# Problem set 5

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# Particles and Nuclear Reactions

1:

1. What it is a thermal neutron?
2. Neutrons are produced with high energy. How do you reduce their energy without losing them.
3. What is a neutron moderator and what is a neutron absorbent? Give two examples of both.
4. Neutrons is often detected by gas- detektors filled with 3He. Why is 3He used and not 4He?
5. Neutral radiation is detected by making charged particles. Which reaction happens when tubes filled 3He is used as neutron detectors?
6. What is the Q-value of the reaction in 5)? Is the reaction endothermic or exothermic?
7. Two charged particles are created in the reactions, which particles?
8. 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.

1. Calculate the Q-value of the reaction.
2. What is the energy of the gamma ray?
3. 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:

1. 40Ca(alpha,gamma)
2. 52Cr(aplha,gamma)
3. 56Fe(alpha,gamma)
4. 58Ni(alpha,gamma)

4: Use Nuclear Wallet Cards to do the following calculations:

1. The maximum kinetic energy of the positron/electron for 14C.
2. The maximum kinetic energy of the positron/electron for the neutron.
3. The maximum kinetic energy of the positron/electron for 18F.
4. The maximum kinetic energy of the positron/electron for 64Cu ( both disintegrations).
5. Nuclei that decays by both beta minus and beta plus are of a special type. Why is this?
6. 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.

1. Write down the nuclear reactions which gives new fissile atoms in a uranium-breeder reactor and in a thorium-breeder reactor.
2. 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.

1. Write down the nuclear reaction that happens.
2. Calculate the Q-value for the reaction.
3. 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.

1. Calculate the Q-value for this reaction.
2. Find a production speed that is able to generate a sample of 1 Gbq of 89Zr with 6 hours of irradiation time.
3. In this case the target material is cheap and there is no need to regenerate it. Why is it so?