induced nuclear reaction was accomplished by none other than Australian physicist Ernest Rutherford, the same guy who bombarded atoms with alpha particles and discovered the nuclear structure of the atom.
∙From his experience with alpha emitters, Rutherford thought that alpha particles might just be energetic enough to breach the nuclear boundary.
∙In fact, he did just that in the following nuclear reaction:
FYI
∙The nuclear reaction above is an example of an artificial (induced) transmutation – where one element is transmuted into another through artificial means. It is alchemy!
∙Here is another induced transmutation that has been successfully accomplished:
FYI
∙At last man’s striving in the studies of alchemy have come to fruition! Recall what a driving force this was in chemistry and physics…
∙Particle accelerators are required.
∙But don’t go home asking mom for one so you can make your own bootleg gold.
∙Both accelerators and energy costs far outweigh the return in gold!
Mass defect and nuclear binding energy
A picture of the reaction 2(1H) + 2n → 4He might help:
∙The reverse process yields the same energy:
Solving problems involving mass defect and binding energy per nucleon
The binding energy per nucleon \( \frac{E_b}{A} \) of a nucleus is simply the binding energy \( E_b \) divided by the number of nucleons \( A \).
EXAMPLE: What is the binding energy per nucleon of \( ^4\text{He} \)?
SOLUTION:
\( ^4\text{He} \) has a binding energy of \( E_b = 4.54 \times 10^{-12} \, \text{J} \).
\( ^4\text{He} \) has four nucleons (2 \( p \) and 2 \( n \), \( \rightarrow A = 4 \)).
Thus,
\[
\frac{E_b}{A} = \frac{4.54 \times 10^{-12} \, \text{J}}{4 \, \text{nucleons}} = 1.14 \times 10^{-12} \, \text{J/nucleon}.
\]
Sketching and interpreting the graph of average binding energy per nucleon against nucleon number
∙Rather than looking at the total binding energy of nuclei, we often look at the binding energy per nucleon.
∙This number tells us about how difficult it is to remove each nucleon from the nucleus.
∙The bigger the binding energy per nucleon, the more stable the nucleus.
FYI
∙The bigger the binding energy per nucleon, the less likely a nucleus will be to want to lose one of its nucleons.
∙Thus it is more stable, by definition.
Nuclear fission and nuclear fusion
∙Nuclear fission is the splitting of a large nucleus into two smaller (daughter) nuclei.
∙An example of fission is
∙In the animation, 235U is hit by a neutron, and capturing it, becomes excited and unstable:
∙It quickly splits into two smaller daughter nuclei, and two neutrons.
Note that the splitting was triggered by a single neutron that had just the right energy to excite the nucleus.
∙Note also that during the split, two more neutrons were released.
∙If each of these neutrons splits subsequent nuclei, we have what is called a chain reaction.
Describing nuclear power stations
∙Nuclear power stations are the same as fossil fuel stations, from the turbine on down.
Solving problems relevant to energy transformations
EXAMPLE:
Create a Sankey diagram for a typical nuclear reactor: Because of the difficulty of enrichment, include that energy in the diagram.
SOLUTION:
PRACTICE:
What transformations were not shown in the previous Sankey diagram?
SOLUTION:
∙Between ENERGY IN ENRICHED URANIUM and ELECTRICAL there should be HOT STEAM and KINETIC.
∙From HOT STEAM and KINETIC there should be a HEAT LOSS and FRICTION.
Mass defect and nuclear binding energy
A picture of the reaction 2(1H) + 2n → 4He might help:
∙The reverse process yields the same energy:
Solving problems involving mass defect and binding energy per nucleon
The binding energy per nucleon \( \frac{E_b}{A} \) of a nucleus is simply the binding energy \( E_b \) divided by the number of nucleons \( A \).
EXAMPLE: What is the binding energy per nucleon of \( ^4\text{He} \)?
SOLUTION:
\( ^4\text{He} \) has a binding energy of \( E_b = 4.54 \times 10^{-12} \, \text{J} \).
\( ^4\text{He} \) has four nucleons (2 \( p \) and 2 \( n \), \( \rightarrow A = 4 \)).
Thus,
\[
\frac{E_b}{A} = \frac{4.54 \times 10^{-12} \, \text{J}}{4 \, \text{nucleons}} = 1.14 \times 10^{-12} \, \text{J/nucleon}.
\]
Sketching and interpreting the graph of average binding energy per nucleon against nucleon number
∙Rather than looking at the total binding energy of nuclei, we often look at the binding energy per nucleon.
∙This number tells us about how difficult it is to remove each nucleon from the nucleus.
∙The bigger the binding energy per nucleon, the more stable the nucleus.
FYI
∙The bigger the binding energy per nucleon, the less likely a nucleus will be to want to lose one of its nucleons.
∙Thus it is more stable, by definition.
Nuclear fission and nuclear fusion
∙Nuclear fission is the splitting of a large nucleus into two smaller (daughter) nuclei.
∙An example of fission is
∙In the animation, 235U is hit by a neutron, and capturing it, becomes excited and unstable:
∙It quickly splits into two smaller daughter nuclei, and two neutrons.
Note that the splitting was triggered by a single neutron that had just the right energy to excite the nucleus.
∙Note also that during the split, two more neutrons were released.
∙If each of these neutrons splits subsequent nuclei, we have what is called a chain reaction.
Describing nuclear power stations
∙Nuclear power stations are the same as fossil fuel stations, from the turbine on down.
Solving problems relevant to energy transformations
EXAMPLE:
Create a Sankey diagram for a typical nuclear reactor: Because of the difficulty of enrichment, include that energy in the diagram.
SOLUTION:
PRACTICE:
What transformations were not shown in the previous Sankey diagram?
SOLUTION:
∙Between ENERGY IN ENRICHED URANIUM and ELECTRICAL there should be HOT STEAM and KINETIC.
∙From HOT STEAM and KINETIC there should be a HEAT LOSS and FRICTION.
Describing nuclear power stations
∙Nuclear fission is the splitting of a large nucleus into two smaller (daughter) nuclei.
∙An example of fission is
∙In the animation, 235U is hit by a neutron, and capturing it, becomes excited and unstable:
∙It quickly splits into two smaller daughter nuclei, and two neutrons, each of which can split another nucleus of 235U.
Note that the splitting was triggered by a single neutron that had just the right energy to excite the nucleus.
∙Note also that during the split, two more neutrons were released.
∙If each of these neutrons splits subsequent nuclei, we have what is called a chain reaction.
We call the minimum mass of a fissionable material which will sustain the fission process by itself the critical mass.
Note that 238U is not even in this list.
This is why we must enrich naturally-occurring uranium for reactor usage
In a nuclear reactor, a controlled nuclear reaction is desired so that we merely sustain the reaction without growing it.
∙In a nuclear bomb, an uncontrolled nuclear reaction is desired so that we have an immense and very rapid energy release.
∙Recall that a typical fission of 235U will produce two (and sometimes 3) product neutrons.
∙These neutrons have a wide range of kinetic energies EK.
∙If the EK value of a neutron is too high, it can pass through a 235U nucleus without causing it to split.
∙If the EK value is too small, it will just bounce off of the 235U nucleus without exciting it at all.
Describing Nuclear Power Stations
Most of the neutrons produced in a reactor are fast neutrons, unable to split the \( ^{235}\text{U} \) nucleus.
These fast neutrons will eventually be captured by \( ^{235}\text{U} \), or they will leave the surface of the fuel rod without sustaining the fission reaction.
Moderators such as graphite, light water, and heavy water slow down these fast neutrons to about 0.02 eV so that they can contribute to the fission process.
In order to shut down, start up, and change the reaction rate in a reactor, neutron-absorbing control rods are used.
Retracting the control rods will increase the reaction rate.
Inserting the control rods will decrease the reaction rate.
Control rods are made of cadmium or boron steel.
The whole purpose of the reactor core is to produce heat through fission.
The fuel rods, moderator, and control rods are all surrounded by water or some other thermal absorber that can be circulated.
Some reactors use liquid sodium!
The extremely hot water from the reactor core is sent to the heat exchanger, which acts like the boiler in a fossil fuel power plant.
The heat exchanger extracts heat from the circulating reactor coolant and makes steam to run the turbine. There are three isolated water circulation zones whose purpose is to protect the environment from radioactivity.
