Problem set 5
Particles and Nuclear Reactions
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- What it is a thermal neutron?
- Neutrons are produced with high energy. How do you reduce their energy without losing them.
- What is a neutron moderator and what is a neutron absorbent? Give two examples of both.
- Neutrons is often detected by gas- detektors filled with 3He. Why is 3He used and not 4He?
- Neutral radiation is detected by making charged particles. Which reaction happens when tubes filled 3He is used as neutron detectors?
- What is the Q-value of the reaction in 5)? Is the reaction endothermic or exothermic?
- Two charged particles are created in the reactions, which particles?
- What energy does each of the to particles receive when a thermal neutron reacts?
2: One of the quite few nuclear reactions that happened during the birth of the universe (“big bang”) is: n + p → d + γ.
- Calculate the Q-value of the reaction.
- What is the energy of the gamma ray?
- What is the energy of the deuterium? Assume a thermal neutron.
3: The most important process for fusion in the sun is, in total 4p → α + 2e++ 2 μ. Calculate the Q-values and determine the end products for these reactions:
4: Use Nuclear Wallet Cards to do the following calculations:
- The maximum kinetic energy of the positron/electron for 14C.
- The maximum kinetic energy of the positron/electron for the neutron.
- The maximum kinetic energy of the positron/electron for 18F.
- The maximum kinetic energy of the positron/electron for 64Cu ( both disintegrations).
- Nuclei that decays by both beta minus and beta plus are of a special type. Why is this?
- Calculate the mass of 228Ra from information from the Chart of the Nuclides.
5: In a breeder-reactor a new fissile atom is created from each atom that fissions. Breeder-reactors can be made from thorium and uranium as starting material.
- Write down the nuclear reactions which gives new fissile atoms in a uranium-breeder reactor and in a thorium-breeder reactor.
- Calculate the work (in watt) that is generated when one kg of uranium metal is irradiated in a neutron flux of 1014 neutrons/(cm2s).
6: Borium absorbs thermal neutrons well.
- Write down the nuclear reaction that happens.
- Calculate the Q-value for the reaction.
- A flux of 1014 neutrons/(cm2s) striking an area of 100 cm2 is completely stopped by a wall of borium. Calculate the work (in watt).
7: The radionuclide 89Zr has a half-life of 78 hours and is often generated in hospitals by a cyclotron. It is generated by the nuclear reaction 89Y(p,n)89Zr. The cross section for this reaction is 0.8 b with 12MeV protons.
- Calculate the Q-value for this reaction.
- Find a production speed that is able to generate a sample of 1 Gbq of 89Zr with 6 hours of irradiation time.
- In this case the target material is cheap and there is no need to regenerate it. Why is it so?