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In 1939 Lise Meitner discovered that the uranium isotope U-238 undergoes fission when struck by a slow neutron - Leaving Cert Physics - Question c - 2008
Question c
In 1939 Lise Meitner discovered that the uranium isotope U-238 undergoes fission when struck by a slow neutron. Barium-139 and krypton-97 nuclei are emitted along wi... show full transcript
Worked Solution & Example Answer:In 1939 Lise Meitner discovered that the uranium isotope U-238 undergoes fission when struck by a slow neutron - Leaving Cert Physics - Question c - 2008
Step 1
Write a nuclear reaction to represent the reaction.
Answer
The nuclear reaction can be represented as:
\,^{238}_{92}\text{U} + \text{n} \rightarrow \;^{139}_{56}\text{Ba} + \;^{97}_{36}\text{Kr} + 3 \text{n}
This reaction shows the fission of uranium-238 when it absorbs a neutron, resulting in the production of barium-139, krypton-97, and three additional neutrons.
Step 2
Why are the neutrons slowed down?
Answer
Neutrons are slowed down in a nuclear fission reactor primarily to ensure they can efficiently cause further fission reactions. Fast neutrons are less likely to induce fission in the uranium-235 isotope, so slowing them down increases the likelihood of collisions that will lead to fission, a process called radiative capture.
Step 3
Step 4
Give one positive and one negative environmental impact of fission reactors.
Answer
Positive Impact: Fission reactors produce no CO₂ emissions or greenhouse gases, leading to a reduction in acid rain and a lesser dependence on fossil fuels.
Negative Impact: The use of fission reactors generates radioactive waste, which poses a potential risk for major accidents and requires safe disposal methods.