7c-Fission and fusion Flashcards
Q: How can nuclear reactions produce energy?A:
Energy is released from the nucleus through:
Fission (splitting of heavy nuclei like uranium-235).
Fusion (joining of light nuclei like hydrogen in stars).
Radioactive decay (spontaneous emission of radiation).
Q: What is nuclear fission?
A: Nuclear fission is the splitting of a large unstable nucleus (e.g., uranium-235) into two smaller nuclei, releasing energy.
Q: How is U-235 split by a neutron?
A slow-moving neutron collides with a uranium-235 nucleus.
The nucleus becomes unstable and splits into two smaller radioactive nuclei (daughter nuclei).
A few more neutrons are released.
Energy is released in the kinetic energy of the fission products.
Q: What are the products of U-235 fission?
Two radioactive daughter nuclei.
A small number of neutrons (typically 2-3).
Kinetic energy released.
Q: What is a chain reaction in nuclear fission?
The neutrons released from one fission reaction strike other U-235 nuclei, causing more fission reactions.
This leads to a self-sustaining reaction.
If uncontrolled, this leads to an explosive release of energy (as in nuclear bombs).
Q: What is the role of control rods and the moderator in a nuclear reactor?
Control rods (made of boron or cadmium) absorb excess neutrons to regulate the reaction.
Moderator (e.g., graphite or heavy water) slows down neutrons, making them more likely to cause fission.
Q: Why is shielding needed in a nuclear reactor?A:
Nuclear reactions release harmful radiation.
The reactor is surrounded by thick concrete and lead shielding to absorb radiation and protect workers.
Q: What is nuclear fusion?
A: Nuclear fusion is the process where two light nuclei (e.g., hydrogen isotopes) combine to form a larger nucleus, releasing energy.
Q: What happens to mass in fusion?A:
The total mass of the fused nucleus is less than the total mass of the original nuclei.
The lost mass is converted into energy (E = mc²).
Q: What is an example of a fusion reaction?
A: In stars:
^2 H 1 + ^3 H 1-> ^4 H 2 + ^1n 0+ Energy (Deuterium + Tritium → Helium + Neutron + Energy)
Q: Why is fusion the energy source for stars?
High temperature and pressure allow hydrogen nuclei to overcome electrostatic repulsion and fuse.
Energy from fusion powers the Sun and other stars.
Q: Why does fusion not occur at low temperatures and pressures?A:
Protons in nuclei have positive charges and repel each other.
High temperatures give them enough kinetic energy to collide and fuse.
High pressure forces nuclei close together.
Fission
-Splitting of large nucleus
Fuel : Uranium-235, Plutonium-239
energy release :Large
Waste: Radioactive waste
condition needed: Slow neutrons
Example: Nuclear reactors
Fusion
-Joining of small nuclei
Fuel- Hydrogen isotopes (Deuterium, Tritium)
-ENergy release: Even larger than fission
Waste: Less harmful waste
condition needed: : Extremely high temperature & pressure
example: Stars, Hydrogen bomb
